Correction of f stops from 150mm to 135mm

**loman** · 19-Feb-2010, 04:02

Hello Everybody.
I have a 150mm f5.6 sironar from around 1971 that's completely infected by lens seperation in both the front and rear cells (commen problem with this batch of sironars). I also have a 135mm f5.6 schneider componon originaly in barrel mount that I just remounted in the copal 0 shutter instead of the sironar. My question is how much "out of whack" will the f stop scale be? when I want say f16 should I put the needle a little before or after 16 or is there no difference and is the scale usable for both lenses?

Thanks for your answers.

Mads Hartmann

**Dan Fromm** · 19-Feb-2010, 04:43

Don't ask us, ask the lens. Here's how:

OIpen the shutter.
Open the diaphragm as far as it will go.
Close the diaphragm until it is just visible through the front of the lens.
Open it until it just disappears.
The indicated aperture corresponds to true f/5.6.
Estimate the difference between true and effective in stops.
And there's your adjustment.