Diffusion with studio strobes
Jonathan Sachs
flash heads roughly at 45 degree angles from the optical axis. One
head is a Normal LH4 with a 10" reflector; the other is a Norman LH2
with a 5" reflector pointing into a white umbrella.
For the sake of convenience and efficiency, I want to mount the lights
semi-permanently on a frame made of Metro shelving. creating a setup
that doesn't have to be assembled and broken down again for each
session. This would make the umbrella impractical, though. I think I
can soften the light enough if I get a second LH4 head and put
diffusers over both heads' reflectors.
At this point reality seems to get in the way. The only detailed
description of a diffuser that I've found (Norman's) states that they
should not be used with halogen modeling lights unless the head has a
ventilation fan. The LH4 has a halogen modeling lgiht, which I depend
on heavily, but it has no ventilation fan.
What are the realistic options for me? Do other manufacturers make
diffusors that fit the LH4 and do not require a fan? Or, is there some
other technique I could use to get soft, even light over my shooting
area?
Send email to jsachs177 at earthlink dot net.
Bushy
just add an ordinary household fan to your setup that blows past your
modelling lights and / or diffusers if the heat is a problem.
If our sessions are short, or the diffusion material heat resistant,
(try rosco.com) or the time your lights are on is short, you may not
even require cooling.
I use two 1000W halogen lights with the diffusers mounted about 2 feet
in front and have no problem if the lights are on for ten minutes.
Hope this helps,
Peter
Jonathan Sachs
>just add an ordinary household fan to your setup that blows past your
>modelling lights and / or diffusers if the heat is a problem.
I have trouble imagining how the fan is mounted, and just what blowing
"past your modeling lights" implies. If the air just flows over the
outside of the reflector, I wouldn't expect it to do muich good. On
the other hand, if air is being pushed through the enclosed space
formed by the reflector and the diffusion screen, that implies more
about how it's done than you've explained so far.
Perhaps we have different unspoken assumptions about some aspect of
the setup.
>If our sessions are short, or the diffusion material heat resistant,
>(try rosco.com) or the time your lights are on is short, you may not
>even require cooling.
>
>I use two 1000W halogen lights with the diffusers mounted about 2 feet
>in front and have no problem if the lights are on for ten minutes.
Sessions of fiften to thirty minutes are typical, but they could be
longer.
Heat resistant diffusion material would help. I'd still be concerned
about the effects of heat buildup on the flash tube and possibly other
components of the flash head, though.
An LH4 head has four 25 watt lights, which are, not that I look at
'em, incandescent, not halogen.
But no way am I going to get two feet of space between the light and
the diffuser! That's very close to a typical distance from the light
to the subject. I will start having problems with the phyical layout
if the diffuser is more than a couple of inches in front of the
reflector's rim.
Bushy
Possibly a few differences in our approaches and subjects. My subjects
are "pretty girls"........ Shooting distances are typically 85mm lens
indoors.
I mainly use my big 1000W floods as the main lights rather than flash as
sometimes I also work alongside a video camera or two. The cases are
sealed like outdoor lights. I have a fan clamped on the stand so it
directs air up past the light.
Depending on the lighting I want to achieve, I use either bare lights
with camera lens colour correction filters, or if matching indoor and
outdoor lighting I colour correct the lights with Rosco gel filters.
Sometimes I use Rosco spun filter material to diffuse the lights more. I
do not control spill of light unless required to keep light off a
coloured wall etc.
The further away from the light, the less meltdown of the gel. At 3
inches in front I can safely use the lights for five to ten minutes, at
2 feet away the lights can be on indefinitely. If the gel touches the
front glass of the lights, it instantly shrivels up leaving a hard
molten mess on the glass. The fan simply increases the time I can get
away with, but can cause fluttering of the filter and / or gel. I'm
currently making a set of frames out of old aluminium flyscreens to
provide more stability and easier setup. They will also allow me to
close off the sides with aluminium foil to control spill.
The 1000 Watt lights give of the same heat as a 1000 Watt heater, but
once the case warms up, it radiates to the rear as well. I also have six
500 Watt lights which I use as fill when possible as this helps to raise
the overall light level and allow me to shoot an extra stop faster. At
least my subjects like them on cold mornings!
The heat generated by your modelling lights is much lower, but in a
confined space will still be of concern. Can you switch the modelling
lights off once you have set up your light angles? If so, the short time
that you would need to have them on would probably not create a problem.
I believe most flash units allow this, and as you seem to be taking
still life, I don't see this as being a problem if you simply use them
to assist placing the flash lights.
Hope this helps,
Peter
Jonathan Sachs
>G'day Mate,
>Possibly a few differences in our approaches and subjects. My subjects
>are "pretty girls"...
I'm taking pictures of books, usually by laying the book face up on a
sheet of grey background paper. Your subjects sound like they're more
fun to work with, but they wouldn't help me sell my wares on eBay!
>Can you switch the modelling
>lights off once you have set up your light angles?
Yes and no. Mostly no, though. This tends to be a production process:
stick a book under the camera (a digital camera, by the way); click;
yank the book and stick another one under the camera. I try to group
the books roughly by size so that I don't even have to adjust the zoom
or lens-to-subject distance too often. Often, though, I find that some
feature of the book is shiny, and I have to fiddle with the lights to
avoid reflections. Each time that happens I need the modeling lights.
Then there are books with nothing at all on the front cover. I have to
stand those ones upright, take the camera off the stand, and shoot a
picture of the spine from a roughly horizontal angle. When I'm doing
that, the modeling lights have to stay on all the time.
The bottom line is: I want to avoid a setup that makes me think about
turning the modeling lights on and off, because it's one more thing to
distract me from taking a lot of satisfactory pictures in the shortest
possible time, and it's one more thing that could go -- disasterously
-- wrong.
Since I realized that my modeling lights total only 100 watts per
head, I suspect I can get away with a couple of inches of air space,
and no forced air ventilation. I won't know until I try it, though.