, Sigma has max aperture of f45 versus f32 on the Canon. In real life that probably won't be hugely significant though. Minimum focus distance is 12" and 6" on the Canon so you get a little more working room. However- the big plus on the Canon over most of the competition is the internal focus ability. On most macro lenses the lens barrel extends outward as you focus closer, but not so with the Canon. Unfortunately I can't tell from the specs on the Sigma if it features internal focusing 
After looking around some more I'm pretty sure the Sigma does not focus internally, so that would be the main downside.
<a href=showthread.php?s=&postid=10707803#post10707803 target=_blank>Originally posted</a> by gregr
Regarding the Sigma pros and cons-- just a few things I'm noticing as I look at the specs: Sigma is cheaper
Which if the OP is willing to consider it is also a very capable macro lens (I've heard both of optics being on par with that of the 100mm Canon macro, and build quality close to that of L glass). All three lenses, 100mm Canon, 105mm Sigma, and the 150mm are all very nice and capable lenses (don't forget the 60mm EF-S macro either). You probably can't go wrong with any of them, lot of what it might come down to is how much working space you need and/or which you'd rather have - a 100, 105, or 150mm prime for those times you're NOT using it as a macro lens. If you also plan to chase things like insects the more working space you can get is usually the better to keep from spooking them, just taking pictures of your tank working space isn't AS important really because isn't like your corals are going to get up and fly off 
, but its nice to have room to get full 1:1 macros of those corals not close to the glass. They are all very capable of delivering great results.
<a href=showthread.php?s=&postid=10714785#post10714785 target=_blank>Originally posted</a> by ct_vol
Well, really I'll claim ignorance as to what I want... lol To be honest, I thought that you had to get right up on the subject in order to get a good macro... Right now I use the 18-55mm lens that came with my camera for all my Macro shots... I also have a Sigma 70-300mm and in order to keep in focus, I have to stand across the room...
So you can use these lenses as non-macro lenses too??? Sorry, this is my first DSLR... I've had it almost a year now and am still trying to figure out how to use it...
Here's my butterfly with the 18-55mm... Made my wife happy... lol I know its nowhere near as good as most people on here, but I don't have PS and don't really know what I'm doing...
I think the picture is quite acceptable! I've taken FAR worse and insects can be tricky to capture because just as soon as you're close enough to get that shot *poof* they're off to the next spot. Picture obviously can be improved but that just comes with practice!
An extension tube is exactly as it sounds - its a tube that goes between your camera and the back of your lens. Just a hollow metal tube (at least most of them) without any optics in it. By moving your lens out farther from the camera you're able to focus the lens closer than you'd normally be able to (such as if your lens has a normal min focusing distance of 10", with tubes you could literally shorten it down to 3"). The good tubes have electrical contacts in them so everything works just the same as if the lens was connected directly to the camera.
<a href=showthread.php?s=&postid=10738225#post10738225 target=_blank>Originally posted</a> by dinoman
There are lots of places that carry them, any major camera store should have some. Kenko tubes are well regarded and are a bit cheaper than the Canon ones. A set of them will run you $170 or so. If you have a 50mm lens it can work quite nicely for a macro lens until you decide that its time to upgrade to an actual macro lens. In which case you'll already have the tubes and can then go super-macro!
