What do you think about this picture? I am not referring to the contents; there are always different opinions about this. I am referring to the quality of the lens which I used here.
I am questioning the quality of a lens only when the pictures which I took with it do not meet my expectations. In this case there was no reason to check the lens in any way. But it is different when a lens is about to be sold. A search with a flashlight is necessary, looking tiny pieces of dust, hair fine scratches or even mold and haze. You can imagine I was pretty surprised when I saw heavy haze in the lens.
This did not correspond to the picture which I had taken not long ago. Did the haze develop in such a short time? Not very likely, but it made me curious.
I assessed the facts with two additional lenses, one of which had little haze and the other was without noticeable faults. I positioned the lenses side by side and placed a dedolight behind them so that it illuminated the backs (the pattern in the left lens is a reflectioin from the plate below it).
This is what I found:
Many would say: throw away the lens in the middle, and preferrably also the one on the left with little haze.
But normally there is no flashlight shining from inside the camera into the lens. So what is the real impact of the haze? It is quite astonishing what could be seen by looking through the lenses from the front to see the structured background.
All three showed a clear picture of my studio background behind them. It seemed, therefore, that the flashlight test grossly overrates the problems of the lens.
I made some pictures with open aperture. The first set shows a tabletop arrangement:
The pictures reflect differences in depth-of-field of the lenses, but there were no obvious differences in sharpness and contrast.
In the second set I photographed the Dedolight which illuminated the arrangement.
The lens with little haze is as contrasty as the clear lens.
The picture made with the hazy lens has flare at few edges. It is visible only where the light source itself is posotioned beside black areas. No flare is visible at the barndoors or at the ventilation holes. Some of my lenses for digital cameras have substantially more issues here even without depicting the light source itself and without any haze being present.
These facts allow the conclusion that even strong haze has no noticeable impact on the image quality with normal subjects. Flare is visible only with extreme contrast. This explains also why the picture which I made from Steph has no technical issues - with a lens that others would have discared.
This tells me: stick to judging what you see on the image. Forget about inspecing lenses without reason and with incorrect conclusions about the image quality they will likely have. This is by no means the same, but hardly anybody knows it.
By the way: my website has also flare on the upper left side. This can be quite effective, if properly handled.