On 02/10/2015 12:16, whisky-dave wrote:

Yep that's how I did it. I never used the DoFocus mark for IR. I
used it a few times for macro when calculatign guide No.s but I
found trial an error worked best.

What's it got to do with guide numbers?

Flashguns have guide numbers which represent the light output at a
particular distance, changing this distance means less or more
intense light which means to cointoll this you need to adjust the
aperature in most cases.

So what's it got to do with guide numbers?