[LargeFormat] Focus Shift on Stopping Down
Clive Warren
largeformat@f32.net
Sat Dec 1 20:18:05 2001
>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