How to analyze lens for contrast and color

[gunjankv]

<p>Just like we have MTF charts to know image quality/resolution..<br>

I am wondering how can we analyze a lens for its contrast and color rendition before using it? Are there any figures to refer?</p>

[bobatkins]

<p>MTF <em>is</em> contrast. In general terms a high MTF at low and mid spatial frequencies indicates high contrast.</p>

<p>For color use a Macbeth color chart to compare two lenses on a given camera at a given set of settings under a given lighting condition.</p>

<p>I'd say differences in lens color rendition (with modern lenses) are very small compared with differences between cameras or two shots on the same camera using different settings for "picture style".</p>

<p> </p>

[yog_sothoth]

<p>MTF results for 10-20 lp/mm show contrast, but the DPreview and Photozone style tests may or may not. </p>

<p>I am becoming somewhat mystified by the differences between some Contax primes and good zooms like the Tamron 17-50. Even when the primes are being used under less than optimal conditions (F1.4 or a hair out of focus) the Contax primes seem to have more visual "punch" than the good zooms. These are lenses known for high contrast, so I have been wondering if the contrast is shining through even when the pixel peeping shows the pics to be less than perfect. A big black field next to a big white field would not be affected by being slightly out of focus, except at the edge, but a larger contrast would make a difference. </p>

<p>BTW, I have heard that rangefinder lenses can have a high resolution but a lower contrast than SLR lenses. Is there any truth to that?</p>

[sarah_fox]

<p>Stephen, I think what you're noticing has more to do with internal flare, more than anything. Primes are generally simpler than zooms and have fewer elements (therefore fewer reflecting surfaces). Therefore they're going to have much higher contrast at low spatial frequencies. (Whether they maintain that contrast at higher spatial frequencies is more a function of the "sharpness" of the lens.) Lenses with better coatings will also yield higher contrast, particularly at lower spatial frequencies. Many complicated zooms with excellent coatings will yield better contrast than many primes with lower performance coatings.<br>

<br />There's no inherent performance difference between a rangefinder lens and an SLR lens of similar design. SLR bodies shake/vibrate more because of mirror movements, and that can detract from overall "sharpness" if the camera is not well secured/held/stabilized, particularly in lighter cameras. The lower contrast you've heard rumored for rangefinder lenses might relate to rangefinders often being older cameras with older, less advanced coatings. For instance, my Leica IIIf outfilt will probably outperform my Canon 5D + L zoom lens outfit in sharpness, but definitely not in overall contrast.</p>

[SCL]

<p>Sarah - some of the Leica magazines from the mid 1970s talked at length about the optimization of the images some of their lenses produced (at full aperture) by slightly emphasizing contrast over resolution, and provided some interesting visual guides explaining how the two interact to produce apparent "sharpness". Unfortunately I no longer have those issues, but I remember the illustrations. And, yes, they did cite coatings and flare reduction as a significant contributor to the contrast side of the equation.</p>

[g dan mitchell]

<p>I'm with Bob on the idea that worrying about differences in "color and contrast" among lenses is probably not worth the effort. These differences, to the extent that they might even be perceptible, are going to pale next to differences in the coloration of the light in which we shoot and even more so next to what we do to the images in post, whether in the camera or in software later on.</p>

<p>Buy decent lenses that provide the functionality you need. Don't compromise these critical aspects of lens selection for some mystical notions of magical color and contrast.</p>

[ken schwarz]

<p>Here's a striking example of the difference in color and contrast between a very good lens and an outstanding one. William Castleman's website has careful test shots that show you exactly what you can expect.</p>

<p><a href="http://www.wlcastleman.com/equip/reviews/aps-c_port/bokeh/85mm/pages/04_ef85_1.2_f2.8.htm">Here</a> 's a mannequin photographed with the 85mm/f1.2II @ f/2.8.<br>

And <a href="http://www.wlcastleman.com/equip/reviews/aps-c_port/bokeh/85mm/pages/08_ef70-200_IS_f2.8.htm">here </a> is the same mannequin photographed with the 70-200/f2.8IS @ f/2.8.</p>

<p>I actually decided to buy the prime lens on the basis of this demonstration. It's not just that the prime lens can open to f/1.2. It really does have better contrast and color at the more practical settings, too.</p>

<p> </p>

[g dan mitchell]

<p>Ken, I think that I can maybe see a slight difference in color and/or brightness and/or contrast in those shots but:</p>

<ul>

<li>I certainly cannot identify one as being better than the other - different maybe, but not better or worse.</li>

<li>I cannot agree with the use of the word "striking" to describe the difference in any case. </li>

</ul>

<p>I'm quite positive that if you did an AB/X test or simply asked people to sort a pile of photos based on which lens was used that no consistent pattern would emerge.</p>

<p>Dan</p>

[ken schwarz]

<p>Dan, you just saved yourself $1800!</p>

[mark_pierlot]

<p>What about the prime's obviously superior rendering of detail, Dan, which is particularly evident in the mannequin's hair? </p>

[michael_young3]

<p>Ken, all I see is about a 1/2 stop difference in exposure. Hard to tell which is veiling flare and which is just that little difference in bright field. I'm eyeballing the sign over her left shoulder, camera right.</p>

[michael_young3]

<p>Well... not quite a half stop. The sign is rendered about 1/10 stop brighter with the 70-200. With that equalized, by bumping down the 70-200 shot, there is some small difference in the left cheek highlight, and depth of nose shadow. The highlights on the face are a bit brighter and sharper with the 85. The left cheek (camera right) seems to wash out a bit with the 85, while the nose shadow is darker and sharper. The highlight on the tip of the nose also is sharper with the 85mm. The 70-200 renders a bit more roundness in the cheek. I see very little difference in the hair detail. The bokeh is round on the 70-200, while the 85 is distinctly octagonal.</p>

<p>Gosh, I sorta miss the old Sunday funnies with the "find the differences".</p>

[ken schwarz]

<p>Michael, Dan:</p>

<p>You guys had me worried, so I loaded the photos into Lightroom and equalized them for color balance and exposure using the sheet music in the background as the reference. The exposure difference was .09 of a stop. It was enough to make the hair look more alike.</p>

<p>The differences, when seen side by side, are that the blacks are deeper and more sharply defined with the 85 prime. Note the clarity of the eyelashes, the contrast of the eyeliner, the lip borders. Also, note how the modeling of the face is more apparent with the prime. Try to match the photos by adjusting contrast and I suspect that you will find, as I did, that you can get one aspect of the photo to match, but doing so will cause more problems than it solves as such adjustments make the rest of the photo look less natural. There is just more to work with in the image from the prime lens.</p>

<p>This is the best example I know of that shows you the difference between two highly regarded lenses in terms of contrast and color. Note that I didn't pick a basket case for the comparison--there's nothing really wrong with the runner-up! I expected them to be effectively indistinguishable, but they really are not.</p>

<p>But in the grand scheme of things, I can't argue with the voice that says that this is a good example of the law of diminishing returns. The differences, while striking, are easily swamped by small lighting or post-processing adjustments.</p>

[michael_young3]

<p>Yup. Yup. All that. :D The 85 definitely has a distinct edge on sharpness and contrast. Earlier, I was rocking the mousewheel between the two, and probably just jarred a contact lens loose on the small difference in image size. Looking at them side by side in Compare, there is no comparison. The 85 is definitely sharper and holds its contrast. It rendered a bit cooler, but no biggee.</p>