An odd finding on a 75mm F1.9 large format lens

[Omega]

So, i got some new toys, part of which was a 4x5 fixed focus large format camera.

After having removed the camera from its CRT (it photographs a CRT), i noticed this oddity on the lens. I have no idea yet as to what it is, or how to remove it, so i thought i might as well ask you guys about it.

I should probably add this camera (and the equipment it was mounted to) have been in storage in a technical closet for the better part of 20 years. I would have said its rather dry there (at least it was that way when i picked up the equipment this morning), though some rusty screws point to moisture being present at some point throwout the 2 decades its been there.

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Has anyone ever encountered something like this before?


edit / note:
I will be putting a sample of this substance under one of my microscopes, and see if its a mold or not, what ever it is, its very odd...

[xkaes]

So, i got some new toys, ...

I have a Minolta MC Rokkor 85mm f1.7, but I think you summed it up perfectly -- it's a toy. Save it to hang on your Christmas tree is 10 months.

[Jim Jones]

It looks like mold. Perhaps it will clean up, but sometimes it etches the glass. Exposure to strong UV light can kill mold, although if it is on an internal surface of the lens, getting enough light to all of the mold may be difficult. These lenses were designed to record relatively dim oscilloscope images. Sharpness was sacrificed for high speed. Most photographers aren't satisfied with their performance for general photography.

[Louis Pacilla]

It looks like mold. Perhaps it will clean up, but sometimes it etches the glass.

It's far more common for mold to eat into the lens coating & in my experience it's far less likely to eat into the glass surface itself. This does not mean that on rare occasion a certain type of mold has not eaten into a glass surface itself but 90% of the time it eats the coating. At least this has been my observed experience.

BTW " A lens at 75mm focal length and a max f stop of f1.9 & I bet won't cover a postage stamp at anywhere near infinity focus so is this a true "large format" lens?

[Omega]

It's far more common for mold to eat into the lens coating & in my experience it's far less likely to eat into the glass surface itself. This does not mean that on rare occasion a certain type of mold has not eaten into a glass surface itself but 90% of the time it eats the coating. At least this has been my observed experience.

BTW " A lens at 75mm focal length and a max f stop of f1.9 & I bet won't cover a postage stamp at anywhere near infinity focus so is this a true "large format" lens?


It is indeed designed for 4x5 sheet film. however its not indented for infinite focus, its a fixed focus CRT recording camera. Im quite sure that at infinite it wont cover anything much larger then a APSC sensor or 35mm film slide. However, i intend to use the camera for its intended purpose, i have the rest of the machine that goes along with the camera. The camera is part of a scanning electron microscope im currently working on restoring. I need to run at least 1 sheet of film threw the camera for reasons that are complicated to explain.

Something slightly off topic, i have a rodenstock XR-Heligon 100mm F1.5 lens from a CT, at macro distances it will cover 4x5, yet at infiniity, it wont even cover a APSC sensor. Though it dose look gorgeous even at infinity.

I also sent a few micrographs of what ever is on the lens off to a friend who is a biologist, i will await his opinion on it as well. If anyone here is interested in the micrographs (all be it of low quality, as i did them rather quick, so didn't bother stacking), here they are:

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The scale bars are calibrated.

If anyone is interested in seeing the rest of the camera, i am happy to provide pictures.

The material on the lens feels a bit like salt when i removed a tiny bit using a cotton swab, from the very edge of the lens (since its used at f5.6 in its intended application, it should be fine), what ever it is is really odd, i have encountered lens mold many years ago, and it felt different. I was also not aware there are multiple species of lens mold. So thank you for informing me about this.

I have seen lens mold before, but never one so opaque and large. Thus i came to you guys for help figuring it out.

[LabRat]

Expect low contrast images from it... ;-)

Steve K

[Steven Tribe]

Some/most moulds on coated lens have an unholy agreement with the fluoride in the coating to use a fancy metabolic process which releases fluoric acid as a waste product. This is the absolute best glass etching compound. The patterns are due to variations in surface cleanliness after the last lens wipe it received! Condensation of both mould spores and water is very dependent on "Invisible" surface conditions. You can do experiments with bathroom mirrors with messages written in slightly oily fingers!

[Omega]

Well, this is an interesting development, the stuff on the lens is actually a water soluble salt, not a mold. I did multiple analysis techniques, and had a long chat with a biology professor about it, and we came to the conclusion that it must be a salt.

A quick test with water later, under the optical microscope showed the dissolving of the salt.

Now the question remains, how did this salt end up on the lens. And what salt it is. It certainly is not sodium chloride, as the crystals do not look anywhere close to sodium chloride in shape. I will put it under my electron microscope once its up and running again. Though i don't have the ability to test the sample for elements. (hopefully in the future)

Has anyone ever seen something like this happen to a lens before?

[LabRat]

If it was sprayed with seawater somehow, there might be an answer... (Or a sea coastal environment, on a ship etc)

I have seen equipment used in labs affected by what was present there...

Steve K

[Omega]

This was mounted to an electron microscope for about 2 years, in a dry technical room for around 20 years, the nearest salt water sea coast is about 400 km away, and to my knowledge it has not taken a sea voyage. I will be continuing to look into what it is. I have spoken with a friend about the possibility of X-Ray dispersive spectroscopy of the salt coating the lens. But this might take mouths before we even get around to running the test. Once we know the chemical composition, we can start drawing conclusions as to where it came from.

Good to know that similar things happen in different conditions.

What ever happened, i want to get to the bottom of it.

[LabRat]

The bottom of it would be if the surface was pitted, and if this residue was from the glass itself...

Interesting investigation, but be aware that this type of lens is not great for LF, as it will cover 4X5 at long extensions, and not nearly as sharp as other specialized macro lenses, but it might be interesting for a special effect application...

Tell us what you find out!!!

Steve K