About DaltonSkyGazer

DaltonSkyGazer Astronomy News Magazine Portal

The DaltonSkyGazer Astronomy News Portal is based on the Flipboard online Magazine format. This section is updated several times a week to highlight the latest astronomy and astrophotography related news releases. The news sources are pulled from a variety of websites on the internet. Some topics I follow include space travel, current events, physics, astronomy hardware, observatory construction and operations, astrophotography, tutorials, mission updates, and general astronomy news.

Flipboard magazines are easily created by anyone, just register an account with Flipboard and use the tools to create your own magazine which highlights content from any source on the internet.

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About DaltonSkyGazer

About DaltonSkyGazer

I created the DaltonSkyGazer Observatory Blog and Website to share the lessons I learn as I progress on my path to mastering the fine art of astrophotography. Everyone has seen beautiful colorful images of space in magazines, yet few truly comprehend just how difficult it can be to capture and process those images. I hope by sharing my experiences along with articles and stories from other amateur astronomers within the community that this website will serve as an inspiration and helpful guide to those just starting out in the dark side of the hobby, astrophotography.

In 2015, I will be expanding the website, starting with a new design and layout. Look for new articles covering observatory and pier construction along with new articles written by others within the amateur astronomy community.

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Observatory Telescopes and Mounts

Observatory Telescopes and Mounts

I purchased my first major telescope, the 12" Meade LX-200 GPS in 2002. The Schmitt Cassegrain is a very versatile telescope design, excellent for visual and imaging use. The LX-200 can be set up at native F/10, F/6.3, and F/3.3. The 12.25" scope excels at planetary imaging when setup at F/25, F/30, and F/40. In 2003, I dabbled into the dark side of the hobby having purchased the Meade LPI and the Sac-8 Mono imaging camera system. I also was using my friends Sac 7 color imaging camera at the time. Most of the gear currently owned was purchased between 2002 and 2011 timeframe. This section covers in details the specifics of the primary telescopes and mounts used at DaltonSkyGazer Observatory.

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Table 3 Maximum Exposure Time in Seconds for an Observer at 60 o Latitudjpge

Alt-Azimuth Mount Tracking Movement and Field Rotation

Alt-Azimuth Mount Tracking Movement and Field Rotation

Introduction

 

ST8OA, SkyWatcher AZGOTO, Canon 1000D

ST8OA, SkyWatcher AZGOTO, Canon 1000D

Three persistent enemies of astrophotography with lightweight alt-azimuth goto mounts are field rotation, vibration, and tracking movement. For lightweight mounts and tripods, wind is a major source of vibration. Wind driven vibration is often enhanced by swinging camera straps, power cables, and wobbly tripods. Needless to say, securing all hanging objects is of prime importance as is having a sturdy tripod. Unfortunately, for many lightweight mounts, their tripods are also lightweight and vibration prone. Now add field rotation on top of this and you have some significant issues to resolve if you wish to use a lightweight alt-azimuth goto mount for astrophotography.

Mount Tracking Movement
Mount tracking movement, not field rotation, is often the major factor that limits exposure times for photography with lightweight alt-azimuth. Tracking movements originate from two sources. An azimuth mount constantly makes corrections in both azimuth and altitude to keep an object centered in the eyepiece. While to the eye an object may appear stationary in an eyepiece, the camera sees a different reality as the mount moves in small zigzag movements in both azimuth and altitude to correct for the earth’s rotation. The magnitude of this movement must be small to use the mount for photography.

Here is a photograph that shows the motion of a SkyWatcher SynScan AZ GOTO Mount over a two hour period using 20 second exposures. In the photograph you will see the galaxy M81 with a dotted red tracks made from a red hot pixel on the camera’s sensor. Actually in the photo the red dotted line is greatly distorted red to gray smear to make it visible for this example.  In reality,  the hot pixel is stationary and the image is moving due to the motion of the mount tracking M81. Keep in mind, if you were viewing with your eye, M81 would appear stationary in the eyepiece.

 

SkyWatcher AZ GOTO Mount Tracking Movement for a Two Hour Period

SkyWatcher AZ GOTO Mount Tracking Movement for a Two Hour Period

 

The gearing of the mount is another source of mount movement. Nothing is perfect and gears do not mesh perfectly. This produces a movement that has a repeatable pattern and is called periodic error. Since most azimuth mounts are designed for visual observation only, periodic error is generally significant. Fortunately while periodic error can be a significant error for long exposure photography, the duration of very short exposures is too short for it to be of concern.

Another characteristic of alt-azimuth mount movement is associated with the period of time after a goto is completed. Lightweight goto alt-azimuth mounts seem to slowly refine their tracking movements after a GOTO is completed and an object can move in the field of view before appearing to be stationary. This “refinement period” can last about 3 to 5 minutes before the mount steadies down. Afterwards, the object actually never is stationary but its movement is such that it is not ascertainable to the eye or sufficient to cause star trails with the camera using very short exposures of 30 seconds or less. Needless to say, photographing during the time immediately following a GOTO is seldom productive.

Fortunately, most lightweight GOTO mounts are capable of periods free of motion before an event (tracking movement, vibration, etc.) moves the mount. It is during these short periods when exposures can be made. Since we have no way of knowing in advance when such a period will began or stop, a trial and error process is used until enough experience is gained with a mount to know its characteristics. I use either a SkyWatcher SynScan AZ goto mount or a Celestron 4SE mount. They have different characteristics. The SkyWatcher mount has a 30 to 40% light frame rejection rate with 20 second exposures while 4SE mount in the azimuth mode has the same rejection rate with 30 second exposures.

