Lens Reflections and Lens Design

[Brian Bullen]

I'm curious about looking at lens reflections to figure out lens design. When I look at the lens from the front I see a total of seven reflections. When I seperate the front and back cells there are four reflections in the front and three in the back. The front cell also seperates into two groups, if that makes sense. So for clarity a total of three cells, 2 in the front one in the back. Any ideas what design this is.

 

[Brian Bullen]

I think I may have found the info, correct me if I'm wrong. It seems from what I've read that this is a tessar design. four bright reflections in the front cell and two bright an one dim in the rear cell.

 

[dr bob]

The lens you describe is certainly like the Tessar which is a variation of the Leitz "Elmar". The Sekor 135mm used on the Mamiya C-series TLRs are of this design. One major difference is the position of the stop and shutter. At their first encounter observing the rear of the Mamiya lens, many Mamiya C-series camera operators are perturbed to see the bare shutter blades facing them.

This design has enjoyed great success since the 1950s so I suppose there is no danger of inadvertent damage given proper care. After all, any agent that might cause damage to the diaphragm and shutter would surely damage a lens. As a best all-around lens, the 135mm Sekor offers excellent resolution, aberration correction, and contrast. Many users proclaim it as their personal favorite.

 

[bobfowler]

The lens you describe is certainly like the Tessar which is a variation of the Leitz "Elmar". The Sekor 135mm used on the Mamiya C-series TLRs are of this design. One major difference is the position of the stop and shutter. At their first encounter observing the rear of the Mamiya lens, many Mamiya C-series camera operators are perturbed to see the bare shutter blades facing them.

This design has enjoyed great success since the 1950s so I suppose there is no danger of inadvertent damage given proper care. After all, any agent that might cause damage to the diaphragm and shutter would surely damage a lens. As a best all-around lens, the 135mm Sekor offers excellent resolution, aberration correction, and contrast. Many users proclaim it as their personal favorite.

The 135 Sekor is indeed the cat's ass of TLR lenses. I hated to see mine go, but the 150mm Bronica Zenzanon PS is a pretty good substitute in the SLR world.

 

[Ian Grant]

The lens you describe is certainly like the Tessar which is a variation of the Leitz "Elmar".

Wrong way round. The Carl Zeiss Tessar was a computation of Dr. Paul Rudolph in 1902, and was itself an advance on the Cooke Triplet, designed by Dennis Tayor in 1893, and produced by Taylor, Taylor Hobson of Leicester.

The Elmar is a very much later "Tessar" type design, around 1925

Ian

 

[Ole]

while a Tessar-type is a distinct possibility, you give far too little information. A Petzval portrait lens would show exactly the same reflections, but completely different pictures.

 

[Brian Bullen]

while a Tessar-type is a distinct possibility, you give far too little information. A Petzval portrait lens would show exactly the same reflections, but completely different pictures.

You're right Ole I did give too little info, the lens is a 320 apo-astragon in barrel. I doubt it's a petzval portrait lens but since no one has any info on this lens I won't be surprised if it is. I will try this lens on sunday to get a better idea of its performance.
I guess I haven't seen enough lenses to figure out the constructon by looking at the reflections. For instance if it is a tessar that means basically 4 elements in 3 groups. So where do the 7 reflections come from? 2 from the first element, 2 from the second element and 3 from the last 2 elelments?
Is there a good book on this subject?

 

[Ole]

... For instance if it is a tessar that means basically 4 elements in 3 groups. So where do the 7 reflections come from? 2 from the first element, 2 from the second element and 3 from the last 2 elelments?
Is there a good book on this subject?

EVery glass/air interface has a strong reflection, every glass/glass a weaker one. So for a Tessar it will be one strong reflection for each glass/air - 6 in all - and a weaker one from inside the cemented pair.

The size and "movement" of the reflections as you move the lens tells something about the curvature, but this can get a lot more confusing when you take the elements between you and the reflection into account. But at least it's easy to tell the difference between the strongly curved surfaces of a wide-angle lens and the nearly flat surfaces of a long FL lens.

I think your Apo-Astragon is probably a Tessar derivative, I would guess a repro lens if it weren't for the "astro"-bit.

 

[dr bob]

Wrong way round. The Carl Zeiss Tessar was a computation of Dr. Paul Rudolph in 1902, and was itself an advance on the Cooke Triplet, designed by Dennis Tayor in 1893, and produced by Taylor, Taylor Hobson of Leicester.

The Elmar is a very much later "Tessar" type design, around 1925

Ian

Quite true. In self defense however, I was referring to the Sekor "Tessar" which is almost a rip of the "Elmar". But thanks for straightening out the historical facts.

 

[Brian Bullen]

EVery glass/air interface has a strong reflection, every glass/glass a weaker one. So for a Tessar it will be one strong reflection for each glass/air - 6 in all - and a weaker one from inside the cemented pair.

The size and "movement" of the reflections as you move the lens tells something about the curvature, but this can get a lot more confusing when you take the elements between you and the reflection into account. But at least it's easy to tell the difference between the strongly curved surfaces of a wide-angle lens and the nearly flat surfaces of a long FL lens.

Thanks Ole this is the kind of info I was looking for, it makes it a little easier to understand what people are seeing in their lenses and why. Can you recommend any books or websites on large format lens designs? I've seen a few websites with little blurbs about a certain design but nothing comprehensive.

 

[acroell]

The classic book on the subject is the one by Rudolf Kingslake (former head of Kodak's Optics Dept.) "A History of the photographic lens" (Academic Press 1989). It is still available. Covers not only LF designs, but a lot of the designs discussed are LF ones.

 

[Brian Bullen]

The classic book on the subject is the one by Rudolf Kingslake (former head of Kodak's Optics Dept.) "A History of the photographic lens" (Academic Press 1989). It is still available. Covers not only LF designs, but a lot of the designs discussed are LF ones.

Excellent. I'll be on the lookout for this, thanks. I think I may have seen a website with Kingslake giving a brief history of different lens companies in the Rochester NY area. The name certainly sounds familiar.