|With the advent of digital sensors fitted to cameras intended to replace film cameras, and so using 35mm cine lenses, we have been plagued by accusations of our cameras being uncollimated: sometimes a focus puller will complain he cannot get focus where he expects to find it. The strange focussing behaviour has been variously blamed on lack of collimation, distored lens mounts, distortions due to heat etc. In fact, the problem is either the construction of the sensor (something to do with the fact that a sensor is physically thicker than film or the angle of light passing through the micro lens in front of each light well) or the presence of an optical low pass filter (OLPF) in front of the sensor or something else. We, at Pirate, just don't know (but we think it's the OLPF and the fact that the lenses aren't telecentric). We've researched it as best we can - see here for a summary of an internet forum postings we've found. If you know 'the' answer, please, please let us know. In the meantime, we have decided to prove on set that our cameras are collimated, right there, right then. That's the best we can do: if focus is still a problem, then there is nothing we can do, it is just the way it is.|
|We have a beautifully made piece of kit made by P E Denz in Germany known as a 'Flange Depth Controller' (FDC) for collimating digital cameras. It contains a laser and lenses, simply mounting on the camera in place of a lens and giving an idiot-proof method of measuring the collimation to within 1 micron. Good enough for most focus pullers.|
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