Pinhole size and distance

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• 05-12-2010, 02:10 PM
Joe VanCleave
I believe there's a thread over on F295 where someone went and calculated what the actual off-axis focal ratio and light falloff would be when taking into account a pinhole made in an actual material of finite wall thickness which, when viewed from an angle, appears to be elliptical, due to the real-world wall thickness of the pinhole material.

It's a great exercise in geometry and math, but really doesn't effect my personal pinhole photography, which I do by imperical testing rather than through calculation.

As for an "acceptable" angle of view, this is really an aesthetic choice that an online spreadsheet can't decide for you. Some people like the "Holga-like" dark corners, or whacked-out extreme wide-angle views, while others like their images more serene and even-exposed from center to corner.

I think it's an interesting technical challenge to determine all the parameters of a pinhole camera and image ahead of time, but that doesn't really make us better photographers, nor do such calculations inform us about aesthetic choices that only we can make for ourselves. The great thing about pinhole photography is that there's no "right" or "wrong" approach, so the idea of hard, fast, fixed rules is a misnomer. Sometimes the best pinhole images are the ones resulting from the most spontaneity, with the least amount of preplanning.

~Joe
• 05-12-2010, 03:11 PM
DWThomas
Actually, even with zero thickness the pinhole appears elliptical from an off axis view; the finite thickness only increases the problem. In truth, I'm in basic agreement with the idea that it's not necessary to calculate the stuff to death, just put something together and take some pictures. I view it a bit like cooking/baking without a recipe, sometimes it's fun to blur some boundaries!
• 05-12-2010, 03:22 PM
RalphLambrecht
Quote:

Originally Posted by DWThomas
...In truth, I'm in basic agreement with the idea that it's not necessary to calculate the stuff to death, just put something together and take some pictures. I view it a bit like cooking/baking without a recipe, sometimes it's fun to blur some boundaries!

Agreed, but I like to understand the facts before I ignore them.
• 05-12-2010, 03:34 PM
Lee L
I feel the same way. I think the difference across a range of pinhole sizes won't optimize an image to the point of making it succeed or not as an image worth looking at. Finding some discrete optimal pinhole size is an exercise in math and theory, not making significant photos, even if you can define precisely where along some spectrum your optimum image quality lies.

I also think there are many other, more interesting things about pinholes to explore, along with slit apertures, zone plates, and other lensless image forming methods. I recently acquired a handmade pinhole from bowzart that I'm hoping to have time to work with this weekend (if I can get out from under other chores and mount it), and the subject matter and other considerations are more important to me than whether it might be possible to get a 5% increase in 'sharpness' from a pinhole. One of those is the fun of using a tool expertly hand-made by a friend.

That being said, the OP does deserve some reasonable answers to his questions, and I think he's gotten that.

Lee
• 05-12-2010, 07:47 PM
Joe VanCleave
Quote:

Originally Posted by DWThomas
Actually, even with zero thickness the pinhole appears elliptical from an off axis view; the finite thickness only increases the problem. In truth, I'm in basic agreement with the idea that it's not necessary to calculate the stuff to death, just put something together and take some pictures. I view it a bit like cooking/baking without a recipe, sometimes it's fun to blur some boundaries!

Yes, of course you're right; I poorly worded my response (or is that "worded poorly"...).

In case anyone's curious, here's the thread over on F295 that talks about "exposure mapping", which morphs into a discussion about real-world pinhole "tunnels" vs 2-D imaginary pinholes, and the difference it contributes to off-axis exposure.

~Joe
• 05-13-2010, 12:27 PM
bowzart
If you've ever looked at your pinhole through a microscope, you've probably seen just how excessive the concern about "optimal" can be. Getting the hole to be clean and free of metal junk when it is new is a real challenge, and keeping it clean afterward isn't much easier. You could have a "perfect" pinhole and still get very disappointing results.
• 05-13-2010, 12:28 PM
Thomas Bertilsson
How do you recommend keeping a pinhole clean?

- Thomas

Quote:

Originally Posted by bowzart
If you've ever looked at your pinhole through a microscope, you've probably seen just how excessive the concern about "optimal" can be. Getting the hole to be clean and free of metal junk when it is new is a real challenge, and keeping it clean afterward isn't much easier. You could have a "perfect" pinhole and still get very disappointing results.

• 05-13-2010, 01:04 PM
bowzart
Usually, if I'm not in my studio, I just blow on the thing really hard from both sides. This isn't really good enough but it makes me feel better. I've washed them, blown them with compressed air, and gently cleaned them with a needle. The last mentioned requires a very delicate touch, but that is the way I get them clean when I make them and I've had a lot of practice. As I've grown older, though, everything about making and maintaining pinholes has become much more difficult as my eyes become less reliable and touch loses some of its steadiness.

I have to wonder about using some sort of sticky stuff to collect transient particles, a kneaded eraser might work (the kind that we use in charcoal drawing).

Maybe some sort of electrostatic device could work; I have one of those gizmos that labs used to clean negatives, but I haven't yet tried running a pinhole through it.

It's sort of impractical to carry an air compressor around all the time. Another idea that seems promising would be to carry a small graduated tube to blow through, concentrating a stream of air. Washing in water is practical, but the hole needs to be dry; a drop of water becomes a lens.

Regardless of what you do to clean a pinhole, it is important to be able to observe its condition. I use a 50x projection microscope to see what's going on if I have it available. Out there when working, a pocket microscope can be helpful if I remember to take it with me. A loupe or magnifying glass doesn't magnify enough.

Or, of course, you can just live with what you get. I think the most important thing is to start out with a clean pinhole and try whatever you think might work when you are using it. If the hole has ragged metal left in it when it's made, it will affect both exposure and image quality.

Now, I must confess that I really like a "sharp" pinhole image, to the point where my pinholes have been criticized as "too damn sharp". The quality possible in a pinhole image can be really amazing. While they don't have that kind of sharpness that lenses can produce, there is a potential for sharpness embedded in softness, if you can visualize what I mean. It's hard to describe.
• 05-13-2010, 01:09 PM
Thomas Bertilsson

The pinhole camera I use has a very good pinhole. It's sharp and clean, and I'm amazed at how nice the prints look when I make the most use of the contrast available in the paper. Even more so than with lens photography, I find that getting the negative 'just right' is even more important, because I feel like I rely on tonal values for sharpness.

I haven't had to clean my pinhole yet, after almost two years of using it. Perhaps it's time to check it with a microscope! :)