A Question about Rodernstock Lens

[jianglinxi]

I have a Rodernstock 150 f5.6 APO Sironar-S lens. I found some ducts between front and back optical module and shuttle. Then I did unscrew both optical modules, and cleaned optics. I found there're two thin black plastic washer rings between front optical module and shuttle, but there's only one washer ring between rear optical module and shuttle. I'm not sure if I lose one washer ring of rear module. Please give me help if you have the same lens with me. Thank you very much!

[Emmanuel BIGLER]

Hello from France!

By 'shuttle', you probably mean: shutter?

Regarding thin spacer rings found between the optical blocks and the shutter, to the best of my knowledge, there is no general rule valid for all lenses, even within the product line of a given manufacturer like Rodenstock.
When un-screwing the elements, you can find: none, or one single in front, or one single at the rear block, or like in your situation, 2 in front and one at the back.

Unfortunately, nobody reading your message from the other side of the planet can guarantee that you actually did not loose one of those very thin spacer rings.
The only thing that you can do now is to replace those rings that you have found, exactly at the place where you found them.

My understanding is that those shims, or spacing rings, are required for fine-tuning the optical performance of the lens.
The Apo-Sironar-S lens is one of the sharpest and most advanced standard lens ever designed for large format photography, hence I am not surprised if each lens is shipped with individuallly adjusted shims or combination of shims.
My understanding is also that those rings or combination of rings, go which each individual lens cell, if we admit that the machining tolerances on the shutter itself are tighter than the global optical + mechanical tolerances (lens refractive indices, lens curvatures & spacings, this makes a lot of tolerances combined together) on the optical cells themselves.

As a general advice to our readers not familiar with view camera lenses, never un-screw your lens cells in the field, unless you know exactly what you are doing, for example if you use a purposedly designed "convertible" lens. In old convertible lenses, you had to un-screw the front element to use the long focal length of the lens combination, and the manufacturer, hopefully, avoided to add a spacing ring in front that could drop-out and be lost in the field.
Many view camera lenses, as originally shipped from the factory, have this kind of spacing rings, and be careful if for any reason you have to unscrew the cells, do it quietly at home on a table and watch for the tiny rings!
Here in the watch-making country, as you can imagine, any serious hobbyist working on lens cells would insist on using the very special and legendary watchmaker's working bench ;) (http://www.baume-et-mercier.com/content/bem/website-com/worldwide/fr/libraries/teaser-library/bm-world-library/_jcr_content/par/stageteaser_bf1b/image.1563422453.jpeg)

So, do not worry too much, and do carefully re-mount your cells with the spacing rings at the proper place where you found them.
And enjoy the superb pictures that you'll soon make with your lens !

[Leigh]

I have that same lens. Mine has no shims (spacer rings).

These are used to accommodate small changes in dimensions of both the lens cells and the shutter itself.
They set the location of the front and rear nodes with relation to the aperture.

They are critical for optimum performance.

Also note that they may or may not all be the same thickness.
You should not consider them to be interchangeable.

Multiple shims in a group can be reversed, individually or collectively, with no harm.
However, you cannot exchange shims between the front and rear groups.

Of course this rule is based on assumptions about the shims, and may not always be true.
However, following the rule will return the lens to its configuration as you received it.

- Leigh

[hoffner]

Hello from France!

--
My understanding is also that those rings or combination of rings, go which each individual lens cell, if we admit that the machining tolerances on the shutter itself are tighter than the global optical + mechanical tolerances (lens refractive indices, lens curvatures & spacings, this makes a lot of tolerances combined together) on the optical cells themselves.

--

The "admission" or, better, supposition is not correct. Just the opposite is true. The mechanical tolerances on the optical surface are much tighter than the mechanical tolerances in the shutter dimensions. The reason is that even much smaller changes in the dimensions of the optical components have greater effect on the lens optical performance than changes caused by shutter's mechanical dimension. Therefore you use the shims on the shutter - it would have no sense to make the shutter with super tight tolerances when even slight deviations in the optical tolerances call for the use of shims in the final assembly of the lens.

