Flash timing

[DriftRoot]

Veteran video makers out there who have used the technique of "flashing" one image, this question is for you:

Generally speaking, how many frames do these flashed images contain? Or, in other words, what length can a flashed image be to register clearly in the viewer's mind while also being extremely fleeting? I realize the timing depends a lot on the music, but I've been trying to flash a certain image on top of a few others and am frustrated with my own perception of what is a decent-length flash. Since I know what the image is, my mind tends to create it accurately, regardless of how clearly it is shown.

Also, if a scene is flashed with opacity changes, do you generally have the fade in/fade outs set back to back or do you razor the original clip slightly to have empty gaps between the fade in/fade outs? Or is this just a matter of preference? (I am keen on using the latter technique to hide gaping holes in my footage, and just am curious to know if this is ever used with smoothly animated footage. I won't feel like such a cheat, if it is.)

[mikestrife]

For the view to be able to see the flash it has to be at least 2 frames. I use 3 just to make it more pronouced.

1 frame isn't enough though and will appear to the view as if the flash is a overlayed on the previous frame.

Question 2 is really preference and also depends on the music, for quick flashes I'd use the razor for longer one maybe i'd use the fade out, but it mainly depends on the music.