Although many people have said that this lens is soft wide open at 200mm, it still surprised me: only the central part of the image is very soft, and the border part is not soft (see the attached image). In other words, the border looks sharper than the center part by the higher contrast at the border region. I don't understand it. I don't even know if this is normal.
The image was shot with D700. Focal length: 200mm. Aperture: 2.8. Distance: about 1.6m. It turns out that the softness problem at 200mm and f2.8 only occurs at very close distance. For distance larger than 3m, the softness problem goes away and the lens is quite decent wide open at 200mm.
Frank
Here are 100% crop of the center, left border, and right border part of the image, respectively:
Can you see any defects inside the lens? Is your rear element clean?
I don't own the lenses and haven't tested it so far, so I can only guess: technically the explanation could be quite pronounced field curvature. You could find out by carefully focusing manually "through the newspaper".
But shapito also has a point: another explanation could be an optical defect, like fungus. You should carefully check the lens for that. Best approach is to fully open the aperture (you can do so manually with the lever at the mount), point the lens towards a light source and carefully inspect it by looking through from the other and. Make sure the light comes in at a slight angle... and slowly adjust that angle while inspecting the lens.
-- Markus
Editor
opticallimits.com
Thank you for your opinions, Markus and Shapito.
I have checked the effect of field curvature. It does not look like there is strong field curvature. In the attached image I focus at the left and right borders (I did not try to make the target plane to be parallel to the image plane in the vertical direction but tried to make the left border and the right border have the same distance to the camera). It appears that the center region is well in focus (I did check this with manual focus). As you can see, the left and right border regions are much more contrasty than the central regions. I would say that the borders are not very soft, but the center is very soft.
I also checked the lens for defects like fungus but I did not find defects with my naked eyes (I did make the aperture fully open and used a back light source for the check).
Kind regards,
Frank
100% crop of the image: left border, center, right border respectively:
Here is how I let the focus go through the paper, each image contains left border, center, and right border:
[ATTACHMENT NOT FOUND]
[ATTACHMENT NOT FOUND]
[ATTACHMENT NOT FOUND]
[ATTACHMENT NOT FOUND]
[ATTACHMENT NOT FOUND]
How do the borders look like when you manually focus on the center of the paper?
Hi Frank, some of the old lenses have aberrations in the center as they are not optimized for the light reflected from the sensor. Check Tom Hogan's website, he explains it in more technical terms... I don't have the exact link, sorry. I used to rent this lens before, but never notice the issue. My impressions are that the lens is sharp at f 2.8, but it shows purple fringing, which is quite visible.
Hi Frank, some of the old lenses have aberrations in the center as they are not optimized for the light reflected from the sensor. Check Tom Hogan's website, he explains it in more technical terms... I don't have the exact link, sorry. I used to rent this lens before, but never notice the issue. My impressions are that the lens is sharp at f 2.8, but it shows purple fringing, which is quite visible.
