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This paper covers the design, construction and testing of a camera latency measurement device. As the latency of a camera used in an adaptive optics system could be the limiting factor to the speed at which the system can operate, and the latency is not readily available from the manufacturers, a device is required to measure this latency. The initial specifications for the device were to deliver a measurement with sub millisecond resolution and measurement uncertainty on the order of tens of microseconds. A system was designed which consisted of a computer sending a signal, via its in built sound card, through some interface circuitry to modulate a LED. The detected light modulation is then time synchronised with the electronic signal by use of the computer’s serial port and the correlation between the two signals used to extract the latency. A proof of concept test was performed and the latency of a Nuvu Hnu 128 was measured as 1.160+/-0.057, 1.202+/-0.042, and 1.227+/-0.045 ms for frame rates of 200, 400 and 900 frames per second, respectively. A proposed next stage of testing is to use the system on a camera with known latency to verify its accuracy. However, to do this test the measurement uncertainty needs to be reduced. Ways to reduce this uncertainty are discussed with the most significant being to change the form of the initial pulse used to time synchronise the signals so as to avoid contraction effects and to replace the LM741 op-amp using in interface circuitry with a better, low noise alternative. |
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