Help with 28mm f/2 AI rough focusing

[Jack Dahlgren]

All of a sudden I noticed that my lens suddenly started having a very rough/dry feeling when focusing at close distances. The transition is very abrupt and almost feels like metal is rubbing on metal with no lubricant.

It changed from smooth focusing to rough within several hours.

Is the best plan to take it apart and check lubrication and internals?

I read Richard's blog on the 28mm f/3.5 and am wondering if the f/2 AI is similar enough that I could apply the same technique.

Any help or advice greatly welcomed!

[Bjørn Rørslett]

As the 28 f/2 has CRC and the 28/3.5 not, they are unlikely to be identical internally. Another potential problem is the f/2 has its CRC implemented to the front group(s), instead of the more common rear position. There is nothing to prevent you from opening the lens yourself, but keep in mind the inherent dangers of ruining a fine lens.

A sudden change in the lens' behaviour, like you describe,  points more to something coming loose than a lack of grease.

[Jack Dahlgren]

As the 28 f/2 has CRC and the 28/3.5 not, they are unlikely to be identical internally. Another potential problem is the f/2 has its CRC implemented to the front group(s), instead of the more common rear position. There is nothing to prevent you from opening the lens yourself, but keep in mind the inherent dangers of ruining a fine lens.

A sudden change in the lens' behaviour, like you describe,  points more to something coming loose than a lack of grease.

Given complexity of this lens, is there somewhere anyone recommends to bring for repair? I'm in California.

[pluton]

I have been disappointed with the independent camera/lens services that I have tried here in the L.A./Southern California area.  Nikon, of course, won't service many/most older Nikon gear.  I have recently, on a personal recommendation, sent my Nikon 16/3.5 Fisheye Nikkor to APS in Illinois for service, hoping that they can correct the inadequate service it received locally.  I'll be happy to report the results when the lens is returned to me, hopefully within a couple of weeks. 

[Jack Dahlgren]

I have been disappointed with the independent camera/lens services that I have tried here in the L.A./Southern California area.  Nikon, of course, won't service many/most older Nikon gear.  I have recently, on a personal recommendation, sent my Nikon 16/3.5 Fisheye Nikkor to APS in Illinois for service, hoping that they can correct the inadequate service it received locally.  I'll be happy to report the results when the lens is returned to me, hopefully within a couple of weeks.

Keith,
Thanks for the information. I await your report with great interest.

[richardHaw]

Jack, send it to me if you are fine with the risk and waiting time 

Like what Bjorn mentioned, it has CRC. probably similar to the 24mm and 28mm that I worked on. which reminds me, I would like to make a guide for the f/2.8 soon

[Jack Dahlgren]

Jack, send it to me if you are fine with the risk and waiting time 

Like what Bjorn mentioned, it has CRC. probably similar to the 24mm and 28mm that I worked on. which reminds me, I would like to make a guide for the f/2.8 soon

Richard,

Thanks for the generous offer. After reading about front element being used in CRC and Bjorn's comment about something being loose, I started looking at how I would take it apart. As I worked the lens in various positions, it suddenly became normal again as I was turning focus ring with front element pointing down.

Closer inspection indicated that the front element moves (and rotates) when focusing, and when focusing at infinity it is actually closer to the front of the lens. Focusing at close range brings it back slightly, opening a small gap in the front. I have a feeling that something small might have gotten trapped in that gap and was preventing the lens from working correctly. 

This appears to be a lens that one should be careful to keep a lens cap or even a filter on to prevent anything from getting in that gap.

For now, the problem is solved. If it comes back I'll update with the new information.

[Bjørn Rørslett]

The appearance of a small gap in the front indeed is the CRC at work. Thus entirely normal and something to keep in mind when the lens is in the field.

By the way, I've used these 28's with front CRC for decades without encountering the issue described by Jack. I guess it's just a matter of bad luck;  fortunately, apparently easy to solve on the spot.