The OP very probably used Google translator to ask his question. A simple answer to it is - put the lens cells back as you best know it was assembled before you disassembled it and hope you did not displace the shim parts.

[jianglinxi]

Thx everybody advises. Does somebody know a professional person can do the lens calibration?

[Emmanuel BIGLER]

From "hoffner":
The "admission" or, better, supposition is not correct. Just the opposite is true. The mechanical tolerances on the optical surface are much tighter than the mechanical tolerances in the shutter dimensions.


Well, I do respect all opinions publicly stated here, and I apologize since I should have mentioned that my argumentation is based on the following facts & figures.

If you look at this excellent reference document:
http://www.largeformatphotography.info/shutters.html

You'll find this interesting specification:

6/front to rear cells flange distance
copal #0 20.0 mm +-0.025
copal #1 20.0 mm +-0.025
copal #3 28.6 mm +-0.025

This refers only to the total thickness of those well-known shutters, I have no data on the tolerances for the precise location of the iris itself.

Nevertheless, 0.025 mm is one mil, this is the typical thickness of a kitchen alumin(i)um foil.

And most shims / spacing rings that I have ever seen so far between lens cells and shutters are much thicker that that. I would say: in the 0.1 mm range or so. Not 0.025.
Hence my conclusions are simple: manufacturing tolerances on the total thickness of modern shutters cannot explain why sometimes a 0.1 mm spacing ring is required.

Now you can make you own conclusions, if the requirement for 0.1 mm shims does not find its origin in the shutter itself ...

At least we can agree on the following: since the adjustment can be only achieved by adding a spacing ring, engineers have to figure out how the actual lens cell characteristics can be "slightly shorter" than necessary, in order that corrections / adjustements can be made by adding some spacers. Subtracting being impossible.

[Leigh]

A lens cell has a thread that terminates at a face (flat mechanical surface).

You simply move that face farther from the mating face (the shutter) than would be required if you could both
increase and decrease the distance, so that in all cases the cell will screw farther into the shutter than need be.

This gives you the option of putting spacers on the front or rear, as needed to properly locate the diaphragm.

This is very common practice in precision mechanical systems.

- Leigh

[hoffner]

Emmanuel,
I think you mix and confuse many things together to the point that it is not really clear what exactly you wanted to say and the debate starts to be irrelevant to the OP's question.

The optical tolerances of lens elements are not directly related to the thickness of a lens shim. The same is valid for the precision tolerances of the shutter dimensions. In the same way as the optical tolerances of lens elements and cells are not directly related to the mechanical precision of your bellows focusing rail and the focusing distance on it - even if one affects the other.

I find Leigh's comment correct.
In any case, the OP's problem lies elsewhere than in optical tolerances of lens cells. If someone changes the thickness of ground glass on his camera it is not directly related to the optical tolerances of his lens either.

[hoffner]

Thx everybody advises. Does somebody know a professional person can do the lens calibration?

Now that is a good question for Bob Solomon who will kindly give you the address for Rodenstock service center, I bet.

[Leigh]

If someone changes the thickness of ground glass on his camera it is not directly related to the optical tolerances of his lens either.
Any "proper" ground glass is mounted by positioning the viewing face (the ground side, not the smooth side) to be on the same plane as the film emulsion.

The viewing face is on the lens side of the glass.

Yes, I know many GGs are mounted incorrectly.
That doesn't make them right. It makes them wrong, even if so designed.

- Leigh

[hoffner]

Any "proper" ground glass is mounted by positioning the viewing face (the ground side, not the smooth side) to be on the same plane as the film emulsion.

The viewing face is on the lens side of the glass.

- Leigh

That is correct. Still it does not exclude the optical effect of the different glass thickness on the film/gg surface registration.

[Leigh]

Does somebody know a professional person can do the lens calibration?
That depends a lot on where you're located, which we don't know.

- Leigh

[Bob Salomon]

Now that is a good question for Bob Solomon who will kindly give you the address for Rodenstock service center, I bet.

If we know where he is located.

[Leigh]

it does not exclude the optical effect of the different glass thickness on the film/gg surface registration.
Sorry to disagree, but...

