SpeedLite focus assist light.

[trencheel303]

no longer required

 

[david1701]

yes, one shot only, but it will let it focus on anything (even a plain white wall) in any light as it makes a new grid that the AF system can see as its own contrast

 

[david1701]

if you don't want it as a flash I think the smaller cheaper guns do it to, mebe even the 270ex

ST-E2 defo does and its <1/2 a 580ex but no actual flash head

 

[david1701]

its not fill if you aren't already properly exposing - its key

mebe worth trying to get into ocf if you want to do it a lot?

a mk2 580ex will also have weather sealing as good as the 1d for if you ever get a weathersealed lens

 

[trencheel303]

I'd love a weathersealed lens and have considered saving for one.

Also could you please enlighten me what's OCF?

 

[david1701]

off camera flash, just about the only way to mostly light pictures with flash and make them look good, I've used it urbexing before coupled with very long exposures to create some funky effects

 

[trencheel303]

Ah right, yes I have been thinking about off camera flash too.

About the most exotic I've been with a flash is just dragging the shutter slightly, and it was with pop up flash.