Slightly large Copal #3 hole

[grahamcase]

I got the lens board for my Tachihara today, and the drilled hole for the Copal #3 seems to be too big - I think I measured it around 65mm-66m, rather than 63mm, which is what I think it's supposed to be. I managed to attach my lens anyway, but was just curious if this was normal, or if I got a slightly defective lens board (entirely possible as I bought it used for 1/3 the price of a new one...)

Just curious - I think I know people who can build me a wooden one quickly, but the one I have now certainly is doing the job, even if it is slightly defective.

Thanks in advance.
G.Case

[TheDeardorffGuy]

Do you have both parts of the retaining ring? There's an un threaded ring called the compression ring and the Threaded ring. I always ask if my customer has both or just the threaded ring. If the hole is too big and you have just the threaded ring it might not fit at all. The compression ring takes up the slop of a too large hole. The hole should be the threaded ring OD + a couple thou. the thickness of the board should be a 1/10 inch if metal like a Linhof Style. Or 2/10 if wood. This is where you rabbet the wood.
Ken

[Keith Pitman]

See grimes: http://skgrimes.com/lensmount/shutmt/index.htm

65mm is the correct size for some Copal 3's (most recent, I think), but some older ones are not this size.

[Leigh]

The correct hole diameter for a Copal #3 is a bit larger than 65mm. Some sources give it as 65.2mm, while others give 65.3mm.

In any case it's a shade larger than the 65.0mm diameter of the retaining ring, so the ring doesn't bind in the hole.

- Leigh

[Keith Pitman]

The correct hole diameter for a Copal #3 is a bit larger than 65mm. Some sources give it as 65.2mm, while others give 65.3mm.

In any case it's a shade larger than the 65.0mm diameter of the retaining ring, so the ring doesn't bind in the hole.

- Leigh

Leigh, Reread his posting. His 65 mm hole is too big. It seems he has an older Copal 3 that is smaller. Suggesting a 65.3mm hole will not help him! Some older shutters marked Copal 3, were actually 3S shutters, but not marked as such. In addition to differences in the board hole sizes differing, the thread sizes differ as well, so make sure you get correct retaining rings or flanges when you buy the lens.

[Leigh]

Reread his posting. His 65 mm hole is too big. It seems he has an older Copal 3 that is smaller. Suggesting a 65.3mm hole will not help him!
No. This comes from the common error of people measuring the shutter thread (M62 x 0.75) and thinking the hole should be just slightly larger.

That's not the way Copal shutters work.

The retaining ring is meant to go into the hole in the lensboard, thus providing clearance between the hole and the shutter thread, apparently to protect the thread although I've never seen a definitive explanation for this.

I believe the older Copals had the same thread dimensions, since changing it would mean older cells would not fit in modern shutters and vice versa.

- Leigh

[grahamcase]

Hmm, so I may be missing a compression ring, OK.

The way I have it set up currently is that my retaining ring is backwards - it flares out at the end enough that I just flipped it around, and it is holding the lens. I can add pictures of this later tonight, but I'm currently at work. I think this will help you help me solve this problem :)

Thanks, everyone!

[Leigh]

it flares out at the end enough that I just flipped it around, and it is holding the lens.
Yep, that's backwards.

The flange on the retaining ring has two notches in it for the spanner wrench to tighten it, so that end must be on the side away from the lensboard.

There should be an additional ring. It's a simple donut with no smaller features. ID is 65.0mm, OD is 70.0mm, thickness is 6.5mm. This thing appears to be made out of a heavy synthetic material, possibly Delrin or similar.

I've attached a drawing from a Schneider lens data sheet that shows the retaining ring and the spacer ring, although it's not really clear. The shutter itself is not shown, but would be to the left of the drawing.

- Leigh

[Keith Pitman]

Hmm, so I may be missing a compression ring, OK.

The way I have it set up currently is that my retaining ring is backwards - it flares out at the end enough that I just flipped it around, and it is holding the lens. I can add pictures of this later tonight, but I'm currently at work. I think this will help you help me solve this problem :)

Thanks, everyone!

