Alley in Pisa, Italy

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In many reviews people describe how a lens can affect the saturation of a picture, especially when it comes down to a comparison of two similar lenses, e.g. 50mm 1.8 vs. 50mm 1.4 or something like that and they point out that one lens is delivering stronger colors than the other one.

What is responsible in a lens to affect the strength of a color?

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Not an answer but a refinement -I think most lenses are pretty neutral color wise. I'm pretty sure the difference is more a matter of contrast than saturation, as an image with stronger contrast will can appear to be more saturated. So the real question is what causes differences in contrast (apart from things like using a lens hood). –  Kendall Helmstetter Gelner Jun 20 '11 at 22:44
    
@Kendall Helmstetter Gelner - this is really the saturation. See my answer below for a demo. –  ysap Jun 20 '11 at 23:15
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3 Answers 3

up vote 8 down vote accepted

The quality and makeup of the lens elements used in a camera lens can have an effect on transmission. Top-notch glass will usually have high transmission, allowing through as much visible light as possible while filtering as little as possible. However, top-notch glass will also usually have coatings, usually multi-coating, that will have its own effect on transmission, and may introduce color cast or affect flaring. Glass that is not coated or cheaply coated will usually exhibit more flaring, which can have a significant impact on scene contrast.

Cheap glass may not have a high transmission index, in which case for a given exposure value, the overall contrast may be lower than quality glass that has a higher transmission index. Contrast affects both luminance as well as color saturation, and lower overall scene contrast in a color photo will usually also affect the apparent saturation of color. Cheaper glass or cheaper lenses may also exhibit various optical aberrations, many of which are explicitly related to the convergence or divergence in how different wavelengths of light focus. This can create purple/green fringing as a scenes depth progresses and focus changes, which can also have an effect on color and saturation.

Higher quality lenses will usually have better control of flare, higher transmission glass, better multi-coating that has a minimal impact on transmitted light, fewer optical aberrations, etc. etc. This all affects the ultimate quality of the images produced, and is most visible in contrast (both overall scene and micro contrast, the latter being an effect of lens resolution) and color saturation. Thus is the benefit of a high quality, more expensive lens...you really do get what you pay for.

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One obvious factor is lens flare. If one lens flares, that will reduce saturation of a picture substantially.

When/if you get lens flare from the sun just outside the frame (for one example) it tends to be pretty obvious. In other cases, however, you have (for example) reflections just outside the frame that lead to much more subtle flare. Depending on the design and coatings, this might affect one lens more than the other, leading to loss of saturation even though it's not obvious that one is from flare.

Another factor can be the simple transmission characteristics of the coatings used. Some coatings have a much "flatter" transmission curve than others; others will tend to filter out some red or blue (or both).

In a lot of other cases, however, I think lack of saturation can stem from other sources that are often only accidentally related to the lens itself. For example, if one has a slightly sticky aperture, that can lead to over-exposure which will often de-saturate the pictures to at least some extent.

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To get a nice demonstration of this effect, see this page, comparing the EF-50/1.4 with the EF-50/1.8.

UPDATE: The drink cans test and the playground test on the page, actually comparing the bokeh and background blur, show how the f/1.4 gives more saturated reds and blues than the f/1.8 lens, both wide open and on f/2, f/5.6. This page was the reason I bought the 50/1.4 lens back then.

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Can you summarize where on that page its demonstrated? I may be overlooking it, but its not mentioned anywhere but the comments and not immediately obvious to me from the images. And you don't do anything more than link the page here. (I guess the images about background blur show it some, but we don't know how the images were processed at all). –  rfusca Jun 20 '11 at 23:19
    
@rfusca - photo.net access is blocked in my office. I just copied the link from a past answer of mine. I'll try to be more specific later, from home. Anyway, from my memory (unless the page was changed recently), there should be a comparison of different effects. One of them is the difference in color rendering between the lens. You should scroll down the page to see it. –  ysap Jun 20 '11 at 23:27
    
@rfusca - see my update. –  ysap Jun 21 '11 at 0:14
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@ysap - I'm not arguing that you're wrong, but personally I don't see it much on the drink cans and while I do see it on the playground - since they weren't testing for that, we don't know how the two pics were processed in regards to the saturation. –  rfusca Jun 21 '11 at 0:17
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@jrista, @rfusca - note that I don't expect substantial differences between two Canon EF lenses of not-so-different price classes (at least compared to the 50/1.2). The difference is indeed subtle, but visible. Also, it can be that the specific two lenses he used have this color deviation, where two other samples will behave differently. –  ysap Jun 21 '11 at 2:25
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