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Hening Bettermann
17-May-2005, 05:26
Hi!

When mounting a lens into a shutter, the spacing of the front and rear cells may have to be adjusted in relationship to each other and to the aperture plane by means of thin spacing rings (shims). How exactly is this measured, and which instruments does it require?

It is not that I want to do it myself. The background:
On a norwegian photo forum, I asked who here in Norway might be able to mount a lens into a shutter. (A taking lens into a fitting shutter, not the adapting of a barrel lens.) I was referred to the former Sinar representative. I called him and he said yes. But when I detailed my question to include the spacing, the answer changed into no.
When I asked who could, he said that they had sent lenses to Schneider in such cases. But while Schneider may be willing to deal with an Angulon, they may not be thrilled about an Apo Ronar or an A Fujinon. Also, in order to keep shipping cost down, I would prefer to send all the stuff to one and the same address.

So, when I try to find somebody else, I feel I have to ask how exactly they do it, and if they have the tools required.

Grimes probably has, but they don't answer my e-mails.

Good light - Hening.

Juergen Sattler
17-May-2005, 06:03
Hi Hening, whenever I needed something done from SK Grimes I called them and always got an answer - I think they are overwhelmed with orders and just don't get around answering email. Why don't you give them a call - I am sure they'll be able to do the job for you.

ronald moravec
17-May-2005, 07:00
Second the S K Grimes.com

Donald Qualls
17-May-2005, 08:44
I've actually gotten e-mail replies from Grimes recently, inquiring about retaining rings vs. flanges (and getting good news on pricing, I might add -- I was fortunate to find the shutters I own without rings have standard #0 threads). Might need to include suitable keywords in the subject to keep your e-mail out of the spam bin...

Meantime, however, ISTM that you'd significantly change the focal length if the element spacing were incorrect. Am I correct in thinking the glass you have is already in cells, and that the cells match the threads in the shutter you wish to use? If so, you should be able to simply screw them in snugly, check that the focal length (from aperture to film plane) is within about 2% of the figure engraved on the name ring, and go take pictures -- they'll normally already have any shims they require inside the threaded cells, which were made to provide correct element spacing when installed in a standard shutter (assuming, at least, that all components were made after about 1930).

Nick Morris
17-May-2005, 09:03
Hello,

I had lens cells that I tried to have mounted to a shutter. It can be a difficult and expense job. The spacing is important, and can be critical for some lens cells. I believe SK Grimes can do it, but I think only if the cells are currently mounted, either in a shutter or barrel, and the proper spacing can be determined from the existing mount. They did not believe they could do it properly for my Dagor cells without an exsisting mount.

Emmanuel BIGLER
17-May-2005, 09:22
My feeling was similar to Donald's ; I clearly remember a French LF tutorial book of the seventies stating that view camera lenses were designed to be relatively insensitive to mis-spacing in order to make the exchange of lensboards easy with simple tools.

This, until I read this notice on the official Schneider Kreuznach web site.
www.schneider-kreuznach.com/service/service_e.htm (http://www.schneider-kreuznach.com/service/service_e.htm)


* Our ranges Super-Angulon (incl. XL types), Super-Symmar XL, Super-Symmar HM, Apo-Componon and Digitar can be only repaired at Schneider-Kreuznach. To optimize the optical parameter in the best possible way an exact re-adjustment of these lenses after repair is absolutely necessary.

* Complete shutters should be only exchanged by Schneider Kreuznach directly (also here re-adjustment).


My conclusion is simple.
You can do what you wish with older standard and long focal lengths. Dissassemble. Swap boards. Swap shutters. Remount. Adapt. And forget about shims.

But for modern wide angle lenses, any kind & any manufacturer, the most critical lenses being ultra-wide angle and 'digital' series, do it at your own "risk" if you believe in what Schneider Kreuznach people officially post on their web site.

To me this is the price you have to pay for the improved performance between and old 'not-super' Angulon(TM) and a brand new super-aspherical-wide-top-notch ;-);-)

RichSBV
17-May-2005, 12:34
I had a lens that needed a new shutter a couple of years ago. My question, to myself, was that with old lens/shutter combinations, how would anyone know if the spacing was correct to begin with???

