Questions/advice on Apo-Lanthar 300/4.5 on Compur 5FS

[Marco Annaratone]

I just took possession of an Apo-Lanthar 300mm f/4.5 on a Compur 5FS. Everything seems to be working just fine but the lens has this weird problem (the seller quite correctly pointed it out upfront), i.e., a rainbow pattern all around the edge of the front lens (or so it seems). More than "all around" let's say 270 degrees. This "rainbow band" at the edge of the lens may be 1/8 of an inch (3mm, give or take) wide, but it shows only if one tilts the lens: if one looks at the lens straight on one sees just a very clean glass, that's it.

The lens + Compur 5FS did not come with a retaining ring or flange. So I have no way to put it on a lensboard. Any hint on where to get a ring for it? The usual SK Grimes?

Can the Compur 5FS owners spare some sound advice on where to get batteries and share some general precautions on how to use this - I understand - finnicky shutter?

Finally, what is the circle of coverage (infinity, f/22) I should expect from the Apo Lanthar 300/4.5?

Sorry for the many questions, but I am very excited about using this lens, if I can figure out a few things :-)

Thanks a million!

[Ole Tjugen]

I don't have a 300mm, but I do have a 150mm and have had a 210mm.

The "rainbow" you are seeing is most likely light element separation. I wouldn't worry about it. The lens is going to be just fine ("just fine"? It''s going to be just GREAT!) even with it. If it gets worse you may consider having it recemented; the lens is certainly worth it.

I estimate the circle of coverage of my 150mm to be just under 200mm at f:16; That would give the 300mm double that or 400mm. Certainly enough to cover 8x10" with quite a lot of movements.

The shutter I know nothing about; I've managed to avoid them thus far. I'd much rather have a Compound #5 - which incidentally is an alternative for your lens.

[Hugo Zhang]

Marco,

Ole is right about the "rainbow" on your lens.

Apo-Lanthar 30cm covers 8x10 and could become your favorite lens even it is very heavy. Expose a few negatives and you will know what I mean.

I got my flange from SK Grimes.

Hugo

[Marco Annaratone]

I went to a reputable lab and what they told me is pretty much as follows:
1. To glue the lenses back together it is necessary to unglue them first :-)
2. The above process requires a lot of heat
3. The main issue they had in the past was a (severe) yellowing of the lens, that may turn after surgery into an exotic paperweight (right now the lens is very clear, except for the rainbow effect on the extreme periphery).

Their advice: do not do anything. If the problem worsens or the usable circle of coverage turns out to be too small, reconsider surgery. But for the time being: have fun with the glass.

Which is pretty much what Ole said, btw. Question: can someone explain to me what this (potentially) catastrophic yellowing is about?

Thanks!

[Ole Tjugen]

"Catastrophic yellowing"?

The lanthanum glass the Apo-lanthar gets its name from contains a little bit of Thorium, too. With time the radioactivity of the Thorium will cause the glass to turn brown - the so-called "yellowing".

This can be cured by exposing the glass to UV radiation - leaving it on a sunlit windowsill will do.

Alternatively leave it as it is (if it's turning yellow), and just think of it as a built-in weak warming filter. That's what I do with my 150mm Apo-Lanthar. I don't consider it catastrophic at all!

[Marco Annaratone]

I think I explained myself poorly.

The lab told me about the risk of severe yellowing when ungluing and then recementing the two lenses together, regardless of the specific lens undergoing surgery. In fact they pointed me to some Germinar lenses being completely ruined in the process of trying to fix them.

Maybe they are all wet or I am too dense (or both...), but their worry seemed to have nothing to do with the Lanthar per se: it was a general concern.

[Gene McCluney]

I think I explained myself poorly.

The lab told me about the risk of severe yellowing when ungluing and then recementing the two lenses together, regardless of the specific lens undergoing surgery. In fact they pointed me to some Germinar lenses being completely ruined in the process of trying to fix them.

Maybe they are all wet or I am too dense (or both...), but their worry seemed to have nothing to do with the Lanthar per se: it was a general concern.

Cemented Lens elements can also be separated by soaking them in various solvents. I am surprised they do not know this.

[Ken Lee]

The rainbow effect is caused by the natural refractive/interference properties of light, when it encounters a "thin film". We can see this when a small amount of motor oil is place on water.