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As a follow-up to this question, I was thinking about how one might build a pinhole camera with extremely long focal length to photo the Sun with a DSLR.

Imagine that pinhole is at the end of a long piece of black PVC which is well sealed to the camera.

A 1500mm tube and 1.6mm pinhole is a combination produced with an online pinhole calculator. This would produce an image that would mostly fill the frame of an aps-c DSLR.

Wikipedia seems to indicate that the circle of confusion is the same size as the pinhole, and 1.6 mm is far too large circle of confusion to be useful on a DSLR.

Can a smaller (0.1mm) pinhole be used to improve the resolution even at long focal lengths?

scottbb
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OrangePeel52
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The max size of the circle of confusion should not exceed 1/2 mm when viewed by the unaided eye at 250mm viewing distance (reading distance). Miniature cameras need the circle to be much smaller because typically we enlarge this image. Most tables and charts are based on making an 8X10 inch print. The 35mm camera image must be enlarged about 8X to achieve. Thus the circle size needs to be 0.0625mm to achieve. The APS-C format is 66% of the size of the full frame. Thus the image needs to be enlarged 12X to get the 8X10. Now you are talking a circle of confusion size of 0.04mm.

Because of diffraction and interference we abandoned the pin-hole for a lens. A lens suffers from the same maladies but now we can enlarge the aperture and gain resolution. We can get about 25X to 35X per inch of aperture with a good lens.

Alan Marcus
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