I asked a lot of people... No one knew the answer....

I asked Grimes about the re-mounting and measuring the spacing. Their answer was simple. If it focuses at infinity, don't worry about the spacing! If it doesn't focus at infinity, they send it out to an optics shop to have it measured on an optical bench, at considerable cost....

Luckily, I found a shutter. The spacing was off from the 'original' by a mm or two. I tried the lens at infinity and closer and could see absolutely no difference (switching between shutters). So I just kept it in the new shhutter and was happy...

As was said, some of the modern lenses might have trouble. Like many things in LF, do it and see what it looks like.... Maybe you'll be as lucky as me?

Hening Bettermann
17-May-2005, 17:47
Many thanks to all of you who responded!

Parallel to my question here, I asked Tim Sharkey from lensN2shutter.com, who has been very responsive to e-mails all the way, and here is his answer:

"If you have the factory barrel, I have the tools to measure and properly space the groups from the shutter. If you only have the lens groups by themselves, the only way to get the proper placement of the cells without the factory barrel would be on an optical bench with an autocollimator. I am in the market for one of these tools but have not purchased one yet."

To Donald: Yes the lenses are in cells, and the threads fit in the shutters (not tried yet for the Angulon 65 though).
- "they'll normally already have any shims they require inside the threaded cells" - I had read about these shims before, but had never seen one when I unscrewed a lens from a shutter. But I have just acquired a like-new Apo-Sironar S 135, and this one has a shim. This thing is *very* thin indeed...

The lenses are an Angulon 65, which I want to move from the Prontor SVS #00 shutter, in which I bought it, into a Compur 00 which I acquired later; an A Fujinon 9/180 purchased used from Adorama for 274 $, which came in an odd model of a Copal 0, and with an f-stop scale starting at 5.6, so this is obviously not the original shutter; and maybe an old, single-coated Apo-Ronar 300, of which I have the orphaned cells, which are in brass. (The cells alone weigh 125 grams; would anybody know the weight of a modern Apo Ronar 300 in aluminum mount?)

Good light! - Hening.

Michael S. Briggs
17-May-2005, 23:59
Hening, with the three older lenses that you described, I would just transfer the cells to new shutters and then take test photographs.





The adjustment shims that I have seen in some modern lenses are between the front cells and the shutter. (Shims are placed on the front because the user is less likely to damage them -- the rear cell generally must be removed to install the lens onto a lensboard.)
It seems that the manfacturers are adjusting the spacing between the front and back cells to compensate for some variations.
The crucial question is whether they are compensating for variations in the power of the lens cells or in the thickness of the shutters. If the shims are because of variations in the lens cells, then there shouldn't be any difficulty in transfering the cells to a different shutter. If the variations in shutters matter, then a different thickness shim might required for a different shutter. Copal provides specs on the accuracy of their shutters, e.g., 0.025 mm (= 0.001 inch) for the thickness of a #1 Press shutter.





Of course one shouldn't go wrong with sending a Schneider lens to Schneider. The question is whether it is necessary, or whether Schneider is trying to increase their repair business. When you buy a new car, typically the manufacturer will assert that all repairs should be done at the dealer by factory authorized technicians. Do you always take your car to the dealer, or to an independent repair place? It would be nice if Scheider stated a accuracy requirement, e.g., lens cell spacing must be maintained to 0.01 mm accuracy.





Does anyone know of patents on some of these modern lenses? They might answer the accuracy questions, at least if someone did a computer analysis with different spacings.





A previous discussion: Interchanging lenses in Copal Shutters. Why does it work? at http://www.largeformatphotography.info/lfforum/topic/498712.html.

Mike Phifer
27-May-2005, 17:26
Hening, The spacing between cells can be very critical to optical performance. Generaly the better corrected the lens design the more sensitive it is to the central airspace distance. Kingslake discusses this in his book ,"A History of the Photographic Lens" (1989 , pp6-7). He states that in a DAGOR a small error as little as 0.4% has a considerable effect on field curvature, and a lesser effect on coma. For example 0.4% of 65mm would be 0.26 mm, or about two sheets of thin copy paper.

