Two of the easiest and most light weight ways of holding the 270EX in place are:
1. an FMMB (front mounted macro bracket). More info about the FMMB here.
FMMB is great for lenses without IF (internal focus) and/or lenses without tripod collar/mount ring. Example: Tamron SP90, MPE65 (both SP90 and MPE65 extends out considerably) , and Nikon 105mm (no tripod collar?)
270EX on the FMMB, MPE65 and 40D. (Edit: this is the old method. New and improved method is here)
Yellow arrow shows that the oce3 cable is preventing the 270ex to be pointed any lower.
The angle between the two green arrows are more than 45 degrees, so the lighting is more like top lighting. A comparison to the MT24EX can be seen below, after a few sample shots.
I used the same concave diffuser like this. More about that concave diffuser here.
Jumping spider. Noticeably much much dimmer catch lights in the jumper's eyes. I personally prefer it to be slightly stronger. I am guessing this is due to the higher light angle.
Fly. Heavy shadow on the lower part of the fly. I am not too concerned about shadow below the subject, I am more concerned about shadow on the lower part of the subject. Again, i am sure this is due to the higher light angle.
270EX on FMMB versus MT24EX
Bigger image here.
The 270EX is just too far out and shines down from a higher angle, whereas the MT24EX flash heads are just on top of the front of the lens/filter, with lower angle too. (Compare the angles between the green lines). These explain why we get dim catch lights on subject's eyes and the shadow on lower part of subject. I think I found the solution already and I will share it in my next posting.
Note: the shadow and dim catch light issues are more prominent in the MPE65's higher magnification range i.e 2x and above. At 1X, with a working distance of 4 inches (front of lens to subject), it should be okay.
(Edit: check out the new and improved method that solves the shadow and dim catch light problem)
For normal 1:1 macro lenses, this setup should still work well.
2) Mount Ring/Tripod Collar
Almost no DIY required compared to the FMMB, but you will need to add in one or more extension tube(s) or teleconverter in order to be able to rotate the tripod collar/mount ring 180 degrees.