brucet@hpgrla.UUCP (brucet) (12/13/84)
With Christmas time rolling around so fast, the request for
portraits seems to ketch me off guard every time. The problems is
that I am tired of standing people up and shooting them down like Clint
Eastwood, distroying their features with a single pull of the trigger.
I am trying to pull myself out of the "mug shot" habit. I own a
vivitar 283 flash and an Olympus T20 flash. I would like to use the
setup below to gain more "professional" looking results.
______
| |
| | subject
|____|
| \
| \
| \
| 45 \ (should be at 45 degree angle from lens axis)
| \
| \
| \
| \_
|_| |_| Key Flash (Guide number 120 at ASA100)
Fill Flash (camera mounted w/Guide number 66 at ASA100)
(assume ASA100 film)
Both of the flashes can be set to automatic mode, but when I've done
this, random exposures results. In the above setup both the flashes are
set to manual. Given the fact that the key light has a guide number
twice the fill flash, if the distance from the flashes to the subject is
the same, the light ratio should be 3:1.
Now, what about exposure? Can I determine exposure from just the key light,
or the key light plus the fill light? Can this be calculated or does it
need to be measured? (And I don't want anyone to say buy a megabuck
flash meter!). I am about to attempt trial-and-error method of a test
roll but I would like to know where the ball park is? (That leaves it
open for smart-alick responses!)
And here's a new twist... (cha-cha-cha)
If I put an umbrella on the key flash, does this just change the guide
number of the flash or does it turn the calculation into a third order
non linear partial differential equation?
Bruce Thompson /Hewlett-Packard