I dont understand contrast in lenses

[profborg]

When people say 'this lens has better contrast' what does it mean? Whilst I'm here, whats micro-contrast?
--
Daniel

'One man practicing sportsmanship is better than a hundred teaching it.' - Knute Rockne

 

[bm bradley]

When people say 'this lens has better contrast' what does it mean?
Whilst I'm here, whats micro-contrast?
--
Daniel

'One man practicing sportsmanship is better than a hundred teaching
it.' - Knute Rockne

--

different lens coatings provide different contrast and color rendition. all manufactures have their own priority process as well as different lenses for the same manufactures will or might have different coatings,

 

[BCJames]

Contrast, when talking about lenses, has to do with the apparent sharpness of the lens. That is a very loose definition, though. Here is a better one....

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Many photographers — even some experienced and knowledgeable ones — seem permanently confused about contrast. The word "contrast" actually refers to how the materials distribute tonal gradation from black to white or lightest to darkest.

When we talk about lens contrast, we're not talking about that quality. What we're talking about is the ability of the lens to differentiate between smaller and smaller details of more and more nearly similar tonal value. This is also referred to as "microcontrast." The better contrast a lens has (and this has nothing to do with the light dark range or distribution of tones in the final print or slide) means its ability to take two small areas of slightly different luminance and distinguish the boundary of one from the other. (And thus appear sharper)

You can have a lens of very low contrast that can be made to transmit the same overall range of light to dark or white to black as one with high contrast. It will just show much less micro detail in the scene, and look relatively muddy and lifeless. Some pictorialist-era pictures actually have a full range of tones from white to black but show (by design) exceptionally low degrees of what we would call lens contrast. Low lens contrast is also created when you put a "softening" filter on a lens you can still print the picture with an overall contrast from pure white to maximum black, but the microcontrast will be severely curtailed.

Savants talk about resolution and contrast being the same thing. Ultimately, they do go hand-in-hand, because you can't distinguish contrast without resolution and you can't distinguish resolution without contrast. But this is for very fine detail, in the range of 30-40 lp/mm or even greater frequencies ("frequency" in this sense refers to the spacing of the equal black and white lines used to determine lp/mm and MTF), which the eye generally can't see in prints and slides.
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Does that help?

--
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[profborg]

For an excellent answer. Much appreciated. Could lens contrast then be compared to JPEG compression because in both a difference in quality results in fine detail being resolved?
--
Daniel

'One man practicing sportsmanship is better than a hundred teaching it.' - Knute Rockne

 

[BCJames]

Well if I understand your question, no I don't think so. I think they are completely different things.
--
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[Dave Martin]

When people say 'this lens has better contrast' what does it mean?

Absolute contrast is the intensity difference between bright & dark areas; relative contrast is a ratio.

One source of low contrast is extra light added by scattering off glass surfaces inside a lens. Here's a telephoto shot of a Zebra's nose:



Some sunlight got into the lens & bounced around (called "flare") causing a low contrast image. This was corrected by subtracting a constant amount of light from the image (about 25% of maximum) and multiplying the remnant appropriately.

Another type of contrast degradation is inherent in the lens. A lens cannot show a perfectly sharp edge as perfectly sharp; there is some fuzziness that increases with f-stop, even for a perfect lens. Here's an example (imatest.com) showing what I mean:



The top of the figure shows perfectly sharp edges, the bottom is a magnified image of what it looks like after going thru a lens. First notice the fuzziness at the edge.

Next notice that as the edges get closer & closer the fuzzy areas overlap resulting in a decrease in contrast. This cannot be avoided - one measure of a lens' quality is how good a job it does in showing contrast at small separations.

Dave

 

[profborg]

Thanks Dave, great explanation. BCJames, because of your explanation I understand that the two are completely different I just thought that strong JPEG compression and a low contrast lens would have a similarly degradatory effect on an image.
--
Daniel

'One man practicing sportsmanship is better than a hundred teaching it.' - Knute Rockne

 

[Dave Martin]

...I just thought
that strong JPEG compression and a low contrast lens would have a
similarly degradatory effect on an image.

There's some truth to that I think. The JPEG algorithm throws away some of the higher frequency (smaller spacing) data. This has the effect of destroying detail as does the second (diffraction/Modulation Transfer Function) effect I showed earleir.

 

[BCJames]

Both are a detriment to the image and reduce the image quality. One through inferior lens design, and do to file compression.
--
Free stuff for the beginners. No charge. Really. Of
course donations are accepted... KIDDING!

http://freephotographytutorials.blogspot.com/

 

[Chris59]

Contrast is the ability of a lens to distinguish between two closely related tones. A lens that can do this also appears sharper even though the resolution when compared to a low contrast lens may be identical. The reason for a lens displaying good contrast include the number of elements used, the amount and quality of multicoating applied, the final "smoothness" of the lens elements (as opposed to their shape or "figure"), the blacking out of lens edges and internal lens barrel surfaces, and so on.

This kind of contrast should not be confused with the sort of contrast you can boost in post processing. Whereas contrast in PP is all to do with numbers and how tones relate to one another, high lens contrast is always a good thing (the higher the better) because all the factors that contribute to high lens contrast are a product of good lens design and build and can't be faked.

It it therefore sad that lens contrast figures or even impressions do not form part of DP Review's testing procedures (unless I have missed something) because images from a low contrast lens look flat, dull, muddy and not very sharp even if the resolution is the same as a high contrast lens.

While we're at it, lenses tend to exhibit their lowest contrast results at large apertures and in the corners of an image and their best contrast in the middle of the image in the middle of the aperture range.

 

[profborg]

--
Daniel

'One man practicing sportsmanship is better than a hundred teaching it.' - Knute Rockne