PDA

View Full Version : A discovery: Dagor-type G-Claron's as the ultimate Casket Set



carverlux
6-Jun-2010, 12:50
Like many on this and other forums, I have used and long since admired the unique quality of Dagors. From century-old Serie III Doppel-Anastigmats to the last Kern MC Gold-Dots, they provide a balance between coverage and sharpness that is hard to beat from 5x7 through 20x24.

For a little while now, I have been reading that the very early G-Claron's were made in a Dagor layout, and were coated. I came to thinking that having a maximum aperture of f/9.0 will have allowed the lens designers to take out the last traces of residual spherical aberration inherent in the Dagor design, which means one of the biggest nuisances of using Dagors - countering focus shift upon stopping down - is finally out of the way of shooting at f/64 and beyond to fulfull the promise of its 85+ coverage.

So I went searching. And as luck would have it, I have been able to amass all 6 focal lengths of the lost series, and yes, Mr. Galli, there really is a 355 G-Claron made like a Dagor and it is coated! Its filter size is 77mm in the front and 72mm in the rear.

First things first - every one of these are usably sharp wide open, and when stopped to f/22, goes about 9/10's of the way between the Goerz Am. Opt. Dagor (post SN 78xxxx) and the Artar-like Kern Gold-Dot. In rendering 3-D objects, they are very close to the Golden Dagor except they do not have the slight dreaminess from the residual spherical aberration that Golden Dagors have wide open.

Given that their cells are completely symmetical, for as long as cell spacing is observed, they can theoretically be combined in the exact same way that the Zeiss Protarlinsen can. The fact that they were not sold this way probably had something to do with the fact that their intended market were initially photocopiers.

Here are the possible combinations based on their actual focal lengths as stated in the datasheet, the red being a close duplicate of an existing prime combination, which are bolded:

355 355 355
355 305 334
355 267 317
355 237 304
355 208 292
355 153 268

305 305 305
305 267 289
305 237 276
305 208 263
305 153 240

267 267 267
267 238 255
267 208 242
267 153 218

238 238 238
238 208 225
238 153 202

208 208 208
208 153 184

153 153 153

17 focal lengths in total, excluding the 4 very close duplicates. The delta between some of these focal lengths being so small, it may not be a practical 17 but nonetheless, the possibilities exist.

The following are the shutter fitting and hence the required basic spacings. This means that some will need custom adapters to combine, while the 210 to 270 all fit to a Compur/Copal 1. Necessary adapters can be made so all of the cells will fit and/or combine into either a Compur/Copal 3 or a Compur/Copal 1.

355 Compound III
305 Compur 2
270 Compur/Copal 1
240 Compur/Copal 1
210 Compur/Copal 1
150 Compur/Copal 0

Who would have thought that there could be a Dagor Casket Set that covers 85+ stopped down and has little to no focus shift? To me, they are true gems and you will have to pry hard from my cold, dead fingers.

Carver

PS Attached is a picture of the handsome trio of 270, 305 and 355.

carverlux
6-Jun-2010, 16:57
Here's the rest of the gang: the 150 in a Compur 0 and the 240/210 combo in a Compur 1.

Enjoy!
Carver

Dan Fromm
7-Jun-2010, 02:57
Um, Carver, Goerz wasn't the only manufacturer of Dagor type lenses. At least one of the others sold sets of unmatched cells. See http://www.galerie-photo.com/boyer-lens-optic.html, read the section on the Beryl.

carverlux
7-Jun-2010, 07:20
Dan,

Thanks for the heads-up on Boyer. I am happy to know that there are even more options available for anyone who is looking for Dagor-type lenses.

All the best,
Carver

cyberjunkie
29-Jul-2010, 21:47
I own an old 355mm G-Claron in barrel, that looks exactly the same as the example shown on the first picture of the thread.
There is a pdf on Schneider web site about first generation (?) G-Clarons. The year of the catalog is 1976, and very oddly the 355mm has no infos reported, just "in Vorbereitung", that means "in preparation". But my lens has a serial # of 11 932 8xx, meaning that probably it was manufactured on the first part of 1972.
So these lenses were produced well before 1976!
The optical scheme of 1976's Clarons is clearly a dagor-type: 6 elements in two groups.
It should be quite obvious, but when i read the first post of this thread, i'm not so sure anymore: my lens has a very different filter thread diameter, from what i recall it should be 67/68mm, both in front and rear, while carverlux reports a diameter of 77mm and 72mm.
Just another information: if i remember, in my lens there are four strong reflections per side (and maybe a very faint one, but i could be wrong about it).
I don't have the lens here (i sent it to a friend, he has to make a new retaining flange, while i patiently wait for a suitable Compound III shutter... but i'm not even sure about that!).
If an owner of a Dagor-like G-Claron is reading, please post the serial of your lens.
Better if it's the serial # of a 355mm like mine :)

have fun

CJ

carverlux
29-Jul-2010, 22:00
Hello Paul,

The quick answer to your question is that my 355 has a serial number of 10 737 xxx. It has a 77mm front filter thread and a 72mm rear filter thread.

