why rack and pignon on large lenses ?

[alex from holland]

Hi all,

i was just wondering
why did they ever made a rack and pignon on large petzval lenses.
Normally with bigger lenses you need a large extention of the bellows.
In that case it is impossible to use lens focus and to look at the groundglass at the same time.

alex

[jp]

Many petzval lenses weren't made for cameras, but for projectors.

Not sure of your camera, but you could focus by moving the back rather than the front standard. That's how studio portrait cameras (century, B&J rembrandt, etc..) work.

[John T]

Some early cameras were just boxes-no bellows or sliding boxes. It was the only way to focus them

A few were also metal tubes with no other way to focus them either.

[alex from holland]

I know that i can move the back. i always work that way on my studiocamera.
So in that case large dallmeyer, Hermagis, Darlot lenses were actually made for projectors and not for camera's ?

alex

[Ernest Purdum]

The earliest Petzval lenses were made for metal Voigtlander cameras which had no provision for focussing other than that built into the lens. Many early studio cameras lacked a fine focussing arrangement, so the lens provided it. Even today, providing a good focus arrangement is a diffiicult part of creating a new camera design.


If you see a lens slotted for Waterhouse stops, it is a camera lens. If it has no stop slot, it is either a projection lens or was made before Waterhouse stops became normal. Some very old lenses have had slots added at a later date, sometimes crudely, sometimes well.

[Mark Sawyer]

I have a few 1880's or later camera lenses that still sport the focusing rack, even though cameras by that time had focusing bellows. I think it was a vestigial tail that persisted for a while, though it occassionally does come in handy getting an extra inch or two of extension on a camera with a short bellows.

[alex from holland]

Ok,

But this all still doesn't explane why LARGE petzval lenses with waterhouse slots have a rack and pignon. In this case i mean 20 to 30 inch lenses. So the really big one's.

alex

[goamules]

The knurling on the focus knob isn't for fingers, it's to hold a belt. The belt ran around another knob, usually missing, on the back of the camera. In operation, this primitive arrangement allowed the photographer to turn his focus knob in the rear while looking at the ground glass, which would then turn the front focus on the lens, via the belt. That's where the term "back focus" comes from. On the really large lenses, sometimes small draft animals were a part of the mechanism, and the belt became a "focus treadmill."

[GPS]

Ok,

But this all still doesn't explane why LARGE petzval lenses with waterhouse slots have a rack and pignon. In this case i mean 20 to 30 inch lenses. So the really big one's.

alex

It was mechanically easier to make the fine-tuning with the big lenses in this way than to make fine movements with the whole front standard and the big lens on it. Not all cameras were equipped with back standard focusing.

[BrianShaw]

The knurling on the focus knob isn't for fingers, it's to hold a belt. The belt ran around another knob, usually missing, on the back of the camera. In operation, this primitive arrangement allowed the photographer to turn his focus knob in the rear while looking at the ground glass, which would then turn the front focus on the lens, via the belt. That's where the term "back focus" comes from. On the really large lenses, sometimes small draft animals were a part of the mechanism, and the belt became a "focus treadmill."

Ya, I read that on the internet once.

Next thing we know Garrett will tell us that "way back then" photographers had logner arms than they do now and could look at GG and focus at the same time... or that every photographer "way back then" had a beautiful bikini-clad assistant who did the focusing at the request of the photographer.