Wilt wrote in post #18397255
As I have already posted, Canon's logic is driven primarily by the range of distances for which the eTTL flash can control via power output (-6.5 levels).
Yes, and I conceded that taking that into account for P mode or full-auto is somewhat acceptable.
The minimum distance assumption (at ISO 100) is 1.6' with f/1.4 lens, so using 'normal' FL GN135 (for the 580EX) that is 1.5' - 96' flash range; the flash autofocus assist is good as close as 2'.
Assuming our ambient light level mandated 1/50 f/4 at autoISO 3200 (a reading just taken indoors in my home), the 580EX would have a Guide Number of 756 at ISO 3200...I would need flash output cut from an effective range of 189' (at GN3200, f/4) by -7EV to shoot as close as 1.5'...beyond the range of flash output control.
Many of us often shoot in situations where we are never close to the subject, never use f/1.4, and use HSS, with very low guide numbers. Why should our flash/auto-ISO functionality be crippled because of what *could* happen if we we shooting close subjects with direct normal-sync flash at low f-numbers?
Even when I shoot indoors with a fast, wide lens, I aim the flash head at a white surface, above, but preferably, behind me, and flash has a lot more area to cover and is less likely to blow out.
I don't see why everyone who wants fill flash with auto-ISO needs to suffer because of people who shoot up close with direct flash with fast lenses, especially when there is P and full-auto mode for those people to use, and the chance of flash blowing the picture is no worse than if I chose that same ISO manually. Plus, I can use HTP giving me a stop of extra highlight headroom for flash.
Too much kindergarten, IMO. You can have kindergarten and PHD on the same camera, but Canon pushes out the PHD program for the kindergarten.