arionelli
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 p.645 #6 · ZE/ZF/ZM Images (Official Thread!) | |
Still clinging to the medium format but I have been following the progression of the Zx lens line since their introduction. Financial needs have made the stepdown to 35mm dslr imminent but I'm not ready to buy in just yet. After skulking around here for a long time, I am beginning to get a feel for how some of these lenses render, even as seen in the thread on my laptop, and am constantly being blown away by many, many pictures here from many IMHO top shooters (and I'm still only on page 535).
Getting to the point of this post, I'd like to ask a somewhat theoretical question on something that perplexes me and that I hope a few of the more knowledgeable and experienced Zx users may discuss:
Zeiss' MTF graphs for the 50 Makro Planar show the 40 lp/mm curves clearly higher, straighter with tan = sag out to 15mm than the 50 Planar. However, in tests by Photozone (not my bible, by any means, as their lens evaluations don't seem to account for focus shift, field curvature or the remarkable photos presented by the "flawed" lenses on this forum), the 50P clearly has significantly higher centre resolution than both the MPs, shown below in line widths per picture height, all at f/5.6, yet its centre contrast mtf value for 40 lp/mm is a mere 60%:
50P centre 3960, border 3320, extreme 3357
50MP centre 3631, border 3229, extreme 3191
100MP centre 3700, border 3357, extreme 3373
At the wide end the 21 and the new 25 Distagons centre contrast values at 40lp/mm are also both about 80% but differ significantly both from each other and the 50P in resolution:
21/2.8 centre 3513, border 3147, extreme 3006
25/2.0 centre 3728, border 3313, extreme 2906
I used to think that mtf and resolution were in somewhat directly related, meaning that a lens with >80% mtf @ 40 lp/mm would be very sharp at that image height, and one with 60-70% would still be good but with significantly less fine detail. Now I am seeing that things ain't so simple. The 100MP (consensus status - "top of the bunch") begins its relatively modest mtf curve at 70% gradually receding towards 15mm. The 50MP's mtf is higher (around 80% at 10mm) out to 15mm. The 50P has a more fluctuating curve with greater seperation of T and S and 80% peaks at 10 and 18mm from centre, but it has the lowest centre contrast value and the greatest resolution. Instead the relationship almost seems inverse.Two other lenses I have (had) whose images I really like are the Hasselblad 120 4 Planar and Leica R 60 2.8 Elmarit, both Makros and both having mtf curves with highish centre values but falling off a cliff with image height.
I should just shoot more and think less, you're right, but I'm at a loss how all these variations are explained. My overall surmise seems to be that the mtf curves are a more comprehensive "preview" as to a lens' performance - higher, flatter, straighter, S=T along a greater image height all being better and presenting more of an image "rightness", ie closer to actually being there in the flesh, and that tests of resolution differences at the levels quoted above really mean bugger all. Any light?
Thank you. I hope this is the right place to ask.
Martin
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