Archived posting to the Leica Users Group, 2013/01/07
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Chris, One edge is sharper than the other. So, with a sharp ridge at "infinity" I take horizontal and vertical shots of the ridge and compare the edges of the frames at the different apertures. I used to test with resolution charts indoors. If you do that, making sure the film/sensor plane and target are absolutely parallel makes it much tougher. Also, the typically greater curvature of field at close focusing distances introduces more variables. Since the critical edge sharpness for me is usually at infinity -- a mountain ridge -- the method I'm using seems not only easiesr, but also more applicable to my landscape shooting. Paul www.PaulRoark.com On Mon, Jan 7, 2013 at 9:27 PM, Chris Crawford <chris at chriscrawfordphoto.com> wrote: > Paul, > > I'm curious about decentering. How can you detect it by looking at the > photos the lens makes...what does decentering do to the image? > > Thanks, > > -- > Chris Crawford > Fine Art Photography > Fort Wayne, Indiana > 260-437-8990 > > http://www.chriscrawfordphoto.com My portfolio > > http://blog.chriscrawfordphoto.com My latest work! > > http://www.facebook.com/pages/Christopher-Crawford/48229272798 > Become a fan on Facebook > > > > On 1/8/13 12:24 AM, "Paul Roark" <roark.paul at gmail.com> wrote: > >>Mark, >> >>I agree, in general, with what you are saying. However, assembly >>costs of Cosina may be enough less that an equal optic can be made for >>less. Also, Leica can command more for the same just because of the >>name. So, there are differences in both the supply and demand sides >>of the equation that may sometimes modify the strict "you get what you >>pay for" formula, particularly if we are just looking at optical >>performance. >> >>I put a fair amount of weight on the published MTFs of the 2 >>companies. While the MTFs of Leica and Zeiss may not be exactly >>comparable, the main performance variances I've seen from either -- >>actually only Zeiss -- appear to be due to de-centering and focus >>distance sensitivity. Specifically, my Zeiss 50mm f/2 has off-axis >>performance that takes its f/4 performance way below what the MTF >>represented. It is also clearly de-centered, and that may well >>account for the deviation from the published MTF. I buy from >>retailers where I can send things back. I did send 2 of the samples >>back. After the third de-centered sample I gave up and decided for my >>uses and given the budget I had to spend at the time, I'd just accept >>an optic that was barely better than the Canon equivalents, and >>clearly not assembled with the perfection of the sample they tested >>for the published MTF. (I have a sharp mountain ridge view from my >>back yard that easily detects a decentered optic.) >> >>Subsequently, I did purchase a Leica 50 f/1.4 ASPH, and it is the best >>1.4 I've used or tested. However, consistent with it's MTF, I can see >>a dip in performance, particularly wide open, half way out from the >>center to the edge. Also, the Zeiss f/2 is sharper in the center at >>f8. So, the Leica is not a perfect optic by any means (and it's way >>heavier). I might add that I've never had/tested a de-centered Leica >>lens, and the Leica MTF representations have been right-on all the >>time. >> >>The 18 ZM -- my other Zeiss disappointment -- is a retrofocus that is >>simply not good in the corners close up. (My Rollei SL66 50 Distagon >>was terrible there also.) It's a likely eBay item in the future. >> >>On the other hand, the ZM optics I have that are well >>assembled/centered, the Biogons, have relative performances -- Leica >>v. Zeiss v. MTFs -- that were very much predicted by the MTFs the 2 >>companies publish. The 35 f/2.8 Biogon image, in terms of sharpness, >>looks very much like that of the 28mm f/2.8 Elmarit ASPH I also have. >>On the other hand, the published MTF of the 35mm Summarit 2.5 is very >>unimpressive wide open -- sufficiently so that I am not interested. I >>believe Leica here and appreciate their honesty. I also believe >>Leica's MTF for its 35 f/2, and at f/2 it is not good enough to pay >>for given my usual landscape shooting. So, the Zeiss simply seemed >>to have the best combination of price and performance for my uses at >>this focal length. Same with the 21mm focal length. >> >>Down the road I may find that the Zeiss optics fall apart, whereas the >>Leica ones are far more robust; they do have that feel. So, far, >>however, the Zeiss Biogons I have deliver performances that are right >>up with the very good Leica optics but at a lower price, and so far >>they have held up fine. >> >>So, I tend to pick the optics based on the MTF as well as price. I >>don't expect magic from either (or any) company. >> >>For those interested, I've posted a Jpeg containing copies of the MTF >>charts of the optics I have and others of interest from Leica & Zeiss. >> See http://www.paulroark.com/BW-Info/Leica-Zeiss-MTF.jpg . >> >>Paul >>www.PaulRoark.com >> >>_______________________________________________ >>Leica Users Group. >>See http://leica-users.org/mailman/listinfo/lug for more information > > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information