Eastman Portrait f-5 6 1/2 x 8 1/2 11.5 inch

[erian]

I managed to acquire this interesting specimen.

It is very similar to the larger variant described here here.

What interest me but what I did not figure out is how to manage its diffusion control if it exists.

I presume that this lens is a variant of Eastman Portrait lens - Series B, f-5 on page 3.

I tried to turn everything possible and ended up with 4 pieces - 2 optic parts, aperture ring and a tube between aperture ring and rear element.

If it has a diffusion control then how it should look like and how to operate it?

[karl french]

The rearmost glass should unscrew from the inner element. That's your diffusion control if this lens has it. Usually there is a hash mark on the inner barrel and sometimes numbers 1-4 to indicate amount of diffusion.

Oh, almost every petzval I've purchased has been mixed up. Make sure the cemented double is up front and the air spaced pair in the back.

[erian]

Oh, almost every petzval I've purchased has been mixed up. Make sure the cemented double is up front and the air spaced pair in the back.

Many thanks.

The lens hood is quite tightly connected to the front element.

The rear element unscrews as a whole. How can I check if it is the air spaced one?

The rearmost glass should unscrew from the inner element. That's your diffusion control if this lens has it. Usually there is a hash mark on the inner barrel and sometimes numbers 1-4 to indicate amount of diffusion.

I do not notice any markings. The treads of the rear element (both glasses if they are there) are behind the flange. I presume this is not the diffusion control.

So far I have discovered 3 threads. Front element to the barrel, rear element to the barrel and between aperture ring and lower end of the barrel. The distance between the front and rear elements can be therefore altered (as could be by unscrewing the front element). Will this create diffusion?

I am trying to understand the description on antique cameras. It says "Dallmeyer touted the feature of being able to unscrew the posterior cell of the lens to obtain greater "depth of definition."". Is the cell lens pair in this case or just the rear most lens?

[karl french]

Usually it's just the rearmost lens, though I think the Wollensak Vitax moves the innermost lens of the rear pair. Dallmeyer copies generally have each rear component in its own mount, so that they can be separated in terms of distance. There should be a retainer (inside) on your lens that holds both rear glasses in place (with the spacer ring between them.)

[erian]

I included the catalog page for this lens.



What is confusing for me is that for my untrained eyes my lens looks very close to the one in the catalog (Series B, F-5, mine does not have a flange) and it says that it has two controls, one for the diaphragm and second for the diffusion.

[karl french]

I feel like I see the index mark on the rear barrel of your lens in the picture you posted. If you want to send me the lens, I'm happy to take a look at it.