Field Rotation

Let’s take a look at the Great Nebula in Orion on a December night. Early in the night, the nebula is rising in the east. In the middle of the night it is due south high in the sky, and before sunrise it is setting in the west. Notice also how the nebula seems to point downward when it is in the east and upward when it is in the west. Also notice how it stays fixed relative to the arc its path makes through the night sky. Actually the orientation the Orion Nebula is fixed as this apparent motion is caused by the rotation of the earth.

Now let’s put two telescopes side by side; one with an equatorial mount and the other with an azimuth mount. Next, let us take three photographs of the Orion Nebula with each telescope; one photograph early in the evening as the nebula is rising, one in the middle of the night when the nebula is high in the night sky, and the other as it is setting to the west as shown in the figure. During the photographic process, the azimuth mount keeps the telescope orientated to the plane of the earth while the equatorial telescope keeps the telescope orientated to the rotation of the earth.

Now compare the photographs taken with the two mounts. The nebula in the photograph taken with the telescope on the azimuth mount seems to rotate in the photographs as the nebula travels from east to west while the nebula in the photograph taken with the equatorial mount keeps the same orientation in all three photographs. This effect is known as field rotation.

field rotation comparison to gem mount orion nebula

 

With an azimuth mount, Field Rotation results in stars and other objects moving in arcs around the center of the camera. This image of M45 has two degrees of field rotation. The rate of field rotation is dependent upon the latitude of the observer on the earth’s surface with a maximum for an observer located on the earth’s equator and a minimum, zero, for an observer located at the earth’s poles where the zenith and celestial poles are one in the same. In addition, the rate of field rotation is also dependent upon the location of an object in the night sky with the maximum rate occurring at the zenith and the minimum rate toward the eastern and western horizons. Since the location of an object in the sky is constantly changing, the rate of field rotation associated with an object’s position is also constantly changing.

M45 with 2 degrees of field rotation

The position of an object in the sky when a photograph is started has an impact upon the amount of time available to capture an image as well as the exposure times used for the light frames. Exposure time limitations are caused by field rotation, the latitude of the observer, as well as the tracking characteristics of azimuth mounts. As we will discuss later, this means that the area of the night sky within 20 to 30 degrees of the zenith where the atmosphere is the thinnest and distortion the least is not attainable with an azimuth mount. A photograph must be completed before an object reaches an altitude of 60 to 70 degrees. The reverse is also true. If an object is near the zenith, a photograph cannot be started until the object’s altitude descends to 60 to 70 degrees and must be completed before it gets too low on the horizon where the air thickens and distorts images. For objects rising near the eastern horizon, this gives approximately three hours of time to complete a photograph. This time is less for objects rising further north or south of the eastern horizon. Keep in mind, an equatorial mount does not have this limitation.

Field Rotation Mitigation

As discussed earlier, with an azimuth mount field rotation will cause objects in a photograph to appear to rotate around the photograph’s center. This produces star streaks instead of stars and distorts other objects. If an assumption is made that 0.125 degrees of field rotation is not objectionable in a photograph, the time for an object to move 0.125 degrees can be calculated for any given latitude on earth if an object’s altitude and azimuth are known. This time can then be used as the maximum allowable exposure time to photograph an object from that specific geographic location on earth without having star trails due to field rotation. If the maximum exposure time is calculated for objects at all positions in the sky, these calculations define the area of the sky available for photography using an azimuth mount.

T = 30Cos(A)/[Cos(L)Cos(Z)]  where

T = maximum exposure time

A = the altitude angle of the object (0 degrees horizon, 90 degrees at the zenith)

Z = the azimuth angle of the object (0 degrees is due North, 90 degrees due East)

L = the latitude of the telescope/camera location

 The following tables show the time needed for 0.125 degrees of field rotation, thus maximum exposure times with an azimuth mount, based upon

• the location of an observer (degrees latitude),
• the altitude of an object (degrees above the horizon), and
• the azimuth angle of the object (0 degrees true North, 90 degrees due East and 180 degrees due South; 270 degrees due West).

Two singularities exist. One is when an object having an altitude of 0 degrees is directly due East and the other when the object is due West (90 or 270 degrees azimuth); thus, the time for 0.125 degrees of field rotation approaches infinity. Also, when an object is directly at the zenith (90 degrees altitude) the time for 0.125 degrees of field rotation approaches zero seconds because the apparent velocity of the object approaches infinity. This holds true regardless of where an observer is located on earth. While these solutions are mathematically correct; in reality they are not relevant as the time that an object can occupy such a point is instantaneous and the object rapidly moves as the Earth rotates. Another oddity is when the latitude of an observer is at either of earth’s poles. At these two locations the zenith and celestial pole are the same and an azimuth mount is also an equatorial mount; thus field rotation goes to zero.

The values in the tables given for 90 and 270 degrees azimuth are actually the values calculated at 95 degrees as the mathematical solutions at 90 and 270 degrees are a singularity, thus, a meaningless number. The table shows several trends.
• The closer an observer is to the equator, the shorter the allowable exposure time.
• The higher an object is in altitude, the shorter the allowable exposure time.
• The closer an object is to the meridian, the shorter the allowable exposure time.

