Pinhole Camera exposure

Discussion in 'Black and White' started by ekoppel, Sep 14, 2006.

  1. Hello, all.

    For my photography class, our first assignment was to design a pinhole camera.
    We're using these things now and it seems like getting the exposure right is
    very tricky. Normally if I don't have a light meter, I try and follow the
    "Sunny 16" rule (shutter speed = 1/film speed, aperture = f/16).

    However, we're not using film for our pinhole cameras; we're using photo paper
    instead...Ilford multigrade RC paper to be exact. Is there a way to determine
    exposure time for photo paper? I calculated the f-stop of my pinhole camera to
    be approx. f/460 (6.5 in / 0.014 in).

    Thanks in advance.
     
  2. If you don't get an answer here, you might check the Pinhole group www.f295.com. I seem to remember hearing that it was the equivalent of ASA/ISO 6, but I could be wrong. Paper is much slower than film, so you exposure times are going to longer, but it is easy to develop (safelight friendly!) and cheap. Check the wwww.mrpinhole.com site as well for more info and for a nice downloadable pinhole calculator check this site http://www.pinhole.cz/en/pinholedesigner/

    - Randy
     
  3. First off you may need to re-think your approach. The paper you are proposing should be perfectly suited to the needs. Regards the developer, I would strongly suggest that you get a can of dry LPD Developer from Ethol. The can runs about 10 dollars. The dry powder is better for this than the liquid. This is easy to mix. You will need a dilution of 1:7 or 1:8. One of the BIG problems you are having is if the developer is of a standard nature it will create way too much contrast and density, this is most important in the pinhole image. By the way, make your prints by contact using the same developer and same dilution.

    Regards exposure, it is simple. Go to the school with your camera. Take and load the camera with the paper and set out your developer (tell the lab tech what you are doing, they should be accepting of this), use all the other chemicals as usual. Load the paper into the camera, go out and make an exposure for one minute. Extremely important, take a picture of you with the full sun on you, no shadows, no under the eves, no trees and stuff around you, trust me you need to do this. Develop the image, if you get no image go back out with your loaded camera and do a five minute exposure. If in 45 seconds you still have no image, get some card stock and build a lifter to go inside the camera, make the paper be closer to the pinhole by half the desistance. Then re-test. Keep this up till you get results. Forget the perfection of your camera. If you can not get an image in one to two minutes with a paper you are just going to have nothing but trouble.

    How do I get off saying this? I over sighted and participated in a children�s program using pinhole photography for 17 years, 9 months out of every year. You can keep it simple and get results that are just incredible. We used Ilford Multigrade products ( we used these papers for the classes, the one with out a number, all the way up to the IV version), here are some important points. Stay out of areas that are high in trees and plants, they eat light (photosynthesis) and you will get your best results from an hour and a half after dawn up to just before noon. After that the light becomes too contrasty due to shifts in color temp and the papers response to that light. As you go into winter the light is reduced but the light gets much better for a match in color temp and the paper. By winter you will find the time easily goes into 2:00 in the afternoon before becoming poor. The print you see here is done with a simple cardboard box pinhole camera, Ilford Multigrade IV Paper, LPD 1:7 for a minute and a half development. Exposure was in shade in early spring in Texas, about 50 percent longer than normal (due to shade). The light line was generated after the exposure by intuitive drawing the light line with the sun (opening the shutter and wiggling the open camera pinhole to the sun). The extended development was to insure a black line in the negative but the burst high on the scale (yes we took over developing from the 12 year old who did the image). If your exposures become too long you will not get an image that results in good images technically. You want an exposure that takes from 20 seconds to about 60 seconds in full sunshine. The best target time is between 30 and 45 seconds. I think your pinhole may be too small. It is the relationship of hole size to paper distance. I am not sure that if your notation of 6.5 refers to inches, if it does then you need to start by knocking the distance down to 2 or 2 and a half inches. We made 2 inch cameras with a sewing needle (number 10, sharp) in simple aluminum that was backed by a dozen layers of newsprint to soften the penetration. This will work well, you can make a dozen quick holes, one will be clean and you get to work. Hope this helps.
     