The factory shutter for it is a "3" but a Compound III/7, not a Copal 3 or Compur 3. A Compound III/7 has cell threads of M55.69 x 40tpi for both front and rear and a spacing of 37mm. Cells that are made for Compound III/7 threads can be made to Copal/Compur 3 and Adam at SKGrimes would be delighted to show you his magic!

I hope this is helpful to you.

Carver

Jim Galli
30-Jul-2010, 07:47
Copal made shutters for Schneider in 1970 that were a direct replacement including cell spacing and thread for the Compound III/7

I have one just now with a Tele Xenar in it but would sell for probably less than Adam charges for the machine work to convert a normal modern Copal 3

I've been using a 225mm G-Claron for years. Never concerned myself to make up others though.

carverlux
31-Jul-2010, 11:28
Adam is always superb but a Compound III/7-compatible Copal would be much more cost-effective for sure.

I did just recently verify the "casketability" of these lenses by combining a 355 front and 210 rear to make a 300. It performed superbly, in fact no different than a native 305 G-Claron or a 12 inch Golden Dagor at the same aperture.

cyberjunkie
31-Jul-2010, 19:34
Adam is always superb but a Compound III/7-compatible Copal would be much more cost-effective for sure.

I did just recently verify the "casketability" of these lenses by combining a 355 front and 210 rear to make a 300. It performed superbly, in fact no different than a native 305 G-Claron or a 12 inch Golden Dagor at the same aperture.

I just found a defective 210mm Xenar on Compound III, the lens is a little foggy and the shutter seems to fire with the same timigs no matter which are the settings.
Probably a friend of mine will fix the shutter, and the lens cells will be cleaned as best as possible... in the end, much cheaper than having the two tubes precision-machined from a solid aluminium bar. For the moment, i would be more than happy to have the 355mm G-Claron set in shutter, at last!

Just a little obeservation about the dimensions of you lens vs. mine.
The pdf about 1976 G-Clarons available on Schneider web site clearly shows a Dagor-like optical project, and the lenses are clearly asymmetrical in shape, like yours. For the 355mm, as i wrote before, there are no quotes.
The strange is that your lens, made a couple of yers before mine, has a different front and rear diameter as well. My lens has a 67mm thread on both sides.
That makes me think that before the model portrayed on the 1976 catalog, probably there was a different one, at least for the longer focal.
Whichever the external shape, it seems that all the G-Clarons made in the seventies have a Dagor-like optical project.
Unfortunately both the 305mm and the 355mm have non-standard cell threads, so their use as "modern casket" is not so easy: custom made adapters are a must.

All in all, my best compliments for your contribution. Learning never ends, and you made me aware of a very interesting, and potentially useful, new bit of information.

have fun

CJ

carverlux
31-Jul-2010, 22:02
Back in the 60's and 70's many lenses made for one shutter size were sometimes requested in shutters of a different size than in the catalog. So the factory made them but did not always put them in the regular catalogs. For example. I have a 135 Convertible Symmar which according to the catalogs were officially only sold in Compur 0 threads. But mine came in a Compur 1 shutter. The adapters were made by Schneider and epoxied in place. I also have a 150 Componon with a Compur 1 thread that came on a Compur 3 shutter, with factory adapters of course.

Looking at these factory adapters, the level of precision is no more or less than what you'd find in a modern filter step-up ring. So while the cost to do these adapters one off is prohibitive, in volume (and/or from China!) the costs would probably be not so bad.

My curiosity around these G-Clarons' "casketability" is due to the fine level of perspective and bokeh control a multitude of closely-spaced focal lengths gives me. It is more a luxury than a necessity. So venture on and as you come across them, just pick them up as they are not expensive. Over a couple of years, you'd be amazed at what you will have at your fingertips.

Enjoy!
Carver

ridax
9-May-2013, 13:45
I own an old 355mm G-Claron in barrel <...> # 11 932 8xx <...> in my lens there are four strong reflections per side <...> If an owner of a Dagor-like G-Claron is reading, please post the serial of your lens. Better if it's the serial # of a 355mm like mine.

Hi there. It's somewhat late for a response, but nevertheless: here is the owner of a 355mm G-Claron exactly like yours. Mine is # 11,833,xxx in barrel.

No it's not a dagor. Neither is yours. We both have plasmat-type ones. I've also recently seen an even earlier (with some 10 thousand less number) 355mm G-Claron with 4 distinct plasmat-type reflections on both halves.... listed for sale as a dagor nevertheless - apparently the only reason being the common belief that all "G-Clarons in the 10 and 11,000,000 serial #'s are Dagor type." No, not all the 11,xxx,xxx's are. I've actually taken apart the front half of mine. There was a good amount of fresh air between the 3rd freestanding element and the two cemented front ones.

