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• 01-16-2011, 12:31 AM
Nick Kanellos
Quote:

Originally Posted by michaelbsc
Is this the Formula for an optimum size?

Yep
• 01-16-2011, 01:23 AM
anon12345
Quote:

Originally Posted by Nick Kanellos
Let me take a stab:

1) The shape of the pinhole. I suppose you could say that the amount of light diffracted is proportional to the perimeter of the pinhole. The smallest perimeter for any given area (e.g. the area of the pinhole itself) is a perfect circle. Anything else adds more 'edge' around which more light can be diffracted. Which results in reducing sharpness. How'd I do?

2) Thickness of the plate material. Let's see. Hmmm.... Imagine light coming into the pinhole at any angle from the axis. Some of that light will "touch" the front edge of the pinhole. Resulting in some diffraction. Some of the light will then "touch" the rear edge of the pinhole. More diffraction. Any thickness greater than zero effectively results in "two" pinholes: one at the front surface of the plate and one at the rear surface. Effectively doubling the diffraction causing edge. Also a thicker plate effectively reduces the pinhole aperture for any light not coming straight from the front.

To remedy this, once you've drilled your pinhole, take a counter sinking drill bit and create a conical shaped hole over your pinhole. If you get it just right, it will result in a near knife edge perimeter for your pinhole. It might make it a bit delicate but no more so than a glass lens.

3) Colour. Not a clue.

I'll go with that. In my own pinhole creations I strive for a clean, round, and very thin pinhole. This has improved my images. I've attempted this with aluminum foil, but ultimately I end up using thin sheet brass. I found that examination under a microscope is necessary to insure there are no entry or exit burrs, and that the pinhole is as clean and round as possible. Black seems to be the color of choice. I have read that blackening the hole with soot from a candle can help absorb light energy that would otherwise be reflected off the inside surfaces of the hole. For my own purposes I've blackened the hole's inside surfaces with black ink. I have included a basic diagram of a pinhole of my own design that has worked quite well so far. If anyone can use this or improve upon it, please feel free to do so.
• 01-16-2011, 02:50 AM
aaronmichael
Quote:

Originally Posted by Cesaraugusta
Beyond focal length and the physical size of the pinhole, I can think of several more aspects that when considered in the pinhole's design will most likely increase the sharpness (reduce defraction) in the projected image.

1. The shape of the pinhole.
2. The thickness of the pinhole plate material (at the pinhole)
3. The color of the pinhole plate material (at the pinhole)

Would someone care to elaborate further? :blink:

I'm just a newbie into pinhole photography but as for the shape of my pinhole, I've tried to get it as round as possible using a needle. For the material, I use the metal from soda cans and sand it down with an electrical orbital sander using 60 grit sand paper. This gets it pretty thin pretty fast. As for the color of the material, I usually paint both sides black. Below is probably the best shot I've done using the methods described.

http://www.flickr.com/photos/aaronmi...7625595921944/

The focal length for the camera it was taken with is 125mm and my new 8x10 camera that I built has a focal length of 190mm - which is what sparked the thread. Wanted to know if there was a reason why making a larger pinhole for the longer focal length would be beneficial. I think the pinhole diameter for the above shot was .46mm.
• 01-16-2011, 05:47 AM
moki
I use regular thin aluminium foil for the hole, because it's thin enough to start with and you don't need to do the trick with denting it in and using very finse sandpaper to prepare it. It's not as robust, but good enough if you're careful. The trick is not to push the needle through, but put the foil onto a piece of cardboard, just lightly set the needle onto it and twist is while applying very little pressure and then shave away the edge with a very sharp razor. I can consistently get holes down to 0,2mm with almost perfectly round shape like that. I usually just do 10 holes at a time and see afterwards, which one fits best for my camera by scanning them digitally and getting the exact size that way.
I don't care too much for the optimal size, because the difference is almost invisible anyway. I just try to find a hole that gives me decent exposure times like 1-2sec in bright sunlight with 100ASA film.

Using a piece of high resolution, high contrast film, photographing a tiny black dot on a white wall and using that as pinhole might be even better, though. I know it is used for zone plates or pinhole sieves, but I don't see, why it shouldn't work for single pinholes. It's probably the easiest to way to get exactly the right size, because it can be calculated beforehand.

