A Tale of Two 305mm f/9 G-Claron (Dagor type) Lenses - Cell Spacing

[Corran]

I've got an interesting pair of lenses here that I want to know more about, and see what is what.

A few months ago I bought a 305mm G-Claron from eBay, in barrel. This is an older model that is a Dagor type. The lens screws right into a Compur #2 shutter from my 150mm f/2.8 Xenotar, but doesn't fit in a #2 from a 270mm f/5.5 Tele-Arton. I was going to send the shutter/cells to SKG to get it refit, but then a 305mm GC in shutter came up for sale here in the forum classifieds.

I bought that 305mm - this one is also a Dagor type (maybe??), but it's slightly newer (higher serial #). These two lenses are interesting in comparison and now I'm wondering about the cell spacing and design(s). I assume it's not one of the newer models because those are much larger (Copal #3).

The first, older one has a 49mm filter thread, while the newer one has a 58mm thread. The two lenses interchange in the barrel/shutter perfectly. However, the older one has slightly less space between the cells either way. The lens barrels that the glass is in is physically longer in the newer lens.

So the first question I had, is what difference does it make? I switched these lenses back and forth on my 8x20. The older, shorter lens covers 8x20 fine with some room to spare. The newer one does not! It clips the corners just barely.

What exactly is going on here? Does a slightly larger cell spacing reduce the image circle? Are these actually the same design, or maybe they are different? Why was the space between the lenses changed physically with the lens barrels? Could/should I have the threads cut down to improve coverage on the newer one?

I can post images of the lenses late tonight if it's important.

[Chauncey Walden]

The older is a Dagor, the newer is not.

[Oren Grad]

I assume it's not one of the newer models because those are much larger (Copal #3).

Late-model 305 GC's came from Schneider in Copal 1. Only the 355 was large enough to require a Copal 3.

[Corran]

Oh! My mistake. So you and Chauncey think the newer one is not a Dagor? What is it then? It still fits the same barrel/shutter as the older lens.

[Oren Grad]

I don't know. My late 305 has a 67mm filter thread, consistent with the specification in my '90s-vintage Schneider LF lens brochure.

[Corran]

Interesting. I assume it's some sort of transitional model. What is the (usable) IC for your lens (as opposed to the specifications provided by Schneider)?

[Oren Grad]

Afraid I haven't tested for the exact limits of mine. I've used it successfully on 11x14, IIRC with a bit of front rise. I've also used my late 270 on 11x14, with good results. In both cases, making negatives intended for contact printing.

[Dan Fromm]

Interesting. I assume it's some sort of transitional model. What is the (usable) IC for your lens (as opposed to the specifications provided by Schneider)?

Transitional model? Dagor to s/n 11,000,000 (although I have an e-mail from Schneider saying 12,000,000, I've never seen a Dagor type GC with s/n > 11,000,000), then plasmat type.

Count reflections. Dagor type, 2 strong and 2 weak from each cell. Plasmat type, 4 strong and 1 weak from each cell. The weak reflections can be hard to see.

[Corran]

I will look tonight. Both of my lenses are over 11 million IIRC. However, I would assume that a Plasmat type 305mm lens wouldn't come close to covering 8x20, which the earlier one does easily and the newer one almost does (and I imagine would equal the other in coverage of the cells were slightly closer together?).

[Steve Goldstein]

According to my PDF of a 1976 G-Claron brochure the 305mm takes a 58mm filter and the 270mm takes a 49mm filter. If there's older documentation I don't have it, nor have I found it on the Wayback Machine.

[Dan Fromm]

Steve, look here: http://web.archive.org/web/201009220...hiv/archiv.htm More generally, when you're looking for lens catalogs etc. start from my list of links: http://1drv.ms/1w0vbMD

Bryan, if you'll follow the link to older Schneider brochures I gave to Steve you'll find that Schneider claims 411 mm for the Dagor type and 381 mm for the plasmat type at infinity and f/22. If Schneider's right neither comes close to covering 8x20 in the sense of putting good image in the corners. Illuminating 8x20 is something else again.

Oh, and by the way, since the two types fit different sizes of shutter there's no mechanical reason for their cell spacings to be the same.

[Corran]

Yes, I knew you were going to talk about the coverage specs, but it certainly does cover 8x20, and sharply too, looking at a couple of negatives I've shot (even in the corners).

Perhaps you misunderstood though - both lenses fit the exact same shutter (or barrel) identically. I can interchange the elements. I will check reflections. They are both 11 million serial numbers I think but I will double-check when I get home.

[Steve Goldstein]

Regarding serial numbers - a Dagor-style 210mm just listed today (161695120609, seller is in Lithuania, no relation) is 11724xxx. I have a 150mm Dagor-style 11325xxx.

