07-10-2013, 02:21 PM
I have made some more tests, using a paper with white letters on a black background. When I tried to manually focus on the center of the paper to make the image of letters as clear as possible, I get the following image, where the letters have well defined boundaries but are imbedded in white halos:
[ATTACHMENT NOT FOUND]
I cannot judge if the "white halos" are caused by spherical abberrations, or by some kind of sensor reflection as suggested by borisbg.
On the other hand, if I try to reduce the "white halos" and get the "sharpest image without halos" by manually focussing the lens, I get the following image with blurry letters:
[ATTACHMENT NOT FOUND]
I don't even know if this can be considered as "in focus".
Again, the parameters are as follows: f=200mm, F=2.8, distance=1.6m (roughly).
Frank
[ATTACHMENT NOT FOUND]
I cannot judge if the "white halos" are caused by spherical abberrations, or by some kind of sensor reflection as suggested by borisbg.
On the other hand, if I try to reduce the "white halos" and get the "sharpest image without halos" by manually focussing the lens, I get the following image with blurry letters:
[ATTACHMENT NOT FOUND]
I don't even know if this can be considered as "in focus".
Again, the parameters are as follows: f=200mm, F=2.8, distance=1.6m (roughly).
Frank