Adapting a Projector Lens

[Ari]

Turning to those who have experience mounting oddball lenses to film or digital cameras. I know nothing about this, and don't want to make a mistake I can't correct.

I have the lens, the helicoid and the camera-to-helicoid adapter.
While doing a test mount, I found that lens worked at infinity when it was about halfway into the helicoid.
There are threads inside the helicoid, but the lens barrel is about 1mm, or 1.5mm, too small. Also there are no threads on the lens barrel.
I'd like to be able to attach the lens securely to the helicoid, and was wondering what people use in these cases.

I could:
1. go to a machinist and make an expensive adapter, then add a thread the lens barrel
2. use thick tape or bicycle inner tube and jam the lens into the helicoid - tried this and it works, but it won't last for too long before the lens starts to tilt or droop

I was wondering if there's some kind of putty I can apply to the outside of the barrel, and mount that to the helicoid. The putty would harden and keep the lens securely in place.
Plumber's putty? Some other magical compound? Other methods I don't know about?

Any suggestions greatly appreciated.

[Daniel Unkefer]

I use JB Weld to attach lenses in certain cases. Of course I'd consider it to be mounted permanently. I mix it up and apply it with flat wooden toothpicks

[Greg]

There is a focusing helicoid extension tube made for the Pentax 67. Also regular extension tubes. I used them with a rear camera adapter (Pentax67 to Nikon). Then got some 67 body caps and easily mounted barrel lenses into them with either JB Weld or a glue gun.

[pgk]

i have used this for a variety of tasks when a putty was needed: https://www.milliput.com its mde in North Wales though and I don't know if it will be easily available but via the web it may well be.

[Ari]

Thanks, everyone.
I have both JB Weld and hot glue here.
PGK, I can get Milliput but it will take 2-3 weeks for it to swim over from the UK.
That's the material I really had in mind, but JB Weld should work just as well. Thanks.

[nerologic]

Hot glue is reversible, at least. If it were me, I’d 3D print a spacer that allowed for a nice friction fit to the lens barrel/helicoid thread. But takes a bit of fiddling and a printer to trial-and-error with.


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[Greg]

I can get Milliput but it will take 2-3 weeks for it to swim over from the UK.

Amazon carries it on this side of the ocean. Just south of you in Connecticut it can be delivered is just a few days. I've never used it but a friend who builds models prefers it over JB Weld.

[maltfalc]

black felt from your nearest craft store and a bit of double sided tape.

[Ari]

Thanks for the suggestions.
I epoxied some hard plastic to the lens barrel as a spacer. Fits snug.
Tomorrow, I'll hot glue the whole thing to the helicoid.

[Ari]

Thanks to everyone's help, the lens is now mounted and some test shots were taken.
These are JPGs, SOOC, no processing at all. I really need a hood for this lens.

https://www.flickr.com/gp/zsari/Y37701

The lens is a Soviet-era KP-35 120mm f/1.8.
Shot on the GFX, that translates to a 95mm f/1.4