School me on pinholes please!

New Hampshire · Mar 29, 2011

Ok, so I have been doing a little research on pinhole photography. I have seen a very simple idea is to take an SLR body cap and convert it into a pinhole "lens". Going even further there is this company that sells laser drilled pinhole body caps:

Digital SLR Camera Caps - LENOX LASER

Now what I hope someone wiser and more knowledgeable than me can answer is a bit complicated. First of all, the hole of the Lenox cap is 240 microns or .24mm. Now, what approximate focal length would that equate to? I am gathering from what I see that it does not equate to a very good wide angle, so what approximate focal length would it come to? Also, would a CMOS sensor vs. a true 35mm size make a difference in calculating what focal length it would be? I know it does when an actual lens is used (i.e. the "crop factor"), so I am assuming it would still be so with the pinhole cap? The truth is I would probably use this mostly on my Canon Elan7 35mm since I read that these pinhole caps tend to have problems on dslr's (mostly in that, due to it's small aperture nature, it heavily exaggerates sensor dust on your images). But since it can't hurt I would probably still try it on my XTi. But just so I have an idea it would be nice to know what kind of focal length I could expect for both the CMOS sensor and a standard 35mm film frame.

Brian

Big Mike · Mar 29, 2011

Also, would a CMOS sensor vs. a true 35mm size make a difference in calculating what focal length it would be? I know it does when an actual lens is used (i.e. the "crop factor"), so I am assuming it would still be so with the pinhole cap?

Actually, the size of the sensor (or film) has no bearing on the focal length. The 'crop factor' is simply a way to compare the Field of View (not focal length)....of DSLR cameras back to the old standard of 35mm film. To repeat, the crop factor does not affect the focal length.

I'm not sure how you would calculate the exact focal length of a body cap pin-hole, but I'd assume that it's something they would give you along with the cap...or you could look it up as most caps (for the same make of camera) are the same distance from the sensor. You could then use the focal length, along with the size of the hole, to calculate the F stop of the pin-hole lens, and use that to estimate your exposure.

But even if you can't figure that out, it's constant, so you could just take some test shots to find what shutter speed & ISO would be required.

enzodm · Mar 30, 2011

New Hampshire said:
First of all, the hole of the Lenox cap is 240 microns or .24mm.

240 microns = 0.24mm.

For the rest, just try it. In particular on digital, there is nothing to loose. I did my pinhole more or less like the second version here (the aluminium foil one). If you have macro rings, with them you may change focal length easily.
This one is 25 seconds:

clanthar · Mar 30, 2011

The pinhole focal length will be the distance from the pinhole to the sensor. If you mount the pinhole 40mm from the sensor then the focal length is 40mm.

Where .00055 and 1.9 are constants that account for the wavelength of visible light and Rayleigh's criterion of sharpness, F = the focal length, and P = the ideal pinhole diameter: P = 1.9F(sqr.00055).

above units are mm.

Joe

Josh66 · Mar 30, 2011

On the EF mount, a body cap pinhole has a focal length of roughly 50mm. (Flange focal distance is 44mm - add a few mm for the thickness of the cap.)

I have one made by Finney Field Cameras. The pinhole diameter is .011" (.2794mm), which makes it f/180 (178.95) if the focal length is 50mm.

The focal length doesn't really matter for figuring out the exposure though. Depending on how bright it is, you might not be able to actually see through it with it mounted to the camera.
What I do is mount a 50mm lens, and compose with that (since the FOV will be similar). I'll set it to f/11 or f/22, zero the meter out, then figure out how many seconds it would be at f/180.

Say I'm getting 1 second at f/22... that's 4 seconds at f/45 (2 stops), 16 seconds at f/90 (another 2 stops), and 64 seconds at f/180 (2 more stops). So, that's my exposure time - 64 seconds. If you're using film, reciprocity failure applies ... so maybe more like 2-3 minutes depending on what film you're using.

Derrel · Mar 30, 2011

Pinholes are great for creative weddings as well!!!

New Hampshire · Mar 30, 2011

Excellent everyone, it's a good start. I am also looking at some nice, but not too expensive, wooden pinhole cameras on ebay. Looks like a neat way to have a little fun on the side.

Brian

enzodm · Mar 31, 2011

Honestly, due to the kind of results, I would not buy anything except a (standard) body cap. Since the aim is fun, add to the pinhole shooting fun the pinhole building fun.

The basics is: do a somewhat large hole in the cap, and cover it with thin aluminium. Do a hole in aluminium with a pin. If you want to know how large it is, photograph it together with some known reference, zoom 100% and measure it with proportions.

Forkie · Mar 31, 2011

Derrel said:
Pinholes are great for creative weddings as well!!!

Seriously, not again! :biglaugh:

JamesD · Apr 1, 2011

With the Elan 7 series, you'll probably want to use the locking cable release; as mentioned, reciprocity failure hits pretty hard in the range of exposure times you'll be looking at with slow film and small apertures. I've never run into grain size problems with pinhole, although I mostly use 4x5, where it's less of an issue... but you might try some faster films to cut down on exposure times, even though they're grainier.

I'm not very familiar with the details of pinholes on digital cameras. With the smaller-frame sensor, the main difference I'd expect to see is lower overall detail resolution. All other factors equal, there has to be a certain angular distance between details, and with small sensors, there's less total angle available. This can be compensated for a bit if there's sufficient contrast between the details, but that's not usually something that can be directly controlled.

I do hope you enjoy your experiments, pinhole can be a lot of fun! It's one of my favorite sides of photography.

New Hampshire · Apr 1, 2011

Thanks James, it should indeed be some fun experimenting. I have sen some surprising work done with pinhole cameras (both in sharpness/clarit and the not-so-sharp/clear artsy style.) I am looking at some nice all wooden pinholes.....I would make one myself if only I could find plans for one (and I mean real hardwood, not paper or matchbox or oatmeal can one). I have access to basic woodworking tools (table saw, jig saw, sander, etc.) and figure it would be neat to have something that LOOKS nice as well as shoots nice.

Brian

Josh66 · Apr 1, 2011

Plans? Make a light-tight box and put a hole in it.

I would make it to fit the film you plan to use, 4x5 sheet for example... Make it big enough for that, with something on the inside to hold the film. Make it so that it's easy to change the film in a changing bag...

Focal length would be the depth of the box. "Normal" (50mm for 35mm film) focal length is the diagonal of the film format, so once you know what film you're going to put in it, you know what the depth needs to be for the focal length you want.

Josh66 · Apr 1, 2011

Example ... say your neg is 6x6cm... The diagonal of that is 85mm. 60mm^2+60mm^2=7200mm. Square root of 7200=84.85...

If you want wide angle, make the box 40 or 50mm deep. Telephoto, 135 or 200mm...

a^2+b^2=c^2 ... easy stuff.