Saving Pentax-M

I’ve just spent pretty much the entire day restoring a Pentax-M 50mm f/1.7.

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Fungus-free!
I not able to do much moving about at the moment and so, rather than mope around and feel sorry for myself all weekend, I thought I’d spend an hour or two doing this. Lesson number one: estimate the time required to clean and restore a lens as bad as this was and then multiply it by three.

The lens arrived this morning from a well-known auction site and my expectations were fairly low from the start; it was at a buy-now price which was about half that of most others, with no real description to speak of and no way to see close detail from pictures. This was a cheap gamble and I was expecting to do some work on it, but I wasn’t quite prepared for the state of the thing when I examined it. Not that it needed close examination to see that it was completely infested with fungus – the worst I’d ever seen.

The outside barrel wasn’t too bad; a little grubby but easily cleaned. The elements, though, looked completely stuffed. Just about every glass surface inside and out was covered in masses of threads and patches of mould. Nasty! I’ve had success at cleaning fungus from elements before but I have to say I was close to giving up on this as it was so badly affected throughout. Pretty much unusable, optically.

OK, so it may take more than an hour, I thought. More than two, even. All in all, it took about six hours! Was it worth all that time, considering price difference between this one and a good one? Well, yes and no but I favour the “yes” because it gave me a project to do whilst unable to go out and, more importantly, I have saved a now-decent lens from the scrapheap. Make do and mend!

Often, it’s said that fungal infestation of lens elements is the end for them: the fungus etches into the coatings and, sometimes, the glass itself, causing irreparable damage. Up to now, though, I’ve been lucky as I’ve been able eliminate fungus on a few old lenses without leaving much permanent damage, if any at all. This lens turned out to be no exception but it’s been the most laborious lens-fix I’ve ever done, without any mechanical fixes, even, as everything mechanical worked perfectly. It was necessary to separate all of the individual elements and clean all surfaces which is very, very difficult to do because, even with fungus all gone, getting truly crystal-clear cleaning results on internal surfaces, without any smears whatsoever, takes a lot of time and patience. Still, time is what I’ve had and it did pay off in the end. Lesson number two: do not use a blower bulb with a metal end too close to an internal surface because one small slip could result in a permanent coating mark. Doh! Thankfully tiny and won’t affect anything but still, a swear-inducing moment.

I wish I’d taken a “before” picture but I honesly didn’t think I could salvage it so didn’t bother. Believe me, it was horrendous! Here it is again, in its fully restored state (I restored the filter, too, which was also in a very sorry, mouldy state but it’s a nice Hoya one so worth saving. I had to take the glass out of the frame to clean everything but all’s well and clear with that now, too):

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When elements and groups are taken apart and re-assembled it’s always a good idea to check for any misplacement or decentring as a tiny amount of misplacement of any individual element can have profound optical consequences. I’m glad to say all is well, wide-open and at high magnification (digital test). I replaced the front name ring and cleaned the barrel exterior thoroughly.

One clean and clear lens to add to the collection, and a very good one at that. I could now sell it for twice the amount I paid but it’s definitely a keeper.

Author: jrhughes

Camera geek and consumer of wine.

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