Sigma 150 Macro Something I've never seen before
- Thread starter Cinto
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It seems a lack of synchronization between the exact moment the shutter opens and closes the diaphragm (stopped down). Difficult to identify the cause of the problem. But it would be very strange to anticipate the diaphragm, and it seems more plausible that the camera shutter had delayed it.
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I imagined another possibility. If the mirror does not respect the right moment to go up and down, could reflect the sunlight entering through the optical viewfinder, and that light reaches the diaphragm of the lens backwards.
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To be able to see the diaphragm in the image, there must be an optically flat surface in front of the lens, such as a filter. If this flat surface is sufficiently close to the subject in focus, and the lens is stopped down, then the reflection of the diaphragm can be within the depth of field, and will appear in the image, especially if there is enough incoming light to the lens that it bounces off the diaphragm (such as if an off-camera flash is pointed at the lens).
Without a flat surface from which a reflection of the lens' interior can be seen, such a phenomenon cannot occur because any internal reflections off the glass-air interfaces on individual elements would not be image-forming.
Without a flat surface from which a reflection of the lens' interior can be seen, such a phenomenon cannot occur because any internal reflections off the glass-air interfaces on individual elements would not be image-forming.
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jrista said:
Even the best multicoating won't completely stop this phenomenon. Think of it this way: if you can *see* a piece of glass, that necessarily means it reflects some incident light, otherwise it would be completely invisible to you. To be immune to this phenomenon, you'd need a glass that would look invisible and fail to show any reflected light over a wide range of viewing angles.
The fact that the flash is throwing a ton of light directly into the lens at an angle that is not image-forming virtually guarantees that there will be a lot of veiling glare. That non-image-forming light bounces off the lens sub-barrel and diaphragm, comes back out, hits the filter, and because it's a macro shot, ends up forming a very nice detailed ghost of the inside of the lens.
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jrista said:chromophore said:
Sure, without doing something more drastic, such a reflection is pretty much guaranteed. I'd love to see a filter like this with a nanocoating. Where multicoating can cancel out enough reflections to allow up to 97% transmission, that's still 3% reflection. A nanocoating, on the other hand, can simply prevent reflections entirely, resulting in 99.95% or better transmission. I bet a nanocoated UV/protect filter would have handled this situation nicely.
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