What do the RX10's flash specs mean?

I think one mistake is not taking aperture into account. Your '20m at ISO 100' for the HVL F20M would be at f1 so it would only be 2.5m at f2.8, the RX10's maximum aperture. I suspect the ISO 12800 distance is a bit of a red herring and what we really need to know is upper range of auto ISO on the camera.

Look like a typical GN6 flash rate at ISO200, ok for close range fill but if take flash serious, get an external one.

Snapsh0t said:

I think one mistake is not taking aperture into account. Your '20m at ISO 100' for the HVL F20M would be at f1 so it would only be 2.5m at f2.8, the RX10's maximum aperture. I suspect the ISO 12800 distance is a bit of a red herring and what we really need to know is upper range of auto ISO on the camera.

Click to expand...

Ah, yes. I knew that the aperture was important and couldn't remember how it fit in. Thanks for reminding me that GN is based on ISO 100 AND f/1.0. So if I were to work backwards from ISO 12800, f/2.8 and 20.8m, I get GN of 1.3 for the RX10 (1.3m @ ISO 100 & f/1.0). The specs for Auto ISO say:

Auto (ISO 160 - 12800, selectable with upper / lower limit), 160 / 200 / 400 / 800 / 1600 / 3200 / 6400 / 12800 (Expandable to ISO 100 / 125)

It makes no sense that the flash specs would say that auto ISO is good to 10.2m but ISO 12800 is good to 20.4m if they both were at ISO 12800 so I suspect they are using Auto ISO up to 6400 for the 10.2m spec (yeah I know what they say about what happens when you assume something). That fits with 20.4m @ ISO 12800.

I guess the upshot is that this is a pretty weak flash and that I won't be wasting any money if I get an external flash unit which is what I was really trying to sort out for myself. Thanks for reminding me of the f/1.0 part of the GN calculations.