Effect of fungus in a lens

[Hollis]

Just wondering but how bad does fungus/haze in a lens have to be to start affecting image quality? I have shot some older lenses that are all scratched and funked up and have never noticed issues but have never shot a fungi-ridden lens.

[ic-racer]

Photographing a high-contrast scene might be compromised by the slightest lens fog, whereas a low contrast scene may be photographed successfully with a hazy lens.

[Jody_S]

Just wondering but how bad does fungus/haze in a lens have to be to start affecting image quality? I have shot some older lenses that are all scratched and funked up and have never noticed issues but have never shot a fungi-ridden lens.

I have. Well I don't know what was inside it, as I still haven't cleaned it. Results are here: Clean it or Leave it? (http://www.largeformatphotography.info/forum/showthread.php?94860-Clean-it-or-Leave-it&highlight=jody_s)

[Math]

Any form of scratches, fungus or cleaning marks will influence image quality. However, if it's enough to be bothered by it is a different question, and differs from person to person.

People often seem to think that if they get a nice image from a scratched up lens, it must not affect the image quality, but that is not true. You just don't have the original lens to compare them.

Fungus however shows up quite a bit faster. Scratches are usually doable as long as they're just single scratches and not all over, and the same goes for fungus. Some tiny spots here and there are fine. All over, and you'll have a not-so-nice lens that is unable to deliver a sharp result. Unless that's what you're into, which can be fun, but there's better ways to achieve such softness.

[E. von Hoegh]

Just wondering but how bad does fungus/haze in a lens have to be to start affecting image quality? I have shot some older lenses that are all scratched and funked up and have never noticed issues but have never shot a fungi-ridden lens.

If it is there, fungus scratch or haze, at all, in any amount, it will affect the image quality.
The real question is, "How much image degradation is acceptable?"

edit - : I didn't read Math's post.

[Ivan J. Eberle]

Are they etched or is this an active new infestation of fungus? There clearly being no lack of good, fungus-free LF lenses in circulation for relatively cheap these days, I'd avoid a fungus-plagued one like, well, The Plague.
Steps to take to keep such fungus from migrating your other lenses, is something rarely mentioned. Since I also work professionally in smaller formats-- requiring tack-sharp optics where any image softening would be disastrous, with lenses more expensive by several magnitudes -- it just doesn't seem worth the risk to keep ones around that might have spores that could travel.

[Bernice Loui]

There are numerous older lenses produced with bubbles in the glass, yet these "defects" have no real effect on the performance of the lens.

I have a 12" Commercial Ektar that looks like some one roller skated on the front element, yet it this lens produces images that are diffraction limited at f16 ( Did not believe this until much testing was done to prove this).

Small scratches do not appear to degrade image quality as much as lens damage to large areas of the optics.

To learn the specific personality of any lens, it needs to tested under many various conditions... beyond what the reputation of a specific lens might be.

Regardless, so many other factors affect image resolution beyond the optics used like camera alignment, ground glass to film holder distance, film flatness in the film holder, focusing error and ......


Bernice

[Hollis]

Thanks for all the info guys/gals, lens purchase is forthcoming.

Second question, anyone ever try and take an infested lens apart and try and culture the fungus? What is it feeding on, the glue? I know that there are so many different types that do odd things (like 'eat' hydrocarbons and some that make biodiesel) so, guess glue is not really that far fetched.

[Teodor Oprean]

It depends greatly on the nature of the fungus and on the film format. Lenses designed for smaller formats (especially 35mm) will suffer more obvious degradation in image quality compared to an equivalent lens for say 8x10.

The least impact is from minor spots of fungus that dissolved a bit of the anti-reflection layer on the front of the first element. Fairly common with single-coated Tessar-type lenses on 35mm and medium format cameras that have been stored in damp basements for several decades. If you're lucky, you merely have two or three "holes" in the coating off-axis. A couple of my Xenar lenses have that blemish. I don't worry about it.

Of moderate severity: If the fungus is a faint haze on an inner element where you cannot reach to clean the glass, that will merely lower the overall contrast. You can use that purposely to add a hint of the dream-like effect of soft-focus lenses. I would expect highlights to attain a slight halo, but I have not conformed this first-hand.

The worst I have encountered is fungus that is almost opaque and has created spider-web-like miniature canyons on the surface of an inner element. That will ruin sharpness for sure. You can tell that the image has no technical quality whatsoever even in the viewfinder, with no magnification aids.

[Teodor Oprean]

The fungus seems to eat both the coating and the glass. The conditions for it to grow are: humid atmosphere, luke-warm temperature and darkness. One Xenar lens I have was afflicted by mild haze fungus internally when I first bought it. I sent that lens at great expense to an expert repair technician who disassembled the lens completely and cleaned every surface very carefully. When I received it, the lens looked stunningly clear, just like new. Six months afterwards, the same mild haze pattern returned. That was quite a shock. I think the type of fungus that leaves holes in the coating is different in nature because I've only seen its marks on the front element, not on any other surface.