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Ed Bray
4-Jun-2012, 01:19
I have a query that I would appreciate the answer to.

If I had a 210mm f5.6 Symmar in a No 1 Compur shutter and later purchased a 210mm f5.6 Apo-Symmar in No 1 Copal shutter would I be able to do a straight swap of the shutters and would everything remain the same (barrel distance, aperture)?

TIA

IanG
4-Jun-2012, 01:27
Straight swap would be fine.

Ian

Sevo
4-Jun-2012, 01:51
A Symmar (convertible) or Symmar-S? The latter is very, very like the Apo-Symmar (cynics say the only difference was the name change). The convertible is older and a more different design - I'd proceed more careful there, even though my shuttered ones seem to have the same aperture scale. In either case, measure the total lens height with a precision caliper before and after - if there is a difference, you may need to rearrange the shims (it is hard or impossible to tell which shim compensated cell and which the shutter tolerances - the latter ought to stay with the shutter, the former ought to be moved).

Leigh
4-Jun-2012, 02:00
The proper depth of a Copal #1 shutter, measured from the front face to the rearmost surface, is 22mm.

If you move lenses between shutters, the first thing to do is measure that dimension on each of the shutters.
Your measurements should have an accuracy of at least 0,1mm.

If the measurements for the two are the same, then move any shims along with the cells.

If the measurements differ, you have a problem and should not proceed without further guidance.

- Leigh

Andrew
4-Jun-2012, 02:01
I've just tried a swapping two similar lenses of nominally equal focal length [210mm]
to convince myself it was OK I focused infinity, swapped over the cells and measured the amount of readjustment needed to refocus infinity
in my case there was a tiny difference that amounted to about 3mm which for a 210mm lens seems insignificant
I think that makes my aperture scale in error by about 1.5%

addit
Leigh, does this fit correctly with our previous discussion?

Leigh
4-Jun-2012, 02:04
in my case there was a tiny difference that amounted to about 3mm which for a 210mm lens seems insignificant
I think that makes my aperture scale in error by about 1.5%
A 3mm (~1/8") difference in infinity focus is huge in terms of the shutter geometry.
It may indicate that the cell spacing is not correct.

The aperture scale is not related to the infinity focus position at all.
It's a function of the apparent aperture (entrance pupil) and the optical focal length (which is invariant).

- Leigh

Andrew
4-Jun-2012, 02:10
it was a swap of a newish 210 g-claron for an older "dagor" style g-claron so it is a different design
but if they're both nominally 210mm optics... ?

Leigh
4-Jun-2012, 02:14
OK. You said similar, so I thought you meant similar. :D

If they were different designs then the flange focal lengths could be quite different.
My lens database shows modern 210mm lenses with FFLs from 177mm to 223mm.

- Leigh

Andrew
4-Jun-2012, 02:39
yeeees... so if you swapped cells and found that you had to rack the standard backwards or forwards by 46mm to refocus infinity then I think anyone woud expect a problem with the aperture scales being incorrect

what if I swapped a nominally 300mm rapid rectilinear into the shutter of a nominally 300mm plasmat and found that focus was perfectly maintained ?

Ed Bray
4-Jun-2012, 02:39
A Symmar (convertible) or Symmar-S? The latter is very, very like the Apo-Symmar (cynics say the only difference was the name change). The convertible is older and a more different design - I'd proceed more careful there, even though my shuttered ones seem to have the same aperture scale. In either case, measure the total lens height with a precision caliper before and after - if there is a difference, you may need to rearrange the shims (it is hard or impossible to tell which shim compensated cell and which the shutter tolerances - the latter ought to stay with the shutter, the former ought to be moved).

It is a Symmar convertible and an Apo-Symmar (no L).

There is nothing wrong with either shutter, I just prefer the more rounded aperture of the Compur to the pentagon design of the Copal aperture.

Leigh
4-Jun-2012, 02:41
so if you swapped cells and found that you had to rack the standard backwards or forwards by 46mm to refocus infinity then I think anyone woud expect a problem with the aperture scales being incorrect
Sorry... wrong.