The point of correlation is along the lens axis.

At outlying points the question becomes one of whether the GG plane is perpendicular to that axis.

In normal use, critical viewing is done perpendicular to the GG, using a loupe.
In that case, refraction within the glass should be zero.

Admittedly, if viewing unaided at an angle, the peripheral areas might exhibit some miniscule error, but
way less than could be resolved by human sight.

- Leigh

[hoffner]

Jianglinxi,
Rodenstock service center will gladly accept your lens sent by post from wherever you live. Just hope Bob Solomon will notice this Rodenstock lens thread sooner than later. For that you made the correct thing - you gave a good thread title.

[Leigh]

Bob responded five minutes ago, with the same question that I asked five minutes prior.

- Leigh

[hoffner]

Sorry to disagree, but...

The point of correlation is along the lens axis.

At outlying points the question becomes one of whether the GG plane is perpendicular to that axis.

In normal use, critical viewing is done perpendicular to the GG, using a loupe.
In that case, refraction within the glass should be zero.

Admittedly, if viewing unaided at an angle, the peripheral areas might exhibit some miniscule error, but
way less than could be resolved by human sight.

- Leigh

Sorry,
but the gg can be supported in its position from either the ground surface or the plain surface. Therefore, changing its thickness can change the gg/film correct registration.

[Leigh]

but the gg can be supported in its position from either the ground surface or the plain surface.
Therefore, changing its thickness can change the gg/film correct registration.
Certainly it "can" be supported on either surface.

However, supporting it on the non-imaging surface places stringent dimensional tolerances on the glass
thickness which don't otherwise exist, thereby dramatically increasing the cost of the part if it's to attain
proper registration with the film.

What can be done does not always reflect best engineering practice.
If an engineer working for me turned in such a design I'd fire him.

I've seen a number of designs over the years that appeared to be copies of previous work, but with
the newer one rendered by an engineer who did not understand the rationale and sensitivities of the
original. This often has unanticipated consequences, varying from trivial to devastating.

- Leigh

[hoffner]

Leigh, life is not always perfect. On this forum there has been many threads about the need of shims for gg positioning on cameras. I even think that Bob Solomon needed to explain to somebody, that changing gg for one of a different thickness on Linhof Technika camera can create problems in the film registration. However, the glass thickness does not need to have any more stringent dimensional tolerances only because it is to be placed in a camera. For that simple shims do excellent job. Now if you want to beat the dead horse for ever, I leave you the scene for a solo exercise.

[Leigh]

I'm a bit of a fanatic about doing things "right", as opposed to just doing things.

If I've offended anyone by advocating that position, I apologize.

- Leigh

[BrianShaw]

That is NOT fanaticism.

[Emmanuel BIGLER]

I think you mix and confuse many things together

No problem, I can re-explain.
The original poster raises a question about shims that can be found inside LF lenses, namely between lens cells and the shutter. This is not directly correlated to the proper placement of a ground glass, so let's forget about the ground glass for a while.

What I say is that manufacturing tolerances on the shutter itself are in the range of 25 microns, one mil.
And that the thickness of shims required to optically adjust the lens is in the range of 100 microns or more.

If you agree on both points, then we can continue to argue. If not, yes, we can stop arguing.

Another important point on which we should agree, is that we are facing a situation where the same lens mounted in the same shutter needs different combinations of shims, or no shim at all.
Of course I can imagine that the manufacturer has to use shims in order to proper fit different shutters from different sources. When I bought my first new LF Rodenstock lens at the beginning of this century, I still had the choice between at least the Compur, the Prontor Professional and the Copal. And I can imagine that fitting different shutters to the same batch of lens cells would need different "fixed" combinations of shims, one set for the Compur, one set for the Prontor and one set for the Copal.

But apparently, this is not the case, and we are very probably facing a dispersion of shim combinations for the same lens cells and the same shutters. And we are trying to explain this. My opinion is that the shutter is not responsible for this situation.

