Optimum pinhole size
Looking over various pinhole math I get wildly varying
What formula should I use
I have a 21 mm focal length and will be using colour film lit with flash
Subject distance will be about 5-10'
What size pinhole should I use ?
I would use a 0.15mm diameter pinhole. This was calculated in Pinhole Designer with a user constant of 1.4, derived through research and experimentation. Pinhole photography is not a matter of mathematical precision; personal preferences are important. Different subjects may work best with slightly different diameters. In wide-angle cameras the diameter may be increased for improved off-axis performance with degraded center sharpness. Others may prefer slightly smaller or larger diameters based on other science or actual photography. The magic and mystery of pinhole photography may be frustrating to those who believe in exact answers to any question. To others, a little quirkiness adds pleasure to photography.
send an email to email@example.com|(me)and I'll send you a free pdf,which may clrify the issue for you a bit.
How powerful is your flash unit?
A Vivitar 285HV on full manual (GN 120) using 400 speed film at 7.5 feet requires f/32.
A Sunpak 622 Super on full manual (GN 200) using 400 speed film at 7.5 feet requires f/53.
A Meggaflash PF200 type A-19 flashbulb (GN 420 at 1/30 sec or less) using 400 speed film at 7.5 feet requires f/112.
A Meggaflash PF300 type A-23 flashbulb (GN 550 at 1/30 sec or less) using 400 speed film at 7.5 feet requires f/147.
That last PF300 flashbulb option would seem to match up closely with Jim's recommendation for a 0.15mm pinhole size, since 21mm divided by 147 is 0.143mm. Unfortunately those PF300 bulbs sell at Cress Photo by the case lot (48 bulbs) for USD$630.00 per case, or $13.13 per bulb. Apparently scientists, railroad photographers and spelunkers are the major users of these still-in-production modern flashbulbs.
The problem here is that for a pinhole camera 5-10 feet away is a lot (unless you have access to some big-boy studio flash units)...
thanks for the replies guys
I know there's a bit of trial and error
but was a bit confused as to why the various online formula and calculators
give quite different results
as my pinhole to film is fixed in this instance
I have ordered a collection of sizes and will see what works best
I can't discuss the actual job but I'm sure you will all be interested
when it's been signed off
it's almost as crazy as the guy who did a wet plate stop Frame animation
Ralph thanks for the offer I have emailed you
Ken re. lighting
I'm very fortunate to have over 60'000 j of lighting
mostly made buy the English company Strobe
I have 2 of their swimming pool lights that have 4x 5' 5000j flash tubes on them
and various other 10'000j and 5000j lights
I have only got 14'000j of flash packs to power them up with but I can borrow more if I need it
we have run tests with tri x which came out great but a bit soft hence the initial question
and portra 400 which came out very contrasty with odd colour and is clearly well under exposed
and soft which I guess is down to the pinhole separating the wave lengths of different colours
vs tri-x general ability to cope with everything
we are testing again today so will use a lot more light as it's colour that we will ultimately be using
probably kodak vision3 500t which has similar properties to the portra 400
There are usually two different approaches for pinhole sizing, resulting in different apertures. The highest contrast is achieved with a slightly larger aperture than the aperture for highest resolution. They differ by about 30% in size, IIRC. The f-stops will be constant, meaning you have to calculate the diameter of the pinhole from the "focal length". I am not near my resources at present, but if you don't find help between the other posters here, drop me a PM and I'll scan and email you the relevant stuff. The higher contrast formula is usually favoured, as higher contrast is usually visually more appealing than lower contrast with higher resolution. It does depend a lot on taste and circumstances, though. For wide-angle, you may experience dark corners with the "optimum" f-stop, so using a larger aperture might help at the expense of resolution and contrast. What size negative are you capturing? 35 mm? Then how can you accommodate such a short register? Unless you use a rangefinder, probably. Still, 21 mm is very short, and you might battle to get even enough illumination. Colour neg film will be better than slide film, no doubt.
i'll try to attach a pdf, but they are usually too big for APUG; TOO BAD.
Sounds like that'll do! You're good to go then. Let us know how the project turns out...
Originally Posted by rbrigham
Me bad, it is actually the other way round, and the f-stops are not quite constant.
Originally Posted by dorff
The formula (based on contrast) is:
d = 1.56 * sqrt (f * L)
where f = focal length in mm, L = wavelength in mm, d = pinhole diameter in mm. For normal purposes, L is taken to be 555 nm, or 0.000555 mm.
The "ideal" f-stop increases with focal length.
In your case, with a focal length of 21 mm, the diameter should be 0.17 mm. This corresponds to an f-stop of 125, i.e. very close to f/128. For such a small aperture, the best would be to have it laser cut. If that isn't an option, consider a thin but sturdy metal foil. I have used copper tape with success. It can be found in craft shops, under stained glass consumables. Dent it with a ballpoint pen or other neatly round object, then pierce with a fine needle, against a slightly yielding backing such as hard rubber or wood.
"Way Beyond Monochrome II" has a chapter on pinhole photography. If you do not have the book yet, it is an excellent resource and worth every dollar.
I second the recommendation for Way Beyond Monochrome II. While it is about black and white photography, it covers the basics of photography that also apply to color, and is one of the most inspiring photographic books that I own. Its chapter on pinhole photography is more reliable than many other published sources. For much information on pinhole photography, look for Eric Renner's Pinhole Photography, available from http://www.pinholeresource.com/ and online booksellers. Two fine online resources are http://home.online.no/~gjon/pinhole.htm and http://www.f295.org/Pinholeforum/forum/Blah.pl.