As shown by the tables; dependent upon the observers distance from the equator, any object with an altitude of 20 degrees or less has an exposure time of at least 28 seconds or more. If we consider an object with an altitude between 40 and 60 degrees, our minimum exposure time drops to 15 to 23 seconds dependent upon where on earth the observer is located. For objects having an altitude greater than 60 degrees, the time available for an exposure drops rapidly and becomes very limited after reaching 75 degrees altitude.

All of this sounds complicated and in a way it is. Fortunately two simple ways to work around the problem of field rotation exist. The first work around is to use a device known as a field de-rotator. This device is used by some advanced photographers but is not recommended for someone who is just beginning astrophotography nor is it suited for a lightweight mount and tripod. A field de-rotator, when attached to a telescope, will rotate the camera at the same rate as field rotation is rotating the image. In theory, this will produce the same results as obtained with an equatorial mount. Overall the results with a de-rotator are mixed. In practice, synchronization of rotator speed with field rotation is often difficult and the movement can be another source of vibration or movement that destroys images. The additional weight can not be tolerated by most lightweight azimuth mounts. Also, de-rotators do not alter the problem azimuth mounts have tracking near the zenith.

 

Table 1 Maximum Exposure Time in Seconds for an Observer at 20 o LatitudejpgTable 2  Maximum Exposure Time in Seconds for an Observer at 40 o Latitudejpg

 

Table 3 Maximum Exposure Time in Seconds for an Observer at 60 o LatitudjpgeThe second work around is a simple rule of thumb; the 60/30/15 rule. Regardless of the location of the observer, objects having an altitude of 60 degrees or less can be photographed to within 30 degrees of the zenith using an exposure time of 15 seconds. 15 seconds is not sufficient for all deep space objects but it is a good starting point. However, this is the worst case. For most observers on earth, longer exposures are possible.

fanned stack DSSWhile a very short exposure time makes the impact of field rotation not noticeable to the eye in a light frame, it does not eliminate the problem. Each light frame is slightly rotated in relation to the previous one. The image of each and every object in a light frame is slightly blurred due to the earth’s rotation. Stacking programs counter the frame rotation by slightly rotating each light frame to keep them aligned with one another. Add to this the adjustments made in reaction to tracking motion discussed earlier. This twisting or fanning effect reduces the area common to all light frames, thus, eliminating information from the photograph. This includes the object being photographed if it is too far removed from the center of the image. After a couple of hours, the common area is noticeably smaller and after three hours, significant areas of the images are not usable. This limits a photographic session for an object to between two hours and three hours overall duration. If more exposure time is required, then the photographic session must be terminated and continued after the object passes the zenith or the next night.

An equatorial mount does not have this limitation. The only variance for an equatorial mount is tracking motion and error. Stacking programs also correct this but the overall impact upon the useful image size is negligible.

 

 

Alt-Azimuth-Astrophotography-Kit-Ready-for-Packing-250x189cover

Alt-Azimuth Mount Astrophotography Applications

Astrophotography Using Very Short Exposures with Lightweight Mounts
Article 1. Alt-Azimuth Mount Astrophotography Applications

by Joseph L. Ashley

Jeff invited me to prepare a series of articles based upon my book “Astrophotography on the Go, Using Short Exposures with Light Mounts” which is part of The Patrick Moore Practical Astronomy Series published by Springer Books. This is the first article of the series. If you have an interest in using an azimuth mount for astrophotography, putting together a portable observatory that you can easily hand carry across town or to a dark spot, no longer are physically able to setup and use a traditional equatorial mount, just don’t like heavy kit, or are only curious; Welcome to Astrophotography on the Go.

My Observing Spot

My Observing Spot, Black Arrow on the roof marks the spot

First, let me say what my book and this series of articles are not. I am not contesting the role an equatorial mount has in the field of astrophotography. I think the capabilities of an equatorial mount versus an azimuth mount are well documented and need not be debated. For anyone wanting to debate the issue, I give up. You are correct.

However, some circumstances and applications do exist where a lightweight and very portable astrophotography kit can play a major role or is superior to a traditional heavy equatorial mount. Here a lightweight azimuth mount may often be the difference between being able to photograph or not. This series of articles will discuss in detail astrophotography with very light, highly portable azimuth, goto mounts using a DSLR and very short exposures.

You can’t do astrophotography with an azimuth mount. That’s an astronomy myth that I’ve heard plenty times over the past several years as I clicked away photographing nebulae, galaxies and a few clusters with my entry level goto mount. Like most myths, this one does have a kernel of truth; in fact at one time this myth was very true. Its genesis dates back to when film was king and the king demanded perfection. No azimuth mount ragamuffins with their field rotation deficiency were permitted entrance into the kingdom of film.

Times change, the digital world was born. With the digital revolution came computerized goto telescopes. Now, just like its equatorial sibling, an azimuth mount can track objects in the night sky for hours on end. However, its handicap, field rotation remains. The new rulers of astrophotography, CCD and CMOS cameras, have sensitivities far deeper than film and gave a dispensation to azimuth mounts known as very short exposure astrophotography. The handicap of field rotation still exists and limits what an azimuth mount can do, especially in relation to an equatorial mount. However, field rotation does not prevent using an azimuth mount and successfully imaging a very large number of objects in deep space.

