A Reader WritesMy comments on lenses, especially those from the Leica M series, have evoked some confused and sometimes angry responses. I hope the following (non angry!) exchange of correspondence helps readers understand more clearly where I am 'coming from'.
Hi Mr. Ashley,
Dear Marc,
Thank you for your email. I will try to answer it as best I can.
I really am not from a future with a much higher standard!
My first comment: don't expect to find the same thing by looking at a different system. The ME clearly has not only a lower resolution sensor, but it is CCD rather than CMOS and has a different arrangement of micro lenses. Effectively, the performance of the lens at a pixel level will differ enough on these two sensors such that, though there will be some common factors, you really can't expect to find the same performance at a granular level. This highlights the reason that I always try to stress, in my reviews, that there's no such thing as lens performance and that what I try to do therefore is compare systems.
Secondly, having established as far as I can what is going on at the pixel level, I then look at the files either on a standard 100dpi monitor at 50% or on a Retina display. These both give quite good approximations to a 200 DPI print but if I am still in doubt I do make prints at 24x36" on a large format fine art printer.
Thirdly, if I find anything problematic or unexpected, I sanity check the result across a spectrum of sources: other reviews, the performance of the lens on other systems where possible, the experience of other users I know well and trust, and, most importantly, the Leica MTF. Clearly MTF has its own 'system' biases but it is still useful especially in doing detective work on field shape and sharpness and in establishing the effects of astigmatism.
Fourthly, my reference standard is - there is is no reference standard! I hold in my head experience from a variety of scenarios. In this case, the primary one is the experience I have of these same lenses on the M8 and M9. The next is my experience of lenses of similar focal length and/or field of view on other cameras. For example, I shoot a lot on a Nikon D800 so when looking at the Summilux 35mm FLE I am bearing in mind the performance of the 'best in breed' 35mm lens on that system, the Sigma 35mm F1.4 HSM. I also shoot a Sony RX-1 and that makes a good reference standard for 25mp full frame on a 35mm lens since it is almost perfect, due to the very smart design of lens and sensor as one system. I also shoot a Phase One IQ180 system and, though it is not perfect, I have reasonable experience of two different 35mm technical camera lenses (FOV= approx 24mm) and a lot of 'SLR' style lenses on the Phase body.
But above all I have one criterion: that, unless I am using a lens purely for its artistic abilities, I expect it to have certain base levels of technical abilities. For example, any high-quality lens from 24mm upwards should be able to achieve acceptable edge sharpness at F5.6 and viewed at about 200dpi. I don't think that's unreasonable as an expectation but it is not universal in practice! I also look for strange field shape effects that can give, for example, mid-field weakness or edge weakness with one focussing method and not with another.
Finally: if there isn't another lens I know in a similar price and quality bracket on a similar sensor size and resolution that can achieve my 'mental internal' target, I adjust the target. There is no point putting hope over experience!
A few years back, I was the first to publicly examine the issue of focus shift on the last generation 35mm Summilux. The threads ran for months and in the course of that experience I learned several things:
I stand by my conclusions about all three of the lenses you mention when used on the M240 but clearly I strongly expect other people to disagree. If I had a lens I really liked and which performed well, I would go with my own experience and not those of a reviewer. And if the reason for that was that I was not a very experienced or discerning user, I would think twice before 'raising my bar' because the only reason to do that is to guarantee a standard of output for certain audiences I might not have. In which case I would end up dissatisfied for no good reason. So generally, my reviews are to share my own finding with those thinking of purchasing a lens and with the same sort of expectations as myself. I would never want to tell existing happy users that they are 'wrong'.
Beauty is in the eye of the beholder!
HTH
best regards
Tim
ps please feel free to share this response with the forum members to whom you refer. My German is very weak indeed!
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