Fungus or Coating or Delaminating?

[Ozark Wolverine]

Hello everyone. I came across a Computar dL 3.5/65 enlarging lens in a box of other Analog accessories at a Camera store in Syracuse, NY for cheap about 7 or 8 years ago . . . The lens was in it's original consumer packaging and appears to never have been sold or used.

On the inside of the rear element something is funky . . . Image 1 and 2 are backlit with an LED flashlight, image 3 is the reflection of the sky, no backlighting.

 

[koraks]

My guess is separation in a lens group, going by the 3rd image.

 

[mshchem]

My guess is separation in a lens group, going by the 3rd image.

+1

 

[Ozark Wolverine]

+1

That was my first guess as well. Bummer, I was going to disassemble it and clean it. I guess it goes into the trash bin . . .

 

[koraks]

I'd still give it a shot. If it so happens we're both wrong and you can clean it up, you've got a usable lens.

 

[mshchem]

How do the images look?

 

[cowanw]

If separated and you can get the cell out, you might soak it apart and reassemble. you won't notice a difference in use I bet.

 

[Patrick Robert James]

I like the Computars but they all did this. I think every one that I have owned had to be re-cemented. It is cement failure.

Don't throw out the lens. The cement they used dissolves in Acetone so they come apart fairly easily. The cement is a part of the optical calculations so just removing it won't make the lens work properly. It really needs to be re-cemented with an appropriate cement.

The 65 that I have is one of the best lenses I've ever used. Almost keeps up with my Zeiss.

 

[Ozark Wolverine]

How do the images look?

I have not tested it. However, when view from both ends one can see the "Fuzzy" through the lens when viewing a light grey overcast sky. So I am sure it will affect the print. Convince me I am wrong

 

[Ozark Wolverine]

I like the Computars but they all did this. I think every one that I have owned had to be re-cemented. It is cement failure.

Don't throw out the lens. The cement they used dissolves in Acetone so they come apart fairly easily. The cement is a part of the optical calculations so just removing it won't make the lens work properly. It really needs to be re-cemented with an appropriate cement.

The 65 that I have is one of the best lenses I've ever used. Almost keeps up with my Zeiss.

Patrick, you have convinced me to try to save it. Where does one send this lens to have it recemented? I do 35mm and 120 so this lens will work with both.

 

[Ozark Wolverine]

I'd still give it a shot. If it so happens we're both wrong and you can clean it up, you've got a usable lens.

Thanks koraks, I will disassemble it and see what we've got. I have read very good things about this lens so unless it is prohibitively expensive I am going to try to save it. I am currently using a Nikon 5.6/80 and a Nikon 2.8/50 for printing. I have been happy with them for three or four years of printing. But I am just a hobbyist I know just enough to be cringe worthy . . . LOL

 

[mshchem]

Perfect for 127 negatives

 

[Jarno]

The cement is a part of the optical calculations so just removing it won't make the lens work properly. It really needs to be re-cemented with an appropriate cement.

Does it then also matter what kind of cement is used, or is it's primary importance that the group behaves as a single lens?

 

[Patrick Robert James]

I'm sure it matters what kind of cement is used. I ended up using Canada Balsam because I had it and it worked fine on all the ones I re-cemented. Modern UV cements are probably better to use but I don't know what kind to use. I forget what the measurement is called that you need to pay attention to- something diffraction. I guess different cements bend the light differently.

 

[Jarno]

Refractive index maybe?

 

[Steve906]

Norland 60 or 61 I think is the one to get, expensive (£33 / $42 / oz). Also some UV source to set.
It has a relatively short shelf life (keep in dark fridge). Where I worked we used it way beyond the date indicated with no problems. Don't shake before use or you'll be popping bubbles with a pin for ever!