Are all plasmats convertible?

[Ethan]

Hey,

So I'm assuming most of us know how the early Symmar lenses from Schneider Kreuznach are convertible, ie: the 300mm f/5.6 becomes a 500mm f/12 when you remove the front element. I was reading up on the symmar lenses for a friend of mine who is thinking of purchasing one, and I read that the Symmar S is also convertible. This got me thinking, there isn't much difference in the various plasmat lenses, so is my fujinon W 300mm I use convertible as well? I took the front element off my camera, and lo and behold, I was able to focus on a distant tree with a bellows length of approximately 560mm.

When using my fujinon without the front element, I noticed that the sharpness was noticeably less in the corners with the lens wide open, but all I had to do to fix that was stop down a few stops.

So, is it just coincidence that both the Symmar S and Fujinon W can act as a longer focal length lens without the front element, or is this the case for all plasmat lenses?

If any of you have other plasmats in your possession, maybe take them out and see what results you can get without the front element, lets see what we discover!

Or, maybe better yet, can anyone who knows about lens design add some insight on this apparent property of plasmat lenses?

Thanks,
Ethan

[Mark Sawyer]

All Plasmats are convertibles, as are all Dagors, from which the Plasmat descended. (Hint: "Dagor" is short for "Double Anastigmat, GOeRtz", so both cells are independently corrected for astigmatism.) And yes, as you noted, the aperture must be closed down to be acceptably sharp, usually around f/45, as the single cells aren't as well corrected as the two used together. And as a general rule, you're better off using a complete lens rather than a converted half-lens.

[Ethan]

All Plasmats are convertibles, as are all Dagors, from which the Plasmat descended. (Hint: "Dagor" is short for "Double Anastigmat, GOeRtz", so both cells are independently corrected for astigmatism.) And yes, as you noted, the aperture must be closed down to be acceptably sharp, as the single cells aren't as well corrected as the two used together.

Thanks for that info! Was the convertible symmar better corrected for use as a single group, or is Schneider just the only company to advertise this more universal feature?

[Mark Sawyer]

Other companies advertised their Plasmats as convertibles, like the Ilex/Caltar Acuton, which featured two aperture scales on the shutter.

[Paul Ewins]

To slightly rephrase what Mark has said about correction, the manufacturer could choose to correct for best results with the indvidual cells or best results with both cells together. As I understand it, the Symmar was a compromise half way between since it was made to be convertible, whereas the Symmar-S was corrected for use as a complete unit only. For best results using a single cell it must be placed behind the aperture.

[BrianShaw]

I did not have very satisfying results when trying to use just the rear cell of a Symmar-S.

[Drew Wiley]

There's a problem with this kind of pigeonhole lens terminology. "Plasmat" implies both an original design by that name as well as an entire class of modern lenses, very few of which are "convertible" without a significant penalty in optical performance. Same could be said about "Dagors", which in fact as a design predate plasmats. According to Kingslake, the first plasmat from 1903 was essentially an airspaced dagor, symmetrically 2+1 / 1 +2, rather than the 3 / 3 of the original dagor design itself, starting in 1892. Later plasmats, generically-termed such, became more complex, while the definition of a dagor always remained three fully cemented elements opposite each other. Most "general purpose" view camera lenses with generous coverage angles are classified as plasmats, although some fully airspaced 4-element designs have also been marketed for general purpose usage. Another design with a long ongoing history is the 1+1 / cemented-2 tessar from 1902. I certainly wouldn't use any of my own lenses of any of these designs convertible-option, one side only; but they're all modern, even the Dagor. I actually have tested for that.

[Mark Sampson]

I once had a Schneider brochure, introducing the Symmar-S lens line (c.1972). In it they explained that they had eliminated the convertible feature in order to improve performance of the whole lens. Oren Grad (researcher extraordinaire) found a copy and posted it in a recent thread here on the same subject; that would be worth looking up.
I'll suggest that yes, all 'plasmat' style lenses are convertible- but the converted lens' performance may not meet your standards.
The folk wisdom of past decades said that the 'convertible' Symmars were meant for portraiture when converted, suggesting that some decreased sharpness in the corners wasn't important. I'll suggest making some tests (as Drew has done) and finding out for yourself.

