How do you 're-centre' or re-align a lens?

[Xpres]

Specifically a CZJ 20/2.8. My, rather beat up user, example of this lens has been great on 4/3 but last week I gave it a try on my 5D and discovered that it, like many it seems, is slightly de-centred, particularly at infinity. The left 10-20% of the frame has that smeared look while the rest is as I'd expect.
So is this an easy thing to correct or do you need an optical bench and technician? And is it worth it? I can spend time but I don't think it'll be worth spending lots on such a well used example.

[scsambrook]

I think this needs specialised equipment and also some know-how, but that's based on what I was told a long time ago by an optical technician. He might have been looking to maintain his business by putting off DIY work

More seriously, I think it is a job for someone with tools and experience. Maybe try contacting (I think) Balham Optical in London, they seem to be one of the few UK firms who still do optical work like this. I also recall reading that the 20mm and 25mm CZJ lenses are particularly difficult to work on, but - again - I don't know whether it's actually true. No doubt others here will have more direct experience.

As an aside, I once had a 25mm Flektogon that I bought as a loose and rattling disaster for next to nothing from a junk shop. When I took it to the firm I usually went to for repairs the silver haired and kindly proprietor smiled gently and said "If you don't mind, I'd rather pass on this one". That was in the days before computers, let alone eBay.

[Sevo]

Simple answer: You can't. It takes a dedicated lens workshop collimator, and lots of experience or a repair sheet for the lens to align a 20mm retrofocus lens.

I've done improvised DIY with a rifle sight collimator on simple large format lenses (Tessar, Plasmat) - but that won't do on a 35mm wide angle, where offsets are in the order of a µm.

[Xpres]

Thanks for the advice Stephen and Sevo. As I feared! perhaps I was being a little optimistic thinking it might be an easy fix.
Balham Optical sounds interesting. I used to live in Balham so I know where they are, but never knew what they did. But I suspect the price may be too high.
Looks like I'll have to keep it for the crop cameras or pass it on.

[LucisPictor]

My Flek 4/20 has a similar problem. I won't do anything against it, since I don't use it often anyway.

[pat donnelly]

Perhaps you should lay down several adapters in the name of this lens? Seek out the brass ones as they will be less brittle than the aluminium ones.

The idea is to find that the adjustment necessary is merely planar? Bend the adapter accordingly, using vice and small hammer.

Test it out beforehand, by finding which area needs the adjustment, aligning the lens by hand or better by rig. Maybe just moving the lens while on camera will determine whether to move the lugs on the right out or the ones on the left.

What sort of photography was this to be used for? Test it at the typical focal distance used for that and at max aperture.

It is unlikely that the current adapter is at fault, as you have used other lenses with it?

[Xpres]

interesting thoughts Pat - I think I may double check the adapter (it's new) and also put the lens on a film camera just to make sure.
As it happens I mostly use it for people/environmental type stuff so the smeared edge is not critical, but if I'm out I'd rather carry one lens I knew I could rely on for all circumstances.