effect of distance

Robin Leadbeater

Hi Derek

>But I think once done and I have a value of the number of pixels the green LASER is dispersed in the first order diffraction, as long as the equipment stays the same, lens, focal length, grating, do you think the calibration will no longer be necessary ?  Oh, I think I need to follow up with Robin’s comments on distance. I will need to do some exposures with various objects at different distances painted with the LASER.  Robin, do you think it’s important to know the actual distances? A problem I have is, I don’t know the distances – they are just roof tops, aerials etc. Is there a way to work out their distances?

I can’t add much I am afraid as expected the dispersion to be a constant of the setup so the effect of the distance to the source came as a surprise to me !  Perhaps it only becomes significant as the focal length of the lens becomes a significant fraction of the distance. I think I would start with something close, a couple of metres away say compared with a few tens of metres to get a feel for the magnitude of the effect.