Even though years have passed since the amateur astronomy world embraced digital technology, two aspects of this digital revolution in astronomy are not fully appreciated by many in the astrophotography community:

  • The sensitivity and internal noise characteristics of modern digital single lens reflex cameras as well as some of the new mirror less cameras are sufficient to capture images of many deep space objects using very short exposures of around 15 to 20 seconds and to do so with a useful signal to noise ratio.
  • Very short exposures have a major impact upon the quality of the mounts and tripods required for astrophotography. No longer is a mount and supporting tripod or pier required that is vibration and movement free for long periods of time. All is needed is a mount that can consistently provide short periods of stability about 50% to 60% of the time while it tracks an object. This requirement is within the capabilities of many relatively inexpensive, lightweight GOTO azimuth mounts used today.

The phrase “lightweight and portable mount” will mean different things to different people. So we all use the same sheet of music here is the definition used in my book and used in this series of articles:

  • Weight not to exceed 7.5kg (16.5 pounds) total (mount, tripod, center tray, and, if applicable, the counterweight)
  • Easily separated into two or more pieces
  •  Has a standard Vixen dovetail saddle
  • Has a collapsible tripod with extendable legs.

This definition is purely arbitrary in many respects but it does describe the parameters needed for a portable observatory that can be hand carried on public transportation.

Just what is a lightweight portable astrophotography kit? One good example is a SkyWatcher SynScan AZ GOTO mount, Orion ST80A 80mm refractor, Canon 1000D single lens reflex camera. The complete kit, except for the tripod and folding camp stool, is easily put inside a salesman’s sample case or in a 40 liter backpack. The total weight of the mount, tripod, OTA, finder scope, and camera is 13.8 lbs (6.3kg)

What circumstances are favorable for lightweight azimuth as well as lightweight equatorial mounts? While these lightweight mounts can produce excellent images for a wide range of deep space objects, they cannot compete with a traditional German equatorial mount. If this is the case, then why use a lightweight mount? That is a good question and one that should be resolved before anyone decides to abandon the traditional approach using a heavy German equatorial mount for astrophotography.

In today’s world over 50 percent of all people on earth live in a city with as much as 80 percent of the populations of some countries living in an urban setting. A large percentage of these people live in mid-city condominiums, apartments, and other high density housing were storage space is scarce and the rules, security lighting, or lack of viewing areas require travel to a nearby park. In this setting, a small, portable kit including a viewing chair that can be carried in one trip from the apartment to the subway and then to a local park can make the difference between pursuing the hobby of astrophotography or not. Unfortunately, few city dwellers realize that they too can get out at night and either view or photograph the night sky.

Urban astronomers often pack-up their kit and drive to a dark spot away from their light polluted sky. Often a good spot is not used because security and other reasons require that the entire kit including power supplies, observing chairs etc. must be transferred in one trip from the automobile to a spot some distance away; something impossible to do with a traditional German equatorial mount. With a portable observatory using a lightweight azimuth mount, these locations can become viable observing sites.

As one completes 70 orbits or so around the sun, time takes its toll for many people. Even with the younger crowd, an accident or illness can greatly reduce physical strength. Lifting heavy mounts and telescopes is often no longer possible. Here, an astrophotography kit based upon a lightweight mount can make the difference between enjoying photographing the night sky or watching television.

Many beginners own a telescope on a lightweight GOTO mount and want to explore astrophotography without spending much money. They can try astrophotography to see if it is something they want to do without buying an expensive mount that they may not use later. All they need to get started is a digital single lens reflex or mirror-less camera, adapters, interval timer, and possibly a focal reducer. For them, using their existing lightweight mount is an inexpensive entry into astrophotography. This is especially true if they already own a digital single lens reflex camera.

Unguided, very-short exposure astrophotography using an alt-azimuth GOTO mount is ideal for the “casual astrophotographer;” a person who primarily wants to visually observe the night sky and occasionally photograph what they see in their telescopes. For them the ease of use of an alt-azimuth GOTO telescope for visual work whether it be a heavy 10 inch Meade LX200 or a portable Celestron 6 SE is more important than the additional photographic capability provided by a wedge or a German equatorial mount that is seldom used.

Lightweight mounts are ideal for people who want an astrophotography travel kit to take on business trips or on vacations. A lightweight mount, small telescope, digital single lens reflex camera, and accessories can easily fit into a small case to minimize space in the family car or to take aboard commercial airliners as carry-on luggage.

Many astronomers simply prefer small aperture telescopes and lightweight mounts even with the challenges and limitations associated with using this equipment. I must confess that I belong to this group.

Last but not least is economics; a short tube refractor on a lightweight, portable, alt-azimuth GOTO mount is the lowest cost entry into the world of astrophotography. This is important for people on a severe budget. However, as we will discuss in a later article, the magnitude of the savings is not as significant many people may think.

M31

M31 ST8OA, 4SE mount on wedge, Canon 1000D, 120×60 seconds

So what is astrophotography on the go about?

“Astrophotography on the Go” is portability; astrophotography with a portable observatory having everything you need including a stool for imaging away from home. Here we are talking about a kit you can easily pack up and carry in one trip from where ever you store your equipment in your home to your observing site whether you must carry it down several flights of stairs, take it aboard city buses, back-pack to a remote spot by walking or on a bicycle, carry it in your car, etc.

“Astrophotography on the Go” is about using unguided, very-short, exposure photography to exploit an ignored paradigm shift created by the marriage of affordable digital single lens reflex cameras and computer controlled mounts. No longer are heavy, sturdy, expensive mounts and tripods required to photograph deep space.

