IQ of 7d w 15-85mm Vs 6d w 24-105mm?

Started Mar 8, 2013 | Questions thread
qianp2k
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Re: Correct
In reply to technic, Mar 12, 2013

technic wrote:

usedtobedontrustme wrote:

Here is some conjecture on my part. I would think that an a asp-c camera with an asp-c lens gets more magnification from the lens and imprecisions in the less would be more conspicuous under the scrutiny of the magnification. However, I'm confesson that I never took a lesson.

Yes, an APS-C lens needs to be more precise for the same IQ. But reality is that it is often easier to make small lenses to better perfection, for a reasonable price. Look at the tiny lenses from e.g. some Panasonic/Leica lenses on the Panny TZ, they often have very high optical quality. But it is impossible to say such a thing in general, because there are lots of factors involved (e.g. homogeneity of the glass and surface finish, precision of the internal lens threads and mounts, etc.). Most of that is related to the lens design / the type of lens.

Actually it's more challenge to design native lenses for smaller sensors.  For example to design a similar zoom as good as Canon new 24-70L/2.8 II, you'd need a 15-44/F1.75 zoom on 1.6x crop, and a 12-35/F1.4 zoom on mFT.  Such zooms either impossible to be manufactured or actually even  bigger/heavier as we saw in Olympus 35-100/F2.0 zoom that is only eq to FF 70-200/F4.0 zoom, and even bigger/heavier than Canon 70-200L/2.8 IS II zoom.  What are the counterparts of Sigma 35/1.4 on APS-C and mFT?  I believe you build up wrong perception.

FF will have higher image quality if you use a good prime, especially those in the normal to tele range and possibly zooms like the 70-200L, as those are relatively close to perfection (but often you can't make a valid comparison, because there are no L APS-C tele primes/zooms). A 4x standard zoom with midrange price is a different story. Quite often such an FF zoom will be a bit better in the image center, but worse in the corners compared to a similar APS-C zoom. Same applies for SWA range, e.g. 17-40 against 10-22.

FF is better with any lenses that also can be used on crop in the same generation of cameras. For example with ANY EF lenses 5D2 outresolves 7D, not only sharper but resolve more details. Again your perception is very wrong regarding FF lenses on corners. ultimitsu points you the equivalence if you really want to compare.

Sure EF-S 10-22 is the best EF-S zoom but EF 17-40L/4.0 is not a slouch either. Let me tell you when I need to shoot wide-open a) in low light then I don't worry about corners too much as those areas in low light are very dim and you hardly can see much anyway; b) in portraiture for better background rendering, then again I don't worry about soft borders as actually what I wanted.

Here are two samples of 17-40L (that I just sold recently as I now own 17mm TS-E) at 17mm and 40mm respectively. At eq F stop, 17-40L is not worse than EF-S 10-22.



17-40L at 17mm



17-40L at 40mm, a 3000-pixel photo

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