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

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