Quote:
Originally Posted by Atmos
Those 10 subs shouldn't make too much difference, they may a tiny bit but certainly not to the same extent.
When stacking a lot of short exposures together, they must be registered for small wobbled between each sub. I also wonder how well star registration works in fraction of a pixel changes in short subs. Maybe a large stack of short subs can be almost as bad as a large stack due to an inability to correctly register such small changes in stellar location. Someone else will know more about how small of a movement the PI Registration can work at.
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Thanks Colin. maybe this is suggesting that short subs will need care in stacking. My thinking was going down the same route - there may be local star-to-star distortion within the short subs that doesn't show up in individual sub FWHM, but will affect the final stack, unless a distortion correcting transform is used. Clearly needs more work, but is sounding plausible.
edit: thinking further, the star-to star distortion (if it exists) could have an origin in the small size of the isokinetic patch - stars will wobble differently in different parts of the image - that wobble will be averaged for longer subs, but will be partially frozen by shorter subs. Interesting that there seems to be a fairly smooth change from 5 minutes down - no sign of any plateau.