I (think??) remember reading a lens test of a DAGOR where the tester rotated (unscrewed) one of the cells (~ 45 degrees ), and noticed a large degredation in lens performance. However the tester wrongly attributed it to problems in optical centering.

renes
3-Dec-2011, 11:51
If the spacing of 0,2mm is critical to optical performance even with old vintage anastigmats (e.g. Dagor, Protar), it seems very risky or unresonable buying cells only or any old lens that is fitted in non original shutter. I have pair of Conley 7" Series V cells that are probably 100 years old and reading what was written above I can hardly believe it will be possible to spacing them properly or close to it. To make thing more difficult, I tried to fit them to Copal #1 shutter, the cells were placed as close as possible to iris (but I do not believe they were so near originally) and I still got 7 1/2" focal lenght. This suggested to me Conley in Series V (4x2 design) was measured the focal lenght from the rear lens instead from the iris (in between the cells) which was rather uncommon FL measurement for anastigmats... still many questions and a few answers. I hope to find someone owning 7" Conley Series V in barrel or in shutter who will pass the barrel lenght, having at least approximate spacing.

Louis Pacilla
3-Dec-2011, 12:58
Hey Renes. Not that it a really matters but this thread was last posted on(before your post) in 2005. I would figure the OP has either rectified his spacing issue of his lens or he has moved on .

renes
3-Dec-2011, 15:47
Hey Renes. Not that it a really matters but this thread was last posted on(before your post) in 2005. I would figure the OP has either rectified his spacing issue of his lens or he has moved on .

I know the last post was in 2005. Hope some forum members who got to grips with spacing issue (vintage cells in modern shutter) will confirm or not they noticed much degradation in image quality after non perfect (+/- 1mm) spacing.

And hope there is somebody also owning 7" Conley Anastigmat Series V.

Leigh
3-Dec-2011, 18:22
...check that the focal length (from aperture to film plane) is within about 2% of the figure engraved on the name ring...
Sorry to disagree, but that's not correct.

The distance from the mounting plane (front of the lens board) to the film should equal the published Flange Focal Length for the lens, which may be quite different from the optical focal length engraved on the lens.

- Leigh

John Koehrer
4-Dec-2011, 16:42
Sorry to disagree, but that's not correct.

The distance from the mounting plane (front of the lens board) to the film should equal the published Flange Focal Length for the lens, which may be quite different from the optical focal length engraved on the lens.

- Leigh

But the shims discussed have no bearing on the mounting plane.
The Q is lens spacing and shims.

Leigh
4-Dec-2011, 17:03
But the shims discussed have no bearing on the mounting plane.
If you'll read the text quoted in my post #14 you'll find that I was objecting to the confusion of optical focal length with flange focal length.

- Leigh

renes
28-Dec-2011, 05:21
The distance from the mounting plane (front of the lens board) to the film should equal the published Flange Focal Length for the lens, which may be quite different from the optical focal length engraved on the lens.

- Leigh

Is it true even with lenses having "equivalent focus" engraved?

I made a few spacing cells test with "Conley Anastigmat Series V Equivalnet Focus 7-inch" I own. Even I had put them into the shutter as close possible to each other, never reached 7inch focal lenght - the closest was 190mm. Actually 7inch I got only measuring the distance from rear lens (outer surface) to the film plane. But as I know - correct me if I am wrong - "equivalent focus" for symetrical lenses - as my Conley - means distance from the aperture plane, and never refers to back focus distance.
I am fully confused.

Dan Fromm
28-Dec-2011, 07:11
Hmm. Leigh and I hardly ever agree, but this time I think we do. His point that flange-focal distance need not be focal length is correct. This leaves open the questions of what focal length is (short answer, it is defined as the distance from the lens' rear nodal point to the film plane when the lens is focused at infinity) and the relationship between the focal length engraved on a lens and the lens' actual focal length.

