Stupid question - Black BG

I'd blue-gel a light and hit the cr4p out of hte background - you can make a black background any color you please!!
A very dark grey would work best.

But, move the subject out from the background and if possible also snoot off the lights to prevent spill (if you can)

colormaniac wrote in post #8566980
I have another related stupid question. I remember that there was a time I needed to get yellow color on the black muslin. I put yellow gel on the flashes. In the first time the yellow was not rich enough and it looked greenish. But the flashes were set at full power already (and they were in manual mode). So, without much thought, I decreased the shutter speed as in the case of ambient light and it seemed that I can get a more yellowish and brighter background. This experience seems incompatible with Robert's claim, which actually I understand and believe. So, I'm a bit confused now.

By increasing the power and having more light pass through the gel you're increasing the brightness. To increase the saturation you need to lower the power. You can also double or triple up on the gel for greater saturation.

Again, it should be noted that is there is no ambient contribution then increasing shutter speed does nothing for you. This is a common misconception. If you were working outside or in a room with tons of ambient contribution then shutter speed would have an effect but in most cases, and in the example I showed in the other thread, even with bright light coming in a window, it doesn't affect background exposure. If you normally shoot at 1/60s and you don't have ambient contribution then increasing shutter speed to 1/200s or 1/250s is not going to change anything.

The reason for the background not being rendered as black is directly related to the spill and falloff from subject area lighting.

colormaniac wrote in post #8566980
I have another related stupid question. I remember that there was a time I needed to get yellow color on the black muslin. I put yellow gel on the flashes. In the first time the yellow was not rich enough and it looked greenish. But the flashes were set at full power already (and they were in manual mode). So, without much thought, I decreased the shutter speed as in the case of ambient light and it seemed that I can get a more yellowish and brighter background. This experience seems incompatible with Robert's claim, which actually I understand and believe. So, I'm a bit confused now.

First of all, to increase color saturation you want LESS light thru the gel! Some time conduct this experiment for yourself, since digital is 'free' and experiments cost no money (in film and processing) like it used to...Aim gel'd head at black background and shoot a series from minimum flash output thru max flash output, and see what happens to brightness and apparent saturation. Do same against a white background, and compare brightness and saturation vs. with the black background. People need to do this experiment to understand light better!

'shutter speed decrease'...I hate to ask, but on POTN sometimes people say one thing counter to the convention (like going from f/11 to f/22 is 'a bigger f/stop' (wrong!) If you went from 1/60 to 1/30 (a real decrease in speed) you would pick up more ambient light, and lower color saturation. If you went from 1/60 to 1/125 (a real increase in speed) you would pick up less ambient light and increase color saturation.

As for Robert's comment about relative effect of ambient on shutter speed, let me put it differently...If you measure ONLY ambient light, and then compare to the flash exposure reading, when ambient is -3EV from flash exposure, it contributes virtually nothing to the total exposure and changing shutter speed will have virtually no effect. But if you measure ONLY ambient light, and then compare to the flash exposure reading, when ambient is within 1-2EV in brightness difference from flash exposure, it contributes something to the total exposure and changing shutter speed will have some effect.

Light is like water...if I fill a bucket from a 3/4" hose, dripping dyed water into the bucket have little visible effect if I slow the drip rate, but a 1/2" hose flowing with dyed water into the bucket has a quite visible effect and I can see noticeable difference from closing the valve down.

Wilt wrote in post #8568864
First of all, to increase color saturation you want LESS light thru the gel! Some time conduct this experiment for yourself, since digital is 'free' and experiments cost no money (in film and processing) like it used to...Aim gel'd head at black background and shoot a series from minimum flash output thru max flash output, and see what happens to brightness and apparent saturation. Do same against a white background, and compare brightness and saturation vs. with the black background. People need to do this experiment to understand light better!

'shutter speed decrease'...I hate to ask, but on POTN sometimes people say one thing counter to the convention (like going from f/11 to f/22 is 'a bigger f/stop' (wrong!) If you went from 1/60 to 1/30 (a real decrease in speed) you would pick up more ambient light, and lower color saturation. If you went from 1/60 to 1/125 (a real increase in speed) you would pick up less ambient light and increase color saturation.

