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The Frugal Astrophotographer


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A.K.A.: "The Beginner Astrophotographer," "The Grab 'n Go Astrophotographer," or "The Lazy Astrophotographer."

     "There's no such thing as cheap astrophotography" is a phrase often repeated.  I beg to differ.  There is a continuum of cost in astrophotography (AP), from a tripod mounted camera shooting star trails, to the Hubble space telescope.  This is what I'd like to share with folks who think they want to try AP.

     It all started when I saw posts on CN forums by nytecam and jgraham.  Their images were short, unguided exposures taken with small refractors using older CCD cameras.  I thought, "hey, I can try this."  That was one year ago.

Before we go any further:

     AP has a steep learning curve.  It can be very frustrating at times.  I recommend that you have a firm grasp of visual observation before you attempt AP.  I can't imagine doing AP without knowing the constellations and how to find objects.  The challenges of AP are twofold: equipment and processing.  I had to learn how to align and use a polar scope, focus my CCD camera (which needed extension tubes), set up my capture software, and take flats.  Processing your pictures to remove dust motes, amp glow, hot pixels, light pollution and noise to get the most detail out of your data takes lots of practice and advice.  I'm not attempting to explain all the vocabulary or how to perform every procedure.  Equipment is the focus of this article.  It takes weeks of trial and error, research and advice from multiple people to develop an understanding of AP.  As long as you keep a positive attitude, you will surmount the obstacles and be joyfully imaging in due time.  

Principles of Frugal Astrophotography:

1. Buy used.  If you can be patient, there is always someone with deeper pockets and shorter attention span out there.  Most of the time you can get gear for 50-70% of retail.  You can re-sell it for the same price and only lose the cost of shipping.

2. Have your gear serve double duty.  When not imaging, the tripod of my equatorial (EQ) mount is used to support my 150mm refractor for visual use.  The EQ mount can also serve as a nice visual mount for my 100ED refractor.  My imaging scope, the ST80, also serves as a travel and quick look scope.  Look at what you already have... can it be conscripted for AP duty?

My AP equipment:

Vixen Super Polaris EQ mount $200 used 

JMI AC right ascension drive $110 new 

DSI color CCD camera $110 used 

Nebulosity capture software $45 

Orion ST80, $90 used 

New Orion dovetail base, $5 

Antares 0.5x focal reducer  with 1" extension tube, $40 used

GIMP image processing shareware, free

Diffraction spike focusing mask, homemade

Total cost: $600

What it allows you to do:

     You can try astrophotography without making a huge investment.  If you don't like it, sell off the things you don't need.  Chances are, with the first image you make, you'll feel giddy as a schoolboy.  The whole setup goes out the door in one trip, which is nice for apartment life.  I only do a polar scope alignment (I'm lazy), so it is possible to have a quick 90min imaging session on a bright object. 

     I can make unguided shots up to 90s of brighter deep space objects.  Most of the time I take 30 or 60 second sub-exposures (subs).  Using the camera without focal reducer, you can nicely frame objects like M13 (Hercules Globular Cluster) and M51(Whirlpool Galaxy).  The FOV is roughly 0.5 degrees across.  Using the 0.5x focal reducer (FR) allows for a wider view and allows you to frame all three galaxies of the Leo triplet .  You can also take lunar and planetary photos with the DSI camera.  However, there are inexpensive cameras better suited for solar system imaging.  

     The camera capture software, Nebulosity, also allows you to subtract darks and flats from subs, stack your subs and do some processing.  (Subtracting darks eliminates amp glow and hot pixels from hour image and flats negate dust motes and other optical blemishes in your imaging train.)  GIMP has more processing/touch up capability like curves and allows me to airbrush away remaining hot pixels.  

     This scope/camera does best on large, bright objects, like star clusters.  But it can also show surprisingly dim galaxies (albeit without much detail).  Here is a shot of M11, the wild duck cluster, 44x30s, no FR:

This is my favorite globular cluster shot, M92, 77x20s, no FR:

What are the limitations:

     This is an unguided system, so you are at the mercy of polar alignment and periodic error (PE).  If you did not polar align properly, you will see star trails when you increase exposure time.  I only scope align, which is a rough process.  Perhaps I should perform drift alignment, but for now I'm content to take relatively short subs. PE comes from imprecise machining of your EQ mount gears.  These imperfections result in a repeated speeding or slowing of your tracking every time the gears complete a revolution.  Guiding manually or electronically is a way of countering these tracking errors, but it requires more equipment and money.  

     To take images free of star trails, you can take short exposures of 30s or less, or you take long exposures and throw away ones with trails.  At 60s, I have to throw away about half of my subs (if I'm being strict), which means it's more work to acquire data.  Star clusters, open and globular, are relatively easy targets that can give nice results with 30s subs.  Bright nebulae like M42, M27 can be done with 30s subs also.  I remember I tried to take a shot of the cone nebula one time.  Nada, bubkes.  That class of object requires much longer exposures and a more sensitive camera.

