The Canon EF 100mm f/2.8 Macro USM is a wonderful macro lens that gives you a magnificationn ratio up to 1:1. It’s a wonderful lens for all types of macro work.
But sometimes you might want to have an even higher magnication ratio or a little more focal length for photographing shy insects. If you own a Canon EF 1.4x extender you might think about adding it to the lens to get more focal lenght or a higher magnification ratio.
Unfurtunately this won’t work as the lens does not work with the 1.4x extender. At least not without a little trick.
You have to add an extension tube like the Canon EF 25mm II between the extender and the lens. AF won’t work with that combination which is not a serious problem because with such a high magnification ratio, manuall focus is the better solution.
Here is a picture of that combination:
EOS 40D with EF 2.8100 Macro USM, 25mm extension tube and EF 1.4x extender
As you can see, it’s mounted on a focusing rail (from Novoflex). I highly recommend using a focusing rail with that combination as this allows for very precise focusing without the need to move the tripod.
The following three picutures give you a comparison of the highest magnificaton ratio with the lens alone, with the 25mm extension tube and with the 25mm extension tube and the 1.4x extender.
EOS 40D, EF 2.8100 Macro USM
EOS 40D, EF 2.8100 Macro USM, 25mm extension tube
EOS 40D, EF 2.8100 Macro USM, 25mm extension tube, 1.4x extender
As you can see, adding the 1.4x extender and the extension tube gives you a much higher magnificaton ratio than the EF 2.8/100 Macro alone. If you are shooting a lot of macro and want to go beyond 1:1, this is a very interesting combination.
Keep in mind that with the extender and the extension tube, the lens won’t focus to infinity. That combination is only useful for closeups.
If you want even more, I recommend the Canon MP-E 65mm f/2.8 1-5x Macro Photo lens, which is a lens designed only for macro work. It gives you a magnification ration between 1:1 and 5:1.
If you have the EF 3.5/180L Macro, you don’t need an extension tube to use the 1.4x extender, as that lens will work just fine with the 1.4x extender. Of course, adding an extension tube will increase the highest possible magnifcation ratio.