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Thread started 28 Mar 2011 (Monday) 12:08

Mar 28, 2011 12:08 |  #1

This may be a real basic question but here goes.
With the Elinchrom BXRi500's there is a digital readout on the back for the power output (2.5, 3.4, etc.). The manual states the watt power of this value but how can this value be related to the f-stop that is so often referenced on this forum for the lights? How can I relate this reading to f9 for instance?
I do understand distance comes into place, like 2.8 goes to 4 if the light backups up 4ft I think.
Thanks in advance and if I have overlooked a link for this in the stickies I apologize.

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Mar 28, 2011 12:42 |  #2

each full number is a full stop. Example if you adjust the power on the strobe from 3.0 to 4.0 would be f9 - f11. (just random numbers thrown out your mileage may vary). It is really easy once you know how it works

Don't try to confuse me with the facts, my mind is already made up.
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Mar 28, 2011 13:15 |  #3

Its a bit more complex then translating the digital read-out into a Fstop, things like distance, modifier make all the difference here.

A 2x diffusion SB will eat up more light then an umbrella. EVen different SBs eat different amounts of light.

So the two are generally kept different, when you want to shoot f9, either meter, or get to know your modifiers, so you'll be able to predict based on distance.

For example, my BD would eat up a stop, so if i set my light at 4.0 and i get roughly 9 feet away, i can predict to get roughly f9. (example)

IIRC, elinchrom's readout is universal to its lights, so a 400w at 3.0 is outputting the same power as a 500w at 3.0 and the same as 1200w at 3.0. (If i remember correctly..) Makes predicting things nice n easy

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Mar 28, 2011 13:29 |  #4

Csae wrote in post #12109839
IIRC, elinchrom's readout is universal to its lights, so a 400w at 3.0 is outputting the same power as a 500w at 3.0 and the same as 1200w at 3.0. (If i remember correctly..) Makes predicting things nice n easy

Correct!
Also makes metering pretty easy.

Dennis
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Mar 28, 2011 13:30 |  #5

Csae wrote in post #12109839
IIRC, elinchrom's readout is universal to its lights, so a 400w at 3.0 is outputting the same power as a 500w at 3.0 and the same as 1200w at 3.0. (If i remember correctly..) Makes predicting things nice n easy

You are correct.

I guess I should have been more clear. All thing equal and you just change the out put on the strobe, thats what it should be like. Of coarse its never perfect.

Don't try to confuse me with the facts, my mind is already made up.
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Mar 28, 2011 18:00 |  #6

Thanks for the replies. I was wondering if there was a simple rule or formula to use. But guess not.
Thanks for the info!
Guess I just need to play more with the soft boxes and get to know the distances.

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Mar 28, 2011 18:14 |  #7

The power scale that Elinchrom uses is one of the thing I love about their strobes it makes mixing different watt strobes together so easy. As to the OP's ? if you want to know the F stop of your strobes at a certain power rating with a certain modifiers that is what they make light meters for, not trying to be a smart ass but a good light meter should be part of any strobe lighting kit.

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Mar 28, 2011 18:25 |  #8

wizard13 wrote in post #12111884
Thanks for the replies. I was wondering if there was a simple rule or formula to use. But guess not.
Thanks for the info!
Guess I just need to play more with the soft boxes and get to know the distances.

I am not following completely here. No matter what i set up at power modifier or distance I just put it at f9 and fire and see what I get. If I am not being lazy I pull out the light meter.

Damian75 wrote in post #12111959
The power scale that Elinchrom uses is one of the thing I love about their strobes it makes mixing different watt strobes together so easy. As to the OP's ? if you want to know the F stop of your strobes at a certain power rating with a certain modifiers that is what they make light meters for, not trying to be a smart ass but a good light meter should be part of any strobe lighting kit.

I love that too. It makes it easy. Light meter or eyeball it. It kind of sounds like he wants a sears set up where he turns on the strobes and measures how far from the subject so its good to go. If its not a permanent set up its hard to do this, and would get boring fast.

Don't try to confuse me with the facts, my mind is already made up.
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Mar 28, 2011 21:20 |  #9

sigma pi wrote in post #12112010
I am not following completely here. No matter what i set up at power modifier or distance I just put it at f9 and fire and see what I get. If I am not being lazy I pull out the light meter.

I love that too. It makes it easy. Light meter or eyeball it. It kind of sounds like he wants a sears set up where he turns on the strobes and measures how far from the subject so its good to go. If its not a permanent set up its hard to do this, and would get boring fast.

Not looking for a sears set-up but more a formula to help calculate the output. Guess a light meter is the next purchase.
Thanks for the replies-

Photography = a constant learning process

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Mar 28, 2011 23:39 |  #10

Well... it exists.

Inverse square law, strobe GN, modifier Light Loss.

Take a shot at 1 meter, with no reflector or softbox or anything. Meter it, f40?Cool. Add modifier, f32? Cool, note light loss down (on the modifier if you want). Then just apply inverse square law for distance to subject and calculate the light.

Rather complicated & not extremely scientific, someone will probably chime in with a better formula.

Its much much easier to meter, or chimp.

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Mar 29, 2011 10:39 |  #11

Csae wrote in post #12113808
Well... it exists.

Inverse square law, strobe GN, modifier Light Loss.

Take a shot at 1 meter, with no reflector or softbox or anything. Meter it, f40?Cool. Add modifier, f32? Cool, note light loss down (on the modifier if you want). Then just apply inverse square law for distance to subject and calculate the light.

Rather complicated & not extremely scientific, someone will probably chime in with a better formula.

Its much much easier to meter, or chimp.

Photography = a constant learning process

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Mar 29, 2011 11:24 |  #12

Csae wrote in post #12113808
Its much much easier to meter, or chimp.

This. By the time I have the calculator out I could have chimped it

Don't try to confuse me with the facts, my mind is already made up.
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Mar 29, 2011 15:12 |  #13

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Mar 29, 2011 16:41 |  #14

ben_r_ wrote in post #12118361

That is perfect!

Photography = a constant learning process

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Mar 29, 2011 20:21 |  #15

wizard13 wrote in post #12119112
That is perfect!

Just found it today myself actually. Only minutes before I fell onto your thread. Thought that might shed some light on it. Glad that helped!

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