broken len element in an old brass lens

himself · May 12, 2013

Mornin'

I recently bought a 14" projector lens from an old magic lantern cheap off ebay, it was a bit banged up and dirty, anyway...

I managed to take it apart and clean it up, the brass cleaned nicely and except for a few stubborn marks looks good, the glass (which I expected to be a bit of a horror show) also came out spotless and except for a couple of chips near the edge on the rear elements was usable.

So I was happy, until, when tightening the ring on the rear elements there was a crack, crack went the element, and in half, broke clean in half.
Now I have a lens with 2 good elements and a decent body, but one, one that's now 2.

So is it worth trying to replace it?
Fix it?
Sell it?

Use it as a door stop?

Dafydd

Ian Grant · May 12, 2013

Give it away to someone who can use the barrel and bits . . . . .

Ian

bernard_L · May 12, 2013

You did not tell us did you intend to do with it?
Suggestion:
Glue the two pieces together. I would do it with UV-curing glue (need sunny day); do not use instant glue. Before you expose to sun, make sure they are precisely aligned, using the match of the crack surface and checking the surfaces and edges match.
Then:
- Either use as-is; at least do a first test
- Or, if you think you see objectionable flare, cover the region of the (glued) crack with a thin line of black paint. All you will suffer is a small loss of effecitve aperture (plus diffraction by the edges of the black region, but this should be negligible wrt te native geometrical aberrations).
When you finally re-mount the lens, use some foam or other between the ring and the glass; three small pieces in a triangle should be OK. Whatever method you use, make sure you preserve the centering as per the original design.

himself · May 12, 2013

that would be a further option...
but I'm hoping someone with the bit I need will come along and give theirs away to me

himself · May 12, 2013

bernard_L said:
You did not tell us did you intend to do with it?
Suggestion:
Glue the two pieces together. I would do it with UV-curing glue (need sunny day); do not use instant glue. Before you expose to sun, make sure they are precisely aligned, using the match of the crack surface and checking the surfaces and edges match.
Then:
- Either use as-is; at least do a first test
- Or, if you think you see objectionable flare, cover the region of the (glued) crack with a thin line of black paint. All you will suffer is a small loss of effecitve aperture (plus diffraction by the edges of the black region, but this should be negligible wrt te native geometrical aberrations).
When you finally re-mount the lens, use some foam or other between the ring and the glass; three small pieces in a triangle should be OK. Whatever method you use, make sure you preserve the centering as per the original design.

I intended to use it on the camera I'm currently building.
I might give that a go, but would prefer not to glue anything just yet... having said that, I can't make it any worse really.
Tomorrow I'll rig something up to see how bad it effects the performance.

Gerald C Koch · May 12, 2013

The curvature of the lens can be determined from one of the pieces. However you would have to find someone to grind a replacement for you. The lesson learned here is do not be hamhanded when working with lenses.

himself · May 12, 2013

Gerald C Koch said:
The curvature of the lens can be determined from one of the pieces. However you would have to find someone to grind a replacement for you. The lesson learned here is do not be hamhanded when working with lenses.

how would I determine the curvature?

and I think the lesson here is that I'm a stupid boy with stupid hands

Tom1956 · May 12, 2013

Sickening as the thought may be, I'm afraid it's finished.

himself · May 12, 2013

tom, tom, tom, tom, tom
nothing is ever finished until the end... I see what you mean

Ian Grant · May 12, 2013

At the camera fair I go to one stall holder was selling off the spares etc from a retired camera repair shop, about 18 months ago. I had quite a few shutters, there was also a box of lens elements all wrapped in their original wrapping material, some marked indicating what lens.

Another trader bought the entire box, as far as I know he still has them. I can find his details (I won't see him until July) if you're interested - he may be able to help. Let me know the diameter, he owes me a favour, and I can see if he has anything the right size, and then that matches.

Ian

ambaker · May 12, 2013

Have you tried shooting with the lens?

This page has some, to me anyway, fascinating info on lens damage.

http://www.lensrentals.com/blog/2008/10/front-element-scratches

Sent from my iPad using Tapatalk HD

Gerald C Koch · May 12, 2013

himself said:
how would I determine the curvature?

Opticians have a machine that can do this. It is used to determine the prescription for glasses when the original paper prescription has been lost.

ic-racer · May 12, 2013

Just glue it back together. What is the concern, are you afraid the crack might improve the optical performance?

Jonathan R · May 13, 2013

If you can find a histology/microscopy lab, scrounge some DPX slide mountant. It's a thin, clear resin, dries quickly. I believe auto windscreen repairers use something similar. My bet is that if you glue the two parts neatly without too much resin, and carefully cut away any surplus with a sharp knife (glass is harder than steel), you won't be able to see any difference in performance.

himself · May 13, 2013

Ian,

That would be very kind of you, the element has a 50mm diameter and is 5mm thick. I'd owe you a favour then.

Ambaker,

Some good news on there and considering the fact that I have to make a ground glass anyway, this now gives me reason to do it sooner rather than later.

Thanks Jonathan and Gerald, I'll be trying that too.
And to you ic-racer, how very dare you, you sir are outrageous

Fotoguy20d · May 13, 2013

What's the construction? Is it a petzval? If the front is a cemented pair, it'll make a nice meniscus lens with FL about twice the lens, and lots of coverage (and funky effects). I have a set of photos on flickr from a lantern lens minus the rear elements. Before you do anything else, try reassembling the two halves into the frame and shooting through it. You can also paint the broken edges with a sharpie (which is easily removed). And, the attached photos were taken using the shown Goerz Syntor ( a 4 element dialyt type - I dropped the front while cleaning it). There's some ghosting and loss of sharpness but I didnt blacken the edges.

Dan

himself · May 13, 2013

Fotoguy20d said:
What's the construction? Is it a petzval? If the front is a cemented pair, it'll make a nice meniscus lens with FL about twice the lens, and lots of coverage (and funky effects). I have a set of photos on flickr from a lantern lens minus the rear elements. Before you do anything else, try reassembling the two halves into the frame and shooting through it. You can also paint the broken edges with a sharpie (which is easily removed)./ATTACH]

It's probably a petzval (cemented pair at the front, then one larger element, a small spacing and a third thin element at the rear. It looks similar to the Dallmeyer design - but is unnamed)
Using it as a meniscus would be a bit problematic, the focal length would be close to 30", which is way too long for anything I have planned.

TheFlyingCamera · May 13, 2013

Ok- Fotoguy's broken lens example is more extreme even than I was thinking - Jim Galli once had a rare Cooke (or Pinkham & Smith, or some such portrait lens) that the front element looked like someone hit it with a hammer, but it still made excellent images so long as you zealously shaded the front to avoid flare. I think he had it in the classifieds here, or maybe it was a thread - search the forums for it.

himself · May 13, 2013

I just finished grinding my view screen (without breaking it), so after a bit of lunch I'll check out just how bad it is...
problem is, I don't have a before-the-brake to go off, so as long as there are no obvious problems I'll count myself lucky

himself · May 13, 2013

I just made a very quick and ugly box camera and it doesn't seem to effect it to a noticable degree...

lucky me then.

now, to glue or not...

broken len element in an old brass lens

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