My first pinhole camera, now what?
The camera is an old voigtlander folder, good bellows, shutter works. The lens had fungus and the diaphram blades are sprung. So it's a good candidate for experimentation.
Here's what I did so far. I smashed the glass out of the lenses. (that was a strange feeling) Inserted a piece of metal from the top of a tin can. punched a hole with a small tack. sanded the hole smooth. The hole is about the size of a large pin, smaller than a thumbtack but bigger than a sewing pin. Is that about right?
Then I blackened the metal with a candle. The pinhole is behind the shutter and held firmly in place with the lens rim.
Now, the camera uses 116 film. I respooled a roll of 120 onto the 116 spools and loaded it in the dark. I covered the red hole with black tape. I can remove it for a second to wind the film. It's all ready to go.
BUT. now what do I do? I'm using 100 speed color film just for testing. How long should an exposure be? 1 minute? 10 minutes? an hour? I need a rough idea to get started with.
And should the bellows be fully extended? Half? 1/4?
I realize I might have to do some shots and record the settings but i need an idea of where to start.
You need to figure out the "speed" (or lack thereof ) of your "lens". So F number=focal length / diameter of the hole.
In the case of a pinhole your focal length is the distance from the film plane to the hole - with bellows you can vary that but let's say you calculate aperture for a particular focal length.
Now you need to know the diameter of the hole you made. You can just guess - say .5mm or so but the most accurate way that I know of involves the following: Cut the piece of metal you are making the hole in and put it on a scanner - a slide scanner is ideal if you can put the sheet in a slide mount but a flatbed can work. Now scan the sheet at the highest resolution possible - this will give you a dark image with a little pinhole in the middle. If you view the image at 100% and crop out just the hole you can find out the length in pixels - if you know the DPI setting then converting this to inches or millimeters is fairly simple. This method is extremely accurate.
Ok, so now you have all the components to plug into your formula. In the case of my Brownie pinhole camera the f number works out to be 90mm/.5mm = f180.
So, now you can figure out exposure in terms of EVs if you can guess at or measure the light with a meter. All that is left is to adjust that time for the reciprocity of your particular film which can be pretty drastic. I've done 10 hours or more at about EV5 with ISO 100 film.
I've found an enlarger (if you have one) to be the easiest way to measure pinholes (BTW I think yours is going to be a bit big if 'sharpness' is your aim). Put the pinhole in the neg carrier and measure the projected circle (this also allows you to see how round the hole really is). Workout the magnification ratio either from reading from the enlarger colum if it has a scale or measure the neg carrier opening and divide that by the image that it projects with nothing in it. Divide the size of the pinhole image by the magnification ratio and that's your pinhole size. Put that into the F no calcs to determine exposure, or surf to www.mrpinhole.com and use their calculator.
For me, a scanner is the simplest way to measure my pinholes. I scan at maximum resolution (2400 ppi, in my case) and after the image is in my editor, I can crop to just include the hole and get a direct readout of diameter on two axes. Optimum pinhole size isn't very critical, you'll get decent images with almost any hole (even f/45 at 135 mm will give recognizable images). You can even choose your bellows extensions, though it'll be easiest to get consistent exposure if you set focus to infinity and extend the bellows to the stop, because that setting is repeatable.
BTW, you can pretty easily make an adapter (four nickels will probably do the job) for the supply side of that camera to accept 120 still on the spool; that will let you load in daylight, at least (though you'll still have to unload in the darkroom), and also keep the film a bit better centered. With a little more work, you can convert one of the 116 spools to an adapter that will drive a 120 spool for takeup as well, and then you can reload in the field. The 616 camera I have (same film as 116, different spools), I was able to permanently tape over part of the red window (on the inside) and keep light from spilling around the film edge, allowing me to advance without having to mess with uncovering and recovering.
I'll admit, I cringed at the thought of smashing the glass out of a Voigtlander -- the thought of a Skopar being reduced to fragments is horrible, especially since it could probably have just been unscrewed! -- but if you didn't have the ability to repair the aperture yourself, it surely wouldn't have been worth paying someone to do so... :P
Photography has always fascinated me -- as a child, simply for the magic of capturing an image onto glossy paper with a little box, but as an adult because of the unique juxtaposition of science and art -- the physics of optics, the mechanics of the camera, the chemistry of film and developer, alongside the art in seeing, composing, exposing, processing and printing.