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.