Astrophotography on the Go” is a story telling how to photograph the night sky without spending thousands of dollars, pounds, euros, etc. All the processes, techniques, and equipment needed to use inexpensive, lightweight azimuth and equatorial GOTO mounts and very short exposure photography to image deep space objects are explained. Currently available light-weight mounts and tripods suitable for photography are examined from an economic versus capability perspective. A similar analysis is presented for entry level telescopes and mounts sold as bundled packages by the telescope manufacturers as well as some customized bundles that I especially like.

“Astronomy on the Go” is about helping people decide what camera, telescope, and mount is the best fit for them. Currently available light-weight mounts and tripods are identified and examined from an economic versus capability perspective. A similar analysis is presented for entry level telescopes and mounts sold as bundled packages by the telescope manufacturers as well as for some customized bundles that are interesting.

“Astronomy on the Go” is about the logistics requirements for transporting lightweight astrophotography systems whether it is in the family car, a short hike to a local dark spot, or flying abroad on vacation or business. The wide variance in major, global, commercial airline, carry-on baggage allowances are discussed along with suggested options for carrying telescopes, mounts, and cameras with you as you travel. Examples of air transportable portable observatories are presented and evaluated from a capability versus weight and volume perspective.

8 inch SCT on a SkyWatcher AZ Mount

8 inch SCT on a SkyWatcher AZ Mount

In closing, why a lightweight Alt-Azimuth mount and not a lightweight German equatorial mount like the iOptron SmartEQ?  The simple answer is that Synta and iOptron GOTO azimuth mounts can take a heck of a lot of abuse and keep on ticking.  Take a look at this photograph.  That is a Meade 8 inch LX200 OTA sitting on a SkyWatcher SynScan AZ GOTO mount. The OTA weighs 12 pounds (~5.5 kg). The SkyWatcher mount has no difficulty with this load for gotos and tracking.  And yes, it’s sitting on the same much maligned tripod used by the SLT mount that is supposed to vibrate, shake, and lean and there is no 5 pound bag of sugar on the accessory tray.

Try overloading a typical German equatorial mount’s stated payload by 50%. I have never tried the 8 inch SCT on the SkyWatcher AZ mount for photography but have used the SkyWatcher mount with my C6S OTA and a DSLR many times.The C6S OTA and the SkyWatcher SynScan AZ GOTO mount are soul mates, a perfect match.

NGC 0253

NGC 0253  C6S @f/6.3, SW AZGOTO Mount, Canon 1000D, 123×30 seconds

NGC 0253  C6S at f/6.3, SkyWatcher AZ GOTO, Canon 1000D, 123×30

The SkyWatcher SynScan AZ GOTO mount is not available in the USA. Electro/mechanically is it very similar to the SLT mount but does have a different hand controller with very spartan programming; a two bright star align that no one can get to work, and a typical two star align that works very well. It gives very little information about the 42,900 objects in its data base.The SkyWatcher AZ mount tripod is identical to the SLT tripod. In Europe the SkyWatcher AZ GOTO mount is 25% cheaper than the SLT mount and 50% cheaper than the SmartEQ PRO.

Bahtinov masks on scopes

Astrophotography 101___Achieve Critical Focus, Using a Bahtinov Mask

Baht masks on scopes

Two Common Designs for a Bahtinov Mask. The APO on left has a mask which can be hung on refractors which fall within a specific range of sizes. The Mask on the right hand side is designed specifically for the Celestron 8 inch SCT, it is cut to fit over secondary. (IMAGE #1)

 

There are various methods one can use to achieve critical focus when preparing for an imaging run. The easiest method requires one to purchase or make a Bahtinov mask. A Bahtinov mask generator is available online, allowing you to create the exact mask pattern necessary for your imaging telescope. You can than print out this pattern and transfer the design to a suitable material which can be cut out with a sharp hobby knife. There are also several manufacturers who offer plastic Bahtinov masks at a very reasonable price in the $10 to $30 range. I purchased several bahtinov masks through Farpoint Astronomy Products, they were well built and available for a reasonable price(Image #1). A Bahtinov mask is a necessity in my opinion for anyone doing astrophotography.  Every astrophotography toolkit should include one for each scope which is to be used for astrophotography purposes.

A Bahtinov Mask was first invented by Pavel Bahtinov, a Russian telescope maker and astrophotographer . He made the design available to the amateur astrophotography community in 2008. The Bahtinov mask is designed with a series of grids, three in all, arranged to produce a six pointed cross shaped diffraction pattern at the focus plane of the camera’s imaging chip. The diffraction pattern has 2 lines intersecting in the shape of an X, with one extra line running down the middle. Critical focus is achieved when the middle line intercepts the X pattern at dead center between of the other two legs forming the X.(Image #2 Below Right)

Daltonskygazer.com focusing with bahtinov mask in focus star image

The 6 pointed diffraction pattern created by the Bahtinov Mask showing a focused star.(IMAGE #2)

In order to use the mask you must be running camera control software with a pc or any device capable of running software which displays the imaging camera view onto the screen. Most of these programs offer a frame and focus mode which includes a framing reticule built into the field displayed by the camera. A few programs which I have used include Canon EOS utility, BYEOS, and Nebulosity 3.0. Currently, I use Backyard EOS Premium Edition to control my dslr for all imaging runs. I find BYEOS offers the most bang for the buck, it includes a lot of great features for the price. The software includes a built in focusing routine which displays the FWHM focusing method. Critical focus using the FWHM method is achieved when the number representing the FWHM value is at is lowest numerical value with mask covering the ota and a bright star in the field of view. I rely solely on the pattern produced by the Bahtinov mask, but I do look at the matching FWHM value when focus is achieved. This at minimum gives me a focus point which I can return to during the evening after the image run has commenced. The star spike pattern should look like the image seen in (image #3) below left when critical focus is achieved.

