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Improving pics on my 6 inch SCT

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#1 John Tucker

John Tucker

    Apollo

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Posted 21 September 2021 - 12:46 PM

Generally I'm not seeing as much detail as I'd like, which is almost certainly associated with the FWHMs of about 5 to 6 arcsec that APP is reporting for my subs. 

 

The gear

  • Celestron 6SE purchased new from HIghpoint
  • Skywatcher EQ6R mount
  • Askar FMA180 guide scope with ZWO ASI120 camera (yeah, I know I spent as much on the guidescope as on the OTA, but I use the guidescope for imaging sometimes!)
  • ASI1294MC main camera, typically with gain set to 240 (a bit above "medium") 
  • Typically with an Optolong L-Extreme filter from my semi-rural backyard
  • ASIAIR - this limits my access to some of the neato PhD2 new features, but its made my life a lot easier
  • Crayford style focuser from GSO - this one https://agenaastro.c...-telescope.html

 

Observations and Practice

  • Typically 1 min exposure times with the filter - probably underexposed but trying to avoid saturating stars or pushing my luck on guiding
  • Guiding RMS typically 0.8 to 1 arcsec
  • I know people will nag me about the guide scope, but I don't see much in the way of elongated stars and if I stack a 2 hour set of subs without alignment, all you see is a symmetrical dithering pattern.  Any "mirror shift" appears to be pretty small with this little scope. 
  • The picture below is an an expansion of an unaligned overlay of about 100 1 min exposures with dithering after every third.  The pattern and the individual stars (each an overlay of 3 exposures) seem relatively free of elongation to my eye at least. The camera is binned 2 x 2 for this picture. 
  • No automatic focuser but I try pretty hard to get it dead on and the FWHMs don't seem to vary much across the night of shooting

What to do next?  Is this what you get with a $400 OTA?  Better guiding?  OAG?  Pitch the ASIAIR and do real PhD2? 

 

Screenshot 2021-09-21 124251.png


Edited by John Tucker, 21 September 2021 - 12:55 PM.


#2 Mark Lovik

Mark Lovik

    Vostok 1

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  • Joined: 09 Nov 2020

Posted 21 September 2021 - 01:11 PM

Your FWHM should be lower unless the seeing is really bad - find the limiting error first then go down the list.

 

- Check your collimation first - don't adjust unless you need to -  but check first.

- If you use the 294 -- try no reducer, no filter, and fast subs -- confirm guiding and reducer are not causing problems.  Use a bright star target high in the sky.

- Confirm you are getting good focus

 

Then work back to your normal imaging system and conditions in increments, checking as you go


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