The thickness of the pinhole material only becomes important, when you want shorter than normal focal length, because thick materials show much more vignetting from blocking the light with the edge. Some unprocessed metal from a soda can might get you an image circle of about 50° without too much light loss, aluminium foil gets you 100° while filed downs brass sheet gives 120° (these are no real or tested numbers, just an example). So if you're not using some ridicilous wide-angle like 30mm on 4x5, it's not that important.
Feel free to criticize me for that - I'm a practical pinhole photographer, not a scientist or someone who examines every picture with a loupe.
• 01-16-2011, 09:22 AM
Jim Jones
Quote:

Originally Posted by Nick Kanellos
d=1.56√λf

where
d = the pinhole diameter
λ = the wave length (about 0.000555mm)
f = the focal length

Taken from "Way Beyond Monochrome. 2nd ed." p. 155

To simplify the formula for panchromatic film, multiply the square root of the focal length by .007 (all in inches) or use PinholeDesigner with a user constant of about 1.5. Reduce the diameter a bit for macro photography, increase a bit for ultra wide angle. Way Beyond Monochrome, 2nd ed. is a magnificant book, although the section on pinhole photography doesn't thoroughly address the often overlooked problems with wide angle pinholes. I prefer .002" brass shim stock over aluminum for making pinholes. Dimpling it before making the hole reduces thickness around the hole even more. It seems to work cleaner than aluminum. Brass can be chemically darkened. One small sheet of shimstock might last a lifetime.

Pinhole photography sounds simple, but like many simple arts, it demands more of the practicioner than something as complex as digital photography. Entire books have been written on the subject without covering all aspects of it: Eric Renner's fine 260 page Pinhole Photography, for example. The art and technique of pinhole photography are discussed at length on http://www.f295.org/Pinholeforum/
• 01-16-2011, 10:42 AM
anon12345
Quote:

Originally Posted by aaronmichael
I'm just a newbie into pinhole photography but as for the shape of my pinhole, I've tried to get it as round as possible using a needle. For the material, I use the metal from soda cans and sand it down with an electrical orbital sander using 60 grit sand paper. This gets it pretty thin pretty fast. As for the color of the material, I usually paint both sides black. Below is probably the best shot I've done using the methods described.

http://www.flickr.com/photos/aaronmi...7625595921944/

Referring to the second image with the tree.

The focal length for the camera it was taken with is 125mm and my new 8x10 camera that I built has a focal length of 190mm - which is what sparked the thread. Wanted to know if there was a reason why making a larger pinhole for the longer focal length would be beneficial. I think the pinhole diameter for the above shot was .46mm.

Forgive me if I have a confused look on my face . . .:confused:

Looking at your pinhole images at flickr, I'm trying to determine what that is framing the central shot. It looks like the edges of ragged cardboard. Is there a lens between the pinhole and the film when taking these images?

For example . . .http://www.flickr.com/photos/aaronmichael/5252385067

What am I seeing here? I guess I'm missing some details of your process.

Thanks.
• 01-16-2011, 11:34 AM
aaronmichael
I spent a while myself trying to figure out what that was - hahah. My pinhole camera is made out of half inch thick plywood and the hole that was cut out in the wood on the front for the pinhole to go behind was too small at first. The hole being too small resulted in light bouncing off of the wood and framing the image. After I finally realized this I made the hole larger and you can see with the bricks and door image that I almost completely fixed the problem. After that photo, I made it even larger but haven't had a chance to try it out yet.
• 01-16-2011, 11:43 AM
anon12345
Quote:

Originally Posted by aaronmichael
I spent a while myself trying to figure out what that was - hahah. My pinhole camera is made out of half inch thick plywood and the hole that was cut out in the wood on the front for the pinhole to go behind was too small at first. The hole being too small resulted in light bouncing off of the wood and framing the image. After I finally realized this I made the hole larger and you can see with the bricks and door image that I almost completely fixed the problem. After that photo, I made it even larger but haven't had a chance to try it out yet.

Thank you for the explanation. It all makes sense, now. :)
• 01-16-2011, 12:18 PM
michaelbsc
Quote:

Originally Posted by aaronmichael
I spent a while myself trying to figure out what that was - hahah. My pinhole camera is made out of half inch thick plywood and the hole that was cut out in the wood on the front for the pinhole to go behind was too small at first. The hole being too small resulted in light bouncing off of the wood and framing the image. After I finally realized this I made the hole larger and you can see with the bricks and door image that I almost completely fixed the problem. After that photo, I made it even larger but haven't had a chance to try it out yet.

Ok. In essence your original hole formed a mechanical vignette hood?
• 01-16-2011, 07:03 PM
aaronmichael
Quote:

Originally Posted by michaelbsc
Ok. In essence your original hole formed a mechanical vignette hood?

Haha - exactly. Sorry for the crappy quality of this photo (it was taken with my phone), but this was the hole before I widened it out.

http://static.zooomr.com/images/9652...57de7a7e_b.jpg

And this is it after making it larger.

http://static.zooomr.com/images/9733...6aa2ab15_b.jpg
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