Screenshot showing the BYEOS FWHM value and a focused star with the 6 pointed diffraction pattern in perfect alignment.

BYEOS STAR FOCUS IMAGE

Screenshot showing the BYEOS FWHM value and a focused star with the 6 pointed diffraction pattern in perfect alignment.(IMAGE #3)

Neils Noordhoek wrote and offered a great focusing program(free) which helps to achieve critical focus when using a Bahtinov mask. It is a very small but powerful program. It offers sound cues when adjusting the focuser which tell you when critical focus has been achieved. Sadly, Neils is among the stars, his final blog at his site written by his wife, “With great sadness I have to let you know that Niels took a one way trip to the stars on October 17th 2012. Please remember him with a good glass of red wine on a bright starry night.” Niels Noordhoek’s Blog can be found at Niels Noordhoek’s Weblog. The program download link page for his free focusing application can be found at Bahtinov Grabber.

I find using the Bahtinov Grabber is a much more accurate way of obtaining critical focus than relying on the eye alone. The program is designed such that it cues critical focus once the proper angle of the spikes is achieved. The program is not a necessity, I use the program because I like the audible cue built into the focusing routine. I do think it works better than relying on my eye. I have checked images of the spike pattern which I thought were in focus against the Bahtinov Grabber program which showed them slightly out of critical focus. After doing these tests, I use the Bahtinov Grabber program 100% of the time during my focus routine. The tutorial offered here at DaltonSkyGazer is based on using the Bahtinov mask with your choice of camera control software. I do not include the Bahtinov Grabber into the tutorial. If you wish to try it out I suggest you download a copy through the link provided above. I think you may find the program is a nice application to add to your goodie bag.

 

 

Astrophotography 101 – How to Use A Bahtinov Mask

Achieving Critical Focus When Using a Bahtinov Focusing Mask in Six Easy Steps

1.  Install the Bahtinov Mask onto the end of your optical tube. It should be hung over the tube; usually the mask includes plastic screws or a means to fit around the secondary mirror holder. See (image#4) below:

Bahtinov masks on scopes

Two different Bahtinov Masks shown hung properly on two types of ota’s The left mask uses three plastic screws which adjusts for 3 inch and 4 inch refractors. Hang this mask using the plastic screws. The mask on the right hand sct is specifically made for the 8 inch HD OTA it is cutout around the secondary mirror to fit the ota snuggly. Be very careful when removing the mask from the sct, you do not want to scratch or damage the corrector plate.(Image #4)

2.  Slew to a bright star which is located near the object you are planning on imaging, using the precise goto function if your mount supports it.

3.  You will now use the camera control software of your choice either in live view or manual exposure mode to focus the star with the mask in place. Most people use live view mode, but I prefer to take slightly longer exposures while in manual mode so that I can easily see the diffraction pattern created by the mask. Center the bright star using your finder scope if the star is not in the field of view of your camera. *Tip-Ensure your finder scope and imaging ota are aligned before imaging at the beginning of every observing session. If the star is way out of focus you will get an image which looks the picture below. You will have to move the focuser in or out until you see a six pointed diffraction pattern displayed in your short exposures. The star will get smaller as you near the focus point. The image below shows a star which is out of focus quite a bit:

out-of-focus-mask-1 Astrophotography 101 achieve critical focus using bahtinov mask

A bright star which is out of focus quite a bit . The only thing seen is the pattern of the Bahtinov Mask.

4.  Continue to adjust focus until a six sided spike emerges.  I have moved the focuser inwards a bit more in the following image, notice the spike pattern is very easy to see now as the telescope nears focus. The star is out of focus by a very small amount. For remaining adjustments, only use fine adjustments to the focuser going forward. See( image#5) below:

Astrophotography how to achieve critical focus

Slightly out of focus star, the diffraction pattern is easy to see but the center spike is off to one side. Use only small motions when adjusting the focuser at this point.(Image #5)

5.  Continue to adjust focus using small adjustments until the star spike pattern is equally centered.  Finally, critical focus is achieved. This image shows the diffraction spike pattern with the spike properly centered in the middle leg. At this point, a program such as Bahtinov Grabber should be run ensuring true critical focus point has been reached. The Bahtinov Grabber application is more accurate than my eye at determining the focuser position where final critical focus is achieved . A bright star showing near perfect focus in (image#6) below:

Astrophotography 101, how to achieve critical focus

The 6 pointed diffraction pattern created by the Bahtinov Mask showing a focused star.(IMAGE #6)

6.  Now that you have achieved critical focus you are ready to start your imaging run.  At this point of time I would do a precise goto for the desired object to be imaged.  Once the goto is finished, I would do a 30 or 60 second exposure to ensure object is in view.  I would than frame the object placing it in view using the rule of thirds.   You should check focus once per hour if the temperatures are falling during the night, using your bahtinov mask. Also be sure you grab dark frames which are temperature matched to your light frames often throughout your imaging run.  Once you practice this routine a few times you will find that it only takes about one to two minutes to focus your telescope using a mask. You should take a one minute exposure once you are on target so that you can check framing and focus one last time by eye.

Clear Skies!

