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Proper "rule" for pinpoint stars with M43

Started Oct 27, 2016 | Discussions thread
OutsideTheMatrix
OP OutsideTheMatrix Veteran Member • Posts: 9,876
Re: Calculation from scratch; practical measurement

Giiba wrote:

boxerman wrote:

OutsideTheMatrix wrote:

I just noticed something really curious. 13 seconds is acceptable if you're talking about stars near the center of the field. But when those same stars drift towards the edge of the field, the star trails appear to blend close stars together. I wonder if stars trailing more near the edge of the field could be caused by lens distortion or perhaps a lower resolution near the edge of the lens?

That sounds right to me. I have read that lens coma, which gives you elongated images for points, is especially critical for astrophotography. So, that's a thing to look for. I don't think it's just lack of resolution, but maybe that contributes, too.

Lack of coma distortions is one of the key things to look for in a lens for shooting stars. Some lenses smear points across 20 or more pixels just from this imperfection. The only place I know of that tests this is Lenstip reviews.

Thanks for the tip I bet Olympus primes like the 75 1.8 are really good in this regard (much better than conventional telescopes like SCTs.)

Would you say that even Olympus zooms are better than SCTs in this regard?

Here is an image taken with an E-PL6 that I found on astrorobin:

http://www.astrobin.com/271196

that is with the 75mm 1.8 lens

 OutsideTheMatrix's gear list:OutsideTheMatrix's gear list
Nikon Coolpix P900 Olympus PEN E-PL6 Olympus OM-D E-M10 II Olympus M.Zuiko Digital 14-42mm 1:3.5-5.6 II R Olympus M.Zuiko ED 75-300mm 1:4.8-6.7 II +9 more
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