As I said above (#6), Flange Focal Length (FFL) has absolutely nothing to do with the aperture scale.
That's because the FFL has nothing to do with the optical focal length. The f/setting depends on optical FL.

- Leigh

IanG
4-Jun-2012, 02:48
The flange focal distanc is slightly different depending on which shutter is used, the 210 Symmar S is 200.9 mm in a Compur and 201.0mm, not critical on a field camera/monorail etc but the Protor is only 199.5mm enough (1.5mm) to affect infinity focus on a camera with a helical mount (like some 617, 612 etc cameras) or where Infinity stops are used.

Ian

Andrew
4-Jun-2012, 04:02
Leigh, so...
by implication I can swap over plasmat/RR/dagor/tessar/meniscus/petzval with impunity so long as the they're of equal focal length?
[we'll ignore cell seperation issues]

Sevo
4-Jun-2012, 04:14
Leigh, so...
by implication I can swap over plasmat/RR/dagor/tessar/meniscus/petzval with impunity so long as the they're of equal focal length?


With what impunity? Aperture scales will differ not quite as much as when switching focal lengths, but they may still change significantly when it comes to asymmetric lenses. And unless the shutter and cells have been independently shimmed (so that you own separate kits of shims to neutralize both the shutter and cell set) it is a matter of luck (and the spacing vulnerability of the lens design) whether the spacing is acceptably accurate or not...

Dan Fromm
4-Jun-2012, 07:20
The proper depth of a Copal #1 shutter, measured from the front face to the rearmost surface, is 22mm.

- Leigh

20.00 mm. See http://www.skgrimes.com/products/new-copal-shutters/standardcopals And although everyone says thickness, the distance is measured from the front of the front tube (front cell screws into it) to the rear of the rear tube (rear cell screws into it)

Leigh
4-Jun-2012, 07:25
20.00 mm. See http://www.skgrimes.com/products/new-copal-shutters/standardcopals And although everyone says thickness, the distance is measured from the front of the front tube (front cell screws into it) to the rear of the rear tube (rear cell screws into it)
Dan,

I took the 22mm dimension directly from the Copal drawing.

Sorry, but SKG does not make these. Copal does.

- Leigh

Dan Fromm
4-Jun-2012, 07:27
yeeees... so if you swapped cells and found that you had to rack the standard backwards or forwards by 46mm to refocus infinity then I think anyone woud expect a problem with the aperture scales being incorrect


No.

You're confusing flange focal distance (the distance from the back of the shutter or the barrel's rear flange to the film when the lens is focused at infinity) with focal length. Focal length is the distance from the lens' rear node to the film when the lens is focused at infinity. Where the rear node is located depends on the lens' design. Most modern more-or-less symmetrical lenses (this includes the Dagor in its many versions and clones) have rear nodal points near the diaphragm. For such lenses flange focal distance is usually not very different from focal length. But not always. Lightly asymmetrical double Gauss types, in particular, seem to be somewhat telephoto.

Telephoto lenses have it in front, sometimes far in front, of the diaphragm. Retrofocus lenses have it behind, often far behind, the diaphragm.

Leigh
4-Jun-2012, 07:30
by implication I can swap over plasmat/RR/dagor/tessar/meniscus/petzval with impunity so long as the they're of equal focal length?
Nope. Sorry.

There are two parameters in the f/stop equation: 1) the optical focal length and 2) the diameter of the entrance pupil.

The diameter of the entrance pupil is the physical diameter of the opening through the diaphragm blades multiplied by a constant that's a function of the lens design. Each of your lens types will have a different constant.

With real shutters the problem is exacerbated by the fact that the diaphragm hole is not a perfect circle, but the f/stop equation assumes a perfect circle. So there's an additional correction factor applied to equate the physical area of the hole with that of a true circle.

- Leigh

Dan Fromm
4-Jun-2012, 07:33
With what impunity? Aperture scales will differ not quite as much as when switching focal lengths, but they may still change significantly when it comes to asymmetric lenses. And unless the shutter and cells have been independently shimmed (so that you own separate kits of shims to neutralize both the shutter and cell set) it is a matter of luck (and the spacing vulnerability of the lens design) whether the spacing is acceptably accurate or not...

