Why do some lenses have better color?
Matty W wrote:
I recently got a 24mm f1.4 Rokinon (which is very sharp, better than expected), but its colors are bit muddy. I know of professional shooters who will not use Rokinon/Samyang lenses because of their bad color. Some speak of lenses being more saturated than others. Maybe this one is desaturated a bit, but I don't have the eye to tell.
I always assumed it was due to chromatic aberrations, specifically LoCAs (see how well true apochromatic lenses render out of focus areas and even in focus areas), but those who are knowledgeable about photography informed me that it's due to coating. That's why, specifically, Canon L lenses have better colors than their non-L and off-brand counterparts. And my 70-200mm f2.8 L does have nice color rendering.
Are L lenses also more likely to be apochromatic or is it just the coating? If it's the coating, why don't more manufacturers use better coatings and why doesn't Canon coat more lenses this way? I know Zeiss has a great coating with great color, but it's too bad that this alone is holding my Rokinon back. Or is it even more complicated than just this? I bet chromatic aberration factors in, but I have an L zoom with CA and good color (17-40mm). Maybe it's different kinds of CA?
Thanks everyone! I'm stumped.
It's a complex issue. Lenstip has done a number of transmission curves for some lenses, alas I didn't find a Canon L lens amongst them. The transmission curves are linked a the bottom:
No lens has "bad" color. What the transmission curves tell you is that some are warmer or colder etc. No lens has a flat transmission curve in the visible range.
When you talk about saturation, you mean basically contrast. If a lens has poor transmission, some of the light entering will bounce around and hit randomly somewhere, causing loss of contrast. Ideally, a lens should have 100% transmission, but none have. Glass does reflect some light, not all goes through. So, the coatings are there to increase transmission and reduce reflections of the glass surfaces ( http://www.canonrumors.com/tech-articles/all-about-lens-coatings/ ). Loss of contrast makes colors less saturated, more mute. The coatings also help reduce bad reflections, i.e. stray light from the sun or strong counter lights hitting the lens elements furthest in front, which can also cause dramatic contrast loss.
So, all in all, each lens is different because it has different numbers of elements in it, and thus also differs in how many coatings are applied and where they are applied. Thus, not all L lenses are the same, in fact some non L lenses are just fine as well. You notice that the Samyang (Rokinon) fish-eye has very good transmission, so does the Canon 85 f1.8. I have a Samyang 8mm, and it compares just fine to my Canon 10-22, which is a very nice, contrast rich lens (flare resistant, probably every bit as "L-like" in color characteristics as a real L lens)
Good microcontrast. A sharp lens will look better, because it will be able to represent fine contrast edges better than a less sharp lens, where the contrast edges are a bit blurry. All the different types of lens aberration (CA, spherical aberration, etc.) will contribute to this of course. Over a whole picture, it will impact how the colors look of course. Lots of blurry edges in foliage look less nice with less saturated colors than one where every leaf sticks out 100% "clean".
I suspect that's one of the major reasons L lenses look better, because they have better microcontrast, since they are usually better designed lenses.
You will notice that any image can be improved in postprocessing, usually be increasing contrast with dull images, and applying sharpening. This indicates that these are the two main factors impacting image perception, and thus should be the two of the main areas where lenses differ.
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