Pinhole test

Recently I wrote about making a pinhole lens for my view camera. The results weren’t brilliant and I wondered if I had chosen the right diameter of pinhole. So I asked laser dude to cut some more pinholes in other sizes, and now I have 0.2mm, 0.3mm, 0.4mm and 0.5mm pinholes, all mounted in 80mm steel plates for easy use on the view camera.

Pinhole mounted on camera

Trouble is with testing things in a view camera, it chews up a lot of film – almost £1 per frame I shoot! But I realised I can also use these pinholes with my DSLR by simply holding the steel plate over the lens mount of the DSLR.

So I took these photos out of my window with the pinhole held over the DSLR’s open mount. The pinhole is approximately 45mm from the sensor, giving it the same field of view as a regular 45mm lens – that’s quite zoomy for a crop-sensor DSLR.

These pictures were all taken at ISO 400. I wasn’t too careful with the exposure. The trouble is, when the camera is “too dark” inside (because the pinhole doesn’t let in enough light) the light meter readings are affected by light entering the viewfinder and are worthless. If you block off the viewfinder with your thumb, the meter doesn’t get enough light to work at all. The only way of exposing sensible is to use manual mode and guess a shutter speed until the picture looks OK. I think overexposed these increasingly as I used the larger pinholes, but never mind 😛

Pinhole Focal length Aperture Exposure
0.2mm 45mm f/225 2″
0.3mm f/150 1″
0.4mm f/113 1″
0.5mm f/90 ½”
0.2mm pinhole
0.3mm pinhole
0.4mm pinhole
0.5mm pinhole

It seems pretty clear to me that the 0.3mm pinhole is sharpest. In theory, the smaller the pinhole, the sharper the image. However, the smaller the pinhole, the more diffraction comes into play and spoils the sharpness. There is a “sweet spot” where you can find the best compromise between sharpness and diffraction, and an optimum size for the pinhole. This depends on the size of your film/sensor and the distance between the pinhole and the sensor. For my DSLR, the optimum should be around 0.3mm and for my view camera, more like 0.4mm. More on this soon 😉

If you’re a geek, you might like to read more about what Jearl Walker has to say about pinhole photography.

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