Old 08-10-2020, 08:51 AM
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PKay (Peter)
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Resolving power Question

I am currently planning my next image, and I do have a question :-)
Sorry about the maths.

See the attached zoom into M42:
Image details are:
Scope used: 150mm APO (resolving power about 0.80 arc seconds)
Camera: 4656 X 3520 pixels
Image scale 0.728 arcsec/pixel.
Dimensions in pixels: about 1012 X 800.
Dimensions in minutes: about 9.27' X 7.3'

Now, using the 305mm f/5 Newt.
The stated resolving power is 0.45 arc seconds.

Image scale: 0.55 arcsec/pixel (using the same camera).

Now I want to zoom in using either a Barlow, or eyepiece projection.

To get the required image, I need to use a 3X barlow (or appropriate eyepiece).

This will result in a FOV of about 10 X 13 arcmin (which is ideal).

However, the image scale will be 0.17 arcsec/pixel.

So I have exceeded the resolving power of the 305mm Newt (I think).

Question is:

Will this matter?
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Old 08-10-2020, 08:58 AM
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Atmos (Colin)
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I’d suggest to forget about resolving power. Being able to theoretically resolve details doesn’t mean you’re going to have the seeing conditions to do it. At 0.55”/pixel you’re probably resolving the best you can unless you move to Chile or Hawaii... or you want to do planetary imaging.
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Old 08-10-2020, 10:25 AM
Startrek (Martin)
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Likewise I was trying to push the envelope earlier this year on the Keyhole nebula in Carina using my 8Ē f5 newt with my Canon 600D pixel pitch 4.3uM and a 2 x Televue Powermate which effectively gave me a focal length of 2000mm and an image scale of 0.44 arc sec per pixel
This image was captured under pristine stable conditions at my place on the south coast , guiding around 0.80 arc sec error total , 20 x 5 minute subs stacked in DSS and processed in Startools
I stretched this image to the max and couldnít get anymore brightness, contrast or resolution out of it.
Iím going to experiment again using the new 2600MC but I donít think Iím going to achieve a great deal more
Mother Nature is always the winner here , the atmospheric conditions govern everything we try to do to get closer
You never know until you try though , physics never stopped anyone having a go !!
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Old 08-10-2020, 11:10 AM
glend (Glen)
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Peter, as the post below have said, it is not likely you can exceed the calculated scope resolving power, even under best conditions. Even chasing the focal length you would need is going to demand larger aperture, exceptional optics, and the nirvana of perfect Seeing conditions. Stick to what is achievable would be my advice, or accept the frustration.
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Old 08-10-2020, 11:43 AM
sunslayr (David)
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I'm no expert but I'd say unless you are significantly undersampled, dithering is going to give you all the detail you are going to get. It might be possible to use lucky imaging techniques to squeeze out a little more out of the sky if your camera is sensitive enough.
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