I bought this lens through a local website, also hoping it was a dagor. The pictures posted had no reflections at all, and knowing the seller's respect for Dagors, I was pretty sure he'd triple the price if he knew the lens was dagor-type. So I took the chance and bought it without asking any further questions. What I got was a plasmat though.

I thought of putting it into a Compound and reselling it but made some tests first. As I expected, the out of focus parts of the image were rude and unpleasant both in front and behind the sharp zone at all apertures from wide open to f/22.... But then at f/32, all the nonsense was suddenly gone. At f/32, it was just like a good old convertible Symmar - but some 1,100 grams less in weight. For me, that certainly justified keeping the beast.

And no, not all the lenses are alike at small f-stops. My 360mm celor-type CZJ Apo-Germinar and my plasmat-type Staeble Ultragon (a.k.a. Eskofot Ultragon and Agfa Repromaster, sometimes claimed to be identical to a G-Claron - to which I cannot agree at all) are both pretty ugly at f/32, in front and behind the focus point alike. And my 360mm Goerz Dagor gives me way more beautiful background blur at f/32 but much less acceptable foreground blur then the Symmar and the plasmat G-Claron.

That actually means I'd certainly prefer the Dagor for my 5x7" but on 8x10" I'd rather use the G-Claron as on 8x10 I want its coverage for tilts, and with those tilts I often have a part of the frame filled with something in front of the sharp-focused zone, and the Dagor would literary ruin my blurred foreground. The G-Clarons's foreground blur at f/32 is still worse then the background blur but the difference is much less then with the Dagor.

I guess I should call this G-Claron my Great Compromise. It's not as nice in rendering the background as a Dagor. And it's better not to be opened beyond f/32, so it's not as universal as the f/5.6 Symmar. But it is small enough and it is wide enough and it is sharp enough to get into the field when the other glass stay on the shelves....

And I guess a dagor-type G-Claron would be less useful for me on 8x10" then this plasmat one.


P.S.: I can't be sure as I don't have the original Schneider .pdf now (converted it to .html for my personal use) but I recall that dagor-type G-Clarons' catalog was of 1968, not 1976. And the 1968 date makes perfect sense with those serial #s.

Jim Galli
9-May-2013, 14:18
I don't think any of the 355's were ever Dagor's. Schneider owned Goerz and if you wanted a Dagor that size you could buy their Goerz Trigor. There is however early and late type 355's consistent with the general make-over of the line up when the rest became plasmat's. The early 355 plasmat is 56mm thread consistent with Size 3 Compound shutter. Later 355 G-Claron plasmats had the 58mm thread for the Copal 3. Some people claim they have a 355 G-Claron Dagor type but I've never seen one so far.

Mark Sawyer
9-May-2013, 18:48
Just a note that the Plasmat was also known as the "Air-Spaced Dagor" when introduced. The separation in a Plasmat of the cemented surfaces in a Dagor allow the surfaces to have slightly different curves, correcting for much of the spherical aberration in a wide open Dagor. The slightly longer barrel gives slightly less coverage in a Plasmat, but the better corrections also allow for a slightly faster lens.

Personally, I've always liked the look of a wide-open Dagor, and otherwise consider coated versions of the Plasmat and Dagor pretty equivalent when the aperture is shut down.

Ian Greenhalgh
9-May-2013, 19:33
Great info Mark. Both my 4x5 lenses are plasmats (Symmar 5.6/150 and Ilex Acuton 4.8/210) so I will definitely try to add a dagor as well.

The spherical abberation will be why the dagor has nicer bokeh, and I do love the look that some residual CA gives so a dagor is on my shopping list.

Mark Sawyer
9-May-2013, 19:52
Great info Mark. Both my 4x5 lenses are plasmats (Symmar 5.6/150 and Ilex Acuton 4.8/210) so I will definitely try to add a dagor as well.


That f/4.8 Acuton is a 215mm, and covers 8x10, so you've got serious movements on 4x5! The f/6.8 210mm Dagor also covers 8x10, but my early uncoated one is soft in the corners, while my later gold-rim is sharp to the edges. The Acuton is sharp all the way out.

Ian Greenhalgh
9-May-2013, 22:40
Yup, 215mm, my memory sucks! :) Thanks for the tips, I haven't tried the Acuton yet, while I have accumulated some film and lenses for 4x5 i still haven't found just the right camera for me at the right price for me, but soon I hope and great to know the Acuton will do nicely, cheers!

ridax
10-May-2013, 03:32
Just a note that the Plasmat was also known as the "Air-Spaced Dagor" when introduced.

Yes a Plasmat is an air-spaced Dagor. And it is also an inverted Planar. In fact, it was invented by Dr. Rudolf when he was 'cheating himself' to make a lens similar to Planar for another manufacturer - a lens not covered by the Rudolf's own Planar patent that belonged to Zeiss. Similarly, Tessar is actually a modified Taylor's Triplet but historically it was constructed by the same Dr. Rudolf as his doublet Protar modification. That's all amusing and fascinating indeed but I wouldn't say it matters too much for taking pictures. :)


Personally, I've always liked the look of a wide-open Dagor, and otherwise consider coated versions of the Plasmat and Dagor pretty equivalent when the aperture is shut down.

