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Advice Greatly Appreciated! Beginner Shooting M42

astrophotography cassegrain dslr dso equipment reflector SCT optics
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#1 Kane0304

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Posted 07 December 2019 - 01:53 PM

Hello All!

 

A new greenhorn here... just took my first photo of the Orion Nebula a few weeks back and have now fallen in love with DSO astrophotography!

My equipment is: Canon 80D (unmodified) and Celestron NexStar 6SE. I am shooting prime focus with a T-ring on the back of the SCT. I have also shifted forward the tube as much as possible to try and balance out the weight of the camera and tube.

 

Just spent my first devoted night out shooting the Orion Nebula, and I have had a few problems:

 

1. Tracking. I tried both Auto Two-Star and Three Star (SkyAlign), and after trying with both multiple times, went with Three Star because I had a bit more success. However, the tracking was TERRIBLE! Even with 10-second exposures, most were unusable. I took 63 30-second exposures and about 2/3rds came out with blur. I have made a GIF of the photos to show: https://media.giphy....g7PQ/giphy.gif 

- So. Would the StarSense module be a good investment, especially with the 10 additional objects that can be entered? Would this improve tracking?

- and is my camera the culprit here? I ran all of the tracking alignment and after that with the 80D attached... pretty sure that the tracking was still bad when I looked through an eyepiece and aligned it with only the eyepiece. 

 

2. Imaging. The telescope is 10 years old, and I know that the telescope is a bit uncollimated. There also appears to be a bit of film/condensation on the corrector plate. I plan on cleaning the interior with alcohol and DI water. When trying to focus, after a certain point, fine tuning is useless because the stars morph between different versions of blurry. I attached an uncropped and cropped photo of my best shot. Also attached a photo of the corrector plate. 

 

3. Probably as a result of this, DSS can't stack any of the light frames. Even when I set the the threshold to 2.

 

Any advice appreciated?

Attached Thumbnails

  • rsz_1rsz_best.jpg
  • rsz_best_cropped.jpg
  • rsz_dirty_telescope.jpg


#2 kathyastro

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Posted 07 December 2019 - 02:08 PM

The SE is an alt-az mount.  Unless you have it on a wedge, polar aligned, 30s is about the maximum you can expect for exposure times.  Your image has evidence of field rotation already.  Your GIF video shows the rotation quite clearly.

 

There is also evidence of coma.  You might need a field flattener.  A field flattener/focal reducer combination will work well, since your scope is pretty slow at f/10.

 

Definitely collimate the scope!


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#3 dan_hm

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Posted 07 December 2019 - 02:10 PM

Congratulations on your first image and welcome to the hobby of astroimaging.

 

GoTo has nothing to do with tracking, so no, the StarSense would not be a good investment if you want better pictures. GoTo simply points your telescope at the object you want it to point at. You could theoretically just use the hand controller to manually find the object in the sky and you'd get the same results. The Nexstar is an altazimuth-mounted telescope that is suited for visual use only. If you want longer exposures you will want an equatorial mount and a standalone telescope to mount on it. That mount would be aligned to the pole and would track in right ascension and declination rather than altitude and azimuth. You could alternatively buy a wedge for the Nexstar to achieve this same function, but I'm tempted to say those don't make sense to buy in this age of ultra-cheap equatorial mounts like the iOptron Skyguider. You can pair that with your 80D and a lens and tripod and get great pictures.



#4 bobzeq25

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Posted 07 December 2019 - 02:38 PM

I have information for you, but likely not what you want to hear.  Sigh.

 

Your tracking issues are fundamental to your mount.  The mount is the most important part of an imaging setup, and a one armed alt az mount has significant limitations.  Especially with your long focal length scope.  There is no magic solution.  A wedge and a reducer and an off axis guider and guide camera ($$$) would help, but, like dan_hm I'm dubious that it's worth the money.  I've seen people dump a lot of money into that setup, and still not be happy with the results.

 

It's not the camera, or the condition of the scope.

 

Sorry.

 

dan_hm has one excellent idea.  You'd get significantly higher quality images with a camera tracker and a lens.  If you do love astrophotography, and are in it for the long haul, that's the way to start.  This book will walk you through the process. 

 

http://www.astropix....bgda/index.html

 

Also, scroll down to the picture of the expert author on the page.  That may look to you like too much mount, and not enough telescope, but this is nothing at all like visual astronomy.  That's an ideal setup for getting started in astrophotography with a telescope.  $1200 Sirius (or HEQ5 Pro) mount, $500 70mm refractor.  No doubt not what you want to (or can) spend.

 

If you choose to continue down your path, that's fine.  You can get some OK pictures.  But don't expect miracles.


Edited by bobzeq25, 07 December 2019 - 02:49 PM.

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#5 miwitte

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Posted 07 December 2019 - 03:01 PM

I would try to bump the iso to 1600 or 3200 and try 2-3 sec exposures until you start to get egg shaped stars. This is where a program like bakers EOS( not sure if your camera is supported) helps. You find where your stars are round, then take a hundred or two and stack them.

The key to this hobby is integration time. With a mount like yours or just a tripod your only going to get 2-3 sec subs at best. However if you stack a boatload of 2sec subs you’ll get a decent image. You may have to go up in ISO but that makes noise bad. However it’s a good way to see what it takes and see if you get hooked. Then it’s off to a tracker or real mount so you can take longer exposures.

Also your focus maybe off a little.
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#6 Madratter

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Posted 07 December 2019 - 03:53 PM

First of all, congrats. I have seen far worse attempts.

 

Second, as mentioned the alt-az mount is a definite limitation. 30 seconds is about as long as you can go at that focal length.

 

Third, you need some kind of field flattener or part of the image will be out of focus. Focusing midway between the center and edge of the field will help even things out, but focus will still be off.

 

Fourth, you are correct. The telescope clearly is in need of collimation.


Edited by Madratter, 07 December 2019 - 09:39 PM.


#7 drd715

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Posted 07 December 2019 - 07:17 PM

Answer is HEQ5

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