  4. Sorry Erick, for got to post the picture!
    00I3IG-32387584.jpg
     
  5. Eric, I've been shooting paper negatives in pinhole cameras since the mid-1990's, and post frequently at f295. Several of my cameras have 'focal ratios' (it's actually a projection ratio, or "P" number, but I won't quibble) of over f/460.

    I also shoot almost exclusively paper negatives, with some good results (shameless display of lack of humility).

    For a camera with a projection ratio >400, I typically will expose paper negatives in *bright* daylight for 1 - 1.5 minutes. What I mean by "bright" is Southwest US bright sunny daylight. Or set an incident meter at EI100, and the light would be around EV15. If you live further north, or under winter sunny skies, I'd recommend 1:30-2:00, based on your test results (see below).

    One cavaet: I shoot exclusively grade 2 RC paper, sold under the Arista brand. I find grade 2 paper gives me much better control of contrast, for about the same speed as multigrade paper.

    For the specific paper you're using, my recommendation is to try several test shots, under brightly lit daylight that is consistent (i.e. no clounds or haze drifting in and out) with a scene that has a good mix of highlight, mid-tones and shadows. Bracket exposure times between 1 and 2 minutes, in increments of 15 seconds. Develop these test negativs and see which ones give you the exposure you require. Don't expect any detail in blue sky; the negative most likely will be almost total black in the sky area, so don't try adjusting exposure times for the sky, or you'll end up severely under-exposing the terrain.

    (I've successfully taken cloud/sky shots using paper in pinhole cameras, with good contrast. The typical exposure time is about 5 seconds. A landscape doesn't reflect much blue or UV, so it would have absolutely no detail at this short of an exposure.)

    One thing that can throw off your judgement of exposure time is the color of the subject. For instance, a light beige object looks very bright to our eyes in bright sunlight, but there's enough red in the beige that the photo paper won't respond the same. Photo paper is essentially blue/UV sensitive, with a bit of green sensitivity thrown in with multigrade; brown and other 'earth tones' will record much darker than our eyes would otherwise reveal. So it helps to be aware of this when exposing paper negatives, and give an extra half stop or so, based on the color.

    Also, if thin, hazy clouds drift over your site during the exposure - enough to soften the shadows but not completely eliminate their edges - just double the exposure time during the portion of the exposure that was obscured. For instance, if you would normally do a 1:30 exposure in bright sun, and thin clouds came over for 30 seconds, then just add another 30 seconds onto the end of the exposure, making it a total of 2 minutes. Or if the entire exposure was obscured by these thin clouds, double the entire exposure time. For thicker cloudy days, I adjustf or 2 stops, meaning I "double twice" (i.e. 1:30 becomes 6 minutes).

    The key to using paper negatives is: 1) test your specific camera and paper combination under bright sun and shaded daylight. These are your two calibration points. Don't try shooting under any other conditions, as exposure times will be too long; 2) understand the color sensitivity of the paper media; it's blue/UV sensitive. You can use a deep blue filter as a viewing aid for your eyes, to give you an idea of how a scene might be rendered, and how to judge exposure.
     
  6. Eric, this is all great information.

    I have not used paper negs. I have seven 4X5 phole cameras.

    Even with the ability to bracket shots, the negs are all over the place. Which produces unexpected results, sometimes great images like the one above.

    If I were teaching such a class, I would try to set it up so I could get quick results and make quick adjustments. Most kids have an attention span like a circus monkey. But if they get a good image, Hah! they will be hooked. Good luck!
     
  7. Hiya!
    thanks for all the useful information! I have built a pinhole camera using paper, completely in LEGO and controlled by Mindstorms, the LEGO Robotics kit.
    Have a look because with just guesswork, an image appeared! http://abiteof.com
    I am now programming the light meter function, that should eventually control the exposure time and this page is exactly what I was looking for!
    Alex - A Bite Of...
     
  8. I am working on a project in college, I chose to build a pinhole camera and explain how it works. I just want to thank everyone that contributed to this thread, the information was very helpful. Again, thanks for the awesome information.
     

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