That's far more interesting IMHO. Would you please post any particular reasons you prefer the Dagor wide open for? Is it in the in-focus details? Anything else?

Myself, I'd never use a Dagor wide open. For me, Dagor is the ultimate background blur machine at the apertures starting from f/10 and all the way to f/45 or beyond. I'm also especially fond of the Dagor's in-focus details rendition from f/10 to maybe f/16 or so. I find the Dagor's foreground blur too bad even wide open and really awful stopped down.

On the contrary, I think the foreground blur of many f/5.6 Plasmats (not only Symmars but even Componons and Rodagons, too) used wide open to be the best ever possible. (An important note is, this foreground blur is ruined by vignetting. So my 210mm Convertible Symmar is great wide open for 6x9cm and is OK for 4x5" if perfectly centered but not at all beautiful wide open on a 5x7"!) And I think there is no Plasmat coming anywhere close to the Dagor in the background blur quality at any f-stop (though some plasmats are much better then others).

As for sharpness, I don't think the difference in the above mentioned lenses matters for me (except for the poor corners of f/6.8 (or f/7.7) Dagors if used as wideangles).

P.S.: Obviously, a Plasmat can be constructed to match the Dagor exactly. But equally obvious is that no manufacturer ever had a goal like that.

ridax
10-May-2013, 03:36
I don't think any of the 355's were ever Dagor's. Schneider owned Goerz, and if you wanted a Dagor that size you could buy their Goerz Trigor. There is however early and late type 355's consistent with the general make-over of the line up when the rest became plasmat's. The early 355 plasmat is 56mm thread consistent with Size 3 Compound shutter. Later 355 G-Claron plasmats had the 58mm thread for the Copal 3. Some people claim they have a 355 G-Claron Dagor type but I've never seen one so far.

Arhhh... that surely sounds true enough to stop counting reflections in the that-bay pics. :)
Thank you for the clarification.

... Anybody claiming to own a 355 dagor-type G-Claron is very welcome to post the proof after taking the lens apart!

E. von Hoegh
10-May-2013, 07:04
Yes a Plasmat is an air-spaced Dagor. And it is also an inverted Planar. In fact, it was invented by Dr. Rudolf when he was 'cheating himself' to make a lens similar to Planar for another manufacturer - a lens not covered by the Rudolf's own Planar patent that belonged to Zeiss. Similarly, Tessar is actually a modified Taylor's Triplet but historically it was constructed by the same Dr. Rudolf as his doublet Protar modification. That's all amusing and fascinating indeed but I wouldn't say it matters too much for taking pictures. :)



That's far more interesting IMHO. Would you please post any particular reasons you prefer the Dagor wide open for? Is it in the in-focus details? Anything else?

Myself, I'd never use a Dagor wide open. For me, Dagor is the ultimate background blur machine at the apertures starting from f/10 and all the way to f/45 or beyond. I'm also especially fond of the Dagor's in-focus details rendition from f/10 to maybe f/16 or so. I find the Dagor's foreground blur too bad even wide open and really awful stopped down.

On the contrary, I think the foreground blur of many f/5.6 Plasmats (not only Symmars but even Componons and Rodagons, too) used wide open to be the best ever possible. (An important note is, this foreground blur is ruined by vignetting. So my 210mm Convertible Symmar is great wide open for 6x9cm and is OK for 4x5" if perfectly centered but not at all beautiful wide open on a 5x7"!) And I think there is no Plasmat coming anywhere close to the Dagor in the background blur quality at any f-stop (though some plasmats are much better then others).

As for sharpness, I don't think the difference in the above mentioned lenses matters for me (except for the poor corners of f/6.8 (or f/7.7) Dagors if used as wideangles).

P.S.: Obviously, a Plasmat can be constructed to match the Dagor exactly. But equally obvious is that no manufacturer ever had a goal like that.

Wide open, a Dagor has a fair amount of uncorrected spherical aberration. This gives a glow overlaying a fairly sharp image that can be nice for portraits. This effect disappears as you stop down, personally I try to use my Dagors at f:16 whenever possible.

One of the big reasons for the switch to Plasmats was economics, the two most inward cemented surfaces (which were separated to form the Plasmat) have short radii and had to be polished one to a block, making the Dagor a very expensive lens to produce. Separating these surfaces also gave the designer one more "element' - the airspace - to use. The Plasmat did not become popular until coatings were available due to it's six internal surfaces.

