Adapting a CP-16 viewfinder to an Eclair ACL

[Geffen Avraham]

Hi! I recently acquired an Eclair ACL, a very early model with the original Angeniuex viewfinder. I've heard that CP-16 viewfinder might be made to work with it, and I have two of them lying around.

 

But I've also heard that unlike the NPR, they cannot be mounted without an adapter. Has anyone ever tried to adapt a viewfinder to the ACL like this, and are there any resources I should know of if I try?

Thanks

[Aapo Lettinen]

you need to have a custom mount made for it. but optically it does work, I tested it by handholding the cp16r finder on the viewfinder opening of the ACL.

one could make a usable mounting system by oneself if not wanting to pay someone else to design and machine a suitable mount. a metal lathe helps if you want to make a mount by yourself but it is not absolutely necessary, one could manage with a press drill and some hand tools if necessary

[Aapo Lettinen]

if your camera has the original viewfinder mount then it might work without modifications, I don't have viewfinder mount on my camera so cannot say for sure. Would be easiest if it just screws on in place of the original finder. Without the mount on the camera body it gets tricky and time consuming as new mount needs to be made

[Duncan Brown]

I have checked, and the standard NPR viewfinder (exact same mount as CP-16R) does not fit up to the original ACL mount.  The tube is too big and doesn't even mesh into the hole.

Duncan

[Boris Belay]

The CP Viewfinder has the same mount as the removable Angénieux VF of the ACL (and both kinds of NPR viewfinders).

The Original ACL Angénieux viewfinder is not removable (unless you use tools), so they are not compatible.

The mount for the later ACL Kinoptik viewfinder is also not compatible.

Optically, I'm not sure.  Aapo's hand-held test may be correct, but hard to tell without an actual mount.

Below is the part you would need.

[Duncan Brown]

OK so wait, I have an Angenieux VF on my ACL, and the mount looks exactly like that (well, flipped 180 degrees but I guess it doesn't matter.)  It's the reorientable VF.  None of my CP or NPR VFs fit it.  The inner barrel is too big to fit in the hole of that mount.  Are there more than two kinds of removable VF mount for the ACL?  

Duncan

Edited December 9, 2023 by Duncan Brown

[Boris Belay]

Duncan, I have to believe you on this one and I stand corrected.  Forget what I have said about the ACL viewfinder !

I believe the NPR and CP viewfinders are swappable...

Sorry about the confusion!

Boris

[Duncan Brown]

8 hours ago, Boris Belay said:

I believe the NPR and CP viewfinders are swappable...

That I can confirm.  I had a CP-16R viewfinder on one of the NPRs I sold.  And both my NPRs accept both the Kinoptik (non-orientable) and Angenieux (magically-orientable!) viewfinders.  So I think NPR is the easy world of interoperability with all NPR and CP-16R viewfinders... while ACLs are the land of frustration, where even the two choices of VF don't interchange with each other, and none of them interchange with NPR.  Darn you, Eclair!

Duncan

[Geffen Avraham]

On 12/8/2023 at 5:46 AM, Boris Belay said:

The CP Viewfinder has the same mount as the removable Angénieux VF of the ACL (and both kinds of NPR viewfinders).

The Original ACL Angénieux viewfinder is not removable (unless you use tools), so they are not compatible.

The mount for the later ACL Kinoptik viewfinder is also not compatible.

Optically, I'm not sure.  Aapo's hand-held test may be correct, but hard to tell without an actual mount.

Below is the part you would need.

 

I guess what I will need to know is the "flange distance" for the CP-16 VF on the ACL - mine is an early model that has the original viewfinder. I do have a CP-16R, so if I study the mount on it, I can likely model and recreate it - but getting the flange distance right seems hard.

[Gregg MacPherson]

On 12/16/2023 at 12:58 AM, Geffen Avraham said:

I guess what I will need to know is the "flange distance" for the CP-16 VF on the ACL - mine is an early model that has the original viewfinder. I do have a CP-16R, so if I study the mount on it, I can likely model and recreate it - but getting the flange distance right seems hard.

You may be able to approximate the ideal position of the CP VF mounted to the ACL. This assumes that the optical path in the CP-16R is not significantly shorter than that in the ACL.

- Unscrew the mount plates on the ACL and the and the CP-16R.

- Place the CP VF with mount plate on the ACL body and check the eyepiece diopter range to see if it focuses at any point. Note where it focuses (+ or - diopter setting).

- If you can't find focus, centre the diopter adjustment and try incrementally lengthening the optical path. You can just hold the VF and shift it, that may give an initial idea. You can add crude shims either side of the VF port. If you can find focus, measure the shim thickness.

I'm assuming that the screw holes for the ACL and CP do not magically match. If adding a shim you can use that opportunity to offset the screw holes. The CP VF mount screws to the shim, and the shim screws to the ACL body.

If the existing optical path is too short for the above, you could try adding a + diopter. Cheap reading glasses work for quick experiments. Small + and - diopters are cheap on eBay, if you can find one small enough, and you probably can.

Gregg.

[Geffen Avraham]

Update: I did it. It took a lot trial and error and stupid mistakes, but it does work.

A fellow user named Pavan Deep showed me how - the two parts for locking it into a specific position on the tube are slightly too wide, so he had removed them.

I didn't want to remove them entirely, so I first tried filing them down - it only takes a few millimeters. After a while, I grew impatient and switched from a hand file to a Dremel. This worked - but by hand slipped and cut a bit into the base. I was now worried it would mess with my alignment. It didn't, but I didn't know that.

I tried screwing it on, and it worked! Unfortunately, the image was still blurry, even when I adjusted it as close as possible. I was confused, because it should have worked at this point. To be clear, I should have stopped here. What follows is a record of my mistakes.

What I did not know was that while I was using the focal adjustment with the thumbscrew towards the rear of the finder, there was a small set screw on the front, that could also be used to focus the front tube.

I decided to mill down the base further to get the finder closer. This was a mistake.

I milled off the two locking positioners, and tried going deeper into the base. Unfortunately, it was hard to get a good vise grip on the finder due to its irregular shape, and it slipped and crashed several times. This chipped the base and locking ring, but did not cause any actual damage.

I milled the base shorter, but found to my disappointment that not only did this not fix the focal issue, but I had removed the part that held on the locking ring. It was now loose, and the finder could no longer be screwed on. As this was a subtractive operation, there was no way to reverse it.

I was convinced I had mechanically destroyed the finder, and it still didn't optically work. But then I finally discovered the set screw on the front element, and lo and behold it finally focused! I now was filled with optimism, and resolved to find a way to fix it.

I ordered a small M1.6 drill bit and tap, and milled a tiny hole into the front of the locking ring. I then used a tiny set screw to secure it in place. Worried about it stripping, I have since replaced it with a standard 5mm M1.6 Torx screw (not a set screw, so the head is always outside).

This works great. The ring is now attached solidly and the finder is perfectly focused. The camera is ready for action.

I made a lot of dumb mistakes, and here I provide a record of them so others know what to do and not to do. I also have the long orientable finder for the CP-16, which is far rarer and more expensive, and if I every try to adapt it I will have to be far more conservative.

Edited June 12 by Geffen Avraham

[Geffen Avraham]

Here you can see the little set screw hole.