Leigh, I agree completely with you about the risks that stuffing any old pair of cells in any old shutter entails. Also about the risks of swapping a pair of cells from one #00 shutter into another #00 shutter; #00s, especially ones used in folding 35 mm cameras, don't all conform to the #00 standard.

But for post-WWII lenses mounted in post-WWII lenses that conform to the Compur/Prontor/Copal/Seiko #0, #1, and #3 standards, moving a pair of cells from one shutter to another seems fairly safe.

On a related point, I've removed a moderate number of cells from shutters and barrels for cleaning, have never found a shim between cell and shutter. Has anyone here done the same and found a shim?

Dan Fromm
4-Jun-2012, 07:35
Dan,

I took the 22mm dimension directly from the Copal drawing.

Sorry, but SKG does not make these. Copal does.

- Leigh

Have you measured? I have. Pukka Copal and Compur #1s are 20 mm. The #1 Copals engraved Polaroid Copal are 22 mm. Which drawings did you consult?

Leigh
4-Jun-2012, 07:42
But for post-WWII lenses mounted in post-WWII lenses that conform to the Compur/Prontor/Copal/Seiko #0, #1, and #3 standards, moving a pair of cells from one shutter to another seems fairly safe.
I agree.

There certainly was a problem of inconsistent dimensions among manufacturers of older shutters. I didn't know when that was standardized.

I've done an awful lot of shutter repairs, most being for complete lenses, and I only recall finding shims in one lens.

Modern machining methods can produce parts (and complete shutters) to very tight dimensional tolerances.

In the days before CNC machine processes, making parts to tight tolerances cost a lot more than using lax tolerances.
In that situation it was much cheaper to make the shutter slightly short and use shims to achieve the correct dimension.
This also provided correction for dimensional errors in the cells themselves, if the lens was set up on an optical bench.

- Leigh

Old-N-Feeble
4-Jun-2012, 07:53
Ed... Any chance you can do a comparison of the two lenses regarding *gasp* bokeh? Then swap the cells and duplicate the test? I'd really like to see the difference between the round vs. penta iris shape. Ill bet others are interested too. BTW, I'll be doing similar comparisons one of these days.

Old-N-Feeble
4-Jun-2012, 08:03
<snip>On a related point, I've removed a moderate number of cells from shutters and barrels for cleaning, have never found a shim between cell and shutter. Has anyone here done the same and found a shim?

Yes, I bought a new 150mm Sironar (or Sironar-N, can't remember) about 36-37 years ago and it was shimmed front and rear with different thickness brass shims. The 210mm and 300mm I bought at the same time had no shims. These were Copal shutters but I can't remember if they were all black or silver-rimmed.

BrianShaw
4-Jun-2012, 08:04
I've only found shims on MF folding rangefinders, never on a LF lens... yet.

Leigh
4-Jun-2012, 08:07
Have you measured? I have. Pukka Copal and Compur #1s are 20 mm. The #1 Copals engraved Polaroid Copal are 22 mm. Which drawings did you consult?
What's a Pukka? Sounds like something you'd apologize for if you did it in public. :D

You're talking about the cell spacing, which is 20mm 0,025mm per the Copal spec.

Different reference surface.

As stated in post #4, the 22mm dimension that I gave is from the front face of the shutter,
not from the cell seating plane, as shown in this drawing (dimension at the very bottom):

http://www.mayadate.org/pix/copal1dimsCr.gif

- Leigh

Sevo
4-Jun-2012, 08:20
On a related point, I've removed a moderate number of cells from shutters and barrels for cleaning, have never found a shim between cell and shutter. Has anyone here done the same and found a shim?

It seems to be very rare in modern taking lenses (like a Apo-Symmar) - the makers now seem to adjust the cells for maximum performance when there is no shim between cells and shutters. And modern shutters are generally dead accurate to standard unless explicitly made in another flange depth.

