separation on lens

[atelier7]

hi, my summitar is being serviced and i've been told there's some separation on the edges. what does that mean? and what is the impact?

 

[richard_l]

It just means that the cement which bonds together a couple of lens elements has deteriorated near the outside edge. (If you see a lens description such as "5 elements in 4 groups" it means that 2 of the 5 elements have been glued together, a standard practice in modern lens design.) Depending on the extent of the separation, there may be a little more tendency to flare and the contrast may drop a bit, particularly when used wide open. Stopped down enough that the diaphragm covers the separated area, I think it should work just fine.

I have a Summarit which looks pretty bad when I shine a flashlight through it (as if someone had spilled dirty shellac all over one of the elements), but the images are fine, except that I have to be careful about flare.

 

[varjag]

Could it be the coating peeling off?

 

[richard_l]

Could it be the coating peeling off?

It might be. I may send it to John Van Stelten (Focal Point) and find out.

 

[SolaresLarrave]

I have a lens with what the honest vendor described as slight separation. A visit to his website and consequent correspondence with John Van Stelten informed me that it can be repaired (although the reparation is risky). It'll cost me $250, and it'll take about a month.

There you go! 🙂

 

[Bertram2]

it means that 2 of the 5 elements have been glued together, .

Stupid question:
Are ALL groups in ALL lenses cemented ot or are there examples where the elements are screwed into each other only ? Did not know that groups are glued.
Bertram

 

[SolaresLarrave]

Not a stupid question, Bertram. And yes, lens elements are glued together.

As always, there'll be those who see in lens separation something worse than cancer, and there'll be always those who, like me, see it as a problem that can be repaired. It's risky, yes, but then so is life.

 

[Sonnar Brian]

The lens elements are glued together in a group. I used index matching oil as a substitute on an inexpensive lens with a pair that had become separated. Without something in between the two glass surfaces, you get "Newton's Rings", a rainbow effect across the two glass surfaces. The surfaces are very closely mated, but not perfect. Something must be used to match the index of refraction at the boundary.

 

[Bertram2]

Without something in between the two glass surfaces, you get "Newton's Rings", a rainbow effect across the two glass surfaces. The surfaces are very closely mated, but not perfect. Something must be used to match the index of refraction at the boundary.

You answered my question perfectly, exactly THIS is what I thought about !!
If the surfaces do not fit 100 % this must cause trouble in the areas where room is left for air, no matter how marginal that room might be!!
Thanks for explainin ,
Bertram