ULF Walk-in Camera?

[mvanderaa]

Hello:
It's been a while since I've been active on the forum, and I have limited experience with large format. I am a high school photography instructor and would like to construct a walk-in camera for my students. The goal is to help student's learn by actually making and developing an image all while inside the "camera". I was hoping to use Harman's direct positive paper by special ordering a roll (24" x 66 feet).

My first thought was to build a large room with a front standard, bellows, and bed mounted on the front wall, and projecting the image inside to the rear wall. The bellows with front standard would give us the ability to fine focus. HOWEVER, I would like the student's to make close-up portraits. At an image size of 20x24", this would be larger than 1:1, perhaps at least 2:1? Using the Schneider XXL 1100mm as an example, I'm guessing I'd need more than 11 feet from the lens to the wall. If we were to shoot using direct positive paper, I'm wondering if this is even feasible given the ultra slow nature of the direct positive paper and the "bellows" factor? We have six 1,000ws Profoto heads, but even this may not be enough light!?

When I talk about close-up portraits I'm suggesting a 20x24" image which is the subject's chin to brow. Any insight or guidance on how to approach a walk-in camera for ULF portraits of this nature will be appreciated. (The walk-in will be helpful to develop the image in trays right inside the "camera", thus it functioning as a darkroom as well.) Thank you in advance.

[Jeff Donald]

When I was teaching at a university, I had a student use a box that a large refrigerator/freezer is shipped in to make a pinhole camera. Two people could stand in the camera during taking the photo, even burning or dodging. Once the exposure was made, the paper was rolled into a tube and processed in the schools darkroom.

[mvanderaa]

Thanks, Jeff. Your solution was far more practical than mine. However, it makes me wonder how large of a pinhole camera I could effectively make? Perhaps pinhole would be a better solution.

[Dan Fromm]

At 1:1, film plane to subject distance is 4 focal lengths plus the lens' internodal distance. With an 1100 mm lens, ignoring the internodal distance gives 4.4 m, a bit over 13 feet. At 2:1, 4.52 focal lengths.

You don't need such a long lens to cover 20x24 at 1:1, but with a shorter lens the dark side of your room cam will be shorter too. The formula is: extension = focal length * (magnification + 1). At 2:1, the lens' rear node to subject distance is 3 focal lengths. FWIW, I b'lieve that Richard Learoyd, an exponent of room cams for enormous scale portraiture, uses a 760 Apo Ronar.

Remember that a pinhole's focal length is the pinhole-to-film plane distance, also that pinholes have infinite depth of fuzziness. Why don't you play with a pinhole in an otherwise covered window, a helper outside and a sheet of white foamcore inside the room. Move helper and foamcore around to see how the dim image looks at various focal lengths (foamcore-to-window distance) and magnifications (helper-to-window distances). I abhor pinholes, but it might do what you want.

[Pere Casals]

We have six 1,000ws Profoto heads, but even this may not be enough light!?

Test it with a DSLR, the XXL is F/22, so take a DSLR at ISO 100 and F/22 and check what flash power / distance you need.

The paper may have some ISO 6, so have to check if the flash power / distance factor can be multiplied by 16, this is 4 stops. My guess is that you will have enough power if not using a softbox.

You know... if flash to subject distance is 1/2 then light power is x4, the square law.

Anyway you can do it also with continuous light and a long exposure, a fixture may be used to help subject stay still.

Regards.

[mvanderaa]

Thank you, Dan and Pere. My experience with the direct positive paper in 8x10 suggests I can probably (but barely) get enough light? I will test it. However, to Dan's point, while I have read that shorter focal lengths can be more practical at this ULF size, wouldn't that create significant distortion of the subject, especially at 2:1?

[mvanderaa]

BTW, Dan: I wasn't familiar with Richard Learoyd's work. His portraits are stunning. I found this video which gives a glimpse into his process https://www.youtube.com/watch?v=1Z589aji2LE Thank you for sharing his name.

[Andrew Plume]

A few years ago I was very fortunate to meet Richard at his East London Studio (shown in the you tube clip) and at that time he was printing images on the 'machine' shown in the video - he's truly a great Artist

good luck with your Project and best regards

Andrew

[Lou Baleur]

the barrel version of the 1100 xxl is f14--so it buys you a bit over a stop of light. You can do direct positives on regular photographic paper if you use reversal bleach and develop as reversal--expect to get about iso 3 or 2--you will need a lot of light or time or a combination of both. I suggest direct sunlight as the source and do short-ish time exposures. the xxl will cover to get you life size at 1:1.

addendum--I checked my notes and I got about iso 6 with faster (multicontrast) regular paper / reversal development and using electronic flash.

[mvanderaa]

Thanks, Lou. Regular paper may be better. My experience with 8x10 direct positive paper is it's close to ISO 1.5. I did a fast but fun test tonight with my 8x10. I took the back off and placed a soccer ball about 12" in front of the lens. In order to focus on the wall that the camera was projecting on to, the front of the lens was approx. 77" from the wall. This was able to reproduce the soccer ball quite large. It was also approximated the size of my subject's head (closer to 2:1). Here was the problem: I put a couple v-flats on either side of lens to block the light and simulate my front wall, and was left with no workable room to place my lights (only 12" of room in front of the lens). I'm wondering Dan Fromm: If I was to use a 600mm (twice the focal length of my test tonight) does that automatically imply I'd have 24" from lens to subject and need 144" of "bellows"?