If you agree on the 3 points above, then my point is that if shims are required to optimize lens performance, it is due to stacked manufacturing errors/tolerances in the lens cells themselves, not due to manufacturing tolerances in the shutter itself. If there was no adjustement needed due to the lens cells, the only mechanical adjustments needed would be within the manufacturing tolerances of the shutter, i.e. 25 microns. Not 100 microns or more like in a situation where various shim combinations or no shim at all are needed to optimize the lens performance on a shutter with manufacturing tolerances in the range of one mil (0.025 mm).

You stated exactly the opposite opinion, i.e. shutter tolerances were at the origin of the need for shims.
I thought I was clear. So far, I stand corrected and peacefully disagree.

[hoffner]

then my point is that if shims are required to optimize lens performance, it is due to stacked manufacturing errors/tolerances in the lens cells themselves, not due to manufacturing tolerances in the shutter itself.




Emmanuel,

as I said, in your reasoning you unfortunately mix different things together and link them as cause and effect where in fact such a relation does not exist.

If shims are required for the correct lens performance it is not necessarily because of overstepped manufacturing tolerances. These tolerances are in fact under very strict QC when lens elements are produced.
There are many other reasons for the shims. The fact that the lens has been optically calculated and consequently constructed with a need of shims in the shutter is just one possibility. Sometimes the optical design does not use the given shutter dimension (its thickness) as the holly cow that cannot be removed from its place. The whole of the optical design already counts with its own shutter thickness, for many reasons, be it the optimal optical performance or other necessity given by production reasons. It would be impossible to ask a shutter manufacturer to produce shutters with the exact thickness needed for a specific lens assembly as it it is impossible to ask lens manufacturer to produce lenses with lens cells separation corresponding exactly to the available shutter thickness. Therefore the optical designer calculates the lens cells and elements with the freedom he needs to have knowing that shims can then nicely save the final differences. In no way do the shims mean the optical design or the lens manufacture was compromised.

Of course, using in the first place cells housing that serves the same purpose as the shims is a more elegant solution but that solution is not always at hand either. The shims have many different reasons to be there even if their purpose is just one - to achieve the correct lens cells spacing.
Hope this will put the shims question to sleep.:)

[Leigh]

The only factors affected by shutter thickness are inter-nodal spacing and diaphragm location.

All other dimensions are internal to each cell.

The design of a cell is orders of magnitude more complex that design of the shutter.
In the latter, only the front to back and front (or back) to diaphragm dimensions are critical.

Within the cell, all of the metal component dimensions are critical, plus the glass dimensions.

- Leigh

[Emmanuel BIGLER]

I think Leigh shares exactly the same point of view as me. Thanks, Leigh !
. plus the glass dimensions.. and the fluctuations in the values of refractive indices, but if the glasses are all of the same batch, this reduces to the effect of non-homogeneity of refractive indices within a given batch of glass. Of which I have absolutely no idea !

Now even before reading carefully the answer, I'm asking to "hofner" if he agrees, or not on the following. Then we'll be able to continue our exchange.

- manufacturing tolerances for a given shutter are plus or minus 0.025 microns. YES or NO ?
- the same lens with same shutter can be shipped with different combinations of shims or no shim at all for optimized performance. YES or NO ? THIS IS THE CORE OF THE DISCUSSION.
- those shims far exceed in thickness the shutter tolerance of 0.025 micron. YES or NO ?

Only if we agree on the 3 points above, i.e. 3 "YES", then we can continue to argue.
Since I still totally disagree with this statement : The mechanical tolerances on the optical surface are much tighter than the mechanical tolerances in the shutter dimensions., I'll be glad to continue the discussion if at least we agree on the premisses!

[Leigh]

I still totally disagree with this statement : The mechanical tolerances on the optical surface are much tighter than the mechanical tolerances in the shutter dimensions....
I believe Dr. Bigler and I agree on this point. The specified tolerance for each individual component and the tolerance for the completed assembly can be wildly different.

Manufacture of an optical assembly is an extremely difficult task, particularly at the levels of performance that we expect from top-tier large-format lenses.

We haven't even discussed issues like centering of the optical axis within the physical perimeter of the lens and centering and alignment of each individual element optical axis with the optical axis of the completed cell.

