Proper "rule" for pinpoint stars with M43

OutsideTheMatrix wrote:

Thanks, it sounds like 5 pixels is my "tipping point" for what I find unacceptable in star trailing. Would you have selected 10 sec rather than 8 sec at 14mm? I'll try again tonight and see what I come up with. For quick judgement of star trails, I'm magnifying the 3" LCD view to 7x first and then 14x.

For my 24 inch print (15 secs, 20 mm lens), I estimated that cutting my star trail down by a factor of 2 would have been fine. That cuts the trail down to 5 pixels! Seems like we're converging on the same tolerance. With a 14 mm lens, 16 mpx sensor, then 5 pixels would be 10 seconds. But, as I say, this is getting down to the psychology of various output sizes and media. On my laptop screen, it seems I don't object to 10 pixels.

I don't exactly recall, but I think 7x turns out to be 100% on my (E-M5) LCD. Sounds like the right magnification to look. 14x couldn't be worse.

13 sec seemed to make close stars blend together so that would be too high, but I could be convinced to go from 8 sec to 10 sec. I'm trying to achieve balance between capturing the most stars (highest possible shutter speed), less trailing (exposures under 13 sec at 14mm) and maintain the most star colors (means keeping the ISO under 3200).

Yes. Lots to juggle. I do hate to go about ISO 1600, though for milky way, you get pushed that far.

My take-away from this for me is 5 pixels seems good for my most optimistic presentation (big print, at close range viewing). This corresponds to 150/f for m4/3, 300/f if you use FF equivalent (i.e., "rule of 500" ... except 300). But, for casual purposes (web or laptop view), I can probably tolerate the full 500 (er, 250/f m4/3 focal length).

Now, camera makers, get the darn noise down...somehow!!