Forum: Reviews Téma: Canon EF 50mm f/1.8 II lens for Astrophotography -------------------------------------------------------- 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. 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. weixing: Hi, Some more shot at F3.2 and F4.0. Have a nice day. kingkong: what caused those streaking effect at larger aperture? weixing: Hi, Quote: 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. 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 weixing: Hi, Quote: 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. kingkong: ah i see. thanks weixing. did you do a comparison of the centers to see if it's usable larger than f/4? weixing: Hi, Quote: 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. kingkong: ah. that's very good. thank you for sharing weixing. MCYM: Hi Weixing, Excellent test results you have posted. This lens is a keeper for both astrophotography and price standpoint. From my limited experience, the pinkish gradient at the edges is not a result of vignetting, but rather an artifact of LPR front filter. Unlike most camera dye filters, astro filters like LPR, are interference filters by design so as to achieve steep and narrow transmission passband. They conform to specs only at incidence and within a limited range of a cone angle. Beyond the certain angle, the spectral response gradually change due to incremental shift in transmission curve. Nevertheless the MW looks great under SG skies on previous posting. Cheers Matthew kingkong: matthew, are you certain the 50mm lens stepped down to a 48mm lpr filter is wide enough to result in what you suggested? i wonder how will hutech idas filter performed on wide angle lens. it comes in sizes up to 77mm, if i remember correctly.