Mark Sawyer
10-May-2013, 13:21
Yes a Plasmat is an air-spaced Dagor. And it is also an inverted Planar. In fact, it was invented by Dr. Rudolf when he was 'cheating himself' to make a lens similar to Planar for another manufacturer - a lens not covered by the Rudolf's own Planar patent that belonged to Zeiss. Similarly, Tessar is actually a modified Taylor's Triplet but historically it was constructed by the same Dr. Rudolf as his doublet Protar modification. That's all amusing and fascinating indeed but I wouldn't say it matters too much for taking pictures. :)


There are similarities between designs, especially if you shuffle the element order around, but the Plasmat was a very direct descendant of the Dagor. I wouldn't call the Tessar a "modified Triplet", other than having three groups. It's evolution is documented from the Zeiss Anastigmat to the Aldis Stigmatic to the Unar, then the Tessar. A telling point of the Cooke triplet is that it corrected all the primary aberrations with three single elements and no cemented achromat for the chromatic aberration. (To me, that's a very elegant design; are there any other well-corrected lenses without a cemented achromat in there somewhere?) The Tessar still has a strong cemented achromat at the rear for chromatic aberration.


That's far more interesting IMHO. Would you please post any particular reasons you prefer the Dagor wide open for? Is it in the in-focus details? Anything else?


Nothing too interesting, just that touch of spherical aberration. Not enough to call it anywhere near a soft focus lens, but enough to take the hard edge off. Plasmats can be a bit harsh and clinical, but that's what many like them for.

Ian Greenhalgh
10-May-2013, 13:28
Yes, the Tessar isn't derived from the triplet, it came about by combining the front of a Unar with the back of a Protar.

The dialyte is well corrected without an achromat, can't quite think of another one though.

Mark Sawyer
10-May-2013, 13:37
The dialyte is well corrected without an achromat, can't quite think of another one though.

I knew I'd forget one or two! :) But such designs are rare...

Trying to remember any others... :confused:

Ian Greenhalgh
10-May-2013, 15:24
You've got me thinking now, there will probably be some uncommon ones, but I really can't think of a well-known and widely-used one apart from the triplet and dialyte (which is really a triplet where the middle glass has been split).

Jim Galli
10-May-2013, 16:04
Arhhh... that surely sounds true enough to stop counting reflections in the that-bay pics. :)
Thank you for the clarification.

... Anybody claiming to own a 355 dagor-type G-Claron is very welcome to post the proof after taking the lens apart!

I'll even settle for pics of reflections with a pen light. ;~'))

ridax
11-May-2013, 02:31
Wide open, a Dagor has a fair amount of uncorrected spherical aberration. This gives a glow overlaying a fairly sharp image that can be nice for portraits. This effect disappears as you stop down, personally I try to use my Dagors at f:16 whenever possible.


Nothing too interesting, just that touch of spherical aberration. Not enough to call it anywhere near a soft focus lens, but enough to take the hard edge off. Plasmats can be a bit harsh and clinical, but that's what many like them for.

Thank you for your answers. So my guess was correct - it sounds that's for the in-focus details mainly. Myself, I rather don't like softness. I believe a hard-sharp lens is just fine for me when combined with a film developer yielding no (or, more correctly speaking, very little) edge effects - or in the digital world, with no post-sharpening. The nowadays common compensating development presents a lot of edge effects and makes the picture of a hard-sharp lens unpleasant for me, too. It also makes a just a bit softened lens picture somewhat better for my personal taste. But I still prefer a hard lens and no edge enhancement in post processing.

But the spherical aberration that softens the in-focus image is also the very thing that rules the out of focus rendition, and that's why I prefer the Dagor at f/10 to f/16 when there is a lot of blurred background, and f/5.6 Plasmats wide open when a lot of foreground is out of focus (if only f/5.6 is sufficient for DoF of course.... and unfortunately, it usually isn't).

Wide open, they both have a lot of overcorrected spherical aberration fine for the foreground blur. But the Dagor also has plenty of undercorrected spherical aberration; that results in much worse foreground blur with the Dagor. Also, personally I find the softness both too pronounced and also too "dirty"/"mushy" for my taste when lots of under- and overcorrected spherical aberration are present at the same time. A f/5.6 Plasmat has its undercorrected SA so much weaker that it doesn't spoil the foreground at f/5.6. And I find the character of the in-focus softness to be way better for my needs when only one type of spherical aberration is dominant.

From f/10 on, the overcorrected SA is gone in the Dagor but the undercorrected SA remains so the lens yields great background blur, and its in-focus rendition also becomes just fine for my taste. A typical Plasmat's overcorrected SA is gone from f/11 on, but the undercorrected SA that remains is too week to make the background as good as with the Dagor, and no trace of softness remains in-focus.

... Sorry I'm really not sure if anybody is interested in these longish theorizings of mine, though. :)

E. von Hoegh
11-May-2013, 06:56
Thank you for your answers. So my guess was correct - it sounds that's for the in-focus details mainly. Myself, I rather don't like softness. I believe a hard-sharp lens is just fine for me when combined with a film developer yielding no (or, more correctly speaking, very little) edge effects - or in the digital world, with no post-sharpening. The nowadays common compensating development presents a lot of edge effects and makes the picture of a hard-sharp lens unpleasant for me, too. It also makes a just a bit softened lens picture somewhat better for my personal taste. But I still prefer a hard lens and no edge enhancement in post processing.

