When doing high key, the background should be 2 stops brighter than
the subject in order to give a good continuous white.  Light the
subject normally but with less contrast, then dump 2 stops more on the
background to wash it out and get a continuous tone.  Less will make it
gray and more will blow it out.

Where do your shadows come form?
First try with right positioning of your main light and then light the
background.
If you use digital, you should probably use M mode and set up your exposure
manually to avoid underexposing your main subject with background brightly
lit.

Mariusz

U?ytkownik Lynn <lynndianah@homechoice.co.uk> w wiadomooci do grup
dyskusyjnych napisa?:fc747ac4.0310080801.650c185d@posting.google.com...

first, mixing lighting can often bring some annoying complications, tungsten
on the background can give it a pleasing warm tone especially if the
subjects are nicely exposed, wedding photogs will light the subjects but let
the very warm room lights supply the background.    depending on how the
images are printed, and this can include digital workflows, your camera's
auto balance may 'see' more warm light or cool fill flash from one shot to
the next.

how are you exposing?  with the camera's auto expo, or selecting an exposure
and using that for the session?   If using the auto expo then the most
obvious problem is likely to be that the sensor is 'seeing' various amounts
of white versus subject color.   and/or your fill flash is not putting out
the same amount of power, either cause you are shooting too fast for it
recharge, or its exposure sensor is also seeing various amounts of white and
varying its output.

if you are shooting film then the lab's printer exposure meter could be
seeing various amounts of white and compensating, these are often the
weakest link, especially consumer labs where they just stick the film in and
walk away.

white background sets are difficult.  the typical and very popular hi key
set, you would have the subject and any props in white, (and right there,
very few clients follow through, especially a family group, on the all white
thing.)  then the only color is the subject's face and hands.  its a way
cool effect, requires that you light the background very evenly, some pro's
will use four umbrellas crossing the background two high and two low with
two on each side, I used two but bounced them off the sidewalls and ceiling.

as for varying the exposure with your flood lights, you can move them
further from the background, you can get a dimmer switch (which would give
you more control, or you can buy smaller bulbs, I assume a 250 bulb would be
one stop less.)

The following assumes that your digicam actually has the controls for
changing f/stop and shutter speed (thus over-riding its automatic
exposure).

Suggestion, set the lighting of the subject. I would suggest NOT using
a fill flash but instead bouncing lights off umbrellas (see your
digicam so that the flash does not fire). Whether you use one or two
light/umbrella combos and what angle and height they are set from the
subject, just depends on what you're after.

Then, without the background lit, meter the subject and calculate the
exposure and f/stop you'll use.

Then set the lights on the background.

By the way, since you wonder about using "lesser lights on the
background" perhaps it is worthwhile pointing out  that exactly how
the background comes out will depend on 1. the distance of the lights
from the background, 2. the distance of the background from the
camera, and 3. whether you also bounce the lights off an umbrella.

-- JC

Not the best way to start. You want a neutral background, usually.

What shadows? From the subject? If that's happening, the subject is
too close to the background. In other words, that's not a lighting
problem.

That's to be expected from your approach.