Quote:
Originally Posted by SkyViking
Hi Paul, it is certainly an interesting debate. I have often wondered how the conditions rate at my site, but there is not much to compare with as these things are not discussed often.
Your guiding graph is very helpful in that regard. I have calculated the numbers for our respective guiding systems as follows:
Camera: ST-1
Pixel size (microns): 7.4
Binning: 2
Focal length (mm): 580
Resolution ("): 5.26
RMS (pixels): 0.106
RMS ("): 0.56
Camera: Lodestar
Pixel size (microns): 8.2
Binning: 2
Focal length (mm): 1273
Resolution ("): 2.65
RMS (pixels): 0.100
RMS ("): 0.27
I changed binning to 2x2 and as a result your RMS of 0.106 now corresponds to 0.5" (so twice as high as I thought, had it been 1x1).
I would think that if you do have sub-arcsecond seeing but your guider resolution is 5.26"/pixel then you might not be getting the full advantage of it? I don't know though since guiding works on a sub-pixel scale. But based on these numbers I'm actually thinking of going to 1x1 binning on my guider. I only bin to get higher sensitivity, but when the guide star is bright enough I'll try 1x1 instead - it's worth a try at least.
When speaking of seeing I consider this to be measured as FWHM over a certain period of time. That is what determines the final resolution of a deep sky image, which must be what we care about. For deep sky purposes FWHM must be measured with exposures equal to or greater than the guiding frequency. I'd say planetary imaging is different because exposures are a lot shorter and as a result of lucky imaging much finer detail can be picked up. I have taken planet images with the ToUCam that show much better resolution than the ~2" I get with longer deep sky exposures.
I'd be interested to know your FWHM's on typical deep sky exposures, are they sub 1"? If they are then you could comfortably be imaging at an image scale of say 0.3-0.5"/pixel (Nyqvist sampling) and take absolute killer images in terms of resolution.  |
I have used 1x1 at times in the past Rolf. If I had a good guide star it did seem to tighten up guiding results. No doubt that is from the higher resolution from the guide cam. That's a good reminder. If I get a good guide star I think I will use 1x1 next time as well to see if I get better results.
Greg.