I've often seen shims on process lenses, as these weren't only optimized for peak performance, but had additionally to be also adjusted to match the nominal focal length precisely, as the all-important magnification scales on process cameras depended on that accuracy - being able to play with inter-cell spacing seems to be helpful there.

But on old (pre seventies) lenses and shutters, shims are common - the pre CNC way of eliminating tolerances was to cut everything to be slightly undersized and bridge the resultant gap with shims.

Sevo
4-Jun-2012, 08:31
The diameter of the entrance pupil is the physical diameter of the opening through the diaphragm blades multiplied by a constant that's a function of the lens design. Each of your lens types will have a different constant.


In real life, there aren't that many fundamentally different lens designs across modern LF lenses. Indeed you often have no choice among design types if the focal length, maximum aperture and shutter size are to be the same. And within a design type, that constant does not vary that much, usually by much less than a third stop - things only start to get difficult once you switch design types...

Bob Salomon
4-Jun-2012, 08:31
All well and good but on Friday I mounted a brand new Rodenstock 45mm Apo Sironar Digital lens in Copal 0 into a Linhof recessed board and sure enough, between the front group and the shutter there were two shims.

On Wed. of last week I mounted a 35mm 4.0 Rodenstock HR Digaron-S lens in Copal 0 onto another recessed board and it also had shims.

2 out of 2 isn't so rare! And these are some of the newest lenses for large format cameras.

IanG
4-Jun-2012, 08:36
My 90mm f6.8 Grandagon hasb a couple of shims between the front cell & shutter, I've only come across one other lens with a shim.

Somewhere Dean Jone (razzledog) mentions he found inconsistent Compur shutters used with early 90mm f6.8 Angulons, some were out of tolerance and the cell spacing was too wide. He found that remaching the shutter housing to the correct tolerances improved the sharpness of what had been previously poor Angulons. Not someting to do at home though :D

Ian

Ed Bray
4-Jun-2012, 08:36
Ed... Any chance you can do a comparison of the two lenses regarding *gasp* bokeh? Then swap the cells and duplicate the test? I'd really like to see the difference between the round vs. penta iris shape. Ill bet others are interested too. BTW, I'll be doing similar comparisons one of these days.

Yes, I can do that although I will do it using my 6x9 back.

I am surprised this thread has had the legs it has and I have been very interested in all the replies, many thanks to you all.

E. von Hoegh
4-Jun-2012, 08:43
Ed... Any chance you can do a comparison of the two lenses regarding *gasp* bokeh? Then swap the cells and duplicate the test? I'd really like to see the difference between the round vs. penta iris shape. Ill bet others are interested too. BTW, I'll be doing similar comparisons one of these days.
It won't make a bit of difference in the character of the lens, only a little difference in the shape of the OOFHs.

Old-N-Feeble
4-Jun-2012, 08:48
It won't make a bit of difference in the character of the lens, only a little difference in the shape of the OOFHs.

True, thank you, and that's precisely what I'm curious about. :)

Leigh
4-Jun-2012, 09:56
In real life, there aren't that many fundamentally different lens designs across modern LF lenses. Indeed you often have no choice among design types if the focal length, maximum aperture and shutter size are to be the same. And within a design type, that constant does not vary that much, usually by much less than a third stop - things only start to get difficult once you switch design types...
My statement was meant to be correct for photographic lenses in general, and I believe it is.

If you use enough assumptions and constraints, one lens and shutter could be used for everything. :D

- Leigh

Andrew
4-Jun-2012, 14:21
sorry to drag this back to my level, but I'm gonna beat my head against this wall until I see the light

I want to ignore issues of cell spacing because I really only care about the aperture scales here
if I swap lens cell between shutters...
how will I confirm that the aperture scales are still correct OR how do I quantify the error so I can make new scales ???

Leigh
4-Jun-2012, 14:25
Hi Andrew,

It's really a question of how accurate you expect your scales to be.

If you want the scale to be right, order one from S K Grimes at www.skgrimes.com
They have all the info to make one for your lens/shutter combination.

An alternative is to shoot some test scenes with a lens having a known accurate aperture,
and the same scenes from the same spot with the new lens (acknowledging a different field of view).

