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Old 14-04-2010, 07:52 PM
Andrew C
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Andrew C is offline
 
Join Date: Oct 2007
Location: Adelaide
Posts: 85
video astronomy capture

Following some dialog on this forum a couple of weeks ago I bought an easycap on the web and downloaded virtual dub for capturing to make a first foray into video astronomy DSO imaging. After some tribulations similar to others I eventually got the easycap working (I have Windows 7 and the driver supplied on the CD didn't work so I had to find and download and further update another driver). I had a bit of bother with virtualdub as well but now that is sorted out as well. The residual issue is that the W7 easycap driver does not permit capturing frames at anything less than the full 25 frames/sec PAL rate.

I can persevere with that and manually delete duplicate frames from each capture prior to stacking (next step in the learning curve), and/or do a workaround by making the capture time and capture file size limits very low compared to the integration time I am using in the camera to limit the number of duplicate frames in each capture.

A question that occurs to me is: what is the optimum integration time for image quality? I notice that many people seem to use the GStar at its maximum 2.56 sec integration time and do X captures (unique frames): is that better than say using 1.28 sec and 2X captures (or some other rule of thumb) instead, or going for about 5 sec (on my Stellacam3) and X/2 captures?

There is presumably a trade-off here, and I see people varying the 'X' quite a bit for different objects, but not using other than 2.56 sec integration time much if at all. I can imagine making the integration time too long will mean the individual frames will have bleeding around stars etc, overexposure and movement from imperfect tracking, but is there a lower limit? Maybe at that end of the scale, very short integration time means too many captures i.e. too much work.

Can anyone who has experimented with this offer advice?

Thanks

Andrew
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