Jeff Turner
aka “DaltonSkyGazer”

Field Power Distribution System from Zengineering

New Astronomy Product: The Zengineering Power Brick- DC Power Distribution System

Field Power Distribution System from Zengineering

The All New Zengineering Power Brick. A 12 volt DC Power Distribution System suitable to power all of your gear in the field or in the observatory, including your laptop via dc power. Note*  A properly sized Marine Deep Cycle 12 Volt battery is required.

New for 2015, the Zengineering Power Brick 12 volt Dc Power Distribution System.  All you need is a 12 volt deep cycle marine battery and the Zengineering Power Brick to provide power for all of your astrophotography gear in the field or while set up at your observatory.  *Note the Power Brick is an Electronic Power Distribution System, a marine deep cycle battery is required and must be purchased separately.  Zengineering has been providing unique hand made astronomy products to the community for many years.  Each product is thoroughly tested and built to order.

With adjustable “switched and fused” laptop power, two fully ISOLATED ports for 12v cameras, two switched ports for DSLR cameras at 8v, real-time voltage monitoring, multiple switched 12v outputs, and full reverse polarity protection, Zengineering’s POWER BRICK is an astronomer’s most valued tool. It is designed to work in conjunction with a 12v Marine Deep-Cycle Battery for optimum performance (+/- 100Ah). It will also work with any 12v battery. Connect your battery to the “12v In” RCA port on the POWER BRICK and it then offers the convenience of providing multiple critical power “switching” options for all your devices in a live situation.

Features:  12v RCA IN (Connect battery here without fear. POWER BRICK has full Reverse Polarity Protection)
Total of NINE 12v Outs + Two 8v DSLR Outs + Fully Adjustable Laptop Power System (Switched & Fused)
1x “Switched” 12v Isolated & Regulated output 1.25A (shared among two RCA jacks)
1x “Switched” Adjustable “Step Down” Outputs x2 RCA @ 3A (Set @ 8v for DSLR Cameras)
1x “Switched” 12v out 6A, with 2 RCA outputs
1x “Switched” 12v out 6A, with 3 RCA outputs (Best for Dew Heaters, Focusers, etc.)
1x “Switched” Laptop Power Output (Factory set to 19.5v, user adjustable 12-36v)
Laptop circuit is protected with externally accessible 6A GMA Fuse
1x Cigarette Style 12v Out (Direct to battery) [Use with our “Cigarette Multi Port Adapter”]
1x 12v RCA Out (Direct to battery)
1x Battery Voltage Meter for Real-Time Voltage Monitoring 3-30v (Red Digital Display)
Full Reverse Polarity Protection on the 12v Input (Connect your battery without fear!!)
Rugged, Stylish, Compact, Solid, Aluminum Housing Rubber Feet (POWER BRICK Stays where you put it!) Rated @ 15A Continuous Load with equivalent 100Ah Marine Deep Cycle Battery Max Current Rating 15A* (Per POWER BRICK & Battery) Chassis Approx. 2.25”H x 4.75”W x 3.75”D

Zengineering’s POWER BRICK contains an efficient “Step-Up” voltage converter that doesn’t simply charge a laptop’s battery, but in fact fully powers the laptop, and the USB devices attached to that laptop, with ease. By default the “Step-Up” voltage is configured @ 19.5v since it is the most common laptop voltage. However, for those that require a different laptop voltage, it is fully user adjustable by turning a small screw inside the unit. Since the built-in “Step-Up” converter is providing laptop power only, it is much smaller and more efficient than a stand alone AC power inverter. Also, unlike most 12v auto power inverters, the POWER BRICK is completely silent. As an added benefit the POWER BRICK generates a small amount of heat when a laptop is being powered. By design, the chassis acts as a heat sink. In practice it is just enough heat to keep the unit free of all but the most serious dew formation. Additionally, the POWER BRICK supports devices Like DSLR Cameras that require a lower non-standard voltage. The “Step-Down” power section is set at 8v to support the majority of DSLR cameras, but is adjustable from 3v to 11v.

PowerBrickAnimation

Note: Some high power devices, including LCD and CRT monitors, may require a second POWER BRICK, and second battery to safely handle the constant high current loads. I do not recommend putting combined loads higher than 15A on the POWER BRICK.

Zengineering’s POWER BRICK is a hand-made precision device. Orders are constructed and shipped in the order they are received. Shipping will be 4-5 Weeks from time of order. Shipping is via USPS Parcel or Priority mail as well as USPS international post.

Zengineering’s POWER BRICK is a compact 12v DC power distribution system for folks that need to efficiently manage all their power hungry devices out in the field, or within their homes and observatories. The POWER BRICK has your next observing session covered. It offers everything you need to power all your gear including those devices with radically different power requirements. The POWER BRICK then takes it a step further and includes built-in ISOLATED outputs to help eliminate noise and interference!

Snowmagedon 2015 – Honest Weather Forecasting or Overblown Media Hype?

Weather forecasters have been going absolutely crazy the past few days calling for a blizzard with historic amounts of snow.  You would think the end of the world was coming based on the various cover story titles posted these past few days.  The governors of several states have called for complete closure of the road systems within respected states ahead of the actual storm hitting.  Since when do states completely close down the road systems, is this the new norm?  Something is not right, something has drastically changed over the past few years the weather forecasters, media, and government need to be held accountable. Perhaps, the “Global Warming” lobby is behind this?  It does appear as if all of the weather forecasters and media outlets are scrambling to come up with the scariest and most gloomy, doom ridden headlines these days.  It appears that accurate weather forecasting has become a thing of the past while profit from viewership and ratings is driving the “headlines machine” these days. Many coastal communites and those located near the coast were affected by this storm, however many areas predicted to receive several feet of snow barely received any snow at all.  The forecasts were highly innaccurate for a substantial part of the forecast areas.

