>>3179623>>3179633A 100/2.8 or the third party equivalents Tamron 90/2.8 and Sigma 105/2.8 are really meant for larger work distance on FF.
For crop I would recommend you getting a dedicated macro lens around 50-60mm. Tamron has a 60/2.
Also when you get a 70-200 (2.8 or 4) the minimum focus distance will give you a nice magnification, not as good as on a dedicated macro lens but the work distance will mean you can easily get the shot, then crop in post.
My own example of this is
>>3165623 and
>>3165625 on a Tamron 70-200/2.8 and
>>3165627 on a Sigma 50-500 at 200mm.
Both cases get you around 1:3 macro ratio, which is borderline for macro, but is already a good macro result.
You will also see that at macro distances the AF will only givern the macro ratio, so you have to manually focus with your body.
