fungus - is it that bad?

I joined yesterday after realising the appalling value of my 35mm equipment - bulk of which is plainly worthless. Despite everything functioning as it should and most but not all being in excellent condition. But still it seems (eBay completed listings) it matters not one jot!

Whilst trawling eBay for prices I was stunned at the pitiful prices of lenses infected by fungus!

Now, I'm not really up on lens design or even coatings - but surely logic says that a lens regardless of its brand doesn't "see" the image but simply allows the light path to pass through it's optic train and whereupon it hits the film emulsion a latent image is formed. Providing the lens was focused correctly the image should be sharpish.
I would dearly love to see a comparison of two identical lenses one that is infected by fungus and the other pristine.

I'm sure that severe fungus will no doubt distort the light path and degrade the image - but I can't help but think a lot of this worry is unfounded in all but the most critical of applications.

Would anyone like to comment - I'm here to learn.

Check out this:
http://petapixel.com/2011/06/16/how-dust-and-damage-on-lenses-affect-image-quality/
another take on it:
http://www.lensrentals.com/blog/2008/10/front-element-scratches

I suspect most film cameras and lenses end up as shelf queens for nostalgia buffs, for which external appearance is everything. I use my cameras, and carry one 100% of the time, which can take its toll, so I've always made a habit of buying trashed stuff at steeply discounted prices. As the movie said, oats fresh from the field have one price, but if you will take them fresh from the horse, those may be had considerably cheaper.

I've had a lens thick with fungus, and the veiling flare was quite extreme if you had it pointed it anywhere near a light source (even a bit of sky light). It was quite a nice effect in its way.

I have a few others with a few threads in that I still use, and I can't tell the difference between them and any of my "perfect" lenses.

By the way, it can be quite an education to shine a powerful LED torch through your most cherished lenses and see just how much haze and dust the damn things contain ...

I'm not sure where the photos are anymore, but I used to have a Leica Summar lens w/ fungus, and the photos from it were just terrible. There was so much flare it was crazy. I sent it over to John at Focal Point for a CLA and even though the glass still had marks where the fungus had etched itself into it, the images from it were stunning. You couldn't get that thing to flare if you tried (w/ a good hood on it of course).

I suspect this is how the old myth of Summars being soft came from. Many had a lot of crap in them internally and took soft, dreamy photos. When they're clean though, they're better than a Summicron in my book (although not at f2). The worst thing about fungus is not only the image degradation that it causes, it's the fact that it just gets worse and worse over time as well.

Normally fungus or fog cleans off and you have the lens cleaned and sell for normal price.

Some lenses have sealed cells.

Some lenses are etched by fungus or fog.

Well I agree with both your comments.
BTW thanks for those links mdarnton - a great insight into what's without doubt a grossly overreaction by many.

A little story...
Years ago...97'-98' II did a small stint as a press photographer. Digital was just emerging back then - the wet process was still in every day use. I needed a 35mm lens for my om1, didn't have online sites back then that I remember, nor did I have time to order a used one from mail order - the answer was the local camera shops. In a rush I picked up a 35mm (f3.5??)for £20?? (It's a long time ago bear with me) well the lens was the only one available anywhere local but it had a massive scratch across the front element - the shop keeper was adamant that it would do until he got me a better one and would take this particular one back as part exchange - great service!!

Well I turned up Monday morning and got sent to an all girls school to photograph the seasons new hockey teams.

Used the 35mm, went back to the dark rooms and developed the films then scanned them in and sat down to select which ones to forward for editing...

Boy oh boy!! Were they sharp!! Jeez!!
The texture in the girls hockey uniforms was just razor sharp - I was completely blown away. And to top it all the regular staff photographers actually commented on the clarity of the pictures I'd taken!!

Just goes to show!!

Never did return that lens...but don't know what happened to it either.

Scratches on front element aren't that bad and normally a few scratches wouldn't show in a photo unless you point the lens to the a source of light. Even then it would just be flare.
Scratches on the rear element is another thing!
A few fungus normally won't affect a photo in normal conditions. Again, don't point it into a light.

I have 2 identical Series E 135mm F2.8 lenses. One has fungus in the front 2 or 3 elements, the other is pristine. In fact, I bought it a few months ago still in its original wrap and box.
The fungus lens I keep it apart from all other lenses, so as not to infect the others.
I might do a test of both lenses one of these days.

The shape and condition of the surface of elements in a multi-element lens determine, along with a few other things, how image bearing light is refracted.

Coatings on lenses help improve how lenses react to flare creating lighting conditions.

Fungus:
1) eats away at coatings, and makes them uneven and uncertain in affect; and
2) actually eats away the lens elements themselves, thereby changing how their surfaces affect the refraction of image bearing light.

Fungus also tends to migrate to other surfaces, and can damage them.

Lenses still work when they have been damaged by fungus - just not as predictably, or well.

I've had a 50mm Flektogon that had so much fungus on the outside of the rear element that it had a huge divot etched in it. It still focussed, but the contrast and flare was so much worse than the next copy I bought, one day I'll sell the rest of it for parts.
I also have some others, like a 180/2.8 Sonnar and Cyclop 85/1.5, that have some little wisps of fungus around the edge of the inner of the front element. If anything, it actually smoothens the outside edges of the unfocused bokeh. Or more than likely it does nothing. Either way, they're both damn fine lenses even with the fungus.

In my East Camera Room I have two el cheapo humidity monitors (~$10), one to check the other, they show high and low temperature and humidity for the past 24 hours. I have a third monitor in a glass cabinet where I keep my Digital stuff.

Ideally, you want relative humidity around 35%-45% to prevent fungus. Over 60% for day after day is not good. Also, having dust on the elements is bad: fungus feeds off of dust particles.

Not fungus, but this gives some perspective on how scratches affect a lens: http://www.lensrentals.com/blog/2008/10/front-element-scratches


Steve.