light loss using umbrella

Hello everybody

I got 2 umbrellas for my flashguns, just to get softer on location light. I'm

wondering how much light do i lose when using flashgun bounced of the umbrella

(canon 430 ex, 100 cm silver lastolite umbrella). I just need to know, how

should i compensate that loss - is that around 1 EV ??? thanks in advance for

your time. best regards. grego

Several factures are involved here, such as the color, silver, white, are you shooting through the umbrellas or bouncing into them. Best way to figure it out is the use of a light meter. My guess is about 2 F stops without knowing exactly what your setup is. This is a primitive guess.

Bob, i have 2 of those umbrellas, both are silver & diameter is 100 cm (as i wrote above). mounted on stands, normally around 1-2 meters away from the model... i know the best way to check how much i lose is to use light meter, but as for now i don't have one. if i know what the loss is (roughly) i can adjust around 1/3 or maybe 2/3 of EV in DPP or PS, as i always shoot .RAW. best regards. grego

How are you determining the correct exposure on site in the first place?

 

If you're using a TTL metering method then that will adapt for the loss of light automatically.

 

If you're manually estimating the exposure with the flash then around 2EV, probably, but it depends on lots of factors like Bob says.

 

Since you're shooting digitally with manual flash settings, just adjust the power using the histogram display - it makes no difference to the method whether the flash is direct, or bounced, or shot through umbrellas.

 

You may find that you prefer an additional small exposure adjustment based on the different quality of the light comparing with and without umbrellas, but this is a different feature to the loss of intensity and you will learn this according to your personal taste.

Alec, thanks for your comment. I found actually similar info on planetneil.com ; anyway i appreciate your answer.

Flashmeter or digicam.

 

There is increased distance from flash to umbrella and back to flash and some reflectivity loss. I don`t know the loss for your umbrella and the increased TOTAL flash distance to subject ( flash to umbrella + Umbrella to subject ) compared to the old flash to subject.

 

Just use the guide numbers and add 1 stop for reflectivity loss.

 

This question is impossible to answer.

You also have the ability, if you choose to do so: put two flash units in a bracket with each umbrella to increase the amount of light for each umbrella.

 

It's an option: dual flash bracket: http://www.denisreggie.net/gear.html

Hmm...I hope you have a film camera! If you have DSLR, you are wasting everyone's time :-)

 

Compared to shooting the subject w/ direct flash, the light loss is at least 2 stops - and I wouldn't be surprised if it is 3 or 4 depending on the umbrella and the distance from the flash to the umbrella. bigger distance means more spread out light = more light loss.

I also think it would be about 2 stops for a white umbrella of the usual 36-42", about 1.5 or less for a silver one. However, if you have no flash meter, you can get a rough idea by shooting the same subject and watching your histogram, making note of the settings.

I recently bought the Denis Reggie double bracket, and I can only say it is extremely over

priced for what you get. The really bad part are the poor (to put it kindly) hot shoe mounts

that require extended effort and time to force the flash shoe into the overly tight slots of the

mount. Far better and cheaper is the Morris MTH-203 Umbrella Tilt Head available at B&H for

$24.95.

I lose 1 1/2 stops from bouncing into a silver lined umbrella. The resulting quality of light is

well worth it.