[LargeFormat] Critical Focusing at f45 Using Nail Polish

[Clive Warren]

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