New Speedlight Softbox

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Archive 2009 · New Speedlight Softbox

wilrobking
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p.3 #1 · New Speedlight Softbox

Scott Clark wrote:
gardenvalley wrote:
Thanks BrianO, this has been bugging me. Using this formula means that using 4 flashes with GN30 is equivalent to using 1 flash of GN60 which is an increase of only 1 stop! Oops! That means, if my calculations are correct, that wedding and event photographers using light-sticks and the like with 2 speedlights are only getting an increase of 1/3 stop, although gaining a potential greater spread of light. Best not tell them !

You must have something wrong...flash power simply put gives you one f-stop every time you double the power. You can prove it for yourself--set your flash to 1/4 power and find an aperture that gives you the proper exposure. Now set it 1/2 power. You'll be overexposed by exactly 1 stop. Close your aperture one stop and you're at the correct exposure again. You can do this all day long across the power range. If you have one flash at full power that gives you f8, and double the light on the subject with another equal flash at full power, you've just doubled your power and would get f11...
This might be of interest:
http://photography-on-the.net/forum/archive/index.php/t-271010.html

That was my understanding.

Jul 30, 2009 at 11:54 AM

gardenvalley
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p.3 #2 · New Speedlight Softbox

I`m getting a sore head. I agree,Scott, about doubling the power of 1 flashgun is increasing the exposure by 1 stop, but this refers to more than 1 light source and the power output of a flashgun is not rated in stops. I read the link you posted, but I think they may be wrong. I refer back to BrianO`s post. If this is true then a lot of people are not going to like the numbers. You can`t change the laws of physics, Captain! Does anyone have 2 identical flashes and a light meter? Now where did I put that box of Paracetamol.............

Jul 30, 2009 at 12:21 PM

Scott Clark
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p.3 #3 · New Speedlight Softbox

gardenvalley wrote:
I`m getting a sore head. I agree,Scott, about doubling the power of 1 flashgun is increasing the exposure by 1 stop, but this refers to more than 1 light source and the power output of a flashgun is not rated in stops. I read the link you posted, but I think they may be wrong. I refer back to BrianO`s post. If this is true then a lot of people are not going to like the numbers. You can`t change the laws of physics, Captain! Does anyone have 2 identical flashes and a light meter? Now where did I put that box of Paracetamol.............

I've got a pile of flashes and a meter...at home

. If nobody beats me to it, tonight I'll put the smack down with a couple of SB-28s and see exactly what happens

Jul 30, 2009 at 12:53 PM

gardenvalley
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p.3 #4 · New Speedlight Softbox

Good on you, Scott. If the formula is right, make sure there`s something nice and soft to prevent your jaw from hitting the floor. I am now intrigued to see if the real world matches the numbers.

Jul 30, 2009 at 01:05 PM

Scott Clark
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p.3 #5 · New Speedlight Softbox

gardenvalley wrote:
Good on you, Scott. If the formula is right, make sure there`s something nice and soft to prevent your jaw from hitting the floor. I am now intrigued to see if the real world matches the numbers.

. Will do. I'll eat my hat if adding a second flash only yields 1/3 of a stop

Jul 30, 2009 at 01:09 PM

Nowhere Man
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p.3 #6 · New Speedlight Softbox

That would suck to have to adjust your flash(es) output x4. Doesn't seem very