[lassethomas]

I tried a couple of G-Clarons as convertibles here:

https://www.largeformatphotography.info/forum/showthread.php?159217-4x5-lenses-telephoto-and-portraiture&p=1561918&viewfull=1#post1561918

[Maris Rusis]

I "convert" my Fujinon-W 300mm f5.6 lens by removing the front group. New focal length is about 600mm. Several precautions:

Add three stops of exposure compensation to allow for the extra bellows extension and loss of magnification of the entrance pupil.
Start focussing two stops down from wide open. Most of the focus shift happens in those first two stops.
Stop down a long way until the corners are reasonably nice.
Safeguard the exposed and fragile iris and shutter blades.

[Embdude]

Even the Angulon was originally marketed as a triple convertible lens...

216789

[lassethomas]

Even the Angulon was originally marketed as a triple convertible lens...

216789

Find a good 6.8/120 Angulon and you have nice triple of 120mm, 180mm, and 240mm. Almost like a very slow zoom.
Together with a Intrepid 4x5 you would have a ultra light set-up.

Not really convinced on corner sharpness though, but I might try, just for the fun of it.
For portraits it's probably ok.

[Bernice Loui]

Convertible lenses were a marketing slogan from a time when view camera lenses were a premium, similar to exaggerated lens image circle.

From an era when view camera lenses were pricy proposition, the idea and projected fantasy of getting more than one lens focal length for a single lens $ was very attractive for the view camera image maker.

Trade off being enforced by the way Nature really is aka current knowledge of Physics, imposing reduced image quality, less light imaged to the film, difficulty to set up the mechanicals of the "convertible" lens.. then the actual working lens apertures must be properly worked out or _!_.

Given the easy availability of so many excellent view camera lenses today, why "covert" any lens for image making when using a proper focal length lens is easy and available and will produce higher quality images from the non-converted lens?

History of convertible lenses goes back to casket set lenses from long ago.


Bernice

[Embdude]

216802 B&L Swiss Army Lens...
Prior to WWII convertible lenses were common on professional LF cameras. After the war it seems only Schneider carried the torch until the 1960's... Even today the Hugo Meyer LF convertible lenses carry a high price premium...

[Dan Fromm]

dude, Boyer sold their Beryl/Emeraude, Color Saphir, Zircon/Saphir BX lenses as convertibles. The Zircon replaced the Color Saphir. Zircon and Beryl were available until the end (1982).

[Bernice Loui]

Swiss Army Knife, has all the "features" does none of the features exceptionally well.
There are very real and GOOD reasons why convertible lenses or casket set lenses went away, Again they are a hassle to use in every way and do not have the optical performance of a lens that has been specifically matched lens elements then assembled to ideal optimization of the lens element set.

Ever used a convertible lens converted or a casket set lens? If yes, what are the results compared to a optimized single focal length lens?

~BTW, been there done this, never again at ANY price. Why did Schneider eventually give up on offering convertible lenses?

Bernice



216802 B&L Swiss Army Lens...
Prior to WWII convertible lenses were common on professional LF cameras. After the war it seems only Schneider carried the torch until the 1960's... Even today the Hugo Meyer LF convertible lenses carry a high price premium...

[Drew Wiley]

Yeah, but if you want to saw down a big limb with something small enough to fit in your pocket, there's nothing better than a Swiss Army knife equipped with a flip-out miniature gasoline-powered chainsaw!

[Rod Klukas]

The Dagors are really improved by stopping to at Least F32. This is due to the fact that red wavelength moves forward much further than the Blue/Green wavelengths, as the lens is stopped down, and the increased depth of focus is required to yield an acceptable negative especially for enlargement.

Remember when most of these early lenses were originally designed the primary way of printing was the contact print. As such, the diffraction caused by stopping down so far, was less of an issue and the diffraction effect was not magnified.

