9" f:4.0 Verito aperture size

[Bill_1856]

What is the correct aperture diameter for this lens? Mine in a Copal #3 shutter is 45mm. I am concerned that this doesn't allow the full soft-focus effect.
Thank you.

[djdister]

What is the correct aperture diameter for this lens? Mine in a Copal #3 shutter is 45mm. I am concerned that this doesn't allow the full soft-focus effect.
Thank you.

I have a 9" Verito in an Alphax shutter at home - will check and post later tonight.

[mdarnton]

How big does the aperture look through the back of the lens, measured? To be f4 it needs to look 57mm. This will be different from the size of the hole without the lens in place.

[cowanw]

Are you sure you look through the back? Don't you use the entrance pupil?
Helen Bach says

"Roger, it's correct to measure 'through the front of the lens' - you should be measuring the entrance pupil, not the physical diameter. The entrance pupil is the virtual image of the physical iris when seen from the front of the lens. If there are no cells in front of the iris, then the iris and the entrance pupil are the same.

Look at the lens from arm's length and hold a scale or other measuring device close to the front of the lens, and view with one eye. That's usually good enough."

And she is pretty smart!

[cowanw]

And my 8 3/4 is 46mm which comes out to f 4.8. which numerically is not 4 either.

[djdister]

My aperture of my 9" Verito (pictured below) measured 42 mm actual at the marked setting of f4, but the apparent aperture opening through the lens measured about 48 mm at f4. Still not truly f4, it would seem. Of course, the Alphax shutter also has a marking for f6, so I'm not sure about the f number calculations when this was mounted in the shutter years ago.

128624

[Bill_1856]

Thanks, Guys. I'm feeling better about mine.
I wonder if the barrel mount lenses are the same? Anybody got one of those?

[mdarnton]

Are you sure you look through the back? Don't you use the entrance pupil?

I do stand corrected. Thanks.

[Mark Sawyer]

My barrel-mounted 8 3/4 inch/222mm has a 50mm aperture, or f/4.4. Many lens manufacturers played it pretty loose with the maximum speed...

[Jim Galli]

One has to scratch his head and wonder if perhaps Wollensak went to the 8 3/4" from the 9" so that the Betax 5 would give a full f4. Pure internet speculation and just adding to the confusion, not helping.

[goamules]

Here is a fun game, everyone measure all your lenses, and see if any match the catalog speed specs! You'll find they won't.