Exposure Calculator Resolution Numbers

[Della]

Hello, I have a question about the numbers generated for resolution under Exposure Opportunities on the Exposure Calculator.     For my Celestron 8 SCT with a ASI 533mc camera with a .63 reducer, it is giving me a resolution of  7.3.   This number is higher than I was expecting so I think I do not appreciate what it is telling me.



I found this in the help: 

• Res. - the effective resolution in arc seconds during the block of time. Effective resolution depends on the imaging system, seeing, airmass, and the Nyquist sampling theorem
  

So looking at the items listed above, 
My system has about 0.6 arc sec a pixel
The Nyquist as best I know how to calculate it is 1.21  arc sec
If is the air mass is as close to 1 as possible and seeing is okay to good, I would expect that to limit me to around 1.5 to 2.x arc sec.

So I am not sure where the 7.3 is coming from or what it is telling me.

Since the exposure calculator under camera data has the correct camera arc sec per pixel at 1x1 bin I know its reading all my setting correctly. 

Anyway, any insight into how this value is calculated or what it it telling me would be appreciated as I am finding the more I understand the data in SkyTools the easier it is to plan  .

Thank you for your help.


I attached a  image of my exposure calculator if that helps


Shawn

[theskyhound]

Hello,

I had to go look at the code to figure this one out. I believe it may be your telescope. The help system left out your telescope optics from the list of effects. For many systems the maximum resolution is set by the camera or the seeing, but in some cases its the telescope optics. Another facyor is the seeing. You have it set to Average. Try setting it to Excellent. Does the number get smaller?

[Della]

It does get smaller.  for good of 1.25" I now have a Res of 5.5.  For excellent of 0.6"  it gives me 4.3,  which still seems high to me. 

If my systems optics have a limit of 0.61" and a Nyquist of 1.2" then it would seem on a night of good seeing if everything is working perfectly,, wouldn't my resolution be close to 1.25" for targets near 1 air mass?

Shawn

[theskyhound]

That seems reasonable. But I'd have to look at the code as it executes for your imaging system to know for sure. If you would like, post it here or send it to me. To do that, open your Imaging Systems, select yours, and click Save. This will save your imaging system to an stx file that I can import.

[Della]

I have attached my imaging system.

Thank you

Shawn

[theskyhound]

Hello,

Thanks for sharing your imaging system. I stepped through the code and found that the calculation for effective resolution looks at the telescope optics, the seeing, and the resolution of the camera. It picks the highest of these values as the resolution limit. For reasons that I will need to spend some time looking into I introduced a factor of 3 during testing, which seemed to best reproduce the results. For the time being, just think of the effective resolution as a sort of practical limit rather than a theoretical one. In the end, its only the relative values that are all that informative, e.g. how does the seeing change it, how does it differ between ystems, etc.

I am currently having a nice chat with ChatGPT about this topic to make sure that I have all the based covered correctly, as the effective resolution isn't a common calculation. Most people just cite the pixel scale.

[Della]

Okay thank you for the update. I look forward to seeing how your conversations with ChatGPT turns out.

[theskyhound]

Actually, it worked out quite well. I made some corrections to the code, and now feel very confident that it is working correctly, although I doubt anyone will ever be able to tell the difference.

But more importantly, I decided to drop the arbitrary factor of 3, which makes the values much more reasonable. It has no effect on the actual calculations because the resolution numbers are only used in a relative sense. Thanks for asking about this!

[Della]

Thank you for looking at that for me. i will be watching for a future update to check out the change.