[Digitalis]

PSF ?

Point Spread Function - in laymans terms it is a descriptor of how a lens reproduces a scene.

So it is as much about a pedigree rather than outright design features.?

Design features can be added or subtracted, what we are discussing here are the base characteristics when there is nothing left to take away.

[kaseki]

point spread function <2D Fourier transform> modulation transfer function

and vice versa.

[desertscape]

The 90 Takumar (leaf) and the 90 Pentax are both double gauss designs on the 6x7. Even though these two designs are not totally symmetrical, the fact that they are close to it, makes it much easier for the designer to correct three of the transverse aberrations.This design type also has very low spherochromatism.

[StanislaVS]

Referring to my limited and recent experience with the P67 165mm f/2.8 lens (a double gauss) I found the lens to be very sharp but most of all the pictures are very pleasant to look at. They are just different. Even my wife, a Nikon super fan, took a picture with it on the 645z and could immediately see a difference without me saying anything. I started to look for other double gauss lenses and surprisingly very little information is available. The most info I got was from Sasha Krasnov's website ( skrasnov.com ) and it looks like there are a couple more in P67, but I could not confirm any P645 double gauss lenses. Then I found a note somewhere that mentioned that most Fuji lenses are based on Zeiss planar lenses (double gauss).

Now I am wondering what are the disadvantages vs advantages and if the advantages outweigh the obvious question comes to mind, as to why did Pentax not continue with the double gauss designs in other focal lengths and P645 mount. I did not look much for the K-mounts, although I saw quite a few older k-mount lenses show up on lists.

I know there are many optical specialists on this forum and will appreciate an opinion from your point of view.

I attach the block diagram of the P67 165mm f/2.8 lens. Credit: Pentax 67 165mm F2.8: Lens review, Bokeh effect, Details and Experience

This optical design is NOT a Double Gauss (Planar). For the first time this scheme was applied in 1934 by Schneider in Xenon lenses. Although it must be admitted that the earlier Xenon of 1925 was also a Double Gauss. Optical design Xenon 1934 was used in many lenses, such as Voigtlander 75 / 2.5 SL, Russian Volna-3 and others. Cosina also uses this Schneider Xenon scheme of 1934, but prefers to call it New Color Heliar, although there is nothing from the true Heliar in this scheme, except for the name.

[TDvN57]

This optical design is NOT a Double Gauss (Planar). For the first time this scheme was applied in 1934 by Schneider in Xenon lenses. Although it must be admitted that the earlier Xenon of 1925 was also a Double Gauss. Optical design Xenon 1934 was used in many lenses, such as Voigtlander 75 / 2.5 SL, Russian Volna-3 and others. Cosina also uses this Schneider Xenon scheme of 1934, but prefers to call it New Color Heliar, although there is nothing from the true Heliar in this scheme, except for the name.

Can you elaborate on the "NOT" part? Don't mean to put you on the spot, but I'd like to understand the "why" component.

[Lord Lucan]

Look, he even took selfies.

So Putin used to be a wine waiter?

[Digitalis]

So Putin used to be a wine waiter?

I don't think cask wine was a thing back in the 1930s.

[StanislaVS]

Can you elaborate on the "NOT" part? Don't mean to put you on the spot, but I'd like to understand the "why" component.

Voigtl

[TDvN57]

Voigtl

Not sure if I understand what you are saying. Are you saying that since Tronnier designed the Voigtlander ULTRON in 1950 based on a double gauss, now any other lens based on double gauss is a "NON"?

Expanding on what you are trying to communicate might help to avoid misunderstanding.

[StanislaVS]

Not sure if I understand what you are saying. Are you saying that since Tronnier designed the Voigtlander ULTRON in 1950 based on a double gauss, now any other lens based on double gauss is a "NON"?

Expanding on what you are trying to communicate might help to avoid misunderstanding.

The optical formula of Double Gauss is 6/4, those in the front and back groups have gluing. You are considering the optical formula 6/5, which was invented by Schneider in 1934 as an alternative to Double Gauss. They still use this optical design today, for example in the Schneider 80/2.8LS lens for Phase One.

[itsdoable]

The optical formula of Double Gauss is 6/4, those in the front and back groups have gluing. You are considering the optical formula 6/5, which was invented by Schneider in 1934 as an alternative to Double Gauss. They still use this optical design today, for example in the Schneider 80/2.8LS lens for Phase One.

I think it depends on how you use the term - As mentioned earlier in the thread, the "Double Gauss" was originally 4 elements (the "Gauss was 2 elements). The Planar (a copy of the Biotar) was a modification of the Double Gauss by making the inner 2 elements doublets (6/4). This was later modified by splitting one of the doublets (6/5), and further more by adding another element for faster lenses (7/6). The lineage of most of these lenses can be traced back to the original Double Gauss design.


(... and some zombie comments - according to Zeiss history, the Tessar was not derived from the Cooke triplet, where as the Leitz Elmar was).

[StanislaVS]

I think it depends on how you use the term - As mentioned earlier in the thread, the "Double Gauss" was originally 4 elements (the "Gauss was 2 elements). The Planar (a copy of the Biotar) was a modification of the Double Gauss by making the inner 2 elements doublets (6/4). This was later modified by splitting one of the doublets (6/5), and further more by adding another element for faster lenses (7/6). The lineage of most of these lenses can be traced back to the original Double Gauss design.


(... and some zombie comments - according to Zeiss history, the Tessar was not derived from the Cooke triplet, where as the Leitz Elmar was).

The fundamental difference between the Gaussian-Double Gaussian - Planar is that schemes never used a biconcave element, which was in the center of the triplet. From triplet
got: Tessar (gluing at the back), Primotar (gluing at the front), Heliar (gluing at the front and back). The 6/5 scheme, that we are discussing, has such an element in the back group, because it has nothing to do with Gauss-Double Gauss. As for thefront group, this part is a typical anastigmat. 😁😂😆

[desertscape]

In Rudolf Kingslake's book, "A History of the Photographic Lens" he shows many examples of Double-Gauss designs. One of them has an air spaced front group with a ++- configuration, followed by a cemented meniscus and a positive element, a -++ configuration. This was a 90mm Summicron f/2 (Leica). The cross sections of this lens and the 165mm f/2.8 lens for the Pentax 67 are nearly identical. The 165 f/2.8 is a Double- Gauss variant.

[StanislaVS]

In Rudolf Kingslake's book, "A History of the Photographic Lens" he shows many examples of Double-Gauss designs. One of them has an air spaced front group with a ++- configuration, followed by a cemented meniscus and a positive element, a -++ configuration. This was a 90mm Summicron f/2 (Leica). The cross sections of this lens and the 165mm f/2.8 lens for the Pentax 67 are nearly identical. The 165 f/2.8 is a Double- Gauss variant.

The Leica Summicron-R 90 mm f/ 2 Lens. Specs. MTF Charts. User Reviews.

This is Zeiss Biometar design!

The bio- in the name is obviously related to the fact there is a meniscus in the back group! Pentax 67 165 / 2.8 does not have a meniscus, but there is a central element from the triplet. This is a completely different Schneider scheme from 1934.

[TDvN57]

It seems that we have diverse and differing opinions from experts. I appreciate and respect your contributions.

May I ask the original question again? What are the advantages and disadvantages of a Double Gauss (DG) lens design? Even if the 165mm is or is not a DG design.