lens contrast

I understand contrast in a scene but I keep

reading about lenses that are and are not

contrasty. What does this mean as far as a lens

is concerned? Could you post example of same

subject shot with equivalent lens (one "contrasty"

and one less contrasty)?

<p>What this means as far as a lens is concerned is that low contrast gives the appearance of less range (distinction) among or between colors, whereas high contrast typically gives the appearance of a greater range or distinction among colors. It, along with resolution, is one of several factors which contributes to apparent sharpness of a lens. I'll try to attach a sample which is pretty self explanatory.</p><div></div>

<p>Stephen visual example works well :)<br>

One of the things that you'll also here in these discussions is the 'micro-contrast'; the ability of a lens to subtly render the (high-resolution) contrast differences in the small details. This especially adds a lot to the apparent sharpness of an image, and can create what many call a "3D effect", where the in-focus subject seems to stand out more from the (out of focus) background. Unlike "global contrast", the effect of micro-contrast is much harder to achieve in post processing, so lenses with good qualities in this sense tend to stand out. A better explanation <a href="http://www.luminous-landscape.com/tutorials/understanding-series/lens-contrast.shtml">here</a>.<br>

Unfortunately, I have no direct comparison shots (while I do have lenses fitting in both categories). The lower contrast is not wanted by most people, but in fact can make a right choice. As always, it depends on subject and desired look of the image.</p>

<p>Why would lens design effect image contrast? The job of the lens is to gather light rays from the outside world and project them as an image on the flat surface of film or digital sensor. This is accomplished by altering the path of light rays. We call this action refraction. This is accomplished by the shape, material of construction, and spacing of the individual lens elements that make up the camera lens. <br>

<br>

All camera lenses suffer from natural defects called aberrations. The lens maker attempts to mitigate but none have been eliminated. To minimize, different densities of glass, each with different figures are packed into the lens barrel. Each element of the array takes a toll reducing the light energy that should make up the projected image. Only about 92% of the light will transverse each element. What happens to the light that reflects off each polished surface? <br>

<br>

Reflected light from each lens surface bounces about. Some will strike the walls of the lens barrel and the hollow of camera body. Some will strike the lens ahead or behind. In other words, the image forming rays are comingled with stray light rays. It is these misdirected light rays that will eventually bath the film or digital sensor with non-image forming rays during the exposure. To migrate the inside walls are painted flat black. To further migrate, each lens is “boomed”. <br>

<br>

It was discovered that older lenses passed more light then new ones of the same design. Investigating, Harold Dennis Taylor (English 1862-1942) discovered that old lenses had a thin film of “bloom” deposited by air pollution. He experimented and artificially aged lenses (patent 29,561/1904). The thin film of “bloom” now applied, drives the transmission percentage up to 98%. <br>

<br>

Optical coating on lens elements and filters is the major mender of stray light in the image forming rays. It is these rays that induce flare. Flare is devastating as it slashes contrast. A singe thin coat mitigates best only one color. The coat thickness must be ¼ wavelength. Complex lenses can have as many as 12 coats. All this adds costs. You get what you pay for. Hats off to Harold Taylor! </p>

<center><B><img src="http://jdainis.com/72_ppi_cannon.jpg"><BR>

Contrasty<P></b></center>

 

 

<center><b><img src="http://jdainis.com/72_ppi_cannon_lo_contr.jpg">

<P>Less contrasty<P></b></center>

 

The sample that Mr. Lewis shows may be a bit misleading. The contrast aspect is on the left two boxes. Ignore the resolution, lessening of sharpness, that is shown on the two right boxes. An image may appear less sharp due to low contrast but it is not less sharp due to low contrast.

<p>James - the operative phrase is "apparent sharpness". Often people with vision issues (many of us as we get older) experience reduced contrast, which contributes to a perception of apparent sharpness.</p>

I believe "may appear less sharp" equates to "apparent sharpness".

<p>How does "Definition", or local contrast fit into this "apparent sharpness" concept?</p>

<p>I'm glad this subject was brought up because I've seen quite a few lenses regardless of price exhibit various levels of this vale of flare demonstrated quite effectively by James' "Less Contrasty" version of the cannon.</p>

<p>And I'ld have to agree that resolution only matters if there's enough pixels to render tonal differences at the pixel level in order to create local contrast too fool the eye into seeing apparent detail, not sharpness necessarily unless you have your nose up to the screen or print.</p>

<p>Most of the lenses I've seen can capture this level of micro contrast. It's just that some exhibit this vale of flare that redistributes the tonal scale requiring more processing most often having to do with remapping foggy looking absolute blacks captured in the scene back to absolute black while maintaining definition in the shadows without posterization.</p>

<p>I have a sub $200 cheap lens that does just that to black points but I've also seen it demonstrated in an online discussion by a $600 lens designed for large format cameras.</p>

<blockquote>

<p>One of the things that you'll also here in these discussions is the 'micro-contrast'; the ability of a lens to subtly render the (high-resolution) contrast differences in the small details.</p>

</blockquote>

<p>That is the contrast that Stephen mentioned. Sometimes people talk about color contrast and then micro-contrast makes it clearer that you're referring to the component of sharpness.</p>

<blockquote>

<p>And I'ld have to agree that resolution only matters if there's enough pixels to render tonal differences at the pixel level in order to create local contrast too fool the eye into seeing apparent detail, not sharpness necessarily unless you have your nose up to the screen or print.</p>

</blockquote>

<p>It helps with cropping too.<br>

<br>

As an example, my Pentax kit lenses (18-55 and 50-200) produced very nice colors, more vivid than the ones I would get from older K/M lenses. But they were suffering from spherical aberration, so microcontrast and thus resolution was not that good. This aspect was a problem when I was taking close up shots of insects - I wasn't getting enough magnification with the 50-200 and when I was cropping, the lack of resolution would be obvious. Here is an example:<br>

<br>

<img src="https://farm6.staticflickr.com/5104/5807225013_9d03a3ab8b.jpg" alt="" width="500" height="333" /></p>

<p>OTOH, a sharp lens will allow me to crop severely and still maintain pretty good detail. This is a much tighter crop than in the previous example:<br>

<img src="https://farm8.staticflickr.com/7342/11230502145_55ace3d965.jpg" alt="" width="500" height="376" /></p>

 

<p>Mike Johnston explains the basics of lens "sharpness" as well as anyone, and better than most. Here's his article on <a href="http://www.luminous-landscape.com/tutorials/understanding-series/lens-contrast.shtml">"Understand Lens Contrast and the Basics of MTF"</a>.</p>

<p>The problem with demonstrating "sharpness" with small online JPEGs is that often we're seeing oversharpening artifacts, jaggies, halos and contrast effects of editing choices rather than anything to do with lenses or recording media.</p>

<p>My bad, I normally link my images to the source page where larger versions can be seen, but I forgot to do that here and I can no longer edit my post.<br>

<br /> FWIW, here are the links:<br /> <a href="https://www.flickr.com/photos/laurentiucristofor/5807225013">First photo</a>.<br /> <a href="https://www.flickr.com/photos/laurentiucristofor/11230502145">Second photo</a>.<br /> <a href="https://www.flickr.com/photos/laurentiucristofor/11230610913">And a wider crop of the second photo</a>.</p>