I'm done with lens reviews

Truman Prevatt wrote:

Jeff Biscuits wrote:

Truman Prevatt wrote:

Microcontrast

Actually it is quite real.

Fill me in in one thing, though…

I’ve done a limited amount of image processing in my career which has involved analysing local contrast/gradient. So “microcontast” as that concept of contrast within a small area of an image (whether analog or digital) makes complete sense.

Where it doesn’t make sense to me is when it comes to lenses. It’s a term that’s explicitly differentiated from just “contrast”, and I can’t get my head around how a lens can provide microcontrast to any different degree than it would provide “macro contrast”. In other words, how could a lens have the capacity to alter tonality just because of the proximity of their tones? It seems obvious that a lens can give more or less contrast, but surely there is no way two lenses with the same macro contrast can differ in terms of microcontrast.

So I’ve always assumed that in the context of lens reviews, microcontrast—though a perfectly real and measurable thing—is used in a somewhat mythical way, because in terms of a lens transmitting light, it’s just contrast.

Or is there something I’ve completely overlooked?

Every component of an optical systems reduces local contrast. Film reduces the local contrast of a scene. An outdoor scene can have as much as 20 stops of almost instantaneous contrast change. No film nor digital sensor can replicate that. In film days one had to chose the type of developer. D76 for example contained silver solvents. It was good for reducing grain but it made the edges smoother with slower roll of so reduced the micro contrast. Acutance ( a term for edge sharpness) developers like Ordinal produced negatives with much better micro contrast (sharp edges) but also made the grain more apparent since the hard edges were maintained.

Color filter arrays reduce micro contrast as the edges will be derived by interpolation from neighbor hooding detectors with different color. Cross talk in the sensor will cause a bleeding current across into neighboring detector hence reducing the contrast across the edges and smoothing the edges somewhat similar to the effect of silver solvents in developers.

The final component which may have the biggest impact is the lens. Lenses don't create micro contrast. No component of the imaging system create micro-contrast. That is a function of the scene. Any distortion will show up across edges as an effect of reducing micro contrast. Some aberrations are worse that others. Chromatic aberration resulting from the wavelength dependence on the refractive index will show up across sharp edges. Fixing one aberration can often result in making others worse.

https://www.lensrentals.com/blog/2010/10/the-seven-deadly-aberrations/

In the image they all show up on sharp boundaries between dark and light - the edges. When I ended up having to worry about R&D for both our signal intelligence/electronic warfare systems and optical systems I have to get an immediate education. The consolidation made sense as the big end image processing that the move to digital cameras for ISR was now simply the two dimensional version we did for signals intelligence and EW. For example an edge in an image is detected using the same basic approach as a radar pulse in detected in an EW system. But there is a lot more subtle to the imaging systems. Lens designs - we specified our lens designs to people like Kodak, Corning, etc. Different lens designs and glass formulations were needed for a camera flying at a nominal 30,000 feet on an airborne platform, from one flying on a U2 at 70,000 feet from one flying on the SR71 "blackbird" at 90,000 feet from one flying in space. But the goal was always the same - minimize the micro contrast degradation of the lens. In the 1960's NASA often contracted with Zeiss to design and build their lenses. Some attribute the "Zeiss pop" to the the fact these lenses degrade the scene micro contrast less than other lenses. That was important to NASA for the exploration of the moon during the 1960's and '70s. Often we would trade other properties of the lens to maintain high micro contrast.

So I expect that when people refer to their opinion that lens A has better micro contrast than lens B, what they mean is Lens A reduces micro-contrast to a less extent than lens B.

There is no perfect lens. Fourier optics tells us that. The very fact that there is an aperture between the scene and film/sensor impacts the recorded image. The point spread function tells us exactly what a point source looks like. The fact that all light rays landing on the sensor are not collimated and the interaction with the lens impacts the image. The fact that the index of refraction of all glass is greater than 1, impacts the image. The fact that there are air/glass boundaries (to per lens element) resulting in both reflection and partial reflection impacts the image. The fact that some of the photons scatter of the air/glass boundaries in random directions results in impacting the image. The major impact of all these things results in reducing the local or micro contrast.

Zeiss and Leitz both got their start in designing microscopes that could increase the contrast between the subject and background so people could see the objects better. While there is a difference in the illumination sources the problem in a microscope and camera vs. a lithography systems for the production of semiconductor devices - the problem is the same. That is to maintain sufficient local contrast to maintain the necessary detail at the edges.

Yes,

i have read these facts many times and I think I understand what this is about - there is a measurable thing. BUT ! are  basically and normally made good lenses really much different - somehow visually different . I have very (or too often ) often  read how people can "see" in an image on a PC screen, that some lens (usually the expensive ones they own )  clearly has more "micro contrast" . I really doubt these observations. How can anyone see some fantastic micro contrast  on a rather low resolution screen?

The facts and science is OK , but I do not believe in people who claim that they clearly see micro contrast .  And some decades ago I had too look in to a microscope quite often

Expensive microscopes were better.... and some binoculars are much better. And some really bad lens was really bad and I had to return it. All other lenses have been OK