Fastest possible shutter speeds for pinhole?
I'm becoming very interested in pinhole photography and am considering desinging and building a 5x7 camera.
Almost all of my applications would require a high shutter speed (of say 1/125) so I'm wondering if decent exposure at this high shutter speed is possible?
Getting a shutter to work that fast shouldnt be a problem, as I'll modify a shutter system from an old SLR and fit it to the pinhole (I'm a fitter machinist by trade, so I like building/destroying things)
I'm just woried that with such a high shutter speed that it wont expose the negative enough.
I was thinking of using Ilford HP5 400asa 5x7 Sheet film. Pushed if nessessary.
Is this at all possible?
i don't understand your basic premise, why a fast shutter speed?
pinhole, by it's very nature means long exposure times
the problem i have with my homemade cameras is keeping the exposure time greater than a second so that i can use the lens cap as the shutter
just as in any other type of camera the exposure is a combinatiopn of shutter and aperture, if you blindly want to use a particular shutter speed then yes the exposure may well be wrong
the determining factor in pinhole photography is that the pinhole has a constant relative aperture, a huge number something like f256 for example
Well, it's late, and maybe I'm befuddled, but I tried a quick check. Consider that using the "Sunny 16" rule, you would use ISO 125 film exposed at 1/125 at f16. Since pinholes run more like f256 -- 8 stops less exposure, you would need a film speed up around (2^8) x 125 = 32,000. That's pretty hot film.
I had a similar experience to Ray. Using 400 film, I needed exposures in the 1 to 2 second range (which jibes pretty well with Sunny 16), so I switched to 100 film to get a more manageable exposure length for a hand operated flap.
Figure out some baseline exposure times.
1) Box speed of film, lets say you picked ISO 400. Sunny-16 "rule" says with the sun over your shoulder and crisp shadows, your base exposure at f-16 is 1/400.
2) Correct for your pinhole size. I'll just guess at your camera focal length since you said 5x7 and pick 8.5 inches (film diagonal) or 215mm (rounding liberally). And I'll assume your pinhole diameter is 0.5mm, close to "optimal" for said focal length. Now we know your effective f-stop is f-430
3) do the math: (430 / 16)^2 = 722 (again with the liberal rounding). So your base sun over the shoulder exposure is 722 / 400 = 1.8 seconds.
4) apply reciprocity failure factor, this depends on the film. If you were shooting HP5+ I'd say you need 2.5 seconds. Lets just call it 3 seconds.
So, 1/125 second is a bit on the fast side.
My Nikon with the f/180 pinhole shoots 400 ASA film at about 0.25 seconds on a sunny day.
f/ seconds @ ASA 400
64 1/25 AA'sfavorite f/stop
180 1/4 <= what I use on a sunny day
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Nothing beats a great piece of glass!
I leave the digital work for the urologists and proctologists.
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I started trying to come up with an analytical example of what you'd have to do to make this fly. It didn't come to me right away, so I started with a sunny-16 example.
If you were metering with an EV meter, that would be (APEX) AV8+TV8.6 = 16.6
If you were shooting 5x7 and wanted 'normal' angle of view, let's assume about 220 mm camera length. One opinion of optimal pinhole diameter is 0.625 mm, say you had a 0.6mm pinhole. that's about f/366. Call it 360 for easy math.
If you'll take my word for it, f/360 is an APEX aperture value of 17.
Let's say it's wee bit brighter and we call the lighting EV17
Again, take my word for it, an APEX time value of 0 = 1 second.
At ISO400 you are roughly 7-8 stops off.
That would be a lot of pushing for the film...right?
Say you went somewhat wide angle, 4.5" or 115 mm camera. One pinhole calculator gives you a suggested pinhole of 0.45 mm, this gives you a roughly f/256 camera.
This only gained you one stop advantage over the previous design.
I have heard of people doing handheld pinhole work with the Ilford 3200 of the old 3000 Polaroid, but can't tell you the math behind how well it should work.
It is said that because pinhole resolution is so much lower, one can hand-hold a pinhole camera at much lower shutter speeds than a lensed camera and tolerate the appearance. I think I heard a factor of 5. That doesn't solve your need for 1/125 sec. If that's based on presuming that is necessary for handheld work, the rule of thumb would be that you could roughly get away w/1/25 sec with pinhole.
Now, some people do manage some amazingly sharp work with slightly smaller than 'optimal' calculator pinholes (say 75% of optimal diameter).
If you want sharpest possible, I wouldn't but all my money on the 1/5 speed rule compared to lens (and that rule for a lens was 1/f.l., so 1/220 s, that gives you about 1/45 for pinhole, between 1/30 and 1/60).
I agree with most of the posters here that 1/125 sec does not seem doable. However, as Murray mentioned, you can get a little more speed by going wider. My favorite focal length for pinhole on 4x5 is 50mm. That translates to about 67mm on 5x7, which (with a .4mm pinhole) yields roughly f/168. With EI = 400, this should get you to about 1/4 of a second on a sunny day.
I've seen photographers go as wide as 25mm on 4x5 (Zeroimage sells such a camera), which is roughly 34mm on 5x7. Using this wide a camera with 400 ISO film pushed to EI 1600, you can get to 1/32 of a second, or 1/64 of a second at EI 3200, which is probably the practical limit. At this point, the cos^4 falloff, along with the lost shadow detail will start to severely restrict your usable image circle.
Sorry, I can't resist the irony here.
If someone wanted to build a ULF 20x24" giganto camera and wanted a cheap 12" lens that would cover, the peanut gallery would tell him to go pinhole.
Here, the proposal almost says 'get a lens'.
He's not down & out yet. Maybe the 1/125 requirement can be relaxed a bit. Landscapes instead of sports.
"get a lens" as Murray suggests is exactly what i did with my homemade cameras
wanting to avoid extremely long pinhole exposures i experimented with magnifying glasses as simple lenses
i came to prefer the look created by these cheap optics, sharp in the centre blurring to the edges, somewhat like the old lenses people here rave about, (Petzvals?)
these magnifying glasses are very cheap, $2 or so, the camera is then designed around the lens, i now have 8 cameras in various sizes, 4x5, 5x8, 5x7, 8x10 and am currently building an 11x14
using FB paper gives a look i prefer and keeps the ISO at about 6, this then equates to exposure times of seconds and minutes
Last edited by Ray Heath; 05-22-2008 at 02:34 AM. Click to view previous post history.