Saving Pentax-M

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

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):


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.

Nikon lens repair: AF-S DX 18-55 f/3.5-5.6 VR

Here’s the background story: my Father-in-law had his Nikon D60, with 18-55 VR kit lens attached, on his shoulder when he dropped the lens cap. The cap rolled away and was about to disappear out of reach, so he ran to get it. Unfortunately his Nikon slammed against a metal railing, lens first; the lens came away, would not re-attach and there was no knowing how much damage to lens and camera had been caused.

When it came to me I could see that the whole mount was badly warped and that bits of it had broken off. The electronic connector block was hanging out and the surface which is supposed be flat to mate with the camera throat looked like a tiny roller-coaster track. My F-i-l was going to dump the lens but what he really wanted me to check was the camera, to see if it had been damaged by the impact. My first thought, though, was to save the lens from going to landfill.

It helps that I have taken a few of my own Nikkors apart before, for minor servicing/repair, and so I went straight to remove the whole mount assembly. I found the cause of the severe warp: a tiny lug had broken off inside and was lodged underneath the shims that it had previously been holding in place. I determined that I could get by without this lug, since it was too small for a reliable fix and the shims had one remaining lug to hold them in place before the main mount screws secured them. I re-assembled everything as best I could (the electronic connector block was still a bit loose as one of the screw housings had also broken away) and tested the lens. I had to hold it against the camera body, since two of three mount catches were missing, whilst testing AF, aperture and VR. All seemed to work fine – which was good news because that meant the camera was probably OK too. I feel sure that, had the lens mount been the usual metal instead of plastic, there would have been some significant damage or mis-alignment inside the camera. As it was, the mount absorbed the impact, breaking and warping, thereby saving the camera from any serious damage.

OK, so everything worked, but I wasn’t sure where exactly to get a new mount. I looked for similar lenses on a well-known auction site, being sold for parts, but found none. Thankfully I found a company in the U.S. which sells parts for camera repairs and they had the correct mount for about a tenner. So I ordered it and it arrived a couple of days ago.

The repair itself is quite straightforward. The three main screws are removed, as well as three much smaller screws holding the central sleeve in place. There are two more tiny (but different) screws which hold the electronic connector block in place. There will be a number of shims, which will be specific to each lens and they are to adjust the distance between main mount and optics (i.e., sensor to lens distance). The image below shows the lens barrel, the broken mount to the left, the electronic connector block and, in the background, the inner mount sleeve and shims. Click on any image for a larger version.

Two things need to be done before the main mount can be replaced: the sprung aperture guide is removed to be attached to the new mount as is the small connector with sprung pin, shown near the centre of the image above. Now we’re ready to prepare the new mount.

The aperture guide slots into the underside of the mount and the spring is attached:

The sprung pin is attached:

Then the shims are returned. Notice the guide lug at the top right; there should be another on the bottom left next to a screw hole but it’s missing, so the shims can shift around a bit. This gets fiddly when finally putting it all together as the aperture guide needs to be carefully placed on the correct side of the aperture pin in the lens, otherwise the aperture won’t work at all, but getting the correct positioning can move the shims so that screw holes don’t line up.

With the aperture guide in the correct position and the main screws loosely in place, all that remains is for the inner sleeve to return to its rightful place. Care must be taken with the five tiny screws: two of them have slightly larger heads and a finer thread pitch. It is these two which hold the connector block in place, whereas the other three secure the inner sleeve to the main mount.

After tightening all screws (not too tight – this is a plastic mount, after all), a good clean and mount to camera body, all is well. Focus is accurate and VR works as it should. One more saved Nikon lens to add to my count (OK, that makes two in all – but hey).

One final thought: those shims are thin. Some of them are extremely thin. They are of different thicknesses and will have been put together in that combination for this particular lens and its original mount, so it could be argued that they are no longer an accurate set for this lens. Since all my testing shows focus to be spot-on, though, they appear to be good enough.