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When a lens is specified not just by its focal length, but also the sensor format for which it is intended, what compatibility limits does that place on the sensors it can be used with?

For example, if I have a CCD camera with a 1/3-inch sensor, must I use a 1/3-inch lens, or will a 1/2 inch lens (or anything greater or equal to 1/3 inch) do just as well?

If I took a pair of test images using a fixed camera and target scene, one image using a 1/3-inch 16mm lens and the other using a 1/2-inch 16mm lens, would the images be virtually identical to the casual observer? What differences should an expert observer see, if any?

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    $\begingroup$ Perhaps Photography is a better place for this question? $\endgroup$ – ACuriousMind Dec 2 '14 at 9:26
  • $\begingroup$ I stripped away the application details to keep the question general, but it has much more to do with physics in our application than with photography. Loosely speaking, we are in the business of making scientific instrumentation based on modern sensor technology. We use those instruments to make non-contact measurements. $\endgroup$ – omatai Dec 2 '14 at 23:08
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A lens intended for a 1/2 inch sensor should work fine. Camera lenses normally produce a circular image called “image circle”, and you want the diameter of this circle to be larger than the diagonal of the sensor. In large format photography, it is quite common to have image circles significantly larger than the imaging medium, as this allows for camera movements. It is also quite common, in digital photography, to use lenses intended for a “full frame” sensor (meaning 24×36 mm), on DSLRs with smaller sensors.

If I took a pair of test images using a fixed camera and target scene, one image using a 1/3-inch 16mm lens and the other using a 1/2-inch 16mm lens, would the images be virtually identical to the casual observer? What differences should an expert observer see, if any?

They should be practically the same. The 1/2-inch lens should probably deliver less vignetting. It may also have slightly less resolution, as it is intended to be used with a larger sensor, with presumably larger pixels. If the lenses are of good enough quality, however, it will be hard to notice any difference.

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  • $\begingroup$ I would expect the larger lens to have higher resolution (not lower) as it will have a higher numerical aperture. $\endgroup$ – nivag Dec 2 '14 at 16:29
  • $\begingroup$ @nivag: 1) The “larger” lens is larger in the sense of having a larger image circle, it need not have a higher numerical aperture. 2) Higher numerical aperture implies higher resolution for diffraction-limited lenses only. $\endgroup$ – Edgar Bonet Dec 2 '14 at 16:54

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