"Why am I doing a homework selfie?" you may well ask.
Well, our Camera Club has been running a short course (each Tuesday for 4 weeks) on using "Speedlight" type flashguns - with special reference to using them off camera, and via autoexposure control (TTL, "through the lens") and manually. It's not been much use to me because (a) I was away for the first two sessions and (b) I don't (yet) actually own such a flashgun. I did manage to attend last Tuesday's session (the third one) however and will be going to the final one this evening.
They set "homework" last week - to take a photo of something (preferably a person) against a window, using flash to light the subject so that they wouldn't be too dark. My Editor declined to pose for me, so you're lumbered with a selfie.
The only flashgun I have is about 45 years old but remarkably it still works (before you ask, it is electronic - it doesn't use old-fashioned use-once flashbulbs, although I did use them all those years ago before I bought this one). The problem I had to overcome is that you can't adjust the light output at all as you can with modern flashguns, so I could only balance the exposure of the outside scene and me by adjusting the distance of the flashgun from me. Fortunately I still had my old long flash sync lead so I could have the flash off the camera (with my longsuffering Editor holding it up high for me to get the best flash angle.
So having measured the exposure for the scene outside the window I then had to do some sums (just like "real" homework!). The Guide Number (distance in metres times f number) for the flashgun is about 30 at ISO 200. Using an aperure of f6.3 meant that the flashgun had to be about 5 metres from me. It actually worked out OK as you can see!
As a comparison, the inset photo shows how dark I looked when I didn't use the flash. Of course, I'm sure my sons would say that it looks better like that as you can't see my ugly mush very well... ;-))