I'm still very new to macro, but even in my limited experience I have discovered that at 1:1 handheld, it is challenging to control the placement of the DOF. The slightest movement back or forth changes where the focus will be, faster than the camera can AF (and AF speed is irrelevant with the MP-E anyway, since it's MF only). This is not too much of a problem at apertures smaller than, say, f/8, but when you get up to 3:1 or higher, the DOF is paper thin even when you are stopped down. I can't even imagine trying to shoot 5:1 handheld and expect to get the focus placement accurate.


The reason why I point this out is because accurate focus in such a situation does not benefit from additional light--you can have all the light you want but if you cannot steady the camera to within fractions of a millimeter, you cannot expect to get accurate focus at 5:1.


Now, that doesn't mean you *must* use a tripod and/or macro rail...some people do quite well by bracing or resting the camera on a surface. There are ways of making sure the camera doesn't move that don't require using a tripod. And not all tripods are big, clunky, heavy deals. Some are quite small and portable.