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# How do I calculate power needed on each flash?

Carlosh
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 p.1 #1 · p.1 #1 · How do I calculate power needed on each flash?

I have the following flashes:
1. Sony TT350S 118' at ISO 100
2. Nissin Di866 ii 198' at ISO 100
3. Godox TT685 197' at ISO 100
4. Godox AD600BM 285' at ISO 100

Realistically, they will be about 4' from the subject and I don't have nor want to buy a light meter.

Number 4 is my main light

Number 2 is my fill light

And to keep things interesting, let's say that I use number 1 as the hair rim light.

This is beginning to sound like a high school algebra word problem!

Let's assume that light number 4 is set at 1/16th power.

If I want to set the fill light at 60% of number 4 and the hair rim light at 80%, What should the actual setting be for number 1 and 4? Even if my percentages I selected for the power of each flash are not correct, I still need to know how to calculate the power required. Is there a photography calculator for this purpose?

Feb 23, 2022 at 10:03 AM
jlafferty
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 p.1 #2 · p.1 #2 · How do I calculate power needed on each flash?

Forget the math and use your eyes. You’re either going to need to chimp a good bit or, forgoing the meter, you should tether into CaptureOne and monitor exposure levels/shadow density/color saturation and the like, and simply adjust to taste.

Feb 23, 2022 at 10:08 AM
tcphoto
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 p.1 #3 · p.1 #3 · How do I calculate power needed on each flash?

If you don't use a meter, you will need to judge it by the small screen on your camera or tether to a computer via Capture One or LR. I own a Minolta meter but it hasn't had batteries in it for a long time.

Feb 23, 2022 at 10:16 AM
frdjohns
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 p.1 #4 · p.1 #4 · How do I calculate power needed on each flash?

While I'm no expert, isn't this exactly what a light meter is for? Not sure why you wouldn't want one. It not only allows you to set up exactly what you are talking about, it allows you to repeat the lighting with consistency each time you decide to use that lighting setup. This is like wanting to measure distance, but not use a measuring tool.

Without a meter you are basically guessing. You can't just use the percentages of power on each light because the numbers reported are not consistent among different manufacturers. So either bite the bullet and get a light meter or plan on chimping a whole lot.

You don't need a fancy, expensive meter; you can probably find a basic one on ebay or here in the buy and sell forum for very little money.

Feb 23, 2022 at 11:54 AM
Carlosh
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 p.1 #5 · p.1 #5 · How do I calculate power needed on each flash?

I've read everyone's answers and let me just say that I really appreciate everyone's perspective. I had to look up the word chimping, but I get what you're saying.

The reason that I didn't want to mess with a light meter is because it would be one more thing to contend with and worry about. That, however, doesn't sound like a sound justification for not owning one. Bottom line is that it sounds like all the guesswork is taken out of the equation with a light meter. How can I argue against that? I can't. Your compelling explanation is good enough for me. I'll only ask one follow up question. Which light meter for indoor and outdoor use?

Carlos

Feb 24, 2022 at 12:03 AM
story_teller
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 p.1 #6 · p.1 #6 · How do I calculate power needed on each flash?

Until you get comfortable with setting up lighting ratios, a light meter can be very handy. If you want your hair light 2 stops lower than your main or want a 3:1 ratio between my main and fill, a meter can quickly tell you how to set your lights in varying situations. It can also tell you what ratios you have, so you can easily recreate that look whenever you want to.

Once you're comfortable with everything, you could sell the light meter. Personally, I always carry one in my bag.

Feb 24, 2022 at 07:14 AM
tcphoto
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 p.1 #7 · p.1 #7 · How do I calculate power needed on each flash?

The Sekonic 358 or Minolta Flashmeter V would be my first choices, I have the Flashmeter IV and it's served me well since about '92. The 358 can be fitted with a Profoto module that connects with their units with built in PW modules. I believe they only measure flash up to 1/200 sec but perhaps a recent generation meter will measure high speed or hyper speed sync. Once you've got the ratio, you can then judge what works for your application.

Feb 24, 2022 at 12:41 PM
JohnSil
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 p.1 #8 · p.1 #8 · How do I calculate power needed on each flash?

It would take a little time but since this is just theoretical it's pretty obvious you've got gobs of time! LoL
You need to shoot everything manual, the camera and the flashes.
Set each flash up one by one with each flash on its own group on the controller. Simply fire each flash separately in it's group until it gives you the light you want that flash to give. Then fire them all at the same time, that will blow everything out from the combined power. Now turn the camera down, f-stop, until the exposure is proper. Each flash is now set to the proper ratio and the lighting will be what you set up.
Now if your controller doesn't have groups, and it probably doesn't since it's probably ancient since you refuse to buy a meter, in which case you'll be screwed!!! LoL
John

Feb 24, 2022 at 01:58 PM
kaplah
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 p.1 #9 · p.1 #9 · How do I calculate power needed on each flash?

Carlosh wrote:
[...]

Realistically, they will be about 4' from the subject and I don't have nor want to buy a light meter.

You certainly don't need one, although they are much faster for setting up portrait lighting.

Set your key/fill ratio; then meter both at the same time; then meter the hair light for one stop (or to your taste) down from key+fill.

Pop the light, read the meter, adjust the light and meter a confirming pop if you wish. Done. It's a lot faster than chimping and doesn't use up your shutter.

If you are replicating a setup - as in, producing the same look from a previous session - it's the only viable method.