Sounds like you have a flange not a retaining ring, but what you've done should work as long as the lens is secure.

[Keith Pitman]

No. This comes from the common error of people measuring the shutter thread (M62 x 0.75) and thinking the hole should be just slightly larger.

That's not the way Copal shutters work.

The retaining ring is meant to go into the hole in the lensboard, thus providing clearance between the hole and the shutter thread, apparently to protect the thread although I've never seen a definitive explanation for this.

I believe the older Copals had the same thread dimensions, since changing it would mean older cells would not fit in modern shutters and vice versa.

- Leigh

As indicated above, I think he has a 3S which is not the same size mounting threads as the 3.

[Leigh]

Sounds like you have a flange not a retaining ring
A flange will have four counter-sunk screw holes parallel to the lens axis but no slots.

A retaining ring will have two radial slots on the wide end but no screw holes.

The lensboard mounting hole is the same diameter for either style.

Remember, we're talking about untoleranced dimensions here. We don't know the tolerance on the 65.0mm retaining ring diameter.

A 65.2mm or 65.3mm nominal mounting hole diameter would be safe at a ±0.1mm (0.004") tolerance, which is reasonable.

- Leigh

[grahamcase]

To make things easier, I have added photos of my lens. I grabbed these from the bay auction I won it from.

You can see from photo one that I have a Copal 3 shutter, not a 3-S.
In photo two, i have marked the retaining ring, and also marked what may be the compression ring, but I can't be sure until I get home.

http://grahamcase.ca/images/CalumetCaltar-1.jpg

http://grahamcase.ca/images/CalumetCaltar-2.jpg

[TheDeardorffGuy]

Hmm, so I may be missing a compression ring, OK.

The way I have it set up currently is that my retaining ring is backwards - it flares out at the end enough that I just flipped it around, and it is holding the lens. I can add pictures of this later tonight, but I'm currently at work. I think this will help you help me solve this problem :)

Thanks, everyone!

Graham I've drilled more Copal 3 holes than nearly anyone. You need a Compression ring. Call: http://www.criscam.com/

[TheDeardorffGuy]

To make things easier, I have added photos of my lens. I grabbed these from the bay auction I won it from.

You can see from photo one that I have a Copal 3 shutter, not a 3-S.
In photo two, i have marked the retaining ring, and also marked what may be the compression ring, but I can't be sure until I get home.

http://grahamcase.ca/images/CalumetCaltar-1.jpg

http://grahamcase.ca/images/CalumetCaltar-2.jpg

you are still missing the compression ring call: http://www.criscam.com/
ken

[grahamcase]

you are still missing the compression ring call: http://www.criscam.com/
ken

Thank you for the quick reply, and link! Do I just ask for a Copal #3 compression ring? Are there multiple kinds to consider, or am I looking at an easy thing to ask for?

[c.d.ewen]

Graham:

For those who have never seen them, this (http://www.largeformatphotography.info/forum/showthread.php?t=73402) is what retaining and compression rings look like. The slots cut into the retaining ring, on the left, aren't visible, as they're facing downward.

BTW, I've had shutters marked Copal 3 which conformed to the Copal 3S specs, so you can't always be absolutely sure unless you measure.

Looks like a flange in your second picture - it's the thing with the holes.



I believe the older Copals had the same thread dimensions, since changing it would mean older cells would not fit in modern shutters and vice versa.

- Leigh

Just to keep the record straight: as per this SKGrimes page (http://www.skgrimes.com/products/index.htm), the flange/retaining ring threads are smaller on the Copal 3S, and thus the lensboard hole is smaller: 64.1mm vs 65mm.

Charley

ps: Listen to Ken

[Leigh]

... the flange/retaining ring threads are smaller on the Copal 3S, and thus the lensboard hole is smaller: 64.1mm vs 65mm.
I thought he meant the internal shutter threads, hence my comment about lens cells.

What's the shutter mounting thread on the 3S?

- Leigh

[grahamcase]

I definitely have a retaining ring, like you were selling in your post - screws on, has slots for a spanning wrench, and has no holes to mount on a lens board like a flange would have.

