Greetings all
I was just catching up with old digests after the Xmas break and
so apologies if the thread has already died....
First off, let me state that the information I provide here is true
and accurate for the F90X and F5 (with an AF-D lens), with the
speedlight mounted on camera and no diffusers or other attachments
used. I don't have access to an F70 so I can't guarantee that this
will necessarily be exactly the same.
Most people complain that they get underexposed pictures when using
3D MSBFF when the flash is the key light and that selecting standard
TTL gives the correct results. This is true.......
BUT the difference in output between standard TTL and 3D MSBFF
(for a scene of average reflectance) is only -0.3EV, NOT -0.7EV
that some people have suggested. However, with MF lenses only the
F90X gives a fixed -0.7EV compensation at all times.....
(To prove this to yourselves, any flashmeter and an old speedlight
(pre SB25) can be used. If using a speedlight with preflash, you will
have to rely on visual comparisons on slide film as the preflash
triggers the flashmeter - the fill algorithm is the same though.)
Interestingly, the F50 (I use one as a backup to my F90X) is
consistent with all the older cameras (F601 etc) and gives correct
exposures with flash as the key light source (below EV10). Above
EV10, -0.7EV is applied.
God only knows why the 3DMSBFF system doesn't work in the same way!
If more compensation is needed to overcome underexposure, I would
suggest having the system checked by Nikon.
Another factor that can affect exposure is the use of a diffuser in
the 3DMSBFF mode - a diffuser will cause the system to think that the
subject is dark (since the reflected preflash amplitude will be less
than expected) and therefore cut the light back during the actual
exposure leading to underexposure.
Also if your camera gives better results with films like Provia or
Velvia derated by 0.3 stop, then the results from the
(unmodified)3DFill mode will appear to be 0.7 stops under when the
films are rated at the correct ISO. This still doesn't alter the fact
that the fill mode output will only be 0.3 stops under std TTL below
EV10!
Happy experimentation!
Regards
Anthony
[EMAIL PROTECTED]