But, if you're going to go without a light metre, then you can try this for metering: http://super.nova.org/DPR/WhiteTowelRatios/

And of course, this for understanding light: http://strobist.blogspot.com/2006/03/lighting-101.html

Feb 24, 2022 at 03:06 PM
rico
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 p.1 #10 · p.1 #10 · How do I calculate power needed on each flash?

kaplah wrote:
If you are replicating a setup - as in, producing the same look from a previous session - it's the only viable method.

This is the compelling reason to use a light meter. Establishing ratios in the first place is an artistic decision, and metering cannot account for those aesthetics—especially when light modifiers are switched up for different looks.

Feb 24, 2022 at 06:24 PM

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jlafferty
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 p.1 #11 · p.1 #11 · How do I calculate power needed on each flash?

kaplah wrote:
If you are replicating a setup - as in, producing the same look from a previous session - it's the only viable method.

You mean: other than tethering, or a ton of experience

Feb 24, 2022 at 08:18 PM
CharleyL
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 p.1 #12 · p.1 #12 · How do I calculate power needed on each flash?

Have you considered TTL ? Let your camera and Key Speedlite tell you how much light you need, and then lock the camera on those resulting settings. A "TCM" button on my flash transmitter takes care of this. If you have that button and use TTL, it's easy. Get your key light correct using this method and then play with the levels of the rest to get the desired result. No light meter necessary, but I highly recommend getting a light meter, especially for portrait work. I have two Seconic L-308X-U, one in studio and one in field kit. I rarely use the one in the field kit, but use the one in the studio all the time, especially when doing portraits. Studio strobes (at least mine) are not TTL.

Charley

Feb 26, 2022 at 10:29 AM
Carlosh
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 p.1 #13 · p.1 #13 · How do I calculate power needed on each flash?

You guys have pretty much convinced me of getting a light meter. I'd rather not use TTL because I prefer to shoot in the Manual Mode if possible. Thanks for the recommendation of which light meter you use.

Carlos

Feb 26, 2022 at 11:36 AM
pasblues
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 p.1 #14 · p.1 #14 · How do I calculate power needed on each flash?

Carlosh wrote:
I've read everyone's answers and let me just say that I really appreciate everyone's perspective. I had to look up the word chimping, but I get what you're saying.

The reason that I didn't want to mess with a light meter is because it would be one more thing to contend with and worry about. That, however, doesn't sound like a sound justification for not owning one. Bottom line is that it sounds like all the guesswork is taken out of the equation with a light meter. How can I argue against that? I can't. Your compelling explanation is good enough

In the old days, we used polaroids for test shots.

Now we basically have a polaroid in our digital capture reviews.

Mar 27, 2022 at 10:44 AM
MRomine
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 p.1 #15 · p.1 #15 · How do I calculate power needed on each flash?

Turn one light on and take a picture, review and adjust light out put. Do the same for the next light but leave the first one off. Do this with each light until you get the exposure of each light adjusted to where you want. Then turn all four on together and do a combined exposure and adjust to taste.

Mar 28, 2022 at 11:34 AM
Carlosh
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 p.1 #16 · p.1 #16 · How do I calculate power needed on each flash?

MRomine wrote:
Turn one light on and take a picture, review and adjust light out put. Do the same for the next light but leave the first one off. Do this with each light until you get the exposure of each light adjusted to where you want. Then turn all four on together and do a combined exposure and adjust to taste.

Thanks!

Mar 28, 2022 at 12:44 PM
mark1958
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 p.1 #17 · p.1 #17 · How do I calculate power needed on each flash?

I generally use the light meter to give me a ballpark and then adjust and play around with the settings for each light .

Mar 28, 2022 at 01:23 PM
tcphoto
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 p.1 #18 · p.1 #18 · How do I calculate power needed on each flash?

You will be able to estimate the power setting with different modifiers with experience. In the beginning, a light meter is necessary to do so in a timely manner and will limit the time chimping, moving lights or cutting into your time with the subject. Besides, when I divide the purchase price of my meter, I'm looking at about .75 a month...

Mar 28, 2022 at 02:57 PM
CharleyL
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 p.1 #19 · p.1 #19 · How do I calculate power needed on each flash?

My previous post implied to use TTL for the Key light and first shot. When you have no light meter and have no idea where to start, let the camera in auto mode and TTL tell you. Then turn off TTL and switch to manual, leaving your key light set to whatever the camera decided. If it was too dark or too bright, there is a compensation adjustment in your camera menu screen. If you make an adjustment, repeat the first shot in TTL and auto mode again. Then go to manual mode with TTL off and you have the key light set.

The trouble with Auto mode and TTL is that the camera averages the light levels of the entire field to determine the settings. Since it does this averaging for each shot, an increase or decrease in average light level may occur between shots. This will change the level settings from one shot to the next. Shoot in Auto and TTL for the first shot and then manual and no TTL for additional shots and the camera won't be trying to average the scene light levels, so all shots following will be based on the settings from that first shot, unless you change them. This is just a good way to get a starting point for your settings when you don't have a light meter.

Then you can start setting your other lights one by one manually to get the desired ratios, turning on one light at a time and adjusting it, taking test shots as needed, until you have all lights set. Then, one final test shot with all lights turned on and you should be good to go.

Using a light meter helps get the ratios much faster with many less test shots. I usually set my lights, even the key light, using just the light meter, to get the levels and ratios that I want. Then one test shot with all lights turned on to see if it is all working as planned, and then I continue with the shoot.
If I move a light during the shoot, I get the light meter out and set it again. Then another test shot to check the result, and if good the shoot continues.

Charley

Apr 11, 2022 at 10:12 AM

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