The media driven forecast for Snowmagedon 2015 has come and gone leaving a very bad taste in my mouth.  We received a few inches of snow in my local area, six inches in total, with the forecast calling for several feet.  I had checked the forecast a few times daily leading up to the actual storm and several times the day and evening of Snowmagedon 2015.  I looked at the live weather map hours before the storm was due and during the storm; I just could not fathom how we were supposed to get so much snow out of this one storm.  I am not a trained weatherman, but point being that it was obvious to me that there was no way we were getting several feet of snow out of this storm, the track was too far East of my location.  Why is it that all of the sudden government has to completely shut down the entire road system for the state?  Why is it that each new storm is talked about like it is the end of the world?  The closing of the road system just adds more drama and more hype to the kettle, something just does not bode well with me.  Personally, I think there is a hint of politics behind the weather news these days, and with it the scent of money.  We have great weather forecasting technology the best of any time historically, can we get back to basics and report the weather accurately and honestly without political motivation or financial gain being the primary concern?

V5 Astro Products ZEQ25 Tefplate

New Astronomy Vendor Announcement_______V5 Astro Products

V5 Astro Products is an online astronomy store, devoted to upgrades, accessories, and modified products for the iOptron line of telescope mounts.  Almost all V5 Astro products are hand fabricated or crafted in the USA. There is no mass production and quantities and availability of items will vary.

V5 offers various upgrades which improve periodic error and smooth out tracking on several iOptron Mounts. The upgrade kits are very easy to install. V5 Astro Products offers replacement knobs, tripod levelers, precision tuning kits, and a few other unique items specific to iOptron telescope mounts.

The company warranties all products against defects in material or workmanship for the life of the original purchaser. Direct replacement will be provided in all cases. Full refunds will be considered on a case by case basis, provided the original component is returned in good condition.

If you own an iOptron telescope mount be sure to check out V5 Astro Products. V5 Astro Products releases new products several times a year.  The items offered are based upon field experience with the actual iOptron Mount models, and are designed to improve upon the original iOptron product.

A Few V5 Astro Product Images Appear Below with Brief Description of the Product

Polar Scope Spacer– Aluminum spacer, precision turned and knurled. Supplied with self adhesive felt tape to center the front of the tube, and a neoprene o-ring which centers the scope in the housing. A longer 3mm socket cap screw and 1.5mm allen wrench are included. Ring secures to polar scope with set screw.

V5 Astro Products Polar Scope Space

V5 Astro Products Polar Scope Spacer -Aluminum spacer, precision turned and knurled. Supplied with self adhesive felt tape to center the front of the tube, and a neoprene o-ring which centers the scope in the housing. Product Number V5_06

V5 Astro Products ZEQ25 Polar Scope Spacer

V5 Astro Products Polar Scope Spacer -Aluminum spacer, precision turned and knurled. Supplied with self adhesive felt tape to center the front of the tube, and a neoprene o-ring which centers the scope in the housing. Product Number V5_06

 

Fine Pitch Belt and Pulley Kit 9mm RA– This is a set of modified ZEQ25 pulleys (2) and a 2mm pitch belt that replaces the original 3mm pitch pulleys and belts. Fits all iEQ45 mounts from start of production to present. Fits standard worm and HP worms. 9mm RA AXIS ONLY, will not fit DEC axis. Easy bolt on installation. Supplied with shortened 1.5mm allen key for easier access to pulley set screws. Downloadable Pdf instructions sent at time of shipping.

V5 Astro Products Fine Pitch Pulley Kit 9mm RA

V5 Astro Products Fine Pitch Belt and Pulley Kit 9mm RA -This is a set of modified ZEQ25 pulleys (2) and a 2mm pitch belt that replaces the original 3mm pitch pulleys and belts. Fits all iEQ45 mounts from start of production to present. Fits standard worm and HP worms. 9mm RA AXIS ONLY, will not fit DEC axis. Easy bolt on installation. Supplied with shortened 1.5mm allen key for easier access to pulley set screws. Downloadable Pdf instructions sent at time of shipping.

V5 Tefplate for the iEQ45-CEM60

NEW HOT PRODUCT!

Fabricated from PTFE (Teflon) sheet, .090′ thick. This Tefplate fits all iOptron iEQ45 and CEM60 mounts from start of production. Fits both tripods and piers. No tools are needed for installation, just remove mount, install Tefplate and reinstall mount. Note: Do not over-tighten the azimuth locks, snug is good.

V5 Astro Products EQ-45/CEM-60 Tefplate

V5 Astro Products Tefplate-Enjoy smooth motion when adjusting azimuth, say goodbye to the stiction and overshooting your Polaris position. Note: Do not over-tighten the azimuth lock, snug is good.

 

 

 

 

Moon Image Triplet 80mm Meade

DaltonSkyGazer Observatory Switching to A New Website for 2015

Moon Image Triplet 80mm Meade

Moon. 80 mm Meade 5000 APO.

I am currently in the process of updating the DaltonSkyGazer Observatory website.   I will be making many changes during coming weeks, during this time many articles and features will be unavailable.  A few of the older articles and tutorials will be back up along with several new ones which have been in the works for some time now.  You will see many changes taking place at DaltonSkyGazer Observatory Blog and Website over the coming weeks as I work on finalizing the layout, site structure, and color scheme.