But the spherical aberration that softens the in-focus image is also the very thing that rules the out of focus rendition, and that's why I prefer the Dagor at f/10 to f/16 when there is a lot of blurred background, and f/5.6 Plasmats wide open when a lot of foreground is out of focus (if only f/5.6 is sufficient for DoF of course.... and unfortunately, it usually isn't).

Wide open, they both have a lot of overcorrected spherical aberration fine for the foreground blur. But the Dagor also has plenty of undercorrected spherical aberration; that results in much worse foreground blur with the Dagor. Also, personally I find the softness both too pronounced and also too "dirty"/"mushy" for my taste when lots of under- and overcorrected spherical aberration are present at the same time. A f/5.6 Plasmat has its undercorrected SA so much weaker that it doesn't spoil the foreground at f/5.6. And I find the character of the in-focus softness to be way better for my needs when only one type of spherical aberration is dominant.

From f/10 on, the overcorrected SA is gone in the Dagor but the undercorrected SA remains so the lens yields great background blur, and its in-focus rendition also becomes just fine for my taste. A typical Plasmat's overcorrected SA is gone from f/11 on, but the undercorrected SA that remains is too week to make the background as good as with the Dagor, and no trace of softness remains in-focus.

... Sorry I'm really not sure if anybody is interested in these longish theorizings of mine, though. :)

I'm having trouble seeing how a lens can display both under- and over- corrected aberration of any type at the same time... and I really should know...:confused:

Ian Greenhalgh
11-May-2013, 09:28
Yes, a lens is corrected to a certain degree for spherical aberration and that level of correction doesn't change. All that happens when you stop down is you are masking any under-correction.

The two main things I like about the rendering of a lens that has some uncorrected spherical aberration are the diffuse glow on highlights and the smoothness and slight swirl in the oof areas.

The simple difference between an old Dagor and a modern Plasmat is the level of corrections, the modern Plasmats are more highly corrected.

A classic example of how lenses evolved in their level of corrections is the CZJ Biotar 2/58 and the Pancolar 1.8/50 that replaced it. Both are about equal in resolution but the Biotar has some uncorrected spherical aberration at large apertures which gives it glow and swirly bokeh. The main change from Biotar to Pancolar was the correction of spherical aberration and this means the rendering is more clinical without the diffuse glow and swirly bokeh. I have both lenses and prefer the Biotar due to it's character.

For me, the main reason I often chose to use an old lens rather than a more modern one is the character of the rendering, old lenses have more character because they are less highly corrected and some residual uncorrected aberration is the reason why they have more character.

ridax
12-May-2013, 13:57
I'm having trouble seeing how a lens can display both under- and over- corrected aberration of any type at the same time... and I really should know...:confused:

Thanks a lot... I was really in a serious doubt if I should go on on the topic or not.

In fact, both the under- and over- correction words are somewhat slang. Its more correct to speak about negative spherical aberration (a.k.a. undercorrected) and positive (a.k.a. overcorrected) one (I guess I should chose the words better from the start. Sorry). It's called negative when the outer zones of the lens refract stronger then the center, and the rays coming through the edges of the lens are focused closer to the lens then the near-axial rays; the other way around, the SA is called positive.

Most of the actual lenses have both the positive and the negative SA. In the SA graph, that is usually shown with a line that goes left first, then bends back to the right. The branch inclined to the left illustrates the negative SA inherited in the middle parts of the lens pupil, and the brunch turning to the right is for the positive SA corresponding to the edge zones of the lens - those that are actually in use only when the lens is not stopped down at all or is stopped down very little. With the aperture restricted (to f/10 for the Dagor, to f/11 for a typical Plasmat or to about f/5.6 for a f/2.8 mf Planar for example), the outer zones are excluded, and all that remains is the negative (a.k.a. undercorrected) SA. That's true for most of the lenses - except that some have "no outer zone at all", with only the undercorrected SA left.

But the quantity of the remaining SA is obviously very different with different lenses. Some have their positive SA very weak and the negative strong, and vice versa. So some lenses are better for background blur, and others for the foreground blur.

And there is more to it. Not only the amount but also the character of the residual SA is different. The famous (and loved by myself, too) f/6.8 (or f/7.7) Dagor has its negative SA already noticeable even in the very slightly off-center zones of the pupil, and very gently growing up to f/10. That's why the Dagor's background blur is still better then that of the most other lenses even at f/32 and f/45: a small amount of SA is still present. On the contrary, a very beautiful Tessar usually has a lot of negative SA in the middle zones but almost none at the zones in use at f/22 and smaller f-stops, and so it looses all its charm if heavily stopped down. And a Plasmat as good as a f/5.6 Convertible Symmar just has that residual SA in the amounts too small to make the background blur as beautiful as a Dagor's.


