Leica Lens Glass Tint, Anomalous Dispersion, 3D Transfer Function, Correction Range

Mustafa Umut Sarac submitted a new resource:

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I am spending much energy to understand my Leica lenses and the Fluro Ektar.

All above lenses have an ability to see the portrait much better than your bare eyes. There is a good experiment for non believers. Find a Leitz lens have a large aperture and brownish tint in the glass. Hold the lens and look to your friends face. You will see much more three dimensionality , elegant curves and grades , much more skin detail and your jaw drops. If you do that experiment at tungsten light , effect...

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Leica Lens Glass Tint, Anomalous Dispersion, 3D Transfer Function, Correction...

Hi Umut,

This is a well-known aspect of certain optical glasses and is not unique to Leitz. It's another (expensive and often unnecessary) tool to correct chromatic aberration. As a designer, I'm more interested in the overall balancing of aberrations of which color is one. Other design techniques such as symmetry and overall low dispersion can be used to reduce spherochromatism and lateral color.

BTW brown-tinted glass in older lenses could indicate a thorium-doped element. Don't store it in your pants for long periods of time.

Slight tints indicate thick elements of certain glass types which I prefer to avoid due to the very slight color shifts and reduction in transmission in violet and near infrared. Those glasses can usually be substituted out for more modern, lower cost glasses. IIRC there's other fabrication issues (staining, softness) which help drive up the cost. Thickness is controlled by overall mass and length requirement. Of course, at the time there was less selection of glasses to work with.

Cheers,
Jason

Hi Jason,

Nice to know You are well.

I had been bought a Leicina Dygon lens and direct it to extremelly bright metal point surface.

There was a two bright point at the lens vertical. I looked to zernike list it was coma.

Than I read there was a research where lenses have deep coma errors was very easy to correct the distorted image.

I thought coma have two images could be used as stereo image pair to create 3d image.

Could leica do a trick like that ?

Thank you,

Umut

Can you post a picture that shows this effect?

BTW brown-tinted glass in older lenses could indicate a thorium-doped element. Don't store it in your pants for long periods of time.


Yes, brownish to yellow tint on early Summicrons, ektars, etc results from Lanthanum contaminated with thorium. Some sources of Lanthanum had more Thorium than others, I have examples of both and the optical properties exist regardless of the Thorium levels so the color change resulting from the Thorium alphas may not be a salient factor. I keep mine in a lead shielded box. Both the brown tinted and non-tinted lenses have exceptional rendering.

I think the intelligent move is not investigate how glass been tinted but why ? I tried to explain it.

I found another interesting graphic at schott site and it shows , higher the abbe number , reddish the final result - may be at tungsten light as I experienced with sonnar, ektar, elmar, summitar.

I found old leitz lenses have higher abbe numbers than today and they make brownish vermillon color at night. When abbe number reachhes to 60 or little bit higher.

Thorium doped glass gives thorium print colors at night shots under tungsten light , this is my experience.

Another finding , 3d transfer function is amount of change in volume change of the object. I have a hektor 135 and took my picture in front of cheap concrete wall. That wall covered with little textures where architects wants to change the appereance of bare concrete , shot crete I think.

When I looked to the print , all the wringles appearead bigger than the normal. If Leica uses 3d otf and if it is about volume change , I think leica transforms a 3d shape in to little bit bigger volume.

Thats the bas relief effect.