Finding a Single Condenser Lens

[Michel Hardy-Vallée]

A while ago, I hastily bought a Vivitar VI 6x7 conversion unit on eBay, in the hope of printing the occasional 6x7 negative in my collection. I buy "as is" obviously, and that time, it bit me back.

When the unit arrived, I gave it a cursory look and stowed it away for a couple of weeks. Eventually, once I put it in the enlarger, I noticed that the condenser unit only had one lens. I thought nothing of it, until I realized that the light was not properly dispersed. I remembered condenser enlarger schemas: they always have two identical positive lenses placed convex-to-convex.

The seller did his best to try to locate the missing lens, and after quite a few checks, nothing was found.

I'm left with the following dilemma: either cry a little bit over the lost money, and save to find another 6x7 conversion unit; or try to find a way to add the missing condenser lens.

Is there any hope? Are condenser lenses more or less standard between brands? Does anybody have a spare?

 

[RalphLambrecht]

A while ago, I hastily bought a Vivitar VI 6x7 conversion unit on eBay, in the hope of printing the occasional 6x7 negative in my collection. I buy "as is" obviously, and that time, it bit me back.

When the unit arrived, I gave it a cursory look and stowed it away for a couple of weeks. Eventually, once I put it in the enlarger, I noticed that the condenser unit only had one lens. I thought nothing of it, until I realized that the light was not properly dispersed. I remembered condenser enlarger schemas: they always have two identical positive lenses placed convex-to-convex.

The seller did his best to try to locate the missing lens, and after quite a few checks, nothing was found.

I'm left with the following dilemma: either cry a little bit over the lost money, and save to find another 6x7 conversion unit; or try to find a way to add the missing condenser lens.

Is there any hope? Are condenser lenses more or less standard between brands? Does anybody have a spare?

Found this on the web:

http://www.thorlabs.com/NewGroupPage9.cfm?ObjectGroup_ID=3835&gclid=CK-RquyDk58CFQWTzAod92euMw

 

[Ian Grant]

Back in the UK I have an article on making new condensors for a Durst, basically you buy a lens as in the link Ralph's posted then get a Glass shop to cut to size. The article was more about making the frame tohold the lens but there nothing difficult and it was very straight forward.

Ian

 

[Michel Hardy-Vallée]

I called Thorlabs, and they can indeed cut something according to spec. I was wondering how could I measure the focal length of my condenser? Infinity focus test?

 

[RalphLambrecht]

I called Thorlabs, and they can indeed cut something according to spec. I was wondering how could I measure the focal length of my condenser? Infinity focus test?

Can you not just give them the dimensions? It's a slice of a sphere, the diameter and the height should be all they need!

 

[Barry S]

I think I saved the condenser unit from my old Bogen 67 enlarger. If I still have it, it's your for the price of shipping. I'll check tonight.

 

[Barry S]

The condenser unit I have is 3 1/8" x 3 1/8" x 1 3/4". If it looks like it'll fit your head, I'll gladly send it to you.

 

[Michel Hardy-Vallée]

Barry, here's a schematics of the lens.

http://dl.dropbox.com/u/8959/VivitarVI-6x7-condenser - copie.pdf

I estimated focal length by focusing an infinity object and measuring the distance between the planar surface and the projected image.

 

[Michel Hardy-Vallée]

Can you not just give them the dimensions? It's a slice of a sphere, the diameter and the height should be all they need!

I asked the Thorlabs guy, and the problem is that they need the approx focal length. I presume that's because for the same shape, different types of glass would result in different focal lengths (i.e. because of the refraction index).

 

[Barry S]

Barry, here's a schematics of the lens.

http://dl.dropbox.com/u/8959/VivitarVI-6x7-condenser - copie.pdf

I estimated focal length by focusing an infinity object and measuring the distance between the planar surface and the projected image.

My condenser unit doesn't easily open, so I can't measure the focal lengths. The size is a little smaller--3 1/8" vs 3 1/2", but it might work. It would sure be a lot less expensive than having a custom condenser lens made.

 

[Michel Hardy-Vallée]

Barry, is your lens of the same shape? Can you try to measure the condenser's focal length like I did and see if it roughly fits?

 

[Barry S]

Barry, is your lens of the same shape? Can you try to measure the condenser's focal length like I did and see if it roughly fits?

Michel--My condenser unit is rectangular--it doesn't have the cut off corners. I can try prying it open to measure the focal length. My guess is it will be a similar (but not exact) match. As long as the condenser illuminates the diagonal of your negative, it will be fine. It's not so critical and you can probably either fit the unit as-is or open it and use one or both of the condensers in your casing--although you may need to make a simple spacer.

 

[Barry S]

I managed to pry open the housing and big surprise--the condenser has a focal length between 110 and 120mm. The condenser lens is square with slightly cut corners. Man, I've never had such a hard time giving something away! How about I charge $50? Maybe that'll work better.