[LargeFormat] Focus Shift on Stopping Down

[Clive Warren]

>The old timers knew all about this. It was normal on lots of lenses.
>I simply refocus. No big deal.
>Mt 12 in 4.5 Velostigmat I have was a NEW OLD STOCK lens when I un
>earthed it. I disassembled it and had it multi coated.
>Imagine my surprise when I had to change the focus 1/4 in at f 64!
>The good thing is that the shift seems to stabilize at 22 - 64
>Ken

You were just so lucky to find that lens new - probably some premium 
glass at the time it was produced and an expensive item that sold 
fairly slowly to professional chaps. Wasn't the ground glass a bit 
dim at f64 Ken? Guess you were using 8x10 or some pretty serious 
movements on a 5x7......

What shutter is your Velo in?

Did you take any photos for a before and after multicoating to get an 
idea of the change in the image quality?  Maybe you have friends in 
the local multicoating shop to keep the cost down or can opticians 
carry out coating on spectacle lenses? Have read a discussion on this 
subject somewhere, maybe even on this list. Coating a single element 
is no problem but the temperatures involved would probably destroy 
the cement between element groups.....  There again you are a 
recementing fanatic from what I recall ;-)

All these questions and on a Saturday night - well early Sunday 
morning actually.

Cheers,
        Clive