     Galaxies are a challenge.  They require longer (60s) subs to bring their faint detail out from background noise.  The brighter ones, like M81, M82 and M51 give nice images.  Other galaxies will be to small or faint to show lots of detail with a small scope and short subs.  Galaxies require the most patience and time.  Small planetary nebulae are also very tough.  M57 looks pretty small if I do not barlow the DSI,  If I do barlow, the image will be dim and require doubly accurate tracking.  The small aperture of my scope falls short here.  

     Oh, and you can't keep up with the big boys.  The casual observer will not swoon over images made with an antiquated, entry level camera.  Only you and a handful of others will appreciate how much work you put into it.  You can learn a lot and have much fun with this setup.  Where you go from here is up to you.

     Considering the limitations, you can tackle a lot of objects with this setup.  I'm going through a lazy stage right now.  Perhaps I'll get my gumption back and push the limits of this setup again.  To date, I've taken 22 images with this setup.  Here is my favorite galaxy capture, M82, 80x60s, no FR: 

Equipment considerations:

     Mount: For AP, a rule of thumb is to limit your payload to half of the recommended visual load.  I wanted a German Equatorial mount capable of carrying a small refractor.  Because of their reputation for good machining, I purchased a used Vixen Super Polaris.  I think the Chinese EQ3 can do fine with a 5 lbs payload, and a CG5/SVP would be better.

     Motor: Vixen motors are expensive.  A motor and controller would have cost around $300.  I went with a plug-in AC motor from JMI.  No batteries to deal with, just an extension cord.  It works well enough.  Again, the Chinese EQ mounts have very affordable drive options.

     Scope:  I wanted a light payload to keep weight and price low.  The inexpensive ST80 refractor was just the ticket.  Its fast f/5 focal ratio is good for imaging.  The short 400mm focal length also meant less magnified images, which demands less accurate tracking.  Another option is the Starblast 4.5 imaging OTA, but I prefer the collimation retention of the refractor.  Yes, there is chromatic aberration on bright stars, but it's not a big bother to me.  

     Camera:  Used DSI color CCD cameras can be had around $100 these days.  There is nothing close to it that I'm aware of.  Granted, it makes small, somewhat grainy images, but the price can't be beat.  Since it is a color camera, it's sensitivity is lower than monochrome, but you don't need to mess with color filters and taking separate LRGB exposures.  You can always sell it to another beginner and upgrade when you are ready to.

     Focal Reducer:  I just got this a couple of weeks ago.  My reasons were twofold: taking a wider shot means fewer star trails and keeping more subs.  For the same exposure time, images would be brighter at the expense of less image scale (magnification).  Comparing images with and without a FR, the reduction was more like .63x on my DSI (spec is 0.5x).  I was able to make images of the Leo triplet, M63 (sunflower galaxy) and M64 (black eye galaxy) with under 30 minutes total exposure time.  This would not be possible without the FR, but the images were small and fine detail harder to see.  There is always a tradeoff.  I think the wider FR shots work best on shots with multiple DSO, like the Leo triplet.

     Focusing mask:  You will need a focusing device.  Just pointing at a bright star and focusing on your computer is possible, but hard to get repeatable results.  I started out using a Hartmann mask, but now I use the diffraction spike mask.  It is simply a cardboard ring with 1cm wide tape forming a cross over the aperture.   When extremely out of focus, a bright star appears like 4 pizza slices.  As you focus, the slices merge and you see a pair of sharp spikes in four directions, 90 degrees apart.  In focus, the spikes merge into a single sharp spike.

     Taking Flats: Some people make light boxes for flats.  I use a variation of the Tee shirt flat.  I rubber band a white handkerchief around my dew shield.  The street light near me illuminates the hanky adequately for darks.  Yes, I do this with urban LP and street lights up and down.

On a typical night:

     I set up the tripod on spots marked with tape to save time on leveling.  Then I polar align the mount.  I hook up the computer, camera, and extension cords next.  Centering a bright star, I check focus with the diffraction spike mask.  It's now time to star hop to my target and make test exposures to determine exposure time and check for star trails.  If it all looks good, I start taking exposures.  Every 20 minutes or so, I re-center the object due to drift.  In between, I stretch my legs, play the Jew's harp, listen to the radio.  When I'm done taking subs, I take darks and flats, pack up and head inside to stack and process my image.  Finally, I share my image on CN.  It's usually 2 or 3am by then :)

In conclusion:

     This setup has allowed my to try AP on a small budget, and it's been lots of fun learning and capturing images.  It's added another dimension to astronomy for me.  These days, I'm gravitating towards seeing the object, but I think visual astronomy and imaging are synergistic.  I'll observe a new object, and get excited about imaging it, and vice versa.  As I get older, I become less of an "all or nothing" type of guy, and this setup gives me plenty more than nothing.  If you want to see more images from this setup, go to member galleries on CN forums and search for mathteacher.  Clear skies and happy imaging to you.

Regards,

Mr. Wang



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