Dan, that link just gave me a 404, but a working URL to the web archive that still works is

http://web.archive.org/web/20100922053809/http://www.schneiderkreuznach.com/archiv/archiv.htm

and points at a September 2010 snapshot, but they've got snapshots back to 2003. My old brochure showing the Dagor-style G-Clarons, downloaded directly from Schneider's site before it became history, actually dates from June 1968.

[sanking]

For ULF I like the Dagor type G-Clarons a lot. The circle of illumination is slightly larger with Dagor type than plasmat type, and the Dagor type also gives slightly greater contrast, other things being equal. This is due to the fact that there are only four air-to-glass surfaces with the Dagor type, while the plasmat type has six. Both types are single coated, thus slightly higher transmission with the Dagor type.

Sandy

[Dan Fromm]

Steve, I must have erred in cutting and pasting, just tried the link in my list and it works. Same as yours, actually.

[Corran]

Okay, so I'm looking at my lenses now.

First of all, I misspoke. The older one, serial # 10 995 xxx, has 58mm filter threads.

The newer one, serial # 11 838 xxx, has 62mm filter threads.

My mistake, I was thinking of something else when I wrote the thread sizes.

Now for the exciting part. The old one is indeed a Dagor. 2 strong, 2 weak reflections from each cell, and the new one is indeed a Plasmat, with 4 strong and one weak.

I assumed they would be the same design due to fitting in the same shutter/barrel, but I guess not. All I care about is the shutter from the new one, which I paid little enough for to make it worth my while. Perhaps the newer plasmat put in the barrel would be good as an enlarging lens? Or just sell it? It would still cover 11x14 easily - like I said, it only just clips the corners on 8x20.

[Chauncey Walden]

The Schneider data verifies that the Dagor-type used a 58mm filter and required a specific Compur 2 shutter giving an overall mounted length of 66mm. This is the one I have. The plasmat-type used a 67mm filter and used a standard 1 size shutter giving an overall mounted length of 68.9mm.

[Corran]

So my Compur #2-sized Plasmat with 62mm filter size is kind of unusual it sounds like. Not that it's a collectors piece or anything, but interesting nevertheless.

[Dan Fromm]

Not unusual, just another ~300 mm f/9 or f/10 process lens, one of many. Few have mystical properties, most are functionally equivalent.

The rule with these beasties is to be happy with the one you have. Go and be happy.

[Corran]

:rolleyes:

Yes Dan. I just mean from a manufacturing perspective. Like I mentioned before, the shutter from the plasmat is all I wanted. I am most certainly happy I have an "unusual" plasmat in #2 rather than #1, to fit the older dagor.

I am building an 8x10 enlarger and have 3 different ~300mm lenses to choose from for the enlarger lens, with the plasmat GC being the smallest, so I'll use that I suppose.

[carverlux]

Bryan,

My heartiest recommendation for your 8x10 enlarger would be a Red Dot or a Low Distortion Artar. I have stopped using Rodagons, Ronars and Componons in favor of Artar on my DeVere 5108. And as much as I use and like G-Claron Dagors to make pictures (read my long-winded posts from a few years ago), they do not hold a stick to an Artar as an enlarging lens. Proof is in the pudding, try it and you will see - good luck.

carver

[Corran]

Hi Carver,

I appreciate your thoughts. Perhaps I was unclear, I was thinking the plasmat design G-Claron would be okay for an enlarger lens. It is pretty small in the #2-size barrel

Mostly, I don't really want to buy additional lenses if something I have works just fine (and I wouldn't be enlarging more than 2-3x tops). What I have other than the plasmat for possible enlarger use is couple of random process lenses - a 305mm Agfa Intergon and a 300mm Konica Hexanon GRII (big!). Plus I probably won't get around to finishing building the enlarger until much later this year or next.

[Tin Can]

Bryan,

My heartiest recommendation for your 8x10 enlarger would be a Red Dot or a Low Distortion Artar. I have stopped using Rodagons, Ronars and Componons in favor of Artar on my DeVere 5108. And as much as I use and like G-Claron Dagors to make pictures (read my long-winded posts from a few years ago), they do not hold a stick to an Artar as an enlarging lens. Proof is in the pudding, try it and you will see - good luck.

carver

Somehow this is obvious, yet I never considered it.

I miss the obvious all the time. :)

I will be trying my RDA's soon.

Thanks for the heads up!

[carverlux]

Bryan,

in terms of resolution and linear distortion, my experience is the perfectly symmetrical dialyte layout has proven superior to the asymmetrical plasmat layout - both in taking and enlarging lenses. This combined with the nearly absolute absence of chromatic aberration in the Artar makes it a naturally choice.

