Can lens or camera have a 'clinical' rendering?

Started 1 month ago | Discussions thread
57even Forum Pro • Posts: 14,725
Re: Can lens or camera have a 'clinical' rendering?

Erik Kaffehr wrote:

D Cox wrote:

Erik Kaffehr wrote:

AiryDiscus wrote:

fPrime wrote:

57even wrote:

fPrime wrote:

57even wrote:

fPrime wrote:

57even wrote:

fPrime wrote:

57even wrote:

fPrime wrote:

I’ve certainly described some lenses as clinical. To me a “clinical” lens is simply one that is highly corrected for optical aberrations, distortion, vignetting, and soft corners when shot wide open. I use the term dispassionately. For some applications (like astrophotography, for example) a clinical rendering quality is actually preferable.

The downside of clinical lenses is that they tend to draw less microcontrast and 3D Pop once stopped down. That can be counterproductive to some photographic use cases.

fPrime

This doesn't make a lot of sense. Why can't a well corrected lens have good microcontrast?

It’s likely that my definition of microcontrast differs from yours.

fPrime

That doesn't answer my question.

I didn't want to sidetrack Erik's thread on clinical rendering into yet another microcontrast debate. But basically, if microcontrast is defined as simply an extension of global contrast with respect to higher spatial frequencies which yields more “bite” in the fine details of an image, then extremely well-corrected lenses will certainly deliver more of that quality.

If, however, we view microcontrast as tonal gradation, then these same, sharper, clinical lenses deliver less image microcontrast. How so? High Refractive Index glass elements differentially absorb fragile blue wavelengths over green and red wavelengths. The more elements that designers use to correct for aberrations and un-sharp corners, the more that low-gain blue wavelengths in the scene are gated out. This muddies the scene's microcontrast globally but especially so in the shadows and dark portions where low-gain blue wavelengths often dominate.

fPrime

Did you just make that up or read it on an internet site?

Unfortunately I can't take credit for the definition. Many professional photographers view microcontrast as tonal resolution including Irakly Shanidze and Mark Wieczorek and Yannick Khong who have all published articles on it. Irakly leads a fine art photography academy in Detroit. What do you lead in the photographic world in comparison?

I am not going to argue about definitions of a term, but I was referring to the pseudo scientific guff immediately following it.

Was that the "guff" that you were unable to cogently refute? Got it. Smearing it was the best you could manage.

However, I will take credit for illustrating the definition with real world image examples so that lay people such as yourself can better understand it. I've also linked the data on blue-wavelength light absorption by HRI glass to a loss of microcontrast transmission in photographic lenses.

Good for you, but it doesn't answer the question. I was asking why a lens cannot be well corrected and have good micro contrast. Using HRI glass is not a prerequisite for a well-corrected lens.

Please show us a highly corrected lens that employs no HRI glass then, haha. In lenses it's been common design practice now for decades to use higher RI optical glass wherever possible to minimize the weight and size of lenses. The reason is simple... the higher the refractive index of the glass is, the less glass it takes to bend light. HRI 1.6 optical glass was even doped with radioactive Thorium as early as 1939 in order to minimize the dispersion caused by the HRI glass.

fPrime

Snell's law is very simple and very useful. It tells you that light bends when there is a change in refractive index, and only when there is a change in refractive index. Using a higher index material allows you to use relatively flatter surfaces, which in turn introduce less aberration. The statement you made which I bolded is wrong, and has no basis in any science.

High index materials are not particularly common, and especially are not the majority material for designs. As an example, the Otus 85/1.4 only has four elements which do not have anomalous partial dispersion. Anomalous dispersion materials are all quite low index, ~< n=1.5. High index glass is typically very dispersive, which makes it useful for negative elements to correct chromatic aberrations, since negative elements are usually a larger source of aberration than positive ones. The dispersion also makes them very difficult to use as a "majority" material because the color becomes uncorrectable. The statement you made which I underlined is wrong and has no basis in any design survey.

Heavy elements are used as dopants in glass to drive up the refractive index, not to reduce dispersion. They do not reduce dispersion. Glasses are lower dispersion when the amorphous structure of the material is more regular, and are more highly dispersive when it is irregular. Adding relatively small amounts of heavy elements to what is a mostly "light" element chemistry makes things more irregular. n=1.6 is not a high index material. The statement you made which I placed in italics is wrong, and is not based on an understanding of glass chemistry.

Well, I think that if Fprime shared the optical specifications of a few lenses he designed, it may give some insights how different glass affects his design?

Best regards

Erik

Even a few examples of lenses that he considers to be good for gradation, and a few that he considers to be bad might help.

Bearing in mind that Leica lenses have often been through several design revision over the years, so a year or serial number would be needed.

I am not Fprime but the OP.

My inital question was based on an observation by a user who preferably shoots on the GFX 100 with the 110/2 being his favourite lens. We know, from Jim Kasson's testing that it is a very well corrected lens. That photographer is looking at an alternative system, essentially to save his GFX system for serious work. He was looking at Sony, but found that the lenses were very sharp but 'too clinical'. Don't know which lenses he tried.

Jim Kasson mentioned that the '90/2 Apo Summicron M ASPH' is a lens having a certain character.

On the other hand, Zeiss Otus lenses are said to near optimally corrected, but no one complains about them rendering 'clinical'.

I think it was mentioned that not full corrected spherical aberration is appreciated, especially among portrait photographers.

Best regards

Erik

The problem is knowing what people mean when they say 'clinical'.

Uncorrected SA definitely improves bokeh on primes but not always on zooms (tends to swap over to strong outlining as the focal length changes).

Uncorrected SA would also indicate lower image sharpness at the edges. Not an issue for portrait photographers but sometimes a pain for landscape photographers.

So maybe the latter would prefer clinical lenses?

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"A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away." Antoine de Saint-Exupery

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