We tried using a small digital nikon at first, since it was small, portable, and I didn't mind having it completely covered in tape.
The disadvantage of conveience was that the camera only had about an 8 second exposure time max. Since our photographs were taken during a typical dreary overcast Pittsburgh day, this had terrible results that looked something like this.
We decided to go get a bigger gun, and rented this beautiful SLR from the school of art. As well as being a much nicer piece of equipment, it allowed us to expose our images for up to 30 seconds. Also since I have excellent exacto skills, we created a tight enough fit that we didn't have to tape our eqipment up to avoid light spills into the camera obscura.
We then set up our camera and captured a series of images containing (relatively) the same scene using 3 different pinhole sizes, 0.1mm, 0.7mm, 1.5mm
pin
med
large
pin
med
large
In both series, the larger aperture did significantly better than the other two. Since the day was slightly overcast, letting in the extra light was a huge help to developing a clear image.
The larger pinhole actually took some decent photographs. How successful final image turned out to be were actually influenced by a couple other factors too.
We manually autofocused the camera using an LED light shining through the pinhole before each image, so some of the blurriness/after effects were due to the fact that I have ridiculously weak noodle arms that have never been used for any sort of physical labor, so pictures where the box was able to rest on the floor or a solid surface worked best. (or when Tim held the camera)
It's also easier to get a clear image if you're photographing an inanimate object that doesn't mind holding still for 30 seconds dispite windblown hair and an itchy nose.
Indoors were were only able to get a decent image if the camera was pointed at an object that emitted its own light, regardless of the aid of the florescents and any windows. There simply wasn't enough illumination otherwise.
These were made by waving an LED flashlight frantically in front of the camera for 30 seconds
I collaborated with max for this particular bell + whistle, since we both had giant cameras, and his camera obscura was made out of a pumpkin, which isn't the most expensive rented equipment friendly. We couldn't get a clear image with this method though, despite focusing both the inserted lens and the digital camera lens. We probably didn't have enough light inside my studio.