Bracket the test exposures with the new lens in 1/3 stop (or finer) increments, if possible.

A perhaps superior methodology would be to use the lens in its original shutter as the standard, then move
the cells to the new shutter and repeat the exposure series. This provides a consistent field of view.

In this case you would use the existing scale and determine a correction factor based on comparison of the negatives.
You could apply that correction in your head, or you could work out a change in film speed for the same result.

- Leigh

Andrew
4-Jun-2012, 14:49
Thank Heaven for good ol' fashioned empiricism... I can cope with that :)

Andrew
4-Jun-2012, 15:01
further to above post
rather than wasting time, film and chemicals
as I have a good quality light meter that reads incriments of 0.1EV can I jerry-rig that to make a measurement device to confirm/calibrate aperture scales?

Leigh
4-Jun-2012, 15:03
Yes.

If you have a way to measure the light on the ground glass and exclude all other light sources,
that would work quite well.

The methodology would be the same. Use the original lens/shutter as your standard.
Take a reading of some uniformly gray subject. A gray card or the side of a building or anything similar.
Then take the same reading using the lens in the new shutter and make the comparison.

Take readings at a couple of different mid-range apertures, like f/11 and f/32.

This would be more accurate than the film test, provided you really exclude other light sources.

A point regarding accuracy when using any digital instrument for comparison:
The greatest repeatability will be achieved when the reading is bouncing back and forth between adjacent values,
e.g. 3.4 and 3.5 EV or some such. (See note below)

This can be used to advantage for the type of tests under discussion.

Set the reference lens at your favorite mid-range aperture (f/22 or whatever) and note the EV reading.
Adjust the aperture ever so slightly until you get the jumping values. This is a very fine adjustment.
Note the aperture setting, then move the cells to the new shutter.
Do the same thing with the new lens, setting the aperture for the exact same pair of values.
This is a very accurate measurement.


- Leigh

Note: If you're unable to achieve the bouncing value setting with your meter, disregard the method.
Some meters are designed to suppress the bouncing value display. There's no way to defeat that.

Dan Fromm
4-Jun-2012, 15:56
Hmm. Photometric methods measure transmission. What does that have to do with geometric f/ stops?

Leigh
4-Jun-2012, 15:57
The meter is being used as a luminance comparator.

When the illumination on the GG is the same for both shutters, then the actual aperture is the same.

- Leigh

Andrew
4-Jun-2012, 16:14
If we're talking relative values... can I bring this onto a table top with a light source behind a diffuser and simply put the light meter on the other side of the lens?

Leigh
4-Jun-2012, 16:24
Sure. Just make sure the light is very diffuse and uniform over the viewing area.

In fact, a defocused subject will give you more uniform illumination than a focused subject,
unless the subject has a very uniform tone and reflectance to start with (like a gray card).

- Leigh

Dan Fromm
4-Jun-2012, 17:11
When the illumination on the GG is the same for both shutters, then the actual aperture is the same.

- Leigh

Think this over carefully. It works for the same cells in different shutters, not for different lenses.

Leigh
4-Jun-2012, 17:16
Think this over carefully. It works for the same cells in different shutters, not for different lenses.
Of course it works for different lenses.

That's why an exposure at f/8 will come out the same for any lens (ignoring differences in FoV).

This is the whole basis for photographic exposure.

- Leigh

Old-N-Feeble
4-Jun-2012, 17:31
I'd think it would work fine with both lenses at infinity focus.

Leigh
4-Jun-2012, 17:36
Focus point (i.e. bellows extension) is irrelevant if the two lenses have approximately the same FFL.

Even a 10mm difference in FFL should result in <1% error (approximation) for lenses in the focal length under discussion.

If the lenses have disparate focal lengths, then yes they should be focused at infinity for maximum accuracy.

BTW, this does not mean that the test target/subject needs to be at infinity, as discussed above.

- Leigh

Old-N-Feeble
4-Jun-2012, 17:47
If both lenses have nearly identical focal distance then, yes, bellows extension is irrelevant. No, the target need not be near infinity focus. In fact, I'd place it very near the lens(es) with them focused at approximately infinity just to blur the target.