The focal length engraved on the lens is a number. It need not be the lens' actual focal length. The lens' nominal focal length -- the focal length if the lens as made perfectly matches the prescription to which it was made -- is another number. The two may differ, and the lens' actual focal length may differ from both. Example: I once bought 20 38/4.5 Biogons. If you read Zeiss' description of that lens you'll find that its focal length, if made perfectly, is 38.5 mm. The camera manufacturer who bought my lenses from Zeiss measured their focal lengths and marked them on the lenses; the range was 38.3 mm - 38.8 mm.

Piotr, EF is another way of saying focal length.

Piotr, some design types focal lengths and performance are very sensitive to cell spacing, others aren't. My friend Eric Beltrando, who wrote and uses his own ray-tracing program, tells me that dagor types' performance is very sensitive to cell spacing and that plasmat types' performance is not. I think you can download his program from www.dioptrique.info; the site also has more than 1,000 prescriptions, mostly taken from patents.

Further on Eric's point, the longer the lens the less a small error in spacing matters.

c.d.ewen
28-Dec-2011, 07:40
I've been curious about the effects of cell spacing for a long time, and, once upon a time, whipped up a device to experiment with altering that spacing (photo below). The front and rear pieces are threaded to accept cells that are meant for a Copal 3. The front piece rotates within the rear piece at a pitch of 0,5mm., i.e., one rotation moves the front and rear half a millimeter closer or apart.

I spent a couple of afternoons in casual experimentation with a 14" Blue Dot Trigor mounted in this device, and posted the results in this thread. (http://www.largeformatphotography.info/forum/showthread.php?t=54988) The limited scope of this experiment, and the unscientific method employed, means that no definitive conclusions can be drawn from the results, which showed little difference in sharpness when cell spacing was altered. I bring it up for the same purpose as the original posting - to encourage people to unscrew their Dagor cells a bit and see what their photos look like :D

Charley

Leigh
28-Dec-2011, 16:26
Hmm. Leigh and I hardly ever agree, but this time I think we do. His point that flange-focal distance need not be focal length is correct. This leaves open the questions of what focal length is (short answer, it is defined as the distance from the lens' rear nodal point to the film plane when the lens is focused at infinity) and the relationship between the focal length engraved on a lens and the lens' actual focal length.

The focal length engraved on the lens is a number. It need not be the lens' actual focal length. The lens' nominal focal length -- the focal length if the lens as made perfectly matches the prescription to which it was made -- is another number. The two may differ, and the lens' actual focal length may differ from both.
Hi Dan,

Yes, we do agree on occasion. :D

Your statements are absolutely correct.

- Leigh

Sevo
28-Dec-2011, 17:22
the results, which showed little difference in sharpness when cell spacing was altered.

Well, this does not contradict the notion that Dagor types are spacing sensitive. Your tests show that there is indeed a difference in focal length which, properly compensated, has little impact on sharpness.

renes
28-Dec-2011, 17:27
Thanks, lots of useful information.

I thought plasmat = 6 element lens, not more. Conley Series V - like Velostigmat Series I - is 8 element: 2+2 x 2+2. Is it plasmat type?

Dan Fromm
28-Dec-2011, 17:59
Well, this does not contradict the notion that Dagor types are spacing sensitive. Your tests show that there is indeed a difference in focal length which, properly compensated, has little impact on sharpness.Sevo, what's lost with incorrect spacing is correction of off-axis aberrations, not central sharpness.

Dan Fromm
28-Dec-2011, 18:07
Thanks, lots of useful information.

I thought plasmat = 6 element lens, not more. Conley Series V - like Velostigmat Series I - is 8 element: 2+2 x 2+2. Is it plasmat type?By definition, no.

carverlux
28-Dec-2011, 18:59
The most significant effect of incorrect cell spacing is that the distance of the iris to the optical system has changed, however minutely. The optical system renders this deviation as losing some of the corrections designed into the system in total. This loss of correction sometimes shows up as a sharp center with fuzzy edges - which means a loss of curvature of field correction. Other aberrations are also probably off, but the most easily noticeable on your film would likely be a loss of edge-to-edge sharpness due to excessive curvature of field.

So sometimes, factories optimize the performance of an individual lens by using shims of various thicknesses to offset the inevitable accumulation of tolerances inherent in production optical components, mechanical components as well as material variances to get it performing closer to the original design intent and specifications. Shimming is not the only fix but it can be one of the fixes.

