[LargeFormat] Critical Focusing at f45 Using Nail Polish
Clive Warren
largeformat@f32.net
Thu Sep 11 18:11:09 2003
Just read one of Steve Shapiro's and Richard Knoppow's exchanges from about
three years ago!
A tip that I found very useful and thought it would be good to pass on here
as we have been talking about Protar lenses recently. The extreme wide
angle Protar is f18 wide open, which makes it a little tricky to focus. The
dodge is to place a sharp pencil mark on the ground glass and then cover it
with a dab of clear nail polish. Richard explains the use of the new clear
spot on the GG better than I could:
'The clear spot and pencil mark allow you to focus using the aerial image
and parallax. You examine the image through the clear spot moving side to
side a little. When the image is in focus it will stand still in relation
to the pencil mark. Its a very accurate method of focusing.' Richard
Knoppow 2000
Convertible Protars suffer from a bit of focus shift as they are stopped
down - unlike the f18 Extreme Wide Angle that is better corrected. So this
tip is particulary useful for using convertible Protars and any other older
lens that suffers from focus shift when stopped down.
Thanks Richard!
Cheers,
Clive