Designing an 8x10?
I happened to have come by two 8x10 film holders. And I don't have an 8x10 camera (yet). With worldwide pinhole day coming up, I figure I might as well design a camera to use the holders. I've made my own pinholes before - one for my 4x5 with a 5" distance between the pinhole and the film (I think it's about f284, IIRC, it's not nearby to check) and several for oatmeal canisters that held 8x10 paper, though not flat out, of course. What's a good hole to film distance and corresponding pinhole size? I won't be striving for perfection, just something usable and fun for the first try. I couldn't find the site with the calculation table I used before, so I thought I'd ask and see how many varied ideas I could glean. :) TIA!
The first question is what size of angle of view do you like?
Your 4x5 inch camera with a focal length of 5 inch has an angle of view of 65 degrees. With a pinhole size of 0.02 inch (= 0,5 mm) you should have a f-number of 250.
Here is a small list with some guidelines for a 8x10" camera:
|angle of view
||255 mm / 10.0 inch
||0,71mm / 0.028 inch
||230 mm / 9.17 inch
||0,68 mm / 0.027 inch
||200 mm / 7.87 inch
||0,63 mm / 0.025 inch
||150 mm / 6.00 inch
||0,55 mm / 0,021 inch
||120 mm / 4.76 inch
||0,49 mm / 0.019 inch
||100 mm / 4.02 inch
||0,45 mm / 0.018 inch
||80 mm/ 3.17 inch
||0,40 m / 0.016 inch
If you would like to know other sizes, send me a PM. I can also make you an exposure table if you have decided on what size camera you're gonna build. If you have an iPhone, you could also use this app to "measure" the exposure times: http://www.pocketlightmeter.com
If you want to experiment yourself with focal lengths, angle of view, pinhole size, exposure times, etc. use this small & easy program: http://www.pinhole.cz/en/pinholedesigner/
BTW: don't forget to post an image of your camera when finished ;-)
Thanks very much! I will definitely post a photo of the camera and what I get from it. I think I'll be aiming for a 150mm or 200mm one this time.
I agree with the ToadMen in recommending PinholeDesigner, a free download from www.pinhole.cz. The last time I looked at www.mrpinhole.com (years ago) it wasn't as useful to the technically inclined photographer as PinholeDesigner. The default constant in PinholeDesigner is 1.9 as determined by Lord Rayleigh well over a hundred years ago. He was a scientist first and perhaps a photographer second. His constant is apparently derived more from theoretical and mathematical considerations than from actual photography. His classic article on the subject is available online. I can send you a link to it if you want to spend more time wrestling with math than making photos. After photographing resolution charts, I prefer a smaller constant, about 1.4. So do some others on www.f295.org. Such smaller constants are apparently used by some of the ready-made pinhole cameras.
Contrary to some pinhole photographers, the size of the pinhole is fairly critical. Deviating from the ideal diameter by 10% can result in a noticeable decrease in image resolution. An optimum pinhole can resolve standard resolution charts with a line/pair spacing less than the pinhole diameter. Also contrary to conventional wisdom, pinhole cameras exhibit chromatic aberration and astigmatism, although moderate amounts in normal focal lengths.
An analysis of pinhole images and formulae shows that the larger the format and the wider the angle of coverage, the better the detail can be recorded in the center of the image. With ideal cameras, doubling the format size doubles the effective "pixel count." In other words, a large format pinhole image optically or digitally reduced to a small size can exhibit more detail than a pinhole image filmed at the small size. It takes a fairly large difference in format sizes for this to be conspicuous.
Wide angle pinhole cameras exhibit considerable light and sharpness loss towards the image edges. In home-made wide angle pinhole cameras, there is a way of slightly increasing illumination. but at the cost of decreasing contrast, near the edges of the image. In addition to the image forming pinhole, four more pinholes are mounted in about the same plane, but in front of the corners of the negative. Light through these is diffused and reduced so it adds a little, but not much, illumination to the corners of the image. This has the effect of giving the corners slight pre-exposure, just as was done in the heyday of film to insure the capture of some detail in shadows.
Back to Bethe's question, for a starter I'd use a focal length of about 6" and a pinhole diameter of about 0.016" for photographing fairly distant subjects. This means f/375. Ouch! For close-ups, the pinhole diameter can be reduced slightly. If interested, I can look up the formula for this reduction. A 6" focal length will cover about 90 degrees, corner to corner. Light fall-off at the corners will be about two stops if the pinhole edges are very thin. This makes film better than the more contrasty photo paper for image capture. The corner fall-off can be used for esthetic effect.
I actually have an 8x10 pinhole project "under way" here, slowed by mundane trivia like getting out an art club newsletter and, oh yeah, #$%^# federal, state and local income taxes!
I still hope to get it done by April 28th. I am glad to see Jim's suggestions, as I had already tentatively settled on about a 90º angle of view or six inch film to pinhole spacing. (Great minds think alike, etc., etc.) I was quite happy with a fairly wide 4x5 I did two years ago and look forward to seeing the even larger format in action. I'll probably go with paper negatives this time, as I don't want to give up a month of Starbuck's visits to buy film that size! :D
I'll be watching this thread as I'm in the beginning stages (still) of an 8X10 build. I'll probably not do film holders at first, but its what I I want to do eventually.
Dave, I agree on the paper vs real film cost dif! I'm thinking of using some Arista lith film I have. It worked well in the oatmeal cans.
Jim, thank you for all that info! And I was thinking about 6" or 7" to start. I have a handy little magnifier that has a measuring device built in (left over from bloodspatter analysis :) ) - it works great for helping make pinholes.
If I can get something started soon enough, I can do a test or two before the 28th. Knowing me, I'll be winging it, though. :rolleyes:
No idea what my eventual subject might be.
Here is a photo of one I built last semester. Would be happy to discuss it with you. I used a Skink pinhole and tripod mount. Bill Barber
Bill, I think I remember seeing pictures of that one before and it looks great. I really like how you hold the film holder to the back. Since I don't have access to power tools (just hand held ones that weigh too much for me to control), mine is constructed of foam core board and Ilford box tops. I'm expecting light leaks when I test it tomorrow. If my next door neighbor ever has some free time, maybe I'll see if he'd be willing to cut pieces for one like yours. Are you willing to give out the measurements and design?