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View Full Version : Dumb Petzval question from a Newbie



Rael
20-Feb-2016, 09:59
OK, I've decided I want to purchase a petzval lens for my 5x7 Korona, and I've been looking at them on ebay. My question is: How the heck do I know whether or not the lens will cover a 5x7? Sometimes if the seller is knowledgable about such things, they will tell you, but other than that, is there a way to estimate? Can you figure it out if they give you the size of the barrel and diameter of the lens? (I think some sellers just call a lens a Petzval if it happens to be made of brass....)

At this point I'm thinking my best option is to put a WTB: ad here in the classifieds so I'm buying from someone who knows what they are selling and what it's capable of.

CCHarrison
20-Feb-2016, 12:29
Read my 23 page article on Petzval lenses here. http://www.antiquecameras.net/petzvallens.html

A Petzval that covers 5x7 will be a hefty lens that will roughly measure 6-7 inches tall (including hood) and glass diameter is going to be around 2.5-3 inches. These are rough guidelines. Focal length will be roughly 9 inches

The other issue is that 5x7 is somewhat between a half plate and whole plate lens. A half plate lens will barely cover 5x7 at the long side edges unless well stopped down. But a whole plate Petzval is going to be much bigger and much more expensive.

Good luck.

Steven Tribe
20-Feb-2016, 12:44
A very sensible question. There is a definite relationship between the focal length/F value and the amount of coverage you can expect. Unfortunately, listers/sellers are not savy about focal length measurements. Petzvals, typically do not have focal lengths written on them - if they do, then they are probably projection Petzvals. It is possible to gauge the approximate F value by the length of the barrel between the lens cells (ignore the size of the lens hoods which do differ a lot) and the width of the barrel. The "slimmer" types will be F6 or more, whilst the "fat" barrels will approach F3. The only problem this is that some makers, very sensibly, used the same barrel widths for different lenses - just the lenses are smaller and mounted in wider fittings.

The basic rule is that the longer lengths combined with higher F values will cover large formats. So ask for the focal length, measured from the waterhouse slot/iris and the diameter of the glass lens in order to find the approximate F value. Then check the values against known Petzvals (cameraeccentric catalogues) and you find a match were the coverage is given.

CC has written a better reply whilst I was writing this! If you want something between F3 and F4 you are talking about a lens that will be around 1.5 kilo. You could get well under a kilo with a sleeveless projection version around F6.

CCHarrison
20-Feb-2016, 13:19
Here's a good visual of Petzval sizes...

Dan

CCHarrison
20-Feb-2016, 13:20
Here's a good visual for you - all the lenses are probably around f/4 in speed (Mammoth 5.6)

146913

Dan

Andrew
20-Feb-2016, 13:51
if you post on the for sale/ wanted section of this forum saying you want a petzval to cover 5x7 there's a reasonable chance that anyone offering to sell you a lens will actually know what the coverage is

Rael
20-Feb-2016, 13:59
Here's a good visual for you - all the lenses are probably around f/4 in speed (Mammoth 5.6)

146913

Dan

Holy moly! The one in the back looks like an artillery cannon. Thanks for the replies -- that helps.

Rael
20-Feb-2016, 14:02
Read my 23 page article on Petzval lenses here. http://www.antiquecameras.net/petzvallens.html

A Petzval that covers 5x7 will be a hefty lens that will roughly measure 6-7 inches tall (including hood) and glass diameter is going to be around 2.5-3 inches. These are rough guidelines. Focal length will be roughly 9 inches

The other issue is that 5x7 is somewhat between a half plate and whole plate lens. A half plate lens will barely cover 5x7 at the long side edges unless well stopped down. But a whole plate Petzval is going to be much bigger and much more expensive.

Good luck.

Great resource! Thank you very much...

goamules
21-Feb-2016, 06:11
Ask the seller to measure the focal length to the waterhouse slot. If there isn't a slot, to the middle of the lens. You want about a 9" lens. An 8" might cover, and would have more edge effects/aberrations. A 10" will have more of a sharp image across the whole 5x7 frame. I'm talking a traditional Petzval speed of about F3.8. Like Steven says, slower ones will cover more. I was shooting a 9 inch American radial drive petzval yesterday on 5x6, and it covered fine, with some edge swirl if you want it.

Rael
21-Feb-2016, 09:59
Ask the seller to measure the focal length to the waterhouse slot. If there isn't a slot, to the middle of the lens. You want about a 9" lens. An 8" might cover, and would have more edge effects/aberrations. A 10" will have more of a sharp image across the whole 5x7 frame. I'm talking a traditional Petzval speed of about F3.8. Like Steven says, slower ones will cover more. I was shooting a 9 inch American radial drive petzval yesterday on 5x6, and it covered fine, with some edge swirl if you want it.

Yes, the edge swirl at portrait and slightly longer distances is specifically what I'm hoping to play around with, so it sounds like I want 8-9"?

Jim Galli
21-Feb-2016, 18:57
Yes, the edge swirl at portrait and slightly longer distances is specifically what I'm hoping to play around with, so it sounds like I want 8-9"?

Yes. You don't really want full coverage. You'll be moved in closer to your subject, and the area of the frame where coverage is ending and you're on the ragged edge of darkness is where the swirls will happen.

There were thousands of 9 - 10" lenses made for projectors that are petzvals and will cover your 5X7 like you wish.