Hi,
Just to say, MTF testing is
a the widely accepted method of lens testing. Zeiss uses it, Leitz uses it, Schneider uses it, Hasselblad uses and Sony uses it, too. Unfortunately it takes a instrumentation that costs a fortune to that.
For that reason, most MTF tests are done with lens mounted on camera. That has the advantage it can be done with very simple mean using a bit of tape (for instance) and some software like MTF mapper or Imatest.
Using MTF testing on the lens alone makes it possible to compare lens data between makes.
Now, all digital cameras have some optical assembly in front of the lens. This is often an IR-filter that used to be combined with two slices of birefringent crystals and a depolariser acting as an OLP filter. This assembly corresponds on Sony cameras to 2 mm of optical glass.
If the outlet pupil is near to the sensor, some of the beams passing trough the lens will pass that optical assembly at a large beam angle, shifting focus for those rays, a phenomena called astigmatism. With SLR lenses the outlet pupil is always distant from the sensor/film plane, so the sensor "glass" causes no problems. With mirrorless the outlet pupil can be close to the sensor plane, and this needs to be taken into account in the design of the lens. A good demo of this has been shown
by 3D kraft, here.
This is Zeiss Biogon 35/2 at full aperture:
And this is the Loxia 35/2 redesigned for the Sony A7 with cover glass taken into account.
This issue is also described in a series of articles on LensRentals:
http://www.lensrentals.com/blog/2014/06/sensor-stack-thickness-when-does-it-matterhttp://www.lensrentals.com/blog/2014/06/the-glass-in-the-path-sensor-stacks-and-adapted-lensesNow, as you may see, LensRentals is very enthusiastic about MTF, but what is that famous number. A good explanation is given by Hubert Nasse of Zeiss
hereand
here.This nice video may give some more insights about lenses:
https://www.youtube.com/watch?v=9cnEnRADDLo&ab_channel=MattGrangerWhat is my own take on the Lensrentals test? Well, it is difficult to MTF test FE mount lenses as they are electronically controlled. Lens rentals managed to build a rig allowing to control the camera in an MTF rig, they have tested a large number of lenses as that is a part of their quality assurance program, they don't want to ship bad lenses to their customers. So they have a lot of experience in this. On the other hand, this thing is new and they may have missed something.
I do own the Sony 90/2.8G and it is very sharp. I don't own any of the other lenses mentioned.
Two points to make. For some reason Lensrentals tests mostly at full aperture, this makes a lot of sense for quality assurance but many lenses are seldom used at full aperture. Personally I prefer to have MTF data for full aperture and for the optimal aperture. In Europe MTF charts are often given at 10/20/40 lp/mm for full aperture and stopped down. Hasselblad, Zeiss, Leica publish data that way. Schneider and Rodenstock sometimes present data at 15/30/60 lp/mm which may be more adequate for digital.
Personally, I feel it is good to have different inputs. Checking out all information can be helpful in making educated buying decisions. I would also say that I would like to see more moderate aperture high performance lenses.
Best regards
Erik
It is wide open. Infinity. They have some additional glass in the optical path. While interesting I think you have to verify with on camera tests to draw any conclusions.