Petzval questions: Focal Length, Focal Ratio of my "new" lens.

[Drew Bedo]

I have gotten a Petzval lens. I am new to this era of gesar. The lens is unmarked in any way but looks good cosmetically and has clear glass. Came complete with flange, rack and pinion, and hood. My intention is to shoot with it.

So I finally got it onto a lens board and put it on my 8x10 for a first look.

Looks to cover 5x7 inches or maybe whole plate . . .fine.

I measured the focal length at infinity from the film plane to the Waterhouse slot (correct?) at around 250mm.

I measured the clear aperture visually from the front, at around 35mm.

Doing the math: 250/35=7.1 . . . . or so depending on how tightly I squinted at the ruler.

From this I get a focal ratio of around f/7.1.

This seems slow to me from what AI understand about Petzval lenses. . .do I have that right?

[Steven Tribe]

All the early Petzvals (say 1839 - 1855) were fast - because they had to be in order to expose on the slow materials. Co-incidentally, the very shallow depth of focus created images of people which was considered attractive as well as saving on retouching time. Speed was rarely over F4 and even under F3. I have a Viennese 50’s Petzval which measures out at F2.7!

There was a gradual reduction in speed as the 20th century approached and F5 and F6 (Dallmeyer’s D series, for instance). So a computed speed of F7 doesn’t seem improbable. Many later Petzvals could be faster but have a restricting internal baffle. I don’t know whether this is because of an inferior product - or the maker trying to ensure the user gets an acceptable result in spite of lesser skills!

[Drew Bedo]

Seven: Thanks for that info.

This lens has a Nickle plated barrel, and so I suspect that it is from the turn of the 20th Century. Another thing is that the metal parts are untarnished. As I said, no markings on it at all.

I will attempt to re-measure with more than eye-ball precision, then try for a more accurate calculated speed. Following that I'll get a friend to put a micrometer on the Waterhouse stops I have to figuree out what they will bring to the imaging process.

I was just surprised by the f 7.1.

[arri]

With f/7.1 it is an aplanat and not a Petzval lens.
The aplanat lenses are much slower in speed and in the consequence much smaller.
This design has much more coverage, a 250mm should cover 8x10"
I have an Emil Busch with 260mm focus length and it is good usable in this size.

A few fast aplanat lenses were made, especially by the Suter company in Switzerland, the fastest are f/5. But this ones are pretty rare.

[Daniel Unkefer]

Wow. Great thread. I too have an unmarked Petzval type (I think). It seems to be about 200mm or, and came with a central stop, which was darkened by candle soot (I think). I say this cause if made a mess of my hands, very sooty. I wanted -speed- so I removed the central stop, it popped right out. Now the lens is (my guess) about F3.5 or so? I did put it on my 8x10 Norma and it looks like it illuminated nicely about 5x7/13x18. I've been using it on my Makiflex which like to be used with speedy lenses. Film was slower back in the '60's.

https://live.staticflickr.com/65535/53008403359_00de298c5f_b.jpg (https://flic.kr/p/2oLaVwX)Makiflex JLane 9x12 Glass Plate EI 1 Key Day (https://flic.kr/p/2oLaVwX) by Nokton48 (https://www.flickr.com/photos/18134483@N04/), on Flickr

Jason Lane Dry Plate 9x12cm Makiflex Plate Adapter Makiflex Automatic Key Day Full Sun. Legacy Mic-X tray developed under safelight. I'm in the process of setting up a film digitizing setup Minolta SRT Copy Stand Minolta Bellows Minolta 100mm F4 MC Bellows Rokkor at F13.5. Sony Nex 7 with SRT Adapter.

[Mark Sawyer]

Drew - Slower Petzvals are uncommon, but not extremely so, (I have a couple). But they're usually projection lenses, so I'm surprised yours has a Waterhouse stop slot, indicating it's a lens for taking.

It's possible the positive rear lens was broken or lost, leaving only the negative element at the rear, so you might check that, either by reflections or disassembly.

[Drew Bedo]

Thanks everyone.

First: This lens seems to be 250mm. I put it on my 8x10 and it makes an 8" image circle . . .so 5x7 or whole plate is reasonable, but not 8x10. This leads me to believe that it is not an aplanat.

Second: There is a slot for drop in Waterhouse stops. The front has a hood with no provision for a sliding or rotating cover as found on many projection lenses . . .given those two observations, I am thinking that it is not a projection lens.

From information posted here and with the lens in my hand, I conclude that it is a later, slower Petzval lens.