Originally posted by X Man I understand that with say a 50mm prime 50mm of extension tubes gets us 1:1.
However, I've always been confused about the way certain zooms act. For instance, Some 70-300 mm zooms have a 1:2 repro ratio while others have a 1:4 ratio and others still have effectively no macro capability at all.
Zooms I think greatly complicate the formula because we may not be certain of what the actual focal length is at various settings.
Regards,
mike
You are correct, the thing with zoom lenses, especially new ones, is that some of them offer macro only at minimum focal length, others move the internal elements differently to achieve close focus.
They do not behave normally but because they have internal mechanizms to move lots of elements around (zoom plus focusing) they can offer capabilities of close focus (not really macro)
for a zoom that goes to 200 or 300mm, macro is really a gimick not a feature, but I always maintain that even though I have a true macro lens, I like to always carry one lens that can do close focus because yo never know when an opportunity arises.
Note that to some extent, lenses with internal focusing also may not behave as you expect. The optical formulas really only work for lenses where the entire group is moved. i.e. most older MF lenses. Internal focusing may cause change in true focal length when close focused, but I can't say that for sure, I have not done a test on my samyang 85mm F1.4 (my only IF manual focus lens) yet