Moreover, the consequences of incorrect spacing is not layout-dependent, but correction-dependent. Different lens layouts require different correction strategies, so theoretically any optical system is no more "sensitive" to spacing differences than any other. In other words, just becase it is a Dagor or Artar does not mean that it is more or less sensitive to cell spacing, it really depends on how the lens layout,, correction strategies and most important, intended performance outcomes were originally conceived by the lens designer and executed by lens factory.

If you now get the sense that building high quality lenses is a bit like juggling 10 or 12 bottles in the air 24/7, you are getting the right picture. I hope this explanation helps.

carver

c.d.ewen
29-Dec-2011, 09:10
Carver:

Thanks for your thoughtful reply. It explains a lot.

Charley

renes
29-Dec-2011, 13:09
Piotr, EF is another way of saying focal length.


Was it possible that "Equivalent Focus" has been also refered to focal lenght measured from the rear lens to the film plane? Or from the iris only?

Dan Fromm
29-Dec-2011, 13:21
Was it possible that "Equivalent Focus" has been also refered to focal lenght measured from the rear lens to the film plane? Or from the iris only?

Neither. From the rear node to the film plane when the lens is focused at infinity.

renes
29-Dec-2011, 13:44
Neither. From the rear node to the film plane when the lens is focused at infinity.

Ok. Where is the rear node "placed" ?

Dan Fromm
29-Dec-2011, 13:49
Ok. Where is the rear node "placed" ?Where it is depends on the lens' design and focal length.

The standard way to find it is with a nodal slide. Ask Google to find an explanation.

The non-standard way that works with all lenses is to focus the lens at infinity. With the lens focused at infinity the rear node is 1.0 focal lengths from the film plane. In principle, not always in practice, a simple measurement.

With lenses of normal construction -- not telephoto, not retrofocus -- and not too long focal lengths the rear node is near the diaphragm. Beware, double Gauss lenses are often somewhat telephoto.

renes
30-Dec-2011, 05:27
Thanks Dan.


The focal length engraved on the lens is a number. It need not be the lens' actual focal length. The lens' nominal focal length -- the focal length if the lens as made perfectly matches the prescription to which it was made -- is another number. The two may differ, and the lens' actual focal length may differ from both. Example: I once bought 20 38/4.5 Biogons. If you read Zeiss' description of that lens you'll find that its focal length, if made perfectly, is 38.5 mm. The camera manufacturer who bought my lenses from Zeiss measured their focal lengths and marked them on the lenses; the range was 38.3 mm - 38.8 mm.


Just last question. I am sure the 7" focal length engraved on my Conley Sewries V lens differs from its actual FL. But the difference seems appreciable: it's 178mm to almost 195mm (measured at infinity from shutter's aperture for the film plane). Is it not 'too' sizable difference??? Has such disparity happened? I measured FL of a few other vintage lenses I own and they cover with engraved FL.

Jim Jones
30-Dec-2011, 06:09
The disparity between the two measurements is often much greater in small camera lenses.

Dan Fromm
30-Dec-2011, 06:38
Just last question. I am sure the 7" focal length engraved on my Conley Sewries V lens differs from its actual FL. But the difference seems appreciable: it's 178mm to almost 195mm (measured at infinity from shutter's aperture for the film plane). Is it not 'too' sizable difference??? Has such disparity happened? I measured FL of a few other vintage lenses I own and they cover with engraved FL.

The rear node doesn't have to be at the aperture. I wrote that for lenses of normal construction it is near the aperture. Near doesn't mean at.

The cells may be farther apart than the lens' designer intended. This will make the focal length greater than intended.

Paul Fitzgerald
30-Dec-2011, 06:47
Hi renes,

"This leaves open the questions of what focal length is (short answer, it is defined as the distance from the lens' rear nodal point to the film plane when the lens is focused at infinity) and the relationship between the focal length engraved on a lens and the lens' actual focal length."

"Neither. From the rear node to the film plane when the lens is focused at infinity."

