My question is: wouldn't a 70-200mm at 200mm, even with a minimum focus distance of 4 ft., get me a closer look than a 100mm at a min. focus distance of 1 ft.? Will the picture be sharper with the 100mm Macro? I don't know the math to calculate and I don't have the lenses on hand to test it out..
No, the 70-200 II delivers a max magnification of 0.21x, while the 100mm macro delivers 1.0x. In fact, your 24-105 delivers a higher native max mag (0.23x) than the 70-200 II. Note that 0.2x - 0.25x is decent for flowers, etc., but often not enough for insects.
Natively, the 100L is very slightly sharper in the center but definitely softer away from the center, compared to the 70-200 II at 200mm.
I've compared the 100L with the 70-200 II plus the 500D close-up lens, which delivers a 0.6x mag. The IQ overall was very similar in real-world shots. But, with the 500D you're limited to a specific 50cm (20") working distance, no more, no less - rather inconvenient. Without the 500D, your 24-105 is a better close up lens than the 70-200 II.
Basically, if you want a versatile telezoom with top IQ, the 70-200 II is a great lens. If you need true 1:1 macro or close to it, get a macro lens. Regarding the 100mm vs. the 180mm L lenses, the latter gives you an extra 4.5" of working distance, useful for shy critters.
Thank you so much for your reply. I got exactly the answer I needed. I have to look at "magnification factors". 1.0x is what makes the 100mm Macro L a macro lens, NOT necessarily the focal length.
As far as extension tubes, I haven't looked at those as an option. from my understanding, they stop down the lens just by having them on and I would rather just get the right lens for the job first. I understand these might be helpful with the long telephoto lenses but for my uses, a $300-500 adapter wouldn't be as efficient as just spending on the lens I need. Now, if I had an $6000+ lens that I wanted to use at slightly longer focal length...maybe. Can anyone chime in on this one? I am most definitely a noob at all of this.
if you use them with the 100 you can go beyond 1:1