Question for the lens gurus...

[bobfowler]

Reading through Jay Allen's book "Pictorial and Soft Focus Lenses of the Past", I noticed that in the section on the Wollensak Veritar (pg 47) it says "The Portrait Veritar differs from an ordinary anastigmat lens in that as the lens is stopped down the depth of field increases only behind the point focused on."

Is that because of the placement of the iris? If so, is the iris closer to the front than normal or closer to the rear? Am I missing something else?

 

[jimgalli]

Bob, I don't have one so I can't answer correctly but I'll add to the question The design looks to be very similar to my much earlier Bausch & Lomb portrait Plastigmat f5.6. That lens only gains about an inch of focal length when the front light is removed (or missing, but that's another story) but the effect of the mis-correction is magnified and I actually like it better. Some of you that have the Veritar, does it act that way with the front removed. ie. the FL does not almost double like a normal semi symmetrical would, but the soft effect simply gets more interesting? Just curious so thought I would aggravate everybody. Sorry Bob. I now return you to Bob's perfectly logical question.

 

[bobfowler]

Oops... I found the answer!

It's just a focus shift issue. From the Vade Mecum:

This has a 3-glass layout and the image is soft due to under corrected spherical aberrations. Thus what you see is what you get- or nearly so. It does change focus away from the lens as it is closed down, so there is little or no increase in depth of focus towards the camera. Thus it may be best to focus on the nose or eyes. Some may be in Alphax shutters, and they were made long enough for some to be in chrome finish. It was still current in 1960, in 1+2 design, and sharp at f11.​

That's what I get for not trying the VM before digging through my other books...

 

[phfitz]

Hi there,

Don't know about the Veritar but this is from a 1922 Wollensak catalog. I think it explains the Verito and other soft focus lenses that get sharper stopped down. They could pick almost any pair of curves to get the diopter but fiddled around to get the results.

Have fun with it.

 

[Ole]

That illustreation shows the effect of internal reflections in a simple uncoated lens causing flare, and I don't think it explains the "soft focus" effect.

I'll see if I can find a good ilustration of spherical aberration, god knows I have enough books to look through!

Or look here and here.