Bizarre Lens Defect

[Kino]

I have an admittedly very cheap Atena Tele Rokunar 300mm f5.6 lens that came on a Minolta SR-1 camera which has a very strange defect in the front element.

Ever seen anything like it? I assume it is the Canada Balsam lens cement eroding between the front elements, but I see no evidence of fungus.

Just for grins, I think I might pull it apart and try to re-cement the elements with a clear UV optical adhesive.

Anyone ever tried this?

 

[E. von Hoegh]

Newton "rings" due to separation. Just for giggles, put a decent shade on the thing & expose a couple frames, you'll be surprised how well it works as-is.
edit- the lens likely is cemented with epoxy, balsam usually looks yellowy & crispy when it gives up

 

[Kino]

I might do that: a before and after study!

I highly doubt it will materially effect the "performance" of this lens...

 

[Dan Fromm]

I might do that: a before and after study!

I highly doubt it will materially effect the "performance" of this lens...

Test it before you use it for anything that matters. I have a beautiful, except for very strong Newton's rings, wide angle converter (25 mm to 15 mm) for a 25/1.4 Cine Ektar. Footage shot with it (for test, naturally) captured the rings, was garbage.

Probably not Canada balsam, probably a synthetic cement. From the late '50s through perhaps the early '70s several European lens makers, most notably Rodenstock and Voigtlaender, used a synthetic cement that separated badly. Out of warranty, of course. I have some really horrible Apo-Skopars and a 58/5.6 Grandagon that arrived with magnificent rings of fire. The big surprise is that the Grandagon seems to have healed.

 

[albada]

Canada balsam will melt under heat (in your oven). Other cements might require that you let the elements soak in acetone for a few months.
Anyway, I used UV-curable cement to replace the Canada balsam in the back of a Soviet Tessar-clone. For that, I had to buy (via eBay) a UV-box for curing women's fingernail-polish.
Mark Overton

 

[E. von Hoegh]

Canada balsam will melt under heat (in your oven). Other cements might require that you let the elements soak in acetone for a few months.
Anyway, I used UV-curable cement to replace the Canada balsam in the back of a Soviet Tessar-clone. For that, I had to buy (via eBay) a UV-box for curing women's fingernail-polish.
Mark Overton

Mary Kay?
Methyl chloride dissolves the synthetic cements in a week or three.

 

[E. von Hoegh]

I might do that: a before and after study!

I highly doubt it will materially effect the "performance" of this lens...

Some of those cheapo lenses are pretty good.
I recemented a Kodak R-R with balsam from local trees, my first try a repairing separation. It's still good after 30 or so years.

 

[AgX]

The big surprise is that the Grandagon seems to have healed.

I assume the seperation got complete and, for whatever reason, the slit became too big for interference phenomenon to occur.

 

[Dan Fromm]

I assume the seperation got complete and, for whatever reason, the slit became too big for interference phenomenon to occur.

Good guess, but I don't think so. Remember, I have the lens and, unfortunately for your ability to explain what its doing, you don't.

 

[AgX]

This means what? That you saw the patch gradually becoming smaller over time?

 

[Dan Fromm]

This means what? That you saw the patch gradually becoming smaller over time?

The rings of fire -- front and rear -- were at the edges and didn't grow. They shrank. There were two silver spots somewhere near the rear cell's axis. They didn't grow, they shrank.

 

[albada]

Mary Kay?
Methyl chloride dissolves the synthetic cements in a week or three.

"Lee UV Nails" is printed on the front of the metal box.
And I'm familiar with acetone and MEK, but I've never used methyl chloride.
Mark Overton

 

[AgX]

Methylen Chloride

 

[E. von Hoegh]

Methylen Chloride

On the label, it says "methyl chloride".

 

[E. von Hoegh]

"Lee UV Nails" is printed on the front of the metal box.
And I'm familiar with acetone and MEK, but I've never used methyl chloride.
Mark Overton

MEK is useful, too.

 

[Nodda Duma]

The rings of fire -- front and rear -- were at the edges and didn't grow. They shrank. There were two silver spots somewhere near the rear cell's axis. They didn't grow, they shrank.

Changes of temperature/humidity can change the air space in the failed bond joint and hence the characteristics of the Newton rings. I’ve seen the phenomena before. No magic self-healing there, unfortunately.

 

[John Koehrer]

On the label, it says "methyl chloride".

paint stripper ^^. Don't forget about it like I did. The glass ended up with a pretty coarse texture.
Wonder if it work for making ground glass?

 

[AgX]

On the label, it says "methyl chloride".

Label is wrong!
Methyl Chloride is a gas not useful as solvent.

We got two chemicals similar in structure, but different in appearance, chemical characteristics and use.

 

[Dan Fromm]

Changes of temperature/humidity can change the air space in the failed bond joint and hence the characteristics of the Newton rings. I’ve seen the phenomena before. No magic self-healing there, unfortunately.

Jason, thanks for the explanation. You'll understand that it was unexpected and a considerable surprise. All this happened a couple of years ago, hasn't reversed itself yet.

 

[AgX]

I recemented a Kodak R-R with balsam from local trees, my first try a repairing separation. It's still good after 30 or so years.

That is true DIY attitude.

 

[AgX]

I have a beautiful, except for very strong Newton's rings, wide angle converter (25 mm to 15 mm) for a 25/1.4 Cine Ektar. Footage shot with it (for test, naturally) captured the rings, was garbage.

That is interesting as one typically expects such artefact being far out off focus. And only would expect two more reflective surfaces.
DOF with small gauge lenses is much larger, but still I am surprised.

 

[E. von Hoegh]

That is true DIY attitude.

Balsam is balsam, same trees. I collected it, let the chunks settle out, thickened it by keeping it warm for a couple days, and it worked well. I'd made microscope slides, so was vaguely familiar with working with balsam; what I needed to work out was a reliable method of keeping the elements centered.
Lens flat on a small surface plate, edges held between two precision ground V-blocks, several days at about 40c for the balsam to set hard.

 

[Nodda Duma]

The edge alignment / v-block method doesn’t compensate for wedge in the elements. Its base assumption is that the optical axis aligns with the mechanical axis, and that both diameters are exactly the same. Commercial optics have really loose tolerances, which is what allowed you to bond them together without degrading optical performance.

Modern doublets are assembled on a vertical chuck with a reflecting laser or interferometer setup to allow the technician to align the optical axes of the elements...that’s the important axis to align. Oftentimes they’ll go back and be edge-ground for installation in a barrel, or one element will have larger diameter than the other.

 

[Mainecoonmaniac]

Seeing from a different perspective. I wonder if the "defect" gives the lens personalty. Maybe it will offer some interesting low fi look that will make the lens a gem?

Maybe be a photographic Zen Master by embracing imperfection?
https://en.wikipedia.org/wiki/Wabi-sabi

 

[E. von Hoegh]

The v-block method doesn’t compensate for wedge in the elements. Its base assumption is that the optical axis aligns with the mechanical axis, and that both diameters are exactly the same. Commercial optics have really loose tolerances, which allowed you to bond them together without degrading optical performance.

Typically doublets are assembled on a vertical chuck with a reflecting laser or interferometer setup to allow the technician to align the optical axes of the elements.

I'm aware of that; I chose the V-blocks because the diameters are identical within my ability to measure, it was that or nothing.