As several have added, the original Symmar convertibles were actually mounted in shutters with double aperture scales and noted as such. But the later ones could be converted, although, also noted above, the quality did drop off.

The thing about the Dagor was its exceptional covering power of 87 degrees at F32 and below along with good sharpness for contact prints. Hope this helps.

Rod

[Rod Klukas]

Just like anything, if you are not better than the competition, you need to move on. Schneider did make Ron Wisner's convertible lens set during the 1980's/early 90's. All of the prints I saw from negatives from these lenses were rather small, The largest was soft 16x20....

Schneider rather fell behind Rodenstock beginning in 1974(Photokina). The Rodenstock Apo-Chromatic correction was superior and Schneider seemed to keep trying until the last film iteration, the Apo-Symmar L which were finally on Par with the Rodenstock APO-Sironar S.


They faired much better in Digital lenses , but the copal issue kind of was the last hurdle they could not surmount.

Rod

[reddesert]

Generally, it seems that all lenses of the basic plasmat design can be "converted" in the sense that the individual cells will make an image, but they probably shouldn't be, for best results. Schneider engraved the Symmars with focal lengths and f-stops, Rodenstock engraved early Sironars with two sets of f-stops but I think they stopped that practice before Schneider did.

I don't know the history but I assume one of the reasons everyone gave up the idea was increased use of color film. The individual cells are usually said to be less well corrected for color, and using a yellow filter with a single cell for B&W was often advised, to cut out the blue, more aberrated, light.

[Drew Wiley]

Again, some of these lens names or categories have a quite a long history, and thus become a moving target in terms of making generalizations. For example, the alleged coverage of Dagors. Apples to apples, an old 14" f/7.7 would have come in a big 4 or 5 shutter simply with less mechanical vignetting than a post-60's version in a no.3. Some of that peripheral coverage was probably less than ideal, but contact printers didn't notice it. Then this lens design wasn't as critically corrected for strong tangential tilts etc than plasmats, once that category had itself evolved awhile. I used the very last two generations of Kern 14" Dagors, both the SC and MC versions, and can attest their are very sharp and well corrected from f/11 down. But you might well need much smaller stops for sake of movements or depth of field issues. The contrast and tonal rendition is remarkable, but apo correction not as good as other LF lenses I use. Sometimes a bit of mythology gets attached to "cult lenses" that outlives their comparative performance or wild asking prices.

Today it was too hot to either take a LF camera hike or work in the darkroom, so for awhile I played in the backyard peeping through some of my unorthodox barrel lenses with the 8x10.

[lassethomas]

Enough talk, lets see the results
I put my Angulon 6.8/90mm to some unscientific action.
Full lens, rear and front cell.
And my short comments but make up you own mind if it works.

Full lens as reference

https://scatteredlightblog.files.wordpress.com/2021/06/angulon6890.jpg

The full lens, f22, Fomapan 200 on my Chamonix 45H-1.
Focused on the chain on the wall of the house.
Scaned on an Imacon Flextight and no added sharpening or processing.
Right click to download full res

Perheps not the sharpest of lenses, lacking a bit of contrast and bite, but reasonably even over the whole frame.
To me this is usable, considering the size and portability.

Back cell, about 1.5 times the focal length

https://scatteredlightblog.files.wordpress.com/2021/06/angulon6890rearcell.jpg

Rear cell, f22, Fomapan 400 on my Chamonix 45H-1.
Focused on the chain on the wall of the house.
Scaned on an Imacon Flextight and no added sharpening or processing.
Right click to download full res

Not very impressive. Soft all over. Not even the center is sharp.
This would not withstand any larger magnifications.

Front cell, about 2 times the focal length

https://scatteredlightblog.files.wordpress.com/2021/06/angulon6890frontcell.jpg

Front cell, f32, Fomapan 400 on my Chamonix 45H-1.
Focused on the chain on the wall of the house.
Scaned on an Imacon Flextight and no added sharpening or processing.
Right click to download full res

Nice center sharpness. Sharpest of all three. Corners are not that impressive.
Not for landscape but for portraits or still life this could work.

