homemade large format paper camera

[artyvisual]

I want to build some kind of photocamera installation. I want to directly expose large format paper (50 cm). First I thought of a pinhole, but for this particular use, I can't have a very long exposure time. So I now want to mount a lens. It will be basicly a wooden box with a sheet of photopaper on one side, and the lens on the opposite site (ofcourse). I need a bit of wide angle result.
Can this be done? What kind of lens will I have to use? How to calulate the correct focus distance?
I hope someone can help me on this.

Many thanks,

Stan

[Jay DeFehr]

Hi Stan,

Paper is slow, and fast lenses that cover Ultra Large Formats are rare/huge/very expensive. Unless you have a big budget, you'll have to live with long-ish exposures, and any lens that covers your intended format will not be cheap. To calculate the distance between the front and back of your box camera, you'll need to know your lens focal length and the distance between your lens and your subject. To know if your lens will cover your intended format, you'll need to know its angle of view. In short, if you start with a given format, your next chore is to find a suitable lens. Sometimes it's more practical to begin with the lens.

To find a lens, calculate the diagonal of your intended format. A 40cm x 50cm format will have a diagonal of 64cm, so any lens that will completely cover the format will have to project an image circle 64cm in diameter at the chosen focus distance. Some of the guys here know lenses in great detail-- maybe someone can recommend an appropriate one.

It's an ambitious project. Good luck!

[Dan Fromm]

Stan, you've constrained yourself into infeasibility. Large coverage and low cost don't go together.

First off, how big is your paper? 40 cm by 50 cm, as Jay assumed, in which case you need a lens that covers 64 cm, as he told you, or 50 cm square, in which case you need a lens that covers 70 cm.

Go to www.cameraeccentric.com and look at catalogs for old lenses. In particular, B&L and Zeiss for Protar Ser. V and Goerz American (I looked in the 1951 catalog) for Dagors. Also visit www.schneideroptics.com and look at their current offerings.

You'll find wide angle lenses that will cover your format in both places, but knowing that they exist won't help you much. Finding them at all, let alone at low prices (low by my standards, the most I've ever paid for a lens was around $800 and that was very painful) is a huge problem.

If you relax your requirements to allow lenses of normal focal length for the format, then there are long process lenses, e.g., Apo Artars (there are others), and also long Tessars and Zeiss triplet aerial lenses that will do. Still not inexpensive, and you'll still have to find a way to time exposures.

Re focusing, a sliding box focusing arrangement may be better for you than calculating flange-to-film distance for the distance you want to shoot at, if only because it will save you from measuring the lens' focal length precisely enough. A process lens with QC slip that has measured, not nominal, focal length would help but few of the process lenses on offer still have their QC slips.

[jnantz]

hi stan

you can find single cell lenses at places like the surplus shed or anchor optical
here in the states, and shipping wouldn't be too bad ... ( depending on the weight ).

single cell lenses have a pretty big coverage and give a nice look wide open,
stopped down they can be sharp. no need to spend hundreds ... with shipping
a single cell will probably cost 10-25$


have fun !
john

[Jim Michael]

Might a zone plate work in place of a pinhole?

[artyvisual]

Thank you for all tour answers so far.
There is a major analog photography fair here in the Netherlands this weekend, I will keep my eyes open for these big (old) lenses. But I will consider some blur (Thats why I started out with pinhole). Those meniscus lenses might indeed be worth trying, I found a dealer in the US:
http://www.thorlabs.de/NewGroupPage9_PF.cfm?Guide=10&Category_ID=143&ObjectGroup_ID=130

[mdm]

I used a circle of confusion of 300micron or 0.3mm
http://www.dofmaster.com/dofjs.html

[Steven Scanner]

I've made a large format camera with a regular magnifying glass as a lens. It works. Well it creates a clear image on the A4 size ground glass. I did some experimenting with a flatbed scanner and this works to.
The lens is about 8cm in diameter and lets a lot of light thrue. I did an anthrotype experiment a couple of weeks ago but due to lack of natural light (it was winter at that time).
How did I calculate the focus distance? I didn't. What I did was, hold the lens above my hand and try to focus the light in the shop on my hand. The camera has got a ground glass to focus. After focussing I remove the ground glass and replace it with the flatbed scanner. I'm going to give anthrotype another chanse next summer. With enough days of exposure it might work.
For what I've found out: the closer you get to a pinhole, the longer the depth of field but the more exposure time you need. Big lens, lots of light, short DOF. Small lens, less light, longer DOF.