As for Robert's comment about relative effect of ambient on shutter speed, let me put it differently...If you measure ONLY ambient light, and then compare to the flash exposure reading, when ambient is -3EV from flash exposure, it contributes virtually nothing to the total exposure and changing shutter speed will have virtually no effect. But if you measure ONLY ambient light, and then compare to the flash exposure reading, when ambient is within 1-2EV in brightness difference from flash exposure, it contributes something to the total exposure and changing shutter speed will have some effect.

Light is like water...if I fill a bucket from a 3/4" hose, dripping dyed water into the bucket have little visible effect if I slow the drip rate, but a 1/2" hose flowing with dyed water into the bucket has a quite visible effect and I can see noticeable difference from closing the valve down.

Good explanation Wilt. Just to clarify to others... I'm not saying that there isn't or can't be ambient contribution and that shutter speed can't have an effect. My point is just that in almost every instance of working in a studio or indoor environment, the ambient contribution is insignificant. By the same token, if you have bright Sun light streaming in through a bank of windows then ambient would be contributing but from a logical standpoint, if you're trying to render something black, why would you do it in front of windows with Sun light pouring in? You wouldn't. You would either work in the evening or find some way to cover the windows or lower the blinds.

Very informative thread. Thanks.

Think of it as such - if you have tinted windows in a car with 10% tint, you can almost see through normally. 20% is half the optical transfer...etc etc.

About the best at demonstrating this effect is a graduated color filter pointed at a uniform light source. You tell me which bit has the greatest color saturation.

A good experiment is to try using hotlights only in your studio. You will quickly see how much ambinent light it requires to affect the exposure. f/8 and down takes a great amount of hot light wattage, I have a couple of 1000w lights I use occasionally and need to use wide apertures and longer shutter speeds when using them.

Thanks everybody! Again, I had some misunderstanding. I'll certainly do some experiments to fully understand the principles there. Yet for the time being, the school semester has just started and it takes a while for me to set up the studio as most stuff is packed, I can only learn by mere discussion.

BCRose wrote in post #8569166
A good experiment is to try using hotlights only in your studio. You will quickly see how much ambinent light it requires to affect the exposure. f/8 and down takes a great amount of hot light wattage, I have a couple of 1000w lights I use occasionally and need to use wide apertures and longer shutter speeds when using them.

If you contrast it to flashes in watt-seconds versus hot lights in watt-hours...

1kWh = .27 watts per second

400w/s flash firing for 1/900 sec delivers .45w in that 1/900 of a second. That's....much more clout!
In the same time (1/900s), the hot light will have emitted .0003w

There is no fight.

Psychobiker wrote in post #8569667
If you contrast it to flashes in watt-seconds versus hot lights in watt-hours...

1kWh = .27 watts per second

400w/s flash firing for 1/900 sec delivers .45w in that 1/900 of a second. That's....much more clout!
In the same time (1/900s), the hot light will have emitted .0003w

There is no fight.

...in the winter in snowy climates, hot lights make nice heaters! The value equation is altered in winter.

Ah! then it comes to efficiency.

Presuming the hotlight is on average 5% efficient, you get...more heat than a 75% efficient strobe. I'm not calculating agian!

You guys are very helpful - I can speak for many people that have enter and view this thread and many others - you guys are very welcome ...

On a side note .. so if I was to use a Gel for the hair light, I normally use it one stop above my main light - If I want great color saturation I should use it like a fill light maybe 3 step lower? Thanks ...

I have a shoot tomorrow and I want to use gels and lord and behold - if I didnt read this I would of have been lost!

Gel the hairlight

Are you shooting someone with wildly tinted hair, where this could provide some complementary color?

Yes gel the hair light and maybe the back light hitting the body ...

but if you must see stuff Im into

http://modelmayhm-0.vo.llnwd.net …0709/00/4a55986​48536b.jpg

You're on your own with that need, I have zero experience doing that wild lighting on portraiture