So why did Schneider go to a plasmat design in the G-Claron if the Dagor layout was good already? Only Schneider knows for sure but my guess would be that the plasmat is easier to design and hold within manufacturing tolerance, as adding an air space between each half gives one more "degree of freedom". Asymmetry in layout and construction adds demands to optical correction in one or both halves of the lens and sometimes leads to under- or over-correction which opens up more cans of worms. The Agfa Intergon and Hexanon GRII are both plasmats.

Artars are extremely undervalued right now and if I didn't already gave my fair share, I'd be buying them all up.

Hope this helps.
carver

[Corran]

While some plasmats are asymmetrical (such as convertible symmars), isn't the "basic" plasmat design actually symmetrical?

http://en.wikipedia.org/wiki/Plasmat_lens

The cells in the newer G-Claron look symmetrical to me, as does the Hexanon (not sure about the Intergon though).

[Bernice Loui]

Dagor types tend to have residual spherical aberrations at full aperture along with focus shift as the lens aperture is reduced (stopped down). In the eye's optical design folks and marketing folks and others, this can be interpreted as a serious problem which the air spaced Plasmat can correct.

What is not often appreciated by optical designers, marketing folks and users, residual aberrations can be a GOOD thing. Consider for a moment why the Dagor has lived on for such a very long time and to this day, it remains a desirable lens.

As for the Artar, It is currently under rated and under appreciated. There is also fashion and hear say regarding camera stuff in general. Best to try and decide with fits one's needs than simply doing ownership by hear say or fashion.

Optics design is as much art as it is science, both are combined to produce lenses-optics with specific personalities. It is up to the user to decide if these lens-optic personality traits are acceptable or not. There are tried and well accepted points of references that should be consider in this process.


Bernice




Bryan,

in terms of resolution and linear distortion, my experience is the perfectly symmetrical dialyte layout has proven superior to the asymmetrical plasmat layout - both in taking and enlarging lenses. This combined with the nearly absolute absence of chromatic aberration in the Artar makes it a naturally choice.

So why did Schneider go to a plasmat design in the G-Claron if the Dagor layout was good already? Only Schneider knows for sure but my guess would be that the plasmat is easier to design and hold within manufacturing tolerance, as adding an air space between each half gives one more "degree of freedom". Asymmetry in layout and construction adds demands to optical correction in one or both halves of the lens and sometimes leads to under- or over-correction which opens up more cans of worms. The Agfa Intergon and Hexanon GRII are both plasmats.

Artars are extremely undervalued right now and if I didn't already gave my fair share, I'd be buying them all up.

Hope this helps.
carver

[carverlux]

Bryan,

The optical layout of a plasmat does not dictate whether it is symmetrical or asymmetrical. It can be either.

In practice most plasmats are implemented as asymmetrical to meet the intended requirements, which in the case of the last generation G-Claron and the others you named, are to provide wider angle of view (using the front cell) and minimizing the light fall off at the edge of the field (using the rear cell). These are 2 different goals and the degree to which they can be met are dealt with using additional glass or an air space. This additional element is known as a "degree of freedom" in optical engineering. It can take form as different types of glass, additional glass, additional air space (which is equivalent to another type of glass) or curvatures, including multiple curvatures on the same surface, commonly known as "aspheres".

The Artar was implemented as a purely symmetrical lens and carries with it all the good and the bad. The good is that it is simple to make to very high performance without the need for managing extreme tolerances, the bad is its rather limited angle of coverage, typically under 50°. A plasmat can be made to provide cover 80° or more by adding more glass or commonly, an air space.

Bernice,

That Dagor designs are not perfect were well known going back 100 years. Zeiss' answer was the Protarlinse designed by Paul Rudolf which was better corrected and used a 4-glass cemented cell. Zeiss dropped their 3-glass cemented Amatar that looked like a Dagor clone after Paul Rudolf developed the Tessar because it performed as well as the Dagor and was much cheaper to make. Even a smart guy like Rudolf could not make the Dagor-formula'ed, 3-glass Amatar perfect - he needed a 4th. The 4th "degree of freedom" took the shape of a piece of glass in the Protarlinse, and an air space in his Planar design at Zeiss, and later on, in the Plasmat at Hugo Meyer in Görlitz.

Lenses can be designed and made to do many things, including leaving behind a small amount spherical aberration for that wonderful "dreamy look" as in the Golden Dagors when used wide open. The problem with under-corrected residual spherical aberration is a corresponding increases in focus shift when the lens is stopped down. This can play serious havoc with unsuspecting photographers or printers. Plasmat's - and other designs - solve these problems since more glass/air means more degrees of freedom and more corrections. You may already know that in modern SLR lenses, many large-aperture types require focus shift compensation mechanisms to avoid surprises to their users.