.... Sorry Ian but the Biotar has little undercorrected SA. It actually has a lot of overcorrected SA. And sorry again but the Pancolar is quite different in all the other aberrations, too. And it is also much sharper (but not as free from distortion though). And stopping the Biotar down, we are masking not the undercorrection but the overcorrection.

But any swirl in the oof areas actually has nothing to do with the SA at all. The swirly pattern most easily seen with the 1.5/75 Biotar and its cousin 1.5/85 Helios-40 and Petzval's lenses and many RRs (and somewhat less with the 2/58 Biotar, a.k.a. Helios-44) is just produced by the strong vignetting in these lenses. Funny enough, the wide-open Helios-40 picture on a Zenith-B and Zenith-E is very different from a picture by the same Helios-40 on a Pentax Spotmatic because the rear lens element is so large that the camera itself adds its own vignetting! (The later Zenith models make pictures somewhat in-between the Zenith-E's and the Pentax's with this lens. And the early Kine-Exacta combined with the 1.5/75 Biotar is similar to the Zenith-E rather then to a Pentax.)

ridax
12-May-2013, 15:26
The famous (and loved by myself, too) f/6.8 (or f/7.7) Dagor has its negative SA already noticeable even in the very slightly off-center zones of the pupil, and very gently growing up to f/10. That's why the Dagor's background blur is still better then that of the most other lenses even at f/32 and f/45: a small amount of SA is still present. On the contrary, a very beautiful Tessar usually has a lot of negative SA in the middle zones but almost none at the zones in use at f/22 and smaller f-stops, and so it looses all its charm if heavily stopped down.

And this also results in different rendition in the far out of focus subjects at wider f-stops. At about f/11 a good Tessar may be virtually equal to the Dagor in rendering the slightly blurred near-background but it often fails to make the very distant parts of the background look as beautiful at the same time while the Dagor usually has no trouble with that. And the best of the Planars are even less suitable for the job then the Tessars.

That piece of theory corresponds with the practical results very well - at least with my own ones. Though tastes differ of course, and the looks I call good may not be liked by other people as well as those I hate may be (and often are) praised here and there....

Roger Hesketh
12-May-2013, 16:32
Interesting I had never considered that an SLR camera bodies design could have such an affect upon the outcome of a photograph and a lenses rendering of a subject. I have always just considered them to be light tight boxes albeit with some of them being better at preventing non image forming light falling on to the film than others. You live and learn. Thank you Ridax. Is it because the M42 lens mount is relatively narrow?

ridax
12-May-2013, 17:19
...an SLR camera bodies design could have such an affect upon the outcome of a photograph and a lenses rendering of a subject. <...> Is it because the M42 lens mount is relatively narrow?

I'd say that's because those lenses are a bit extreme, and the designers of the newer cameras probably did not consider using that type of glass on the bodies they constructed. With the 1.5/85 Helios-40, not just the M42 cameras but almost all the other SLRs would add some new vignetting. The modern cameras usually have a rectangle tunnel not much wider then the 24x36mm frame going just up to the lens mount; add a lens with a rare element wider then that and standing rather close to the tunnel, and you get the out of focus picture changed.

The old Exacta has enough of empty space instead of the tight tunnel on each side of the frame - except the top where the mirror is placed (and corresponding to the bottom of the image when the frame is 'landscape'). So one side of the Exacta image is the same as with a Pentax or a Canon but the other three sides are not. And that also means you actually get different out of focus rendition holding the Exacta up side down with a lens like that!

Not many lenses are that crazy though. And I am really glad LF does not offer me any surprises of this type with any lens. ;)

P.S. I never tried a modern fast 85mm on an Exacta, though. Not sure no strange things would come up either....

Ian Greenhalgh
12-May-2013, 18:03
.... Sorry Ian but the Biotar has little undercorrected SA. It actually has a lot of overcorrected SA. And sorry again but the Pancolar is quite different in all the other aberrations, too. And it is also much sharper (but not as free from distortion though). And stopping the Biotar down, we are masking not the undercorrection but the overcorrection.


This makes zero sense, sorry. There is no difference in resolution between the Biotar and Pancolar, the difference is in the level of corrections, the Pancolar used lanthanum glass and was more highly corrected because they had electronic computers by the time it was designed - the Biotar was computed pre-war by hand.

The swirl of the Biotar 2/58 and 1.5/85 has nothing to do with vignetting. The image circle of the Biotar 2/58 is 60mm, I've measured it, this is quite a bit more than the 43.2mm diagonal of 35mm so vignetting never comes into play.

Triplets also swirl at wide apertures, and it is for the same reason the Biotars swirl - residual spherical aberration.

