Hi, Am 24.02.19 um 13:32 schrieb Florian W:
> 1 This reasoning is mixing description of digital features with analog > ones . A lens quality and specs is not defined by MP resolution (rather > by like purity of the glass, glass curvature homogeneity, CoC, TCA, and > so on). You are right, things work a bit differently on the optics side before the sensor. Hence my use of "oversimplyfing it a bit". But the resolution of an optical system can still be measured (see e.g. Optical transer function [1]), and you can specify how much contrast you expect to see in details and what level of details you expect to still be visible. It's hard to make exact quantitative statements like "this lens has an optical transfer function which gives enough contrast for x line pairs per millimeter, and that would be enough for an x megapixel sensor of this and this size". Especially because glass quality even differs within the same manufacturing batch. But for example with my blurry 70-300 it's easy to judge that it would probably be sharp enough for a 12 to 16 megapixel sensor, but nothing better. > 2 Some of the lenses we're talking about were developed and (partially) > targeted to FF cameras having a sensor with less MP than a current APS-C > (for example in Canon, the 6D is a 2012 FF with 20MP). > > If the reasoning is valid, a lens released at times of FF with 24MP or > higher wouldn't be a good match to the previous cameras with less MP. > Which doesn't seems to be the case. > > What I mean by this is that at some point, to ensure a lens will perform > well on FF cameras that will be released the following decade, one can > assume that the optical manufacturing quality is probably one order of > magnitude above the quality required to fit the current camera sensor > capabilities. Maybe explaining why you can see problems in older lenses. I'm not saying that I see a general problem with older lenses, and I already noted that your prime lenses probably won't cause much of problem. There's simply a very, very wide range of lenses out there, and the pricing, engineering and manufacturing decisions can lead to extremely different optical properties. There are some prime lenses from the 1980s which are still extremely sharp on today's sensors, but primes are easy. Most have just seven or eight glass elements. My Nikon 24-70/2.8 on the other hand has 20 lens elements in 16 groups. The older Canon 70-200/2.8 has 23 lenses in 19 groups. Even the Nikon 16-35/4 has 17 lens elements. Obviously it is much harder to keep the optical resolution at the same level when light has to pass through that many pieces of glass and the lens still has to be affordable. So there are FF lenses out there which will give good results on APS-C bodies, but not all will. And you can easily end up getting worse image quality with a FF lens on an APS-C body when you expected a better one because the FF lens was more expensive and is supposed to be better. Also manufacturers don't generally design lenses so thewy will work perfectly with cameras released a decade later. They will design the current top model so it has enough room to still be good on the next model, but they still want you to buy the new "sharper than ever" lens every five years. cheers, Simon [1] https://en.wikipedia.org/wiki/Optical_transfer_function ___________________________________________________________________________ darktable developer mailing list to unsubscribe send a mail to darktable-dev+unsubscr...@lists.darktable.org
