Where to find screw for LF lens?

[joshx]

I recently acquired a large barrel lens which had a "stuck" iris. I took the

whole thing apart, cleaned it with Ronsonol, reassembled it (all 16 blades), and

found that it sort of works. I say "sort of" because every once in a while the

aperture ring sticks.

 

The iris opens and closes fine by itself, but I believe that when the aperture

got stuck the first time, someone tried to force it, and the screw that goes

through the aperture ring and into a groove of the rotating ring of the iris

caused stripping of the latter ring at the edge of the groove. (I don't know the

proper words to describe parts, but hope someone understands my explanation.)

 

Basically, the screw is now too short. If it were longer (it could extend almost

another 2mm into the groove of the iris ring) then it couldn't "slip out" of the

groove and cause the aperture to jam. (There is this extra space; why the screw

doesn't fully extend into the groove is beyond me.)

 

Were there generic screws/sizes for these particular screws in barrel lenses? (I

believe this might be an aerial camera lens.) I don't know the nomenclature for

describing a screw, but it is about 7mm long, with the 3mm at the tip being

threadless and about 1.5mm in diameter (this part goes into the groove of the

rotating iris ring), the next 3mm is threaded with about 8 threads in the 3mm

length and is about 2mm in diameter (this holds the screw in the aperture ring),

and the last mm is the head which is the same diameter as the threaded part

(about 2mm).

 

I've looked up machine screws (the only name I could think of to describe this),

but the ones I have seen are threaded full length. Any help in locating an

appropriate screw would be greatly appreciated. I would prefer to just buy one

somewhere, and only resort to contacting a machinist/repair shop if necessary

(e.g., SKGrimes; I only want a screw and I am not sure any sort of CLA would be

worth it for this lens right now). Thanks in advance!

[joshx]

By the way, are parts of the iris/diaphragm ever oiled/lubricated? I have read that I shouldn't put oil on the blades of the iris, but what about the outside of the ring where it turns/rubs against the metal of the barrel?

[pete_andrews10]

You need to find the proper size of the screw to start with. It could be 2mm x 0.5 (diameter x thread pitch), or 8 BA. Those are the two most likely sizes from your description.

 

Source a screw the right thread, diameter and length, and simply file the threads off the last 3mm at the tip. You can make a neat job of this by holding a flat "needle file" lightly against the threads as the screw is rotated in an electric drill.

 

As for lubricating the iris - don't! If the friction of the collar needs to be reduced, use some graphite from a soft pencil, and blow any excess dust away before re-assembly.

[joshx]

Thanks for the help Pete. I thought about having to file down threads myself, but I still wanted to throw the question out there in the event that somebody knows something I don't (which seems to happen often).

 

And I won't put lubrication near the iris at all. Promise.

[nancy s.]

Not looking at this I have this idea:

Can you drill the hole where the head site to recess the head slightly so that the shank extends deeper? This would be a delicate operation, but it sounds like it would be machinable without trying to find parts.

[joshx]

Nancy, it is certainly possible. I don't have a drill with a metal bit that I think could do the job, but there is no reason I couldn't get one.

 

I also had another idea, in the event that a longer replacement screw isn't readily available: the shaft of my eyeglasses screwdriver that I use for camera/lens 'repair' is narrow enough to fit all the way to the end of the recessed notch in the iris ring. If I leave screwdriver in place I can turn the aperture ring and the iris opens and closes without any trouble. I think I might just buy another screwdriver (cheap eyeglasses repair kit), cut off an appropriate length of the shaft, and superglue it to the threaded part only. The drawback is that this is semi-permanent: it will require acetone and a bit of work to undo the superglue, and cleaning those screw threads (if it ever becomes necessary) won't be fun.

[pico]

Don't mickey-mouse it with superglue and a shaft. You might regret it soon.

 

If you can afford it, spend a few bucks on a tap and drill and do it right. I don't know

where you are, but Ace Hardware here has much that I've needed to replace small screws.

 

Walk in with the part and screw, get the sales guy to help. Tell him you want the drill bit,

tap and screws (get a few in case) that will replace the one you have. Chances are you can

drill the hole out a tiny bit, and tap it using a handheld pin vise. (Pin vise looks like a short

screwdriver handle with a dremel-compatible end to hold very small drills, etc. They have

a wooden handled one that is very comfortable.)

 

A guy can't have too many tools.

[joshx]

Pico, thanks for the response. I didn't know what a tap or die was until I just looked it up. I suppose it comes from having no space to put tools other than a hammer, pliers, screwdrivers, etc in my miniscule NYC apartment. Someday, when I finally leave this place I will have a workshop filled with tools I'll rarely use. Someday...

 

Until then, I will look into the suggestion you presented. It seems like the correct way to permanently fix my lens. However, I am a bit hesitant to do anything permanent just yet. My solution, although very makeshift, is not permanent. I must dwell on this.

 

If anyone else has any other ideas or suggestions (especially where to perhaps find a new screw!), please let me know. Also, if anyone knows the proper names of any of the parts I described, feel free to educate me. Thanks!

[ole_tjugen]

Unless the lens was made in the last 50 years or so, the screw is likely to be completely non-standard. Is it US made? British? German? Fremch? They all had different "standard" dimensions and threads...

[joshx]

Ole, I have no idea where exactly the components were made, as it is a Burke and James lens, and my understanding is that they bought stocks of photo gear and rebranded it with their house name. The lens is a 14-inch f/5.6 anastigmat barrel lens with mounting flange. The serial number on the lens is TT287892.<P>

I do not know when it was made or what it was made for. I suspect it was an aerial camera lens. But that guess is only based on <a href="http://hosting.photo.net/bboard/q-and-a-fetch-msg?msg_id=00996q&tag=">this thread</a>. (I haven't yet tried examining the front and rear lens elements more closely.)<P>

I do know that the circle of illumination is ridiculous: I 'mounted' it on a 14.5"x17.25" cardboard box and only the corners appeared to be in shadow when a viewing screen was in place. And that was wide open focused at infinity! What the usable image circle is I don't know, as I haven't built my 12x20 yet. ;)