What level of de-centering is acceptable in an 18-250 lens? - Printable Version +- Opticallimits (https://forum.opticallimits.com) +-- Forum: Forums (https://forum.opticallimits.com/forumdisplay.php?fid=4) +--- Forum: Just Talk (https://forum.opticallimits.com/forumdisplay.php?fid=17) +--- Thread: What level of de-centering is acceptable in an 18-250 lens? (/showthread.php?tid=3345) |
What level of de-centering is acceptable in an 18-250 lens? - boren - 03-06-2011 I'm considering buying a Tamron 18-250 lens (probably second hand), and as far as I understand most of these lenses suffer from some level of de-centering. For sure I won't purchase a copy that isn't totally free of any signs of de-centering at f/11, but is it reasonable to expect this at f/8.0? If it isn't a pipe dream then this is the benchmark I'm going to set for myself when testing the lens. If it isn't reasonable to expect this, then I may just give up the whole thing. Thanks! What level of de-centering is acceptable in an 18-250 lens? - Rainer - 03-06-2011 [quote name='boren' timestamp='1299415742' post='6553'] For sure I won't purchase a copy that isn't totally free of any signs of de-centering at f/11 ... [/quote] If you take this serious, you should eventually not buy such a lens. For most of the focal length, f/11 is not yet 2 stops down ... not much to let the mentioned centering weaknesses completely disappear. You buy such a lens for a reason ... that is flexibility an convenience. There is a price to pay for that. Just my 2cts ... Rainer What level of de-centering is acceptable in an 18-250 lens? - boren - 03-06-2011 I'm well aware of the compromise, but if I can't get rid of the de-centering by stopping down, then there's really no point in buying it. I don't expect to be able to use such a lens wide open for anything but emergency shots. There's no free lunch. If the lens is sharp at f/8.0 throughout its zoom range and across the frame then I'd be more than happy. When I'm traveling I usually get by just fine with shooting around this aperture value. What level of de-centering is acceptable in an 18-250 lens? - boren - 04-05-2011 I'm going to meet the seller today, so any last minute opinions on this issue will be appreciated <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='' /> Thanks! What level of de-centering is acceptable in an 18-250 lens? - Klaus - 04-05-2011 [quote name='boren' timestamp='1299415742' post='6553'] I'm considering buying a Tamron 18-250 lens (probably second hand), and as far as I understand most of these lenses suffer from some level of de-centering. For sure I won't purchase a copy that isn't totally free of any signs of de-centering at f/11, but is it reasonable to expect this at f/8.0? If it isn't a pipe dream then this is the benchmark I'm going to set for myself when testing the lens. If it isn't reasonable to expect this, then I may just give up the whole thing. Thanks! [/quote] Yes, it is reasonable that centering should not play a real-life role when stopping down by 1 f-stop. From a lab perspective you will, of couse, see it beyond in any case but who cares. What level of de-centering is acceptable in an 18-250 lens? - boren - 04-05-2011 Thanks for the affirmation Klaus. If I find it difficult to detect obvious de-centering at f/5.6 for the wide-end and f/8.0 from mid-range on then I'm buying this lens (assuming it's fine in other regards, such as AF functionality, external condition etc). What level of de-centering is acceptable in an 18-250 lens? - Klaus - 04-05-2011 [quote name='boren' timestamp='1301985171' post='7381'] Thanks for the affirmation Klaus. If I find it difficult to detect obvious de-centering at f/5.6 for the wide-end and f/8.0 from mid-range on then I'm buying this lens (assuming it's fine in other regards, such as AF functionality, external condition etc). [/quote] Well, depends. All it takes is flat scene at a longer distance. That's not exactly a shop scenario though. I will try a little centering experiment this evening with you folks which includes a very basic test. That'll be interesting. What level of de-centering is acceptable in an 18-250 lens? - boren - 04-05-2011 I'm buying the lens from a private person, so hopefully it would be possible to step out and shoot a subject that's far enough to make DOF a non-issue. What level of de-centering is acceptable in an 18-250 lens? - boren - 04-05-2011 I checked the lens and decided not to buy it. It was difficult to test for de-centering, but since nothing was really sharp I guess de-centering would have been the least of its problems. To make matters worse, the AF was very slow AF and the MF ring felt as if I attached the lens to a Kenko tele-converter, in other words - it was noisy and difficult to turn. Maybe this whole ultra-zoom thing is not for me... |