The problem is that tolerances are cumulative, and not in a predictable manner.

You may luck out such that all of the plus tolerances cancel all of the minus tolerances, resulting in
a lens that absolutely meets the original design calculations.

Or, all of the tolerances may accumulate in the same direction, resulting in a lens that's substantially different from the design.

We've all seen examples of one particular lens being superb, while another is only mediocre.
That's the nasty tolerance snake biting you in the posterior.

I believe this issue of accumulating tolerances is the reason for using the shims.
Some cells will need them, while others won't.

The other issue we haven't discussed is "binning". Binning is a pre-screening process in which new assemblies are measured for the parameter of interest, then accumulated in groups representing different values for the parameter.

This enables the manufacturer to mate one cell that's over-tolerance with one that's under-tolerance, in whatever manner makes sense for the assembly.

This may require the use of one or more shims to bring the assembly within overall tolerance.

- Leigh

[BrianShaw]

I'm finding this discussion interesting, as I do every time it occurs, and hesitate asking, for fear of seeming even more ignorant than I really am... but how common are shims in LF lenses? Statistically speaking? Or on what types of lenses? I've not seen as many LF lenses as a lot of folks but have never seen a shim. The only shim I've ever seen was on a 35mm rangefinder where shim appears to have ben used to correct infinity focus.

[Leigh]

how common are shims in LF lenses?
Hi Brian,

I used to repair LF lenses.

Of the several hundred I disassembled, I would estimate perhaps 5% to 10% had shims.

Many of that number were sent in to be mounted on lensboards, so I only removed the rear cell.

I should qualify the observation by saying that over 95% of my work was on modern lenses, post-WWII.
I think the problems, and the use of shims as a corrective measure, were more common with older lenses.

- Leigh

[hoffner]

Since I still totally disagree with this statement : The mechanical tolerances on the optical surface are much tighter than the mechanical tolerances in the shutter dimensions., I'll be glad to continue the discussion if at least we agree on the premises!

Emanuel,
If you take the value you give (shutter tolerances +- 0.025 mm for Copal shutters) compare it with just some tolerances in the optical industry: high precision manufacturing - lens elements diameter +0.0000/- 0.015 mm ; sagitta +- 0.015 mm; shape irregularity +- 0.5 microns (!), wedge lens - 0.005 mm. Make yourself the conclusion...

That being said, let me comment on your premises:
1) the value you give for Copal shutter, I can agree with. Let's put aside the fact that old shutters have not necessarily this tight tolerances.
2) "the same lens with same shutter can be shipped with different combinations of shims or no shim at all for optimized performance." Depends on what you mean by "the same lens". A Rodenstock lens in question, for example, can be shipped with different shims. to correct the optical manufacturing tolerances effect on the lens. But not all shims are there for that reason only, that's what I try to tell you.
3) "Those shims are thicker than the shutter tolerance value." So what?

What I try to tell is that shims are put to the lens also for many other reasons that just to correct the lens manufacturing imprecision effect on the lens performance. Other reasons can be the use of different parts in the production of the said type of lens (lens cells originally used in a different shutter are used in new type of shutter, lens being calculated from the scratch as used with shims in the given shutter, etc. - just some possibility among others.) What is so difficult to understand in it, I don't know.

[hoffner]

You stated exactly the opposite opinion, i.e. shutter tolerances were at the origin of the need for shims.


Well, sorry if you misunderstood me, by I never meant this and, it seems to me, never said this. There probably lies the reason for our disagreement.

[hoffner]

Now even before reading carefully the answer, I'm asking to "hofner" if he agrees, or not on the following.

Hoffner, je vous en prie. :)

[Jim Andrada]

re 3) "Those shims are thicker than the shutter tolerance value.", That's quite common. We manufacture high precision mechanical assemblies and we purposely make the most critical mating surfaces "undersized" by a small amount to allow us to use shims of a practical thickness between them

[john borrelli]

I have owned two 150mm Rodenstock apo sironar n lenses and they both had shims. I owned a 90mm nikkor f8 lens that I believe also had a shim. I think shims may be used more than a previous poster noted.