I guess my explanation must have been OK. You certainly seem to
understand it now.
Chuck Norcutt
Peter Bell wrote:
> Chuck/Dr. Flash,
>
> Thanks for a lucid explanation about determining the flash's power. It was a
> great help. I did a few calculations and discovered that with a guide number
> of 80 at 50mm, F8 gives me a max distance of about 10 feet (probably less).
> My subject was about 12 feet away, so that explains why earlier the camera
> gave me flash confirmation at F5.6 (max range is about 14 feet) but not at
> F8. Underexposure.
>
> You were right on about the flash's auto settings' apertures being chosen
> for a reason. I'm simplifying things a bit because I think there are some
> variables I'm not taking into account, but my conclusion is that generally,
> TTL mode on the 266D allows one to pick apertures between and including
> those two aperture values marked on the two auto settings. I can only infer
> this, because the Sunpak can't test in TTL mode.
>
> To test that inference, I used 400 speed film, set the flash to TTL, and
> took four shots at F16, F11, F5.6 and F4. Shots two and three represent the
> two auto settings' apertures, or what I believe to be the smallest and
> largest f-stops that can still give good exposure in TTL. Both those
> apertures produced flash confirmation in TTL. Shot two, just barely - which
> supports the notion that my flash, like others, is a bit weaker than spec.
> Neither shot one or four produced a flickering LED confirmation in the
> viewfinder, so shot one will likely be underexposed, and shot four
> overexposed. I repeated this test at a slightly further distance with
> accordingly different fstops, and got the same results. Now I know alot more
> about my flash, including how to intentionally over- or under- power it with
> some degree of control.
>
> One other thing I noticed about the auto settings is that when bouncing, the
> auto setting with the larger of the two apertures must be used to get an OK
> signal from the flash. The smaller apertured auto setting and the large one
> both give the OK lamp for head on flash, but only the larger aperture will
> give the go-ahead when bounced. This seems to be the case no matter what
> film speed the flash is set to. So, my rule of thumb for bouncing TTL will
> probably be to use apertures within 1 stop of that larger auto aperture.
>
> PB
>
>
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