I plan to listen to Ken :) I have emailed CRIS cam, as it is late, and I am in Canada. My fingers are crossed I'll have a response when I wake up tomorrow :D

[TheDeardorffGuy]

Thank you for the quick reply, and link! Do I just ask for a Copal #3 compression ring? Are there multiple kinds to consider, or am I looking at an easy thing to ask for?

I pulled Criscam.com out of my head as I used to get copal repair parts from him.
I went to his site and see nothing about Copal Shutters..........I'd still call. He will know. And if he does not SK Grimes has them.
www.skgrimes.com/newcopal/index.htm

[John Schneider]

I believe the older Copals had the same thread dimensions...

Nope.


...since changing it would mean older cells would not fit in modern shutters and vice versa.
- Leigh

Yep. Older Copal 3 shutters (of which I have plenty; e.g., the first batch of Kern 14" GD Dagors) have the same cell thread sizes as the shutter now available as a 3s (M56); a modern Copal 3 for comparison has a cell thread of M58.

[grahamcase]

So, after reading all this and also going to sk grimes site, it seems that there are (and correct me if I'm wrong) two slightly different things we are calling retention rings, or maybe two classes of retention rings: those that need a compression ring, and those that don't. The ones I can find on sk grimes do not appear to need a compression ring, while mine is taller, and I think I see how it works with a compression ring. Assuming this is true, is one method preferable to the other?

[Leigh]

Older Copal 3 shutters (of which I have plenty; e.g., the first batch of Kern 14" GD Dagors) have the same cell thread sizes as the shutter now available as a 3s (M56); a modern Copal 3 for comparison has a cell thread of M58.
Yep. I found that on the SK Grimes site. I was looking in the wrong place.

Interesting differences.

- Leigh

[Leigh]

So, after reading all this and also going to sk grimes site, it seems that there are (and correct me if I'm wrong) two slightly different things we are calling retention rings, or maybe two classes of retention rings: those that need a compression ring, and those that don't.
Only the Copal #3 uses the compression ring, which is just a thick washer with no other features. (The 3S might use a compression ring... I don't know.)

All sizes use a retaining ring, which has internal threads and slots for the spanner wrench. The retaining ring configuration is slightly different for the smaller sizes.

- Leigh

[grahamcase]

Ha! I am home now, and can clearly see how it is all supposed to work together (I think). I think I better understand how the compression ring works. My temporary solution is working, for now, and it will allow me to shoot while I find, and purchase a compression ring.

Thank you all for your help, and the links! I've emailed CRIS cam, but will email SK Grimes as well, and cover all my bases.

[TheDeardorffGuy]

Whewwww.............

[Oren Grad]

Thank you all for your help, and the links! I've emailed CRIS cam, but will email SK Grimes as well, and cover all my bases.

Last time I needed a compression ring for a Copal 3 I got it from Calumet. That was a few years back, and they've scaled way back on LF gear since then, but if you have trouble reaching the others it might be worth a call to Calumet.

[rdenney]

Aside from the separate compression ring for Copal #3 shutters, retaining rings may or may not have a lip that inserts down into the hole. I always buy my lenses used and don't know who makes the retaining rings, but some have lips and some don't. Flat rings want a hole in the lens board sized slightly larger than the threads, while lipped rings require a hole large enough for the lip to insert into.

It sounds as though the Copal 3's lip is a separate ring. It's a heavy shutter and the lenses that go in it are heavy, so they probably wanted to design it to completely fill the hole to keep the lens from sliding around if the retainer isn't tight enough to provide the required clamping force. I don't have any lenses that use a Copal 3, but I've run into many holes for other sizes that had to be enlarged to accommodate retaining rings with a lip.

Rick "who'd be tempted to cut some brass strips from shim stock to fill in the slack, tighten down the retainer, and use the darn thing" Denney

[grahamcase]

Hey everyone, thanks for all your help. I was able to find the ring at a local camera shop for $9! I actually got a second retainer ring along with the compression rng for that price, so I'm doing well :)

Thanks to all the helpful info on here, I knew exactly what I was looking for, and recognized the piece as soon as I saw it.

Cheers!