[Tin Can]

Thank you!

More proof, less babble!


Enough talk, lets see the results
I put my Angulon 6.8/90mm to some unscientific action.
Full lens, rear and front cell.
And my short comments but make up you own mind if it works.

Full lens as reference

https://scatteredlightblog.files.wordpress.com/2021/06/angulon6890.jpg

The full lens, f22, Fomapan 200 on my Chamonix 45H-1.
Focused on the chain on the wall of the house.
Scaned on an Imacon Flextight and no added sharpening or processing.
Right click to download full res

Perheps not the sharpest of lenses, lacking a bit of contrast and bite, but reasonably even over the whole frame.
To me this is usable, considering the size and portability.

Back cell, about 1.5 times the focal length

https://scatteredlightblog.files.wordpress.com/2021/06/angulon6890rearcell.jpg

Rear cell, f22, Fomapan 400 on my Chamonix 45H-1.
Focused on the chain on the wall of the house.
Scaned on an Imacon Flextight and no added sharpening or processing.
Right click to download full res

Not very impressive. Soft all over. Not even the center is sharp.
This would not withstand any larger magnifications.

Front cell, about 2 times the focal length

https://scatteredlightblog.files.wordpress.com/2021/06/angulon6890frontcell.jpg

Front cell, f32, Fomapan 400 on my Chamonix 45H-1.
Focused on the chain on the wall of the house.
Scaned on an Imacon Flextight and no added sharpening or processing.
Right click to download full res

Nice center sharpness. Sharpest of all three. Corners are not that impressive.
Not for landscape but for portraits or still life this could work.

[Bernice Loui]

90mm f6.8 Angulon was intended for 4x5, image circle of 152mm @ f22 or image circle just enough for 4x5.
In later Schneider catalog literature, Schneider dropped the convertible lens marketing moniker.
216831


IMO, would not consider using a 90mm f6.8 on 4x5 given there are so many easily available modern wide angle lenses that have better performance trading off weight/size. Lightweight field folder style images are not much of a consideration, putting out the idea or need for using this particular Angulon as a prime lens or far lesser as a convertible lens.

That said, do use a 165mm f6.8 Angulon in barrel (never converted) with Sinar shutter on the 5x7 Sinar Norma with good enough results.

Again, this thing about convertible lenses was significant in the early days of view camera when lenses were an absolute premium and the idea of owning one lens that offered more than one focal length was believing ya got "three" lenses for the cost of one.. The optical performance trade-offs were not discussed, but the photographers figured this out and the availability of GOOD view camera lenses increased with their cost dropping.


Bernice





Enough talk, lets see the results
I put my Angulon 6.8/90mm to some unscientific action.
Full lens, rear and front cell.
And my short comments but make up you own mind if it works.

Full lens as reference

Perheps not the sharpest of lenses, lacking a bit of contrast and bite, but reasonably even over the whole frame.
To me this is usable, considering the size and portability.



Back cell, about 1.5 times the focal length

Rear cell, f22, Fomapan 400 on my Chamonix 45H-1.
Focused on the chain on the wall of the house.
Scaned on an Imacon Flextight and no added sharpening or processing.
Right click to download full res

Not very impressive. Soft all over. Not even the center is sharp.
This would not withstand any larger magnifications.

Front cell, about 2 times the focal length

Front cell, f32, Fomapan 400 on my Chamonix 45H-1.
Focused on the chain on the wall of the house.
Scaned on an Imacon Flextight and no added sharpening or processing.
Right click to download full res

Nice center sharpness. Sharpest of all three. Corners are not that impressive.
Not for landscape but for portraits or still life this could work.

[lassethomas]

90mm f6.8 Angulon was intended for 4x5, image circle of 152mm @ f22 or image circle just enough for 4x5.
In later Schneider catalog literature, Schneider dropped the convertible lens marketing moniker.
216831


IMO, would not consider using a 90mm f6.8 on 4x5 given there are so many easily available modern wide angle lenses that have better performance trading off weight/size. Lightweight field folder style images are not much of a consideration, putting out the idea or need for using this particular Angulon as a prime lens or far lesser as a convertible lens.

