jlw
Rangefinder camera pedant
I've been puzzling over an artifact that I've noticed in some of my R-D 1 pictures: very bright areas against a dark background sometimes seem to show a well-defined "halo" in one direction only. For example, see the area below the red line in the attached file.
Normally I'd suspect lens flare or some other optical fault, but I've been getting these artifacts with lenses that do NOT produce the same type of effect on film. Some sort of image-handling quirk within the R-D 1 might be another possibility, but that seems negated by the fact that even under the same lighting conditions, I see the effect with some lenses but not others. So if it's not the lens and it's not the camera, what is it?
My latest suspicion arose in reading an article somewhere (Pop Photo?) about the "digital optimized" lenses that manufacturers now are offering for DSLRs. The article said that one of the ways these lenses differ from film-only designs is that the manufacturers take greater care to reduce reflections that might be bounced off the digital sensor and then re-reflected by the lens' rear element.
The article didn't give a name for this phenomenon, so I've decided to dub it "sensor bounce." You can see why it might be an issue: since the surface of film has a fairly matte finish, reflections off it would be diffuse (rays going in all directions) while a sensor is fairly glossy, so reflections off it would be specular (rays that remain directional.) Apparently there are cases in which image rays can bounce off the sensor, hit the rear element, and be bounced back toward the sensor again, which (I'm theorizing) would often just lower overall contrast, but in some cases could form a fairly well-focused, slightly offset "ghost" of the original scene. Apparently, the DSLR lens manufacturers are trying to avoid this in the design of the rear elements and/or by applying special coatings.
I'm wondering if this might explain the artifacts I've been seeing occasionally in my R-D 1 pictures. They DO look rather well-defined, like reflections, and this also would explain why they tend to extend in one direction rather than being evenly distributed around the bright part (as you'd expect with ordinary flare.) I'm guessing that a lens with a relatively flat rear element would be more likely to bounce back well-focused reflections than one with a steeply curved element, and this could explain why I see the effect with some lenses but not others under the same conditions.
But for the life of me, I can't think of any way to test this hypothesis! I experimented a bit with shining a laser through a lens onto a glossy surface, but the beam was broken up enough that I couldn't tell whether it produced a "sensor bounce" reflection or not.
Any ideas? Any thoughts?
Normally I'd suspect lens flare or some other optical fault, but I've been getting these artifacts with lenses that do NOT produce the same type of effect on film. Some sort of image-handling quirk within the R-D 1 might be another possibility, but that seems negated by the fact that even under the same lighting conditions, I see the effect with some lenses but not others. So if it's not the lens and it's not the camera, what is it?
My latest suspicion arose in reading an article somewhere (Pop Photo?) about the "digital optimized" lenses that manufacturers now are offering for DSLRs. The article said that one of the ways these lenses differ from film-only designs is that the manufacturers take greater care to reduce reflections that might be bounced off the digital sensor and then re-reflected by the lens' rear element.
The article didn't give a name for this phenomenon, so I've decided to dub it "sensor bounce." You can see why it might be an issue: since the surface of film has a fairly matte finish, reflections off it would be diffuse (rays going in all directions) while a sensor is fairly glossy, so reflections off it would be specular (rays that remain directional.) Apparently there are cases in which image rays can bounce off the sensor, hit the rear element, and be bounced back toward the sensor again, which (I'm theorizing) would often just lower overall contrast, but in some cases could form a fairly well-focused, slightly offset "ghost" of the original scene. Apparently, the DSLR lens manufacturers are trying to avoid this in the design of the rear elements and/or by applying special coatings.
I'm wondering if this might explain the artifacts I've been seeing occasionally in my R-D 1 pictures. They DO look rather well-defined, like reflections, and this also would explain why they tend to extend in one direction rather than being evenly distributed around the bright part (as you'd expect with ordinary flare.) I'm guessing that a lens with a relatively flat rear element would be more likely to bounce back well-focused reflections than one with a steeply curved element, and this could explain why I see the effect with some lenses but not others under the same conditions.
But for the life of me, I can't think of any way to test this hypothesis! I experimented a bit with shining a laser through a lens onto a glossy surface, but the beam was broken up enough that I couldn't tell whether it produced a "sensor bounce" reflection or not.
Any ideas? Any thoughts?