Leigh
4-Jun-2012, 17:49
In fact, I'd place it very near the lens(es) with them focused at approximately infinity just to blur the target.
Yep, exactly.

- Leigh

Dan Fromm
4-Jun-2012, 19:18
Of course it works for different lenses.

That's why an exposure at f/8 will come out the same for any lens (ignoring differences in FoV).

This is the whole basis for photographic exposure.

- Leigh
Stuff and nonsense. Transmittance makes a difference

Why do you think that the very serious folks in "Hollywood" use lenses with diaphragms calibrated in T/stops?

Leigh
4-Jun-2012, 19:24
Dan,

Have you been drinking?

T-stops are just accurate apertures, used because they want extremely accurate exposures.

They DO NOT measure luminance at the film plane, as I've suggested for this application.

- Leigh

Jim Andrada
4-Jun-2012, 21:54
Interesting comments re shimming a few posts back. CNC machining hasn't obsoleted shims by any means. We manufacture complex mechanisms with micron level tolerances - would be a matter of testing a zillion of them to find a few in tolerance - very expensive. Shims are our salvation.

By the way, found the following

T-stops
F-stops are purely geometrical, the ratio of aperture to focal length, regardless of actual light transmitted. Since all lenses absorb some portion of the light passing through them (particularly zoom lenses containing many elements), f-numbers do not accurately correlate with light transmitted. F-numbers corrected to measure light transmission rather than aperture ratio, called T-stops (for Transmission-stops), are sometimes used instead of f-stops for determining exposure.[7] A real lens set to a particular T-stop will, by definition, transmit the same amount of light as an ideal lens with 100% transmission at the corresponding f-stop.

And the following

T-stops
In practice, even the best lenses exhibit light absorbance, effectively “stealing” some of the light going through them. This means that if you calculate the exposure based on the f-stop of the lens, you will end up underexposing the image, because less light is reaching the film plane than is expected in theory. T-stops are the f-stop of the lens corrected for its absorbance and reflectance. The T-stop is the true speed of the lens, calculated by compensating for its light absorbance and reflectance, and will result in accurate exposure.

Leigh
4-Jun-2012, 21:58
T-stops v. F-stops...

Irrelevant. The shutters in use, and the exposure meters, and the film speeds, all use f-stops.

The focus of this thread is to determine the accuracy of the f-stop scale on the new shutter v. the original shutter.

- Leigh

Andrew
5-Jun-2012, 03:07
this is great... I finally feel like I'm near a point that I can do something practical.

Leigh, please let me know if this is flawed before I invest the effort trying to put it into practice.

Ive got a technika, a minolta IV-f, some lenses that I trust and couple more that have been monkeyed with, either by myself or someone else

I can make a light source that can be pretty much anything diffused but basically something that'll act like a light box. Then I get a piece of MDF cut to sit in the universal back of the technika, drill a hole in the MDF to take the diffuser of the light meter and use some felt to make it all reasonably light tight when the meter is pushed into place. I think I can make the diffuser sit pretty much at the film plane.

Next step is to focus a trusted reference lens to infinity, stick it at a specified point in front of the light source and measure the light intensity in EV at the film plane as a de facto index of the aperture.

NOW... if I've got this right, when I get another lens of same focal length to my reference lens that is also focused to infinity, I should expect to get the same EV values for each lens at the same apertures? And if the dodgy lens is NOT correct, I use the EV values from reference lens to determine the correct apertures?

I hope this is correct too... if I get a lens of a *different* focal length to the reference lens that is also focused to infinity and then put it at the same point relative to the light source, I should get the same EV values as on the reference lens?

And this set up should get rid of any artifact arising from variation in flange to film distances for different lenses???

Leigh
5-Jun-2012, 03:23
I would recommend limiting the number of lenses involved in the comparison test to just the original shutter/lens and those same cells in the new shutter. There may be some difference in transmission between lenses of different makes and designs, particularly as regards coatings.

