The greatest difficulty is in remembering the signs of the variables. I think the easiest way to do it is the following: do is always positive di is positive for a real image, which is of course in front of a mirror, or behind a lens. f is positive for a converging lens or mirror.

fov和焦距的关系

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Hey there, I thought this would be the best sub to ask this but I just got a new lens for my Canon EOS RP and something seems weird to me. I have the cheap EF 50mm prime from Canon and just got the EFS 18-135mm f/3.5-5.6 zoom lens. The field of view with the zoom at 50 is far less than with the 50mm prime. I found that it's almost identical at 35mm. Does anyone know why this is? Made for different size sensors? Have to do with IS? Thanks in advance for all answers.

All of the possibilities are listed in the following table. I think this is an unnecessarily complicated way of summarizing the different cases; but some students prefer to have it stated this way: