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Full Frame APS-C "crop factors" etc.

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But if you consider quite a few (genuine!) Astronomers may not be
able to calculate field of view (resolution) from such information? :p 

To me, this raises interesting questions about how one gives and
receives information. When I was last *working* I was quite often
told (by "unitiates") I was the "only scientist they dared to ask"! :o

I am (despite better judgement?) wont to ask "stupid questions"
on internet forums. But I sense people don't get irony / rhetoric?
Personally I still see a real role for good BOOKS on the subject! :D

For that reason, Kudos to the (published) authors among us...


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My generation learnt photography using 35mm cameras. Knowing the 35mm equivalent lens is very useful, especially with something like my bridge camera. It zooms from 4.3 to 180mm. Looking at random picture, its properties say I took it at 12mm which is meaningless to me, but it also lists the 35mm equivalent as 70mm, which lets me know I took it with something rather longer than a 'standard lens' and mentally place it in the range of the camera's capabilities.

The fundamental issue, for conventional photography at least, is there is no accepted language for the field of view of a lens beyond the vague 'wide', 'standard', 'portrait' and 'tele'. At least these tell you  something  based on the principle that a standard lens gives what we perceive as a 'normal' perspective.

If we want to compare the perspective and field of view of a range of lenses in practice, then we need a yardstick. If you have a camera, it is useful to know roughly what a lens will show you without having to use it or fire up the terrestrial equivalent of Stellarium and fee din your focal length and sensor size. The alternative would be to use the field of view in degrees, just like binocular users do, but would you use the short edge, long edge or the diagonal... useful for astrophotographers who know the angular sizes of their targets, but how many degrees do I need to take a picture of my kids or a bird up a tree?

The standardisation to 35mm equivalent does this, and if it didn't we would have to use some arbitrary number that did the same thing.

Perhaps the answer is simply to multiply the 35mm equivalent by 2 so a 'standard lens' becomes 100, smaller numbers are wide angle lenses and longer ones teles. Call this number the 'standardised focal length' and stop wingeing...


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