Back to the G-Claron Dagor's. Being an f/9.0 (not f/6.8 like a Dagor) makes it much easier to minimize any residual spherical aberration artifacts. My experience using G-Claron Dagor's wide open is that they do not have visible spherical aberration and perhaps more importantly, very little if any chromatic aberration. They are a pure joy to use. And when everything lines up well, they are as sharp as the Red Dot Artars.

carver

[Corran]

Carver,

That is all well and good, but, the GC and Hexanon still look like symmetrical cells, as opposed to the Symmar-S and Symmar lenses I have/had that were clearly asymmetrical, with much larger front cells.

I flipped the front and rear cells of the Hexanon once and the image did not change at all.

Regardless, I imagine the degree of potential improvement going from the plasmat GC lens to a RDA for enlargements of modest enlargements would be slim to none, or would you say I am wrong? I mean, are we talking about top-notch enlargements (assuming good technique!) from a RDA, to totally so-so, soft, or crap enlargements from a GC? This is all in the future anyhow but I'm curious if we are splitting hairs here? The GC was a process lens, after all.

[Dan Fromm]

Regardless, I imagine the degree of potential improvement going from the plasmat GC lens to a RDA for enlargements of modest enlargements would be slim to none, or would you say I am wrong? I mean, are we talking about top-notch enlargements (assuming good technique!) from a RDA, to totally so-so, soft, or crap enlargements from a GC? This is all in the future anyhow but I'm curious if we are splitting hairs here? The GC was a process lens, after all.

Neither drove the other off the market. They're functionally equivalent, except that G-Clarons have more coverage. If coverage matters for your application -- it shouldn't -- be happy you have a G-C. If it doesn't you won't get much benefit from buying an Apo-Artar, any of the various Apo-Germinars, dialyte type Apo-Nikkor, or Apo-Ronar. They're all much better than good enough.

[Corran]

That's what I am thinking, but I have no experience with one or the other as an enlarging lens. I would also have different criterion if I was going to enlarge to a much higher degree, but I have no specific plans for that at the moment. Luckily I don't expect to find some magic APO Nikkor whiz-bang lens for $10, nor do I think I need it.

[Dan Fromm]

Taking lens at 1:4, enlarging lens at 4x, what's the difference?

[Corran]

Well that should be obvious, no? :)

I don't own a RDA nor have I even shot with the GC plasmat, just the dagor, so, I have no point of comparison either way.

[carverlux]

Carver,

That is all well and good, but, the GC and Hexanon still look like symmetrical cells, as opposed to the Symmar-S and Symmar lenses I have/had that were clearly asymmetrical, with much larger front cells.

I flipped the front and rear cells of the Hexanon once and the image did not change at all.

Regardless, I imagine the degree of potential improvement going from the plasmat GC lens to a RDA for enlargements of modest enlargements would be slim to none, or would you say I am wrong? I mean, are we talking about top-notch enlargements (assuming good technique!) from a RDA, to totally so-so, soft, or crap enlargements from a GC? This is all in the future anyhow but I'm curious if we are splitting hairs here? The GC was a process lens, after all.

First on whether your 2 plasmats in hand are symmetrical. Without looking at the drawings and reading the radii, it is hard to tell if these are symmetrical, be they GC or Hexanon. The GC Dagors were symmetrical because the Dagor layout relies on both halves being identical to cancel out the imperfections inherent in each half. Plasmats with more degrees of freedom provide the designer with a lot more to work with to make a "better" lens. Advancement in coatings allows the designers more and few if any designer pass up the opportunity to do so. Back over 100 years ago when the original Celor/Artar and Dopp-Anastigmat/Dagor designs were conceived, they did all the calculations longhand and correcting both halves separately would take double the time and no beancounters would ever allow that. Now with optical design software running on up to 32 CPU cores, which designer do you think will really pass that up and stick to a perfectly symmetrical design? I am sure some might, most would not.

Second, on the RDA. I have never been disappointed by a RDA. They look unassuming and plain jane with an old-fashioned single-layer blue coating. But slip a negative in the holder, rack your lamphouse up and you'll see. I don't ever wonder if I do my job whether the RDA did or not. I don't feel this way about any other lens. The RDA is a champion both in front of the camera, and on the enlarger.

Bottom line - use what you like. My comments are intended for your consideration and "entertainment" only. I have a great deal of respect for Konica Hexanon's and it's a shame they are no longer.

carver