Hyy guys, since I'd right now have to learn for some exams and am therefore periodically frustrated and/or bored while sitting around at home quite a lot, I've started taking pics of a printed out (simple laserprint, A4-sized) sharpness table. I've already taken some pics with most of my K-mount (and two M42 adapted) lenses, and I'm glad to share the results, but at the same time I'd like to ask for some advice - first of all, while center sharpness is what I adjust the lens for, how can you make sure that the lens has a good chance of even picking up the peripheral sharpness at the same time? With the 28mm lenses (which don't exactly count as ultra-wides on an APS-C camera in my book), I'm already only about 50cm away from the sharpness table, and since A4 paper is about 36cm in diagonal, I arrive at a distance of 50cm to the center and squareroot((50cm)^2+(18cm)^2)=53cm distance for the edges. That is obviously a significant difference when it comes to focus at F/2.8, so I'm not too surprised to see that the periphery always looks blurry until I step down to f/5.6 or so. Is there a better way to measure peripheral sharpness than this?
Actually, is there some sort of accepted and simple-to-replicate testing method for this kind of thing?
In total I have tested the following lenses:
SMC-M 50/1.7
SMC-M 28/2.8 Version I
SMC-A 28/2.8
Sigma Mini-Wide I 28/2.8 (M42 adapted)
Porst Weltblick 35/2.8 (M42 adapted)
Rikenon 50/2
Cosina Cosinon-S 50/1.4
Pentax 18-55 WR kit lens (just for reference at wide-open apertures, since I just wanted to see how the tele side competes wide-open against some old primes)
Testing conditions were: Cheap tripod, artificial light only (did this last night at 1:00AM, after finally coming to the conclusion that I won't be able to shove much more into my head anymore), manual exposure set to same shutter speeds for each aperture (might have screwed that up every once in a while), manual focus through viewfinder+magnification function, tried several times with each lens until I found the best (or in some cases, the least blurry) focus spot.
Well, first batch of results for the Asahi SMC-M 50/1.7 coming up... First set of pics are center and periphery at F/1.7, second set is shot at F/4.
Last edited by dec.net; 10-12-2014 at 04:51 AM.