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Canon EF 50mm f/1.8 II lens for Astrophotography
Posted: Thu Jul 13, 2006 6:21 pm
by weixing
Hi,
I done a simple test at various f-stop (F1.8, F2.0, F2.2, F2.5, F2.8, F3.2, F3.5 and F4.0) and below is the result showing part of the image at the edge. The image of the test shot (60s exposure @ ISO800) is at actual size and no processing had been done.
The test shot show that at F3.5 or slower, the stars image looks the best.
Have a nice day.
Posted: Thu Jul 13, 2006 6:38 pm
by weixing
Hi,
Below is the full image (no other processing done other than scaling down the image) at F1.8 and F2.8.
Can see the that the stars got tail even the image is scale down at F1.8, but the stars look ok at F2.8 when scale down.
Have a nice day.
Posted: Thu Jul 13, 2006 6:55 pm
by weixing
Hi,
Some more shot at F3.2 and F4.0.
Have a nice day.
Posted: Thu Jul 13, 2006 7:05 pm
by kingkong
what caused those streaking effect at larger aperture?
Posted: Thu Jul 13, 2006 7:23 pm
by weixing
Hi,
what caused those streaking effect at larger aperture?
I think it is cause by the uncorrected aberrations of the lens at wide open and vignetting cause by the LPR filter which is smaller than the lens.
Also, I think the pink and greenish colour at the edge is cause by the vignetting of the LPR filter when the lens is at faster f-stop... you can see some pink and greenish colour on the LPR filter if you look through it at an angle.
Have a nice day.
Posted: Thu Jul 13, 2006 9:58 pm
by kingkong
yes weixing, the vignetting caused by the filter is pretty obvious....
could you please indicate where the test shots came from the full frame?
i'm curious since with the filter the shots should be from a relatively center location of the frame...
thanks
Posted: Thu Jul 13, 2006 10:18 pm
by weixing
Hi,
could you please indicate where the test shots came from the full frame?
I have mark (by the white box) the location of where the test shot was taken from on this F3.5 image.
Have a nice day.
Posted: Thu Jul 13, 2006 10:53 pm
by kingkong
ah i see. thanks weixing.
did you do a comparison of the centers to see if it's usable larger than f/4?
Posted: Thu Jul 13, 2006 11:27 pm
by weixing
Hi,
did you do a comparison of the centers to see if it's usable larger than f/4?
Center is usually ok even at wide open.
Anyway, below is the center of test shots... 300x300 pixels at the center. The open cluster in the image is the M6 butterfly cluster.
Have a nice day.
Posted: Thu Jul 13, 2006 11:55 pm
by kingkong
ah. that's very good. thank you for sharing weixing.