As I stated in the other thread you started, there really is no reason to worry about flash hurting the animals' eyes. I think off camera flash, using a bracket, (I personally like the Wimberley Macro Bracket-
http://www.fieldherpforum.com/forum/vie ... 15&t=22374), is the easiest and best method when you need to slosh around in some pond after dark. A single flash on a bracket like this provides nice, directional, yet often still very open lighting. A lot depends on how far away you are from the subject. You can always add diffusion to the flash to soften it up if you like. If your camera's built in flash will work as a master, (all but the entry level Nikon DSLRs will), then you don't need any other chords, etc. If you have an entry level Nikon then you can get a TTL chord, (I still have an old SC-17 and it works fine with the newest Nikon cameras and flashes, just no AF assist light). I always use my flashes in TTL. Some people prefer manual, but I've found Nikons are very accurate with TTL and its just easier when you change distance frequently.
As far as what to have an assistant hold on the frog for focusing, I've found a dim flashlight works best. You want it just bright enough to frame and focus. Sometimes if the only flashlight I have with me is too bright I'll aim it at the frog so that only the dimmer outside part of the light cone illuminates the frog. I'd like to experiment more with red focusing lights, but all the ones I've tried have been too dim for me to focus well. I usually work alone, so I rarely have anybody along to hold a focusing light for me. What I do instead is to use velcro to attach a small flashlight to the top of the flash. This gives me a focusing light and helps me make sure I've aimed the flash correctly, though since I usually have the flashes set to their widest zoom setting I can actually be a little sloppy in my aiming and still get the subject properly lit. I don't turn the flash light off before taking the picture. That simply doesn't work when you are hand holding and since I'm using a fairly dim flash light anyway it gets completely overpowered by the flash.
I love tripods and use them frequently, but not when photographing nocturnal amphibians!
As far as what lens to use, I would go for the 55-300. The 45 is going to be too cumbersome in the field, what with it having only manual focus and a pretty short working distance. You don't need the tilt and the shift features of that lens for frogs either. To use the 55-300 though you'll need to purchase a diopter. I often use the Nikon 70-300 vr with a Nikon 5t for calling frogs. Since your 55-300 has a 58mm filter I would buy a Canon 500D diopter in that size. The nice thing about the zoom with the diopter is that you can zoom to change your magnification and framing from the same spot. Image quality when you stop down into the f11 or so range, (where you need to be for macro stuff anyway),
should be quite good, though I must admit I've never used that particular combo.
. I'm trying to stock up on helpful information for next summer's Arizona monsoon herping trips. 
