Dispensing with normal lens ?

You are using a fabulous lens for macro. The minimum distance is usually written on the lens itself. As in your case it is 30cm.

100 mm lens whether its designated macro or not, is a good portrait lens…
portrait lenses on 35 mm film cameras are classically 105 mm…
because the DSLR chip registration area is 1.6 times smaller .. for a same size print it SEEMS that there is 1.6 fold magnification….
so to get and equivalent pic as 35 mm film one needs to stand further away…. so 100 mm digital macro lens will behave like the 60mm nondigital/35mm film camera lens….

100mm digital lens with a dslr will give the same resolution as a 60mm regular format lens on 35mm film camera… yet there is a caveat… if you stand at the same position with both sets of equipment… the
digital picture will seem as if its magnified… but in actuality its just cropped tighter because the digital chip is smaller than 35 mm film…it records less area… for the same angle of view….

So if you want the same high quality resolution, of a 200 mm macro lenses of 35 mm film camera you will have to go to 200×1.6 mm lens for digital camera….

that’s very very expensive… so one has to still resort to extension tubes or bellows… but I don’t think bellows are made with digital coupling … so digital extension tubes is still the best option with a standard 100 mm macro for going very close….

but people make a mistake … and say that a 100 mm lens of the 35mm camera when attached to digital camera behaves like 100×1.6 mm lens…. its wrong… its not enlarging things as it records, but its
simply recording a smaller field in a cropped area so it seems enlarged when printed in a similar area paper or computer screen…

i hope this is clear…
I know its gets confusing the way people write and argue about it, the internet is full of such arguments…
THERE IS WONDERFUL 3 PICTURE COMPARISON OF REAL PICTURES WITH 3 LENSES ON A CANON CAMERA (HE IS USING 7D BUT ANY DSLR WILL HAVE THE SAME KIND A RESULTS…)
TAKE A LOOK: http://www.digital-photography-school.com/will-a-close-up-lens-suffice-in-place-of-a-macro-lens

THINGS WILL GET A LOT CLEARER….