Re-cementing lens elements question.

As far as I understand, lens centration is more important than end thickness, for image quality.

If the thickness is not the same after cementing, the end effect is to change the focal distance.

If you change it a lot, you may have to reset the lens flange focal distance, which typically involves a shim.

For an SLR, it may not make any difference, depending on where the new focal point ends up. e.g. if it can't focus to infinity any more, you'll likely need to move the entire lens head closer to the film, which may translate to a thinner shim.

I don't recall the tolerances, but I would look at the lens formula 1/f = 1/d1 + 1/d2 as a guide

regards
Vick

 

I've done two Nikon 5cm f1.1 rangefinder lenses (the rear doublet) and one Nikkor 5.8cm f1.4 lens. Lots of fun.
I've also repaired about three Leica M3 rangefinder prisms that separated.

All successful.

Vick

 

Why not on three points? You know, a three-legged stool never wobbles.

 

I know what oak is
I know what a letterpress is
I know what furniture is

What is "oak letterpress furniture"?

 

it is letterpress oak furniture.

 

You might look on the Large format website, Steven Tribe has written about recementing lenses in a few Forum threads.

Ian

 

I know what letterpress furniture is. You're kidding right?

This is what to use. You won't need the clamps though - http://www.mcmaster.com/#starrett-v-blocks/=nl80kb

 

Tolerances in optics are not measured with a micrometer but in wavelengths of light. They're worse than watches. But - if you botch a recementing job with balsam you get all the second chances you need. You could make V-blocks on a milling machine, lapping them to the final finish - and they'd be just as good as the Starrets for recementing. For this purpose the vee need not be precisely 90 degrees, it just needs to be straight, smooth, and at 90 degrees to one end of the block.

 

Not neccesarily. I'd use a surface plate for this because I have a small one. I'd place the cemented pair flat on the plate, if both surfaces were convex I'd make a ring and lap it flat/parralel. Use the V-blocks against the edges to keep everything centered, and give the balsam a few weeks at least to set. Personally I'm hesitant to use UV curing cement, it's much more difficult to decement the lenses.
I recemented a R-R on an old Kodak folding camera using balsam from local trees. The camera was my mother's father's, I now have pictures of her taken with that same camera over a span of almost 80 years.

 

Now I know you're joking. Right? You're joking, right?

 

You could use the article I wrote: http://www.fotomozaic.ro/
Your tongue is probably sensitive enough that you won't need to worry about clamps or jigs. At least mine has always worked just fine for work like this. Students of dentistry learn early just how tiny of a difference in height the tongue can detect. I offered to send Canada Balsam to anyone who needed it in another thread weeks ago. When that is gone I also have some very high grade rosin (some from Honduras, some from China, and more from other places). It will work just like Canada Balsam, actually.
If the element is etched on the front surface, you will have a much more expensive and complex repair. Good luck, however.
Jon

 

Do you have any clue what that entails? You can always do it yourself...

 

I was afraid of that. The last time I checked into having one polished and re-coated it was about the same price. I couldn't justify it either...
Jon

 

Polish and recoat is obviously expensive. If you're going to trash it anyway, you have nothing to lose by trying plastic polish. I have used it for removing haze that wasn't touched by any solvent I had. Only Acetone, Alcohol, Ammonia and some common household stuff.
Astronomers will grind their own lenses by hand, Their polishes can go from fine to huh? Don't worry about changing the optic unless you use power tools.

I use two pieces of 1" angle aluminum with rubber bands to hold it in place. It holds the glass in alignment very well.