[Leica] 90 Summicron (Canada): still front-focussing!

[DANTE STELLA]

Sorry for the backwards information; I read your email wrong the first time and somehow concluded you were experiencing the usual back-focusing. Scotch tape and varnish fix back-focusing, and they are primarily an accommodation. The long-term fix is to change the master focus of the lens (i.e., the position of the optical unit).

A little bit of front-focusing is necessary with that lens due to the focus shift when you stop down. If you set the lens to be right on target at f/2, it will back-focus for a couple of apertures. 

Either DAG or John can fix it. DAG might be cheaper, but it could take longer.

Dante

> On Jan 7, 2017, at 04:21, Peter Cheyne <peter.cheyne at gmail.com> wrote:
> 
> Before Xmas, I sent my 90mm Summicron to a repair-man in Japan to fix the
> front-focusing problem. By front-focusing, I mean that when I the
> rangefinder makes it look like the lens is focussed on the eye, the focus
> of the lens is actually on the tip of the nose, or even a little closer to
> the lens. The repair-man said a few days ago that he took the lens
> completely apart and couldn't come up with a way to fix it!
> 
> It's back in my hands today, and, as the man said, it's still
> front-focussing.
> 
> I tried Dante Stella's suggestion of adding Scotch tape to the focus cam,
> intending to add 3 or 4 coats of nail varnish if that helped, but the tape
> only increased the front focussing problem. Am I right to deduce from this
> that making the focus cam protrude a little more (by, say, adding nail
> varnish) will bring the focus nearer? Here is a photo showing where I am
> putting the Scotch tape:
> 
> https://flic.kr/p/PHj5ho
> 
> Without the tape, the lens is front-focussing about 2 or 3 cms from about a
> 120 cms away. With the Scotch tape, this becomes worse, front-focussing by
> 4 or 5 cms.
> 
> The repair-man in Japan was recommended by a colleague who also uses
> Leicas, but he is stumped at how to correct this lens. I asked Leica Japan
> too, but they say they can't correct lenses that old, and don't have the
> parts. I didn't know you needed new parts to calibrate a lens. I suppose
> that's a stock answer for anything to do with older lenses.
> 
> So, I don't know what to do. Am I not properly understanding Dante's
> suggestion? Should I send to someone in the USA, such as Dan Goldman? What
> is his turn-aroud time like, and is there anyone a little faster but still
> competent?
> 
> Still looking for advice!
> 
> Peter
> 
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