[PacificCanuck]

A while ago my wife and I were browsing around a camera store, and an old Pentax M 50mm f1.7 caught her eye. We checked it out, asked the salesguy if it was in ok condition, and he said yes. Checked it out a little, seemd ok to us - our first time buying a used lens, didn't really know what to look for. Price was ~$60CAN, which seemed pretty good.

Been a great lens! Really enjoyed using it, takes very nice sharp pictures. Has been a real joy learning to use a low aperature, manual lens. But a while after I bought it I noticed that there are some 'clouds' on one of the interior lenses. Hard to notice when both caps are off, but easy enough to see it with the front cap off, and tilted at just the right angle. It looks to my primitive eye to be one glass layer below the front glass. From reading, I guess that there is (or was) some fungus, whose acid scratched the lens a little.

I'm not really concerned with image degregation, I haven't noticed it in any of my pictures. (Maybe my photo skills are the limiting factor :-). ) However, I've heard that any lens with fungus should be maybe gotten rid of, or kept away from all other lenses since the fungus can spread. I don't have any very valuable lenses, the DA18-55 II and a DA50-200, but nowadays whenever I put the M-50mm on I get a little twinge... is a fungus spreading to my other lenses? to the camera body?

I'm wondering what, if anything I should do about it... Is that really a fungus? Images of fungified lenses I've seen online look more like a spider's web than mine does. Even if it is a fungus, the lens has had a long lifetime. My fungal friend may have came and went 10 years ago...

Should I relax and keep using it? Irradiate it? Boil it in oil? Toss it, using fungus to explain to the wife why I need to buy a FA-43 Limited?

Attached a picture of the lens, and a recent picture taken with it.

Any advice much appreciated,
David

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[JeffJS]

Usually, Fungus will have more of a spiderweb pattern. At least any I've ever seen. That looks more like cleaner residue left behind due to the circular type pattern.

[szurinaga]

I concur with JeffJS. But still a mark like this isnt likely to degrade picture quality, an old friend of mine once told me that you'd be surprised how much can be inside of a lens before it affects your photos.

If what Jeff describes starts to appear in an alarming quantity then you might want to take it to a professional photo store that can fix this. I've even heard that the UV rays from direct sunlight is enough to kill some fungus in lenses.

In my amateur opinion, keep on shooting! But try avoid touching or cleaning front or rear glass elements with micro-fiber cloths or lens tissue unless necessary

[macTak]

It could just be some light haze (from the helicoid grease) or some sort of mark caused by water (condensed humidity, or perhaps someone opened it up and didn't clean the element very well). Anyway, it doesn't look bad so I really wouldn't worry very much. My opinion is that if it's only visible from just the right angle, then it will have a minimal impact on image quality.

[PacificCanuck]

Glad to hear it doesn't seem like a fungus, I'll rest easier using this lens now. Really appreciate the advice from some more experienced folk, I'm really new to SLRs and lenses.

Thanks!

[Marc Sabatella]

BTW, this would have been more apporpriate for the Lens forum. I didn't notice it before now, but I'm going to go ahead and move it.

[jjdgti]

You may want to give it a shot to clean it yourself. I do not have the lens diagram, but you can find some instruction on how to clean such lens. I have clean some F lenses with good success. Some I have to send them to an expert.