speculative question about optics

You are going to need more data. Likely distances involved?. Accuracy required?. Is the object illuminated, or radiating?. What is the background?. Why optical?. - likely to be the hardest, and most expensive solution... Automatic, or manual?.

Simplest for manual, the simple optical rangefinder system (adjust the angle of two telescopes, till the images align). For automatic, 'low accuracy' systems, could be done based on camera autofocussing systems (though the cheaper ones use ultrasonics, or infra-red reflection, rather than optical alignment). For higher accuracy, much easier if the object can be connected to an RF source for example.

Best Wishes

Thanks very much for the reply. I hope this information might help... The maximum distance from sensor to object would be approximately 45 centimetres, the minimum distance would be approximately 6 centimetres. The accuracy must be to the nearest millimetre ideally, however in most scenarios to the nearest half centimetre is probably good enough. The object is not illuminated or radiating. To correct myself in the first post, the object is likely to be made of either brass, nickel or tungsten, with varying degrees of reflectivity. Would dipping the object in any kind of liquid make it more easily detectable? A light source is always placed above the object, however the far background (approximately 190 centimetres away) is likely to be dark. The choice of optical was arbitrary, if ultrasonic or infra-red methods are possible then that's great. However I'd ideally want just one sensor, I'm concerned that ultrasonic methods would require multiple sensors for triangulation, which would make this rather unwieldy. The process of detection must be automatic.

An RF source would have to be very small, as the object is approximately 1 inch long and roughly 1-2 millimetres across. I've thought about RFID chips however I'm unsure about how effective they are to 'give up' their location, and also they appear to be hard to source and possibly very expensive. I'd be grateful to hear any other ideas associated with RF though.

Many thanks