ULF Walk-in Camera?

[Dan Fromm]

Michael, measure from the lens' diaphragm, not from the front, whatever that means. This because most LF lenses' nodes are close to the diaphragm. The front node, from which lens-to-subject distance is calculated, will be a little in front of the diaphragm. The rear node will be a little behind the diaphragm.

I take it that you used a 300 mm (12") +/- lens. Since distances given magnification are calculated in focal lengths, doubling the focal length will double all distances, holding magnification constant.

About measurements and such. The closest the rear node can be to the film plane is one focal length. The subject will then be at infinity. This is, in fact, one definition of focal length. The closest the front node can be to the film plane is one focal length. The film plane will then be infinitely far from the rear node. Your measurements are a bit, um, sloppy.

About good practice. Lenses intended for general purpose use, such as the ungodly expensive XXL 1100 are optimized for a big subject in front and a small (relatively) negative behind. When used at magnifications > 1:1, there will be a small (relatively) subject in front and a large negative behind. To get the most out of the lens' optimizations when working above 1:1 the lens reversed.

To be fair, the XL 1100 is a dialyte and might be nearly or perfectly symmetrical. Quick check, compare the two cells' focal lengths. Equal means symmetrical, doesn't have to be reversed for > 1:1.

There's a big exception. Dialyte type process lenses, e.g., Apo-Artars, symmetrical type Apo-Nikkors, Apo-Ronars and Repro-Clarons, are perfectly symmetrical and don't have to be reversed when used above 1:1. Plasmat- and Dagor-type process lenses are also perfectly symmetrical but the likely ones, G-Clarons, are too short for your application. Apo-Tessars and clones are asymmetrical and should be reversed when used above 1:1.

[aaronnate]

I turned my classroom into a camera obscura one year. Totally blew the kids away once their eyes adjusted and they were 5th graders.

It requires a window to the outside world.

Blackout the classroom. Cut a dime sized hole in the covering of the window and wait. The smaller the hole the better the focus but it takes a long time for the eyes to adjust. What sized lens does Ian Ruhter use?

[mvanderaa]

Hi Aaronnate: I'm jealous of this idea. The only view outside my classroom is into a very small and shallow courtyard, which I don't think will make a very interesting images. There are other classrooms in the building, however, that would work great.

[Tin Can]

1/2 the class could pose in the courtyard with others inside.

Don't limit your photography to film, use phones to capture the image obscura both with still and video.

Hi Aaronnate: I'm jealous of this idea. The only view outside my classroom is into a very small and shallow courtyard, which I don't think will make a very interesting images. There are other classrooms in the building, however, that would work great.

[aaronnate]

Hi Aaronnate: I'm jealous of this idea. The only view outside my classroom is into a very small and shallow courtyard, which I don't think will make a very interesting images. There are other classrooms in the building, however, that would work great.

There is the challenge. Make it interesting. Make the students make it interesting. Whatever is in the courtyard will be projected into the room. The classroom I did this in had a great view, fall folliage, shapely trees against a deep red mesa. When I moved, my next classroom had what I called a prison yard view; cement and red brick. I chose not to do this because it was boring. I should have because, one day I looked out, two students were sitting against the wall and it was the most amazing image. The next year I switched subjects and rooms, and the project did not fit the standards or the dictated program.

Randy has some good ideas too.

[DougD]

If you are interested in a camera obscura, these folks have a product to help out. (no affiliation other than I bought one).
https://bonfoton.com/

[Tin Can]

What a great simple product and something actually affordable!

I will be getting 2 soon for my cargo trailer.

If you are interested in a camera obscura, these folks have a product to help out. (no affiliation other than I bought one).
https://bonfoton.com/

[aaronnate]

If you are interested in a camera obscura, these folks have a product to help out. (no affiliation other than I bought one).
https://bonfoton.com/

Awesome!!!!

[mvanderaa]

Thanks for sharing that product, Doug. I'm going to order one to play with. I also just purchased an 800mm f/9 Apo-Ronar to play with. My interest here goes beyond the obscura — I'd like to see if we can make large direct positives. The 800mm seemed like an economical way to do some testing. (I was able to get a nice, bright image circle larger than 1:1 with the 300 on my 8x10, but will lose one stop with the 800 and that's not taking into account "bellows" extension.) I have a handy-man stopping by this weekend to help with a hole in the classroom wall out to the hallway (instead of the courtyard) so we can set-up our studio strobes for portraiture. I've sketched-out how I want the hole trimmed and a simple rig to accommodate rise / fall. To get up and running fast, I'll use a magnetic chalkboard on casters to mount the paper and try to focus, although I recognize I'll never get the chalkboard perfectly parallel to the lens. All said, it seems like the best and least expensive way to do some down-and-dirty testing and then I can pivot from there. I'll keep this thread updated with my progress. Thanks to everyone who chimed-in!

[mvanderaa]

I turned my classroom into a camera obscura one year. Totally blew the kids away once their eyes adjusted and they were 5th graders.

It requires a window to the outside world.

Blackout the classroom. Cut a dime sized hole in the covering of the window and wait. The smaller the hole the better the focus but it takes a long time for the eyes to adjust. What sized lens does Ian Ruhter use?

I'm sure (but not certain) Ian's lens is huge. I'm also in the suburbs of Chicago which means a lens pointing towards our narrow and bland courtyard doesn't work for portraits during the winter months. (I would love to have a room with a view of some movement / cars — that would persuade me to do the obscura. If you've seen my latest post, you'll see I'm headed a different direction with a lens. BTW, I showed an Ian Ruhter video to my students — they were fascinated. It's cool stuff. Thanks, Aaronnate!