I would like somebody a bit more seasoned with filters than I to clear up some confusion I have been having. I decided recently that a more a cost effective way to dabble with some macro photography and/or increase my focal length capabilities would be to purchase a macro filter or set of filters.
Then came the diopter rating attached to each individual filter. These came in plus +1 +2 +4 +7 +10 etc.
They confused me. I think I've managed to fathom what they are about and this is the conclusion I have drawn.
focal length of the macro filter = 1000 divided by the diopter rating
This would be for example:
1000/+4 = 250mm
which would then give me 305mm focal length? (my current lens is a 18-55mm kit).
which is a zoom from 3x increased 16x
Is that right?
Also, is it true that the lowest + numbers give the highest focal length or is that my imagination?
+10 would only give 100mm?
Sorry for the long post. Thanks