Hello! I made some improvements withe my mount stability with my 8" LX200 and SBIG ST-402. I was getting an image scale at 1x1 binning of 4.5 to 5.5 or so - occasionally down to 4.0 - when each pixel was at 1.2 arc-seconds
I was using a Meade 0.67 reducer. The spacing to the camera; however, gave 0.75 reduction and a focal length of 1540mm.
After sabilizing the mount, I also decided to try my Atik 0.5 reducer. At 1000mm focal length, the image scale was 3.72, or 1.86 arc-seconds per pixel, so I decided to give it a try.
After testing, many images have FWHM in the higher 3's, and a fair number at 3.5. The occasional image was even down to 2.9.
It appears that stabilizing the mount has yielded an excellent return Star images were nice and round. However, the down side, is the undersampling.
Would undersampling with FWHM of 3.5 be acceptable with an image scale of 3.72? I suspect that anything less would be undersampled too much.
I suspect that it would be better for me to return to the Meade 0.63 reducer and get a spacer to increase the reduction. I've got about an inch of free space before the the camera would hit the base of the fork mount, so I doubt that I'll be able to get the full 0.67 reduction. Best regards.
Mike
"After stabilizing the mount, I also decided to try my Atik 0.5 reducer. At 1000mm focal length, the image scale was 3.72, or 1.86 arc-seconds per pixel, so I decided to give it a try."
Mike,
I'm having trouble understanding your terminology. For a camera with 9 micron pixels with telescope of focal length of 1000mm the Image Scale is ~1.86 arcsecond per pixel.
"...the image scale was 3.72."
Perhaps you mean the FWHM of the seeing disk was 3.72 pixels. Please clarify what you mean when you use the term "Image Scale".
Phil
Sorry! 1.86 arc-sec per pixel and 3.72 arc-sec FWHM. A number of frames had good seeing that dropped the FWHM to 3.4 arc-sec.
This is below the Nyquist theorem of 2 pixels per FWHM by about 10%. Thanks.
Mike
Okay, Mike, thanks for the clarificaton. Let's round to one tenth arcsec.
I'll just state your situation slightly differently. You have 3.7 arcsec seeing and an image scale of 1.9 arcsec. This would give a sampling of the FWHM of the seeing disk of 1.9 pixels. ...certainly good enough that no changes need be made to correct this.
With a seeing of 3.4 arcsecs and the same image scale, the sampling of the FWHM of the seeing disk woulld be 1.8 pixels. ...still okay in my book.
...and these are the just the calculated numbers. Just be a little out of perfect focus, and you could be at 2.0 or more pixels.
Thanks! I'll have to see how many images have seeing in the low 3s arc-seconds. I think in that case, the undersampling would be too severe.
Mike