freaklikeme wrote:
That's an odd pattern of optical vignetting on the thin-mod shot. It looks like hundreds of tiny D's.
the Ds aren't that odd, lots of lenses do those, but usually the hard edge is towards the outside of the frame whereas with the cv the hard edge is on the inside. i might be misremembering, but i think the rokkor MD 50/1.2 did that too?
the Ds aren't that odd, lots of lenses do those, ...
It's most likely Coma which is fairly common, especially with a lens wide open.. The signature changes with the size/shape of the point light source and it's distance, i.e. point-of-focus to background (if other than infinity).
sebboh wrote:
the Ds aren't that odd, lots of lenses do those, but usually the hard edge is towards the outside of the frame whereas with the cv the hard edge is on the inside. i might be misremembering, but i think the rokkor MD 50/1.2 did that too?
It's possible. I'm not seeing it in any of my images from the lens, but I don't have a comparable image. It doesn't show the problem with OOF Christmas tree lights, but I was much closer to that tree than you were in the sample shot. Unfortunately, I no longer have the lens to confirm.
Now you've got me curious. I'm going to have to do a "D" check on my lenses.
mapgraphs wrote:
It's most likely Coma which is fairly common, especially with a lens wide open.. The signature changes with the size/shape of the point light source and it's distance, i.e. point-of-focus to background (if other than infinity).
Maybe. I've only heard people discuss coma in the focus plane, but I suppose it could impact OOF highlights as well. How do you explain the hard edge, though?
I wouldn't call the artifacts hard edged. But I suspect they are related to the distance from the point of focus. The two examples have different points-of-focus so it's hard to draw a meaningful conclusion, but they do look like what one can get with coma...
M-240, 7A M 50 @ f/1.2
I wouldn't call the artifacts hard edged. But I suspect they are related to the distance from the point of focus. The two examples have different points-of-focus so it's hard to draw a meaningful conclusion, but they do look like what one can get with coma...
M-240, 7A M 50 @ f/1.2
freaklikeme wrote:
...but the shape still seems like a combination of problems to me, not strictly coma.
The size and shape of the light source is a major influence.
A distant point source will most likely give a classic coma but when the source is somewhat diffuse (like light through leaves) the size and shape of the effect deviates from the classic coma - and it is influenced by the distance, accurate registration of the lens, etc. etc.... These are take-aways from my own work and whatever technical data I've been able to (try and) digest. Lens designers/manufacturers aren't exactly verbose about what corrections are or are not made and to what degree and in what combination and the intent of the design (optimum at 2m, 3m...?) so we're left with interpretations of elephants... ; - )
A slight digression....
If you look at the upper right edge, you'll see a bright D. The other highlights are more subdued and don't exhibit the effect to that extent...
