If you happen to find an old lens that isn't marked in any useful way, how do you determine what format it can cover? Just try it? Or is there a way to figure that out without having a camera to try it in? I'm also thinking of when you're in an antique store and come across a lens.
I don't think I have photos of it, but I have an old brass barrel lens that I was given that likely just covers 4x5, but I'd love to know if it can cover more.
Bethe, there are two coverage concepts. Circle covered with acceptable image quality. Circle illuminated.
The first can be calculated if the lens' prescription is known. When the prescription is unknown testing is the only way to find out how far acceptable image quality extends from the center.
The second can be estimated crudely by looking at the image of, say, a window the lens projects on a wall.
If the lens isn't obviously for 35 mm still or medium format (usually 6x6), apply the rule of thumb "all lenses cover their focal length until proven otherwise" and be prepared to be mistaken.
1) Put it on a really big camera, focus and measure the circle on the ground glass.
2) Set up a matt board on a stand just inside the door of your darkroom. Keep the darkroom dark and switch on all the lights outside, if it is not sufficiently well lit - hold lens in front of the matt board and it should project an image on the matt board. If you had marked off inches on the matt board, you can read the coverage off that.
Cheers, DJ
Put it on your 4x5, make sure the front and rear standards are perfectly parallel, focus carefully, and apply maximum vertical and horizontal shifts front and rear. That might be more accurate than trying to improvise a way of shooting on large photo paper.
I agree with Dan, sometimes though there's a third way if you know the make and focal length and can find adverts for the lens. Focal length is quite easy to measure if not marked.
Sometimes you can be very luck because rather than focal length the coverage is marked on the barrel. My Wray R-R is marked 8"x5" but is actually 12" FL it's on a Half plate camera currently.
There's some very misleading claims of lens coverage, sometimes in adverts on the forums, it's wise to check what literature you can find where possible and see what manufacturers state for yourself.
Ian
Thanks all! I guess once I'm done wrapping presents, I'll be doing some experimenting. Focal length is pretty easy (there's a method in "Primitive Photography") and the one lens I have is about 210mm-ish. I'm hoping it will cover 5x7, but sorta doubtful at the same.
Jim, I'll try that, too.
In case it matters, now that I found the lens, it's a Carl Zeiss Jena Tessar 1:4.5 21cm. The only hits that pop up on google are on ebay and for under $50. I haven't seen a description of what it covers and how images might look.
Bethe, it is an f/4.5 Tessar like many of the other f/4.5 tessar types. The rule of thumb for these beasties is that they cover 110% of focal length at f/22 and that they are good sharp lenses except near the edge of coverage. The images look just fine, no funk, no swirlies, none of the poor image quality that some folks exalt.
There's another rule of thumb, to the effect that very early f/4.5 CZJ f/4.5 Tessars cover less than you'd think. Redesigns and, I suspect, new glass types brought increased coverage. What's the lens' serial number?
Dan, thanks! And there are two numbers. Right after Jena, it has "Nr 111169" then "Tessar 1:4.5 R21cm D R P 142294" So I'm not completely sure if the serial is 111169 or 142294.
It was given to me by another photographer whose father had used it. The one who gave it to me is probably around his early to mid 70s now so his dad was likely born in the early 1900s. He also gave me my Beseler 45MX.
As I understand it, the 142294 is like a patent # and the 111169 is the serial number.
I believe DRP = Deustches Reichspatent = German (imperial) patent
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