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Thread: getting started (hopefully0

  1. #1

    getting started (hopefully0

    I'm new to this but I've just drilled a hole in a SLR body cap & taped some kitchen foil over it & put a hole through it with a needle. When I look through the viewfinder none of the image is in focus. What do I do now?

  2. #2

    getting started (hopefully0

    Hi Doc:

    It's probably also very hard to see with the small amount of light getting thru.

    Assuming the aperture you made is reasonably close to the right size for the distance it is located from the film, estimate it's size and divide it into the distance from aperture to film plane. Say, for example, you have a 1/4 mm hole at 45 mm spacing. 45/(1/) = f/180.

    You can estimate exposure based on this. If you end up with times longer than 1 second some lengthening of exposure may be needed to correct for film reciprocity failure at long exposure.

    If you have a 'reasonable' geometry of construction, just proceed...don't worry too much about what you can see thru the viewfinder...it's only good for aiming. Keep in mind with an SLR that bright light can enter the eyepiece of the viewfinder and go thru the pentaprism to the film. Cover if exposed to bright light. I've never had a problem with it but it IS there.

    Go ahead and shoot some film if you are open to experimentation and won't be discouraged by a need to make adjustments and retry.

    If you prefer to have more variables eliminated (as I do) before proceeding, come back with more info on your camera geometry, film type, etc and we'll help you pre-determine if you are on track or off track.

    Murray

  3. #3

    getting started (hopefully0

    murray has pretty much covered it, but i would add that aluminum foil doesn't make for very good or stable pinholes, unless you use the heavier gauge stuff from pie plates, etc. brass shim stock will give you a stronger metal at thinner dimensions, and can be found in almost any auto or hardware store. you can sand the hole even thinner and it won't tear as easily.

  4. #4

    getting started (hopefully0

    No pinhole image is perfectly sharp. Unsharpness is aggravated by pinhole diameters of more or less than the optimum size. A versatile and free program for determining pinhole size is available at http://www.pinhole.cz/en/pinholedesigner/. I recommend a user constant of 1.5 with this program for an image sharpest in the center. For a site with much good information, and links to many other good sites, go to http://home.online.no/~gjon/pinhole.htm. Pinhole photography can be simple and fun, or it can be demanding. The harder and smarter you work at it, the more rewarding it will become.

  5. #5

    getting started (hopefully0

    Thanks for the info. At the risk of sounding really stupid, how do I determine the distance between the body cap & the film plane accurately & how do I measure the size of the pinhole?

  6. #6

    getting started (hopefully0

    You can probably find a rererence to the film-to-flange distance of any SLR lens mount, and then measure your body cap carefully to determine where your hole is relative to the body cap's flange mating surface.

    Pinholes are most easily measured with a scanner (at least for me). Scan at highest resolution, enlarge the image so you can see the invididual pixels well, and crop to the exact hole size, then look at the image size and multiply by the pixel dimensions (i.e. 2400 ppi, you'd multiply by 1/2400 to get a diameter in inches). There are other methods, some of them potentially more accurate, but none are as simple if you have a high resolution scanner available...

  7. #7

    getting started (hopefully0

    35mm SLR bodies are typically about 45mm from lens flange to film. It's easy to measure with the lens removed and the shutter open. This isn't a very critical measurement. Pinhole diameters are more critical and more difficult to measure. ImageMaker's suggestion of using a scanner is a good solution. Exposure is critical when you do this. I had to tinker with the exposure when using a transparancy adaptor on my scanner to prevent overexposure from giving too large a reading. Another method of measuring pinhole diameter is to place the pinhole in the negative carrier of an enlarger and measure the enlarged diameter. It's a bit tricky, and involves a little math.

  8. #8

    getting started (hopefully0

    Thanks everyone. I'm off to do some experimenting. I'll let you know the results when I develop the film.

  9. #9

    getting started (hopefully0

    Quote Originally Posted by ImageMaker
    You can probably find a rererence to the film-to-flange distance of any SLR lens mount, and then measure your body cap carefully to determine where your hole is relative to the body cap's flange mating surface.

    Pinholes are most easily measured with a scanner (at least for me). Scan at highest resolution, enlarge the image so you can see the invididual pixels well, and crop to the exact hole size, then look at the image size and multiply by the pixel dimensions (i.e. 2400 ppi, you'd multiply by 1/2400 to get a diameter in inches). There are other methods, some of them potentially more accurate, but none are as simple if you have a high resolution scanner available...
    curious if one could* measure a pinhole by the size of the light it passes. mount it a fixed distance from a wall, shine a light on it, measure the pool of light and then . . . .*

    Would that work?*

  10. #10
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    getting started (hopefully0

    Quote Originally Posted by paulbeard

    curious if one could* measure a pinhole by the size of the light it passes. mount it a fixed distance from a wall, shine a light on it, measure the pool of light and then . . . .*

    Would that work?*
    I had that same idea when I first started playing with pinholes. I used a candle for the light source, as it was handy in the room I was in. I had to laugh when I did not see a circle of light on the wall, but rather an inverted image of the candle flame. If you used a light, you could easily measure the image of the light source and not be able to see the edges of the pinhole. The light source has to be very close to the hole, and then this method should work. It is hard to get the measurements as exact as you can with either the scanner or the enlarger, though.

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