adhesive for an old lens part?

[derekmadge]

Hello- this seems to be the closest forum I can find for my  problem.

I have just bought a Pentax screw lens to K mount adapter and dug out my old screw mount Takumar lenses.  The back of the lens- the part that screws down against the (in this case) adapter but would screw down against my old Spotmatic F body, has a slight problem. It's come loose. I can set it in place and everything works fine but I'd like a recommendation, should anyone have experience, for an adhesive that will keep that light metal part on to the heavier lens barrel. My fall-back will be contact cement but I'm hoping someone knows of a thinner, less gooey adhesive.

Thanks,
Derek

[spyglass]

Take a photo and post it so we can see exactly what you are up against.


Spyglass

[derekmadge]

Thanks for your reply. I'll be out of commission for a few days but will post a picture early next week.

[derekmadge]

Hello again-
attached is a photo of the lens. The detached piece is lightweight and I've seen some references on the internet (which is never wrong, right?) to using contact cement in such situations. That would seem a bit thick to me though I suppose with care, it need not be.  Does anyone have any experience with this?
Thanks,
Derek

[blackcloudbrew]

Well, personally, I'd just use a few drops of super glue and be done with it.

[Pacerr]

** Caution **

Super glue (cyano-acrylic) stuff can out-gas a vapor that can 'frost' certain plastics and may leave a film on optic surfaces. It's like that stuff the CSI guys use to vapor-lift fingerprints.

It's worth doing a little research on the web with "hazard, caution, super-glue" tag words anyway,. Although I admit to judiciously using Super-glue on lens barrels myself I've always protected the parts with self-stick kitchen wrap. I HAVE messed up plastic reading glasses with that stuff in the past.

I doubt that lens part's glued as manufactured so I'd look first to see if there's not a loose set screw or other mechanical solution, although I don't see anything obviously exposed on my own Pentax lenses.  Is that a Pentax 135/3.5? Some of my non-Pentax M42's do have screws to adjust the orientation of the lens barrel when seated in the body mount.

H2

[blackcloudbrew]

Good point Hank. I used super glue to put back a thin cover on the outboard end of my cheap Vivitar 28mm lens that fell off. Didn't think too much about it really, but then I never watch CSI...thanks.

[derekmadge]

** Caution **

Super glue (cyano-acrylic) stuff can out-gas a vapor that can 'frost' certain plastics and may leave a film on optic surfaces. It's like that stuff the CSI guys use to vapor-lift fingerprints.

It's worth doing a little research on the web with "hazard, caution, super-glue" tag words anyway,. Although I admit to judiciously using Super-glue on lens barrels myself I've always protected the parts with self-stick kitchen wrap. I HAVE messed up plastic reading glasses with that stuff in the past.

I doubt that lens part's glued as manufactured so I'd look first to see if there's not a loose set screw or other mechanical solution, although I don't see anything obviously exposed on my own Pentax lenses.  Is that a Pentax 135/3.5? Some of my non-Pentax M42's do have screws to adjust the orientation of the lens barrel when seated in the body mount.

H2

Yes, it is a Pentax 135/3.5. It took me years (being rich neither when young, nor now) to get the money to buy that lens! We have been through a lot but it, like me, seems to be falling apart a bit!  I could not see any screws or tabs or any other means to secure that light little piece of metal. I'm an audiovisual technician and am used to looking for tiny screws or other means of "hidden" attachments but this baffled me.

Crazy glue did occur to me but in the past it seems to fail at the most critical moment possible.

I'll do a bit more research- there's no rush. Thanks for your replies.
Derek

[spyglass]

Pacerr brings up a good point regarding super glue. There are a lot of silicone adhesives on the market that will not damage plastic. There holding power is directly proportional to surface area. I do like some two part epoxies and their fast curing times. A little controlled dab can provide tremendous holding power. They are just think enough to act as a minute filler. The fast cure time means you do not have to babysit it too long. The danger is that they are not always compatible with all plastics.

If I was in your shoes and was worried, I would go to your local eyeglass shop and chat up the technician. They have powerful glue that is used to glue plastic lenses to frames. I bet if you worked your charm you would walk out of there with lens glued. Swing back later and drop of a coffee gift card to show your appreciation. 


Spyglass

[Pacerr]

As Spy sez, epoxy is a good choice . . . if you're absolutely sure you're fixin' the right thing, that is.

One trick that helps is to thin the epoxy a l'il bit with acetone if it's too thick (you can try fingernail polish remover in a pinch).  Just mix up a dab of 5-minute epoxy and stir in a drop of thinner. It evaporates quickly and has no practical effect on the strength of the bond.  Experiment on scrap first to get the amount right for the joint.

When using epoxy as a filler, you can also add a drop of modeller's enamel to color the glue joint. I like to put a drop of thick, no-drip epoxy (very carefully!) on the Green Button so to make a small 'tit' to make it easier to find the button by feel.  Use a tooth pick. Some day I'll even remember to add the green enamel first, too. Fluorescent orange is colorful! Use silicon sealer or Silly Putty first for a temporary trial run.

H2