![]() ![]() Thanks for your insights on this - I'd really love an authoritative explanation. However, I don't think they would be a big effect until you get to extreme designs and very fast beams. I can see these possibly giving a small color shift with focal ratio (and also with field position). ![]() You also change thickness of the glass through which the beam travels. As you change the focal ratio, you change the distribution of angles at each surface. However, coating efficiency changes with incident angle. I think you'd see something this large with your naked eye, looking at the lens from the front, and it should certainly be visible with a macro lens. For a 50/1.4, the aperture is about 35 mm in diameter, so we're talking about a 1/3 mm difference in radius between red and blue. However, quantitatively, in order for this to be noticeable the effect would have to be say 2% in area and so about 1% in radius. You can imagine a large chromatic aberration between the object and the iris that, effectively, means that the iris appears to be bigger in the red and smaller in the blue. I can understand qualitatively what you're describing, but I don't think it makes sense quantitatively. I've not got your vast experience with old lenses, but I do have a fair bit of experience with laboratory and astronomical optics. I find this odd and at odds with the constant demand for “better” kit. At least B&W can be acknowledged for its technical capture objectivity without our brain needing to see a happier cast or saturation level to fully appreciate it. That is why happy more saturated warmer images are so popular.Īnd here we are constantly fussing over the ability to make perfect images. The human eye-brain relationship is quite happy to believe that any image within reason is “correct” as far as cast and saturation is concerned no matter how “unreal” to the actual true life it might be. But good “art” nevertheless and a worthy challenge winner. The side screen image in Finished Challenges of an excellent (posed?) kite-boarder in action without a drop of water in sight, perfect flowed hair and over-saturated over-hdr applied style is a very fine image but “real life”? Maybe not. Maybe it is better but one might wonder if this was simply swayed by popular demand for something a little warmer than natural. To the point where Panasonic has more recently revised its saturation levels and has now received plaudits for their excellent colour balance. Similarly Olympus has always been praised for its slightly over-saturated images whilst Panasonic has been criticised for its less saturated colours. He had a run-away popular business and he explained to me that the demand for the big bright highly saturated prints was so high that he was having trouble fitting a matte finish sequence in. In any case within 12 months he was having his matte finish product reduced to once per week when he had saved up enough film to be worth changing his chemicals. He charged much the same and introduced me to the matte finish product which was more true to life colours. Many years ago when photolabs were in their infancy the first one in our little city was started by a client of mine and probably pushed my interest in photography off to its first floundering start.īut in any case he produced two types of prints - cheap bright finish glossy highly saturated ones that quickly showed fingerprints, and also matte finish with more subdued much more natural colours that had a harder surface and fingerprints could not be seen. Maybe it is inbuilt into our genes - warm and comfortable with richer colours is “happy”? This is a subject in its own right - not the one of just why sensors and lenses give different casts and staturations - but the one on just why most people prefer more saturation and warmer casts than real life representation. The interesting thing is that many of us likethe incorrectly warm coloring. In such a case, stopping down trims off the rays that are missing blue, thus restoring the natural coloring of the scene. It is thus fairly common that blue light from the edges of the lens doesn't get where you want it, causing a warm color shift. Index of refraction isn't the same for all wavelengths. Lenses are designed for two or more visible wavelengths to focus at the same point in the same plane, but that doesn't ensure things are well-behaved between or before or after those wavelengths. I'm not knowledgeable enough about optics to really explain it, but here goes - please somebody correct whatever I get wrong. Oddly enough, it's pretty common that lenses show less blue near wide open - you might see a significant color shift simply stopping down the same lens! ![]()
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