I really don't understand what you're talking about with different cameras giving different renderings with the same lens. I know from experience this isn't true and I have tons of pictures to prove it.

ridax
13-May-2013, 01:28
Vignetting is not a thing that happens abruptly at a certain point just to cut-off the image circle. As is the case with many things in this imperfect world, vignetting starts long before the image circle ends, and gradually grows stronger. Indeed the 2/58 Biotar covers more than the 43.3 mm diagonal of its frame but wide open, it has vignetting already at work as close as 5 mm from the axis. Vignetting is still more prominent with the 1.5/75 Biotar and the 1.5/85 Helios-40. Coming back to LF to get less off-topic, I'd mention my 1000mm f/12 CZJ Apo-Germinar covers 126cm diameter field at infinity with no problem but vignetting is already present at the corners of the 5x7" frame with this lens wide open. And as I said before, I'd rather not use front movements with my 210mm f/5.6 Convertible Symmar wide open on 4x5" as I do not like what vignetting does to its out of focus blur - despite the fact that the lens actually covers my 8x10" at infinity (though Schneider is way more conservative in their specs).

A swirly pattern is a result of the out of focus 'circles of confusion' being actually not circles but some asymmetric shapes. The spherical aberration is well symmetrical (when vignetting is not at work, too), and it does not make the defocused image swirly. Some other aberrations may influence that (coma comes to mind first. And yes generally speaking coma is the field version of SA - so yes I may stay corrected on this point), but still the main reason for any swirls is vignetting.

And resolution is just a concept poor enough up to the point of making zero sense itself sometimes. (And in fact any concept in physics operates a model of the real world, not the reality itself, and so has its own limitations and is unusable beyond those.) All lens resolution numbers published here and there actually correspond to the so-called photographic resolution which is the resolution of the lens and a film combined. With a film with a poor to average own resolution, the resulting lens resolution figures are indeed often similar to identical with lenses very different in sharpness and contrast (which both influence the resolution of a lens). But the same pair of lenses yields very different resolution figures when combined with an ultra high-res emulsion. And visual resolution (as opposed to the photographic one) is even more funny. As the eye is a very short focal length system with enormous DoF, most aberrations fatal to the thin flat film do not matter much for the human eye, and visual resolution of any common SLR lens very well corresponds to the 1800/(f-stop) diffraction limit formula at apertures as wide as f/1.2 (and may actually get greater - because the formula itself is just an approximation).


I too try never to post anything that I do not know to be true from my own experience. Though I still can make mistakes of course, and I have to change my opinions from time to time. What I post today well corresponds with my present day personal experience though. And I am really sorry when my words make zero sense. That's a pity but yes such things do happen. Thanks Ian for pointing that out and helping me to clarify those words of mine.

chris77
30-Mar-2019, 05:14
Vignetting is not a thing that happens abruptly at a certain point just to cut-off the image circle. As is the case with many things in this imperfect world, vignetting starts long before the image circle ends, and gradually grows stronger. Indeed the 2/58 Biotar covers more than the 43.3 mm diagonal of its frame but wide open, it has vignetting already at work as close as 5 mm from the axis. Vignetting is still more prominent with the 1.5/75 Biotar and the 1.5/85 Helios-40. Coming back to LF to get less off-topic, I'd mention my 1000mm f/12 CZJ Apo-Germinar covers 126cm diameter field at infinity with no problem but vignetting is already present at the corners of the 5x7" frame with this lens wide open. And as I said before, I'd rather not use front movements with my 210mm f/5.6 Convertible Symmar wide open on 4x5" as I do not like what vignetting does to its out of focus blur - despite the fact that the lens actually covers my 8x10" at infinity (though Schneider is way more conservative in their specs).

A swirly pattern is a result of the out of focus 'circles of confusion' being actually not circles but some asymmetric shapes. The spherical aberration is well symmetrical (when vignetting is not at work, too), and it does not make the defocused image swirly. Some other aberrations may influence that (coma comes to mind first. And yes generally speaking coma is the field version of SA - so yes I may stay corrected on this point), but still the main reason for any swirls is vignetting.

And resolution is just a concept poor enough up to the point of making zero sense itself sometimes. (And in fact any concept in physics operates a model of the real world, not the reality itself, and so has its own limitations and is unusable beyond those.) All lens resolution numbers published here and there actually correspond to the so-called photographic resolution which is the resolution of the lens and a film combined. With a film with a poor to average own resolution, the resulting lens resolution figures are indeed often similar to identical with lenses very different in sharpness and contrast (which both influence the resolution of a lens). But the same pair of lenses yields very different resolution figures when combined with an ultra high-res emulsion. And visual resolution (as opposed to the photographic one) is even more funny. As the eye is a very short focal length system with enormous DoF, most aberrations fatal to the thin flat film do not matter much for the human eye, and visual resolution of any common SLR lens very well corresponds to the 1800/(f-stop) diffraction limit formula at apertures as wide as f/1.2 (and may actually get greater - because the formula itself is just an approximation).


I too try never to post anything that I do not know to be true from my own experience. Though I still can make mistakes of course, and I have to change my opinions from time to time. What I post today well corresponds with my present day personal experience though. And I am really sorry when my words make zero sense. That's a pity but yes such things do happen. Thanks Ian for pointing that out and helping me to clarify those words of mine.

thank you ridax. very interesting all that!