This is why I limit the number of makes and models in my lens inventory to the greatest extent possible.
All of my mid-range lenses are Rodenstock Apo-Sironar-S, while those 120mm and shorter, and 360mm and longer are Nikkors.

The methodology sounds like it will work fine.

You can certainly run the test with other lenses as a comparison, to see how uniform the performance really is.

- Leigh

Steve Smith
5-Jun-2012, 03:29
CNC machining hasn't obsoleted shims by any means.

Also no reason why CNC would be more accurate. A properly set up manual machine run by a competent operator can have the same level of accuracy.


Steve.

Andrew
5-Jun-2012, 04:44
The methodology sounds like it will work fine.


Thank Heaven I've finally got something right !!!

I'll agree that this ought to kept as limited in scope as possible but if you aren't hammering the logic that's all I need.... in practice, if I can test some of my older lenses and be reasonably sure of my apertures to within say 1/3 to 1/2 stops I'll be more than happy

thank you :)

Leigh
5-Jun-2012, 04:54
A properly set up manual machine run by a competent operator can have the same level of accuracy.
True, but not at the same cost of production (disregarding capital equipment costs).

I can hold sub-thou on my Bridgeport mill all day long, but I can't do it as fast as a CNC mill.

One major advantage of CNC milling is flood coolant, which allows much higher cutting speeds than a manual mill.

- Leigh

Steve Smith
5-Jun-2012, 05:48
If I was making a lot of shutters without the benefit of CNC I think I would cut and thread one side then mount the shutter part on a custom made threaded mount and machine the other side's depth relative to the first side. Probably on a turret lathe to perform many operations consecutively.

But I agree about the speed and other advantages of CNC (spoken as someone who programmes and runs CNC equipment as part of his job!).


Steve.

Leigh
5-Jun-2012, 05:52
But I agree about the speed and other advantages of CNC (spoken as someone who programmes and runs CNC equipment as part of his job!).
Yeah. I'm a journeyman tool & die maker, over 50 years now. When I got into the trade CNC didn't exist.

- Leigh

Dan Fromm
5-Jun-2012, 06:01
Dan,

Have you been drinking?

T-stops are just accurate apertures, used because they want extremely accurate exposures.

They DO NOT measure luminance at the film plane, as I've suggested for this application.

- Leigh

Leigh, I stopped drinking alcohol years ago.

I'm sorry, you're misinformed. Please see http://en.wikipedia.org/wiki/F-number

Steve Smith
5-Jun-2012, 06:43
I think I would cut and thread one side then mount the shutter part on a custom made threaded mount and machine the other side's depth relative to the first side.

Actually, that's complete nonsense as the two threads are on different pieces of metal. But the point is still valid that parts on a piece can be machined relative to other parts using a previously machined feature as the holding point for subsequent machining.

If both front and rear threads were in the same piece of metal, there would be no gap for the shutter and f stop blades!


Steve.

Ed Bray
7-Jun-2012, 03:35
Ed... Any chance you can do a comparison of the two lenses regarding *gasp* bokeh? Then swap the cells and duplicate the test? I'd really like to see the difference between the round vs. penta iris shape. Ill bet others are interested too. BTW, I'll be doing similar comparisons one of these days.

I received my Apo-Symmar lens this morning, and whilst it is in a Copal #1 shutter the aperture has 7 blades as opposed to the 5 blades I was expecting. I now see little reason to swap the shutters but if you would still like me to do the 'Bokeh' test I will but it will not be until next week. I am sure that at least one of my Copal apertures has only 5 blades?

Leigh
7-Jun-2012, 06:38
I am sure that at least one of my Copal apertures has only 5 blades?
The #1 and #3 Copals have always(?) had seven blades.

Earlier Copal 0 shutters had five blades.

Then Nikon got them to do a special seven-blade version for the Nikkor lenses.
Those have a capital letter 'S' in a circle on the side of the shutter.

Then apparently Copal made the seven-blade version standard for the 0 shutter.
I don't know if the non-Nikkor shutters have the "circle-S" or not.

- Leigh

Ed Bray
7-Jun-2012, 09:11
Thanks for the info Leigh, much appreciated.