Equipment

[MPpro]

I have a 5d and a 100mm macro that I bought for portraits. How can I make that lens get real close? What extension tubes or set up should I get?

[Choderboy]

So you understand the 100 macro will achieve 1:1 magnification?
So that means with the 5D sensor about 33mm or so on the long side , that's as close as you will get ie , a 10mm long bug will only fill about a third of the frame.
Most common choice is Kenko tubes. Obvious choice is to buy a set rather than individual tubes - more cost effective.
I splurged on the Canon 25mm ext tube as I use a Sigma 180 Macro lens which is very heavy as well as the fact that my flash bracket mounts to the lens so it's a fair bit of weight for the tubes to support. I've got some kenko's but I get quite a bit of movement with my setup.

There's a table available somewhere to calculate how much magnification tubes will achieve, but a full set won't get to 2:1, more like about 1.5:1.

If you want to get really high magnification an MP-E 65 is the way to go.

And you need some way of getting the flash in a useful position and a way of diffusing it. There's a thread "show us your macro rigs" which shows there are lot's of options with various flash brackets which all achieve pretty much the same thing - getting the flash head somewhere near the font of the lens.

Or just spend and get an MT24 flash with a couple of Gary Fong puffer diffusers if you want what seems to be the best lighting setup available.

[LordV]

The 100mm lens will give you 1:1 magnification at minimum focus distance- just set minimum focus and focus on the subject by moving the camera- should focus about 6" in front of the lens.
A full set of kenko ext tubes will give you 2:1 with that lens.
Brian V.