That said, do use a 165mm f6.8 Angulon in barrel (never converted) with Sinar shutter on the 5x7 Sinar Norma with good enough results.

Again, this thing about convertible lenses was significant in the early days of view camera when lenses were an absolute premium and the idea of owning one lens that offered more than one focal length was believing ya got "three" lenses for the cost of one.. The optical performance trade-offs were not discussed, but the photographers figured this out and the availability of GOOD view camera lenses increased with their cost dropping.


Bernice

I agree, for most situations and needs a modern better performing lens would be a more resonable choice.

And the Angulons are old, so there are a large copy variations. I've got two 90mm (both as part in a larger deal). Both are from the fifties, one is OK (the one used above) and the other one is a sure lemon.
I guess that goes for the 165mm too, even though they are more rare.

I wouldn't mind a good 6.8/165mm for my 4x10 back though.

[Vaughn]

To correct for the out of focus (no longer corrected) blue light when using only front or rear element, a yellow filter can sometimes be used to increase sharpness. It was recommended when using the TR convertibles.

[Bernice Loui]

Schneider Angulon was Schneider's answer to the wide angle Dagor which was NOT advertised as focal length convertible, while in theory the wide angle Dagor IS convertible. The folks at Goerz knew better and valued optical performance over perceived marketing value.

Based on real time experience, it is true testing the Angulon before accepting the Angulon is a very, very good idea as they varied lots in optical performance. Some were good others were absolute duds. Back when this 165mm Angulon happened, part of the deal was right of return, if it proved to be a dud, it went back to the seller. This 165mm Angulon proved to be ok enough for 5x7 _ 13x18cm. Compared to the 150mm f5.6 Super Symmar XL, the modern lens has significantly better optical performance. Higher contrast, much "snappier" image in every way and the image circle is larger with inherent light fall off baked into any wide angle lens. Compared to the 165mm f8 Super Angulon, it is also better than the Angulon at larger taking apertures, contrast (more elements yet better optically), much larger image circle, better resolution at the edges of the image circle which is HUGE and this is a HUGE lens.


Bernice




I agree, for most situations and needs a modern better performing lens would be a more resonable choice.

And the Angulons are old, so there are a large copy variations. I've got two 90mm (both as part in a larger deal). Both are from the fifties, one is OK (the one used above) and the other one is a sure lemon.
I guess that goes for the 165mm too, even though they are more rare.

I wouldn't mind a good 6.8/165mm for my 4x10 back though.

[J. Patric Dahlen]

Corners are not that impressive.
Not for landscape but for portraits or still life this could work.

Utmärkt test! While most people would agree that the blurry corners make the single lens cells not suitable for landscape, I feel that the optical faults contribute to the image in a positive way, making it less "boring" to look at. They add a pleasing quality to the bottom picture. A perfect lens shows exactly what's in front of it in an undistorted way, making it feel like the lens is out of equation as it adds no character to the photo.

[Drew Wiley]

Depends on what one is after. Sometimes what appears to be an acceptable nuanced flaw in a contact print resembles a gross hippopotamus wallowing in mud in a big enlargement.

[Bernice Loui]

Brings up the topic of audience and perception of what is "desirable" then why is any image "desirable".

About 3.8 Billion images and 750,000 hours of video is up-loaded to the internet world wide daily. Given this vast flood of images and the ease of image making, what makes any individual image "desirable" or have value in some way?

This brings up the question of why film, why view camera, why alternative process images (tin types to carbon to many others) to the current fashion of using "vintage" or optics from around 1900 to make images today, this included "sorta-focus" lenses, all with the idea and such these "items" will self produce images that are distinctly different than the ~3.8 Billion images and 750,000 hours of video~ in process daily. Does this mean this media is better, individual, distinct or such? or does it really mean greatly discounted media creation allowing anyone to proclaim a moment of public notoriety ?


Bernice

[Tin Can]

Yes