Re: A thinner sensor stack may be possible after all!
xbarcelo wrote:
At the risk of sounding a bit like a scratched record, could anyone check for field curvature? Has there been any changes? How about sensor reflections? Thanks so much!
Regarding reflections, as I posted previously, I have shot some dusk images including streetlights. Not a before and after test, but have not had issues that troubled me. I can, if I shoot in the dark at night, cause reflections from streetlights, but I can make almost any digital camera do that with the right (or wrong) combination of lights and exposure. Not having an unmodified camera handy I can\'t do comparative shots, unfortunately, but will upload a couple to the Flickr group when I\'m back home next week.
Regarding curvature and corners, the primary reason for the improvement from thinning the stack is not changes to the lens field curvature performance. Curvature doesn\'t smear - it just causes the image to be out of focus. The smearing results from a asymmetrical increase in astigmatism as you move off-center in the image field.
Again, I don\'t have a way to test before/after, but ALL film lenses should perform closer to their designed film performance regarding curvature. If adding glass to the stack improved field curvature vs. the performance on film, that would seem to be a very lucky accident for some particular lens. But it would be at the expense of smeared edges which, being an asymetrical distortion, tends to be much more disturbing that simply not being sharp. Yes, as the ray angle toward the edge, the filter glass increases the path length, and that would create some focal plane curvature. But a thinner stack would always has less effect than a thicker one. So performance on a film lens is closer to the designed performance. That\'s the fundamental goal of the mod. Getting closer to the as-designed performance of a film lens. Not to try to create a lucky combination of the stack with some particular lens. And I think all the results show that it does that.
I would be interested in any results or theory that suggest otherwise or show how adding glass plate to the path would generally improve curvature.
Re: A thinner sensor stack may be possible after all!
xbarcelo wrote:
At the risk of sounding a bit like a scratched record, could anyone check for field curvature? Has there been any changes? How about sensor reflections? Thanks so much!
Regarding reflections, as I posted previously, I have shot some dusk images including streetlights. Not a before and after test, but have not had issues that troubled me. I can, if I shoot in the dark at night, cause reflections from streetlights, but I can make almost any digital camera do that with the right (or wrong) combination of lights and exposure. Not having an unmodified camera handy I can\'t do comparative shots, unfortunately, but will upload a couple to the Flickr group when I\'m back home next week.
Regarding curvature and corners, the primary reason for the improvement is not changes to the lens field curvature performance. Curvature doesn\'t smear - it just causes the image to be out of focus. The smearing results from a asymmetrical increase in astigmatism as you move off-center in the image field.
Again, I don\'t have a way to test before/after, but all film lenses should perform closer to their designed film performance regarding curvature. I would be interested if you can point me to any tests or theory that suggests otherwise.
Michael
Feb 21, 2015 at 10:12 AM
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