NO, it isn't, that's called 'back focus'. :eek:
There have been multiple ways the factories have measured focal length:

1) old school, direct comparison of magnification at the GG to a simple lens of known focal length, also called "Equivalent Focus"

2) modern, direct measurement of distance difference from inf. to 1-1

3) +/- 10% production tolerance on most consumer lenses, (close enough is good enough) :D

Dan Fromm
30-Dec-2011, 07:28
NO, it isn't, that's called 'back focus'.

"Back focus" is conventionally used to mean the distance from the lens' rear vertex to the film plane when the lens is focused at infinity.

renes
30-Dec-2011, 08:27
"Back focus" is conventionally used to mean the distance from the lens' rear vertex to the film plane when the lens is focused at infinity.



There have been multiple ways the factories have measured focal length:

1) old school, direct comparison of magnification at the GG to a simple lens of known focal length, also called "Equivalent Focus"
(...)

And I get perfectly 7inch FL measuring from the "Back focus" with my "Conley Equivalent Focus 7 inches" lens, which reaches 195mm FL measured near from the iris aperture/center in beetwen the cells.

But could the "known FL lens" which was used for comparison have estimated focal length measured from "back focus"?

E. von Hoegh
30-Dec-2011, 08:33
Hi renes,

"This leaves open the questions of what focal length is (short answer, it is defined as the distance from the lens' rear nodal point to the film plane when the lens is focused at infinity) and the relationship between the focal length engraved on a lens and the lens' actual focal length."

"Neither. From the rear node to the film plane when the lens is focused at infinity."

NO, it isn't, that's called 'back focus'. :eek:
There have been multiple ways the factories have measured focal length:

1) old school, direct comparison of magnification at the GG to a simple lens of known focal length, also called "Equivalent Focus"

2) modern, direct measurement of distance difference from inf. to 1-1

3) +/- 10% production tolerance on most consumer lenses, (close enough is good enough) :D

You forgot the nodal slide.

c.d.ewen
30-Dec-2011, 14:39
renes:

How many 7" lenses do you have? Take identical pictures of the horizon with each lens, print them, and measure the distance between objects on each print.

If you want to determine the FL more precisely, there are several methods described in various archived postings here and other places. Just because I had a sextant, I used to measure the viewing angle between objects, then measure the distance on a print, then do some trigonometry (when you've got a hammer, a lot of things look like nails). You can probably do the same thing using Google Earth.

Charley

renes
30-Dec-2011, 16:36
Charley,

I thought I have one, but it turned out it's 7,7" in spite of different marking. So, I have no one :) I just try to understand why this occured. I think only "back focus" method of measuring FL seems to be the answer in case of my Conley.

Dan Fromm
30-Dec-2011, 17:09
Nodal slide. And, as has been pointed out, there are other ways. Look for posts here by Emmanuel Bigler who gave a lucid explanation of one.

Paul Fitzgerald
30-Dec-2011, 18:25
Happy New Year's people.

All of this is 'salesman's blather', imagined by the sales dept., intended to comfound the market place and doesn't make a tinker's damn worth of difference to photography. You will 'zoom with your feet' to frame the photo, did exposure tests with this (film, lens, meter) combo for exposure and DOF goes wherever with movements. :eek:

The manufacturers have known of "modern measured focal length" and the "f/scale" since Voightlander was making petzvals, that is how they advertised them by f/scale size. They were all mucking about for grins and giggles. :D

E.F. stands for "Equivalent Focus", explained above, simple lens.

E.F. also stands for "Effective Focus", explained above by Dan, back focus.

Before that they were marked in format size they would cover at inf. Just to confuse this Continental was for cm, US and British were inches

Before that they were marked in series size #, never standardised even by the same manufacturer between lines.

Before that they were only marked with the manufacturer's name and maybe a size #.

Along the way we have had a dozen different exposure scales. The manufacturers have known of "modern measured focal length" and the "f/scale" since day 2 and have all been mucking about just for grins and giggles. :D

renes
31-Dec-2011, 06:53
Nodal slide. And, as has been pointed out, there are other ways. Look for posts here by Emmanuel Bigler who gave a lucid explanation of one.

I was tempted to chose "back focus" way becouse I get exact 7" FL measuring from the rear lens, but it does prove nothing of course.