Lens-cap STUCK on old Jamin-Darlot -- advice for removal?

[Kiev]

Hello All!

First time post from new member with request for advice: I recently acquired an old Jamin-Darlot cone centraliser, portrait/landscape (vis a portrait/vis a paysage) lens, c. 1860. Looks to be in good condition, mechanism works smoothly; but the lens cap is stuck, seemingly impossible to remove. In my research I've been unable to determine if the cap is threaded or simply a push-on sleeve. Glass appears to be in pretty good shape, but I can't be sure until I can get the cap off and see through the barrel. (See pix below.)

Any thoughts, advice, ideas, or suggestions on how best to proceed with lens-cap removal? Or perhaps recommend a professional service that might be better equipped to effect removal? (I suspect that the cap is not threaded, and it's merely the 150 years of patina and gunk that's frozen it in place, so maybe with the right tools . . . ? )

Many thanks in advance for your time and expertise! Great forum here; learned a lot already!

Kiev

[goamules]

I've never seen one on the rear. But have seen lots on the front, and I have one. They are just a friction fit. Try gently heating it up with a hair dryer. Then grab with a rubber grip pad, and try to gently turn it a little while pulling. Don't unscrew it counterclockwise! You don't want the rear element unscrewing and coming off in the brass cover, or you'll never get it out.

[Kiev]

Hello, Garrett --

Ah-a! So, at some point somebody must've forced the lens-cap onto the rear of the lens; that's probably why it's stuck: capped on the wrong end.

In any case, your idea intrigues me; just might work, too! But will the heat adversely effect the glass . . . ? Meanwhile, it's very helpful to have confirmation that it's a friction fit cover -- many thanks for that infomation!

Now when you say counterclockwise, the orientation is when looking down on the cap, correct?

Kiev

[Steven Tribe]

I use heat to loosen brass on a regular basis and there is absolutely no problem with Garrett's solution.

Let's hope the cap hasn't been forced on to cover up some defect!

My approach would be to drop the gentle warming, but go over to a small blow touch. The cap is very thin with a super fast conductivity of heat and will be over 100 deg C in seconds. And the cap provides automatic projection from stray heat reaching the lens surface. I would spray with impregnating fluid, both before and after heating (if it doesn't come of first time) - a few small flames, and fumes, won't be of consequence.

[Regular Rod]

I use heat to loosen brass on a regular basis and there is absolutely no problem with Garrett's solution.

Let's hope the cap hasn't been forced on to cover up some defect!

My approach would be to drop the gentle warming, but go over to a small blow touch. The cap is very thin with a super fast conductivity of heat and will be over 100 deg C in seconds. And the cap provides automatic projection from stray heat reaching the lens surface. I would spray with impregnating fluid, both before and after heating (if it doesn't come of first time) - a few small flames, and fumes, won't be of consequence.

+1, a cook's blow torch is about the right size and intensity. Circular wafting is the way.

RR

[alex from holland]

Never seen a cap at the back of a cone lens.
There is only just a few mm where that cap could hold on the lens. so it makes no sense to mount one
You should be able to take of the black back part (cone). This just to have a look inside.

again, where that cap is on, there is only a few mm to hold it.

Alex

[DrTang]

hammer
















hahhah - just kidding

[Jerry Bodine]

I just stumbled into this thread. Pardon my ignorance, guys, never having seen such a lens. But, looking at the first pic, it seems to me that the cover is cylindrical and is inserted into the INSIDE of the rear element (cone). So applying heat to the cover would only make it tighter, in which case it would be more sensible to apply COLD (maybe ice cubes in a ziplock bag) to the cover to shrink it and get it to release, while grasping the "grip surfaces" on the cone and cover to wiggle it off. Or not!

[Kiev]

Thank you all for your input! I've provided a few more photos of the lens to better show the cap and elements in detail. (See below.)

Steven: I think heating the cap will work, but using a torch seems a bit overkill -- I'd hate to inadvertently damage the glass! Hopefully, the cap will slide loose with less extreme measures. In any case, I can try with a conventional hair-dryer first, and then go up from there.

RR: Ditto.

Alex: I believe you are correct. I've seen pictures of similar assembles, and the lip didn't appear that wide -- it's amazing how tight a tension just a few millimeters can exert on that cap!

Jerry: The cap is definitely over the end of the opening. In fact, it was slightly cockeyed when I found this lens; and while I am unable to twist it off, it did tap down easily enough into a flush position (hence I suspected this was a case of stripped threads).

DrT: Right.


Meanwhile, I've contacted S.K. Grimes about cleaning the glass lenses. They're willing to have a go at the cap, as well; but I'd prefer to get the thing off myself so I can properly determine if the lenses are worth investing in a pro cleaning. Will keep you posted . . .

Again: Many thanks for your assistance!

[Steven Tribe]

Thank you all for your input! I've provided a few more photos of the lens to better show the cap and elements in detail. (See below.)

Steven: I think heating the cap will work, but using a torch seems a bit overkill -- I'd hate to inadvertently damage the glass! Hopefully, the cap will slide loose with less extreme measures. In any case, I can try with a conventional hair-dryer first, and then go up from there



Meanwhile, I've contacted S.K. Grimes about cleaning the glass lenses. They're willing to have a go at the cap, as well; but I'd prefer to get the thing off myself so I can properly determine if the lenses are worth investing in a pro cleaning. Will keep you posted . . .

Again: Many thanks for your assistance!

Warming the edge of the thin brass cap with a flame for a fraction of a second is the best way to create a marked temperature differential between cap and the thicker brass underneath. This will loosen the cap. Warming slowly with an air blowing system will ensure that the whole assembly (including the two rear lenses!) will gradually warm up with very little temperature differential between the end section and the cap.

I am not sure what you mean about "cleaning .. pro cleaning"? There is no cleaning process that Grimes can do that you cannot do. If there is mechanical damage on the rear pair edges or scratches on the final rear surface - then they will always be there. Mostly likely with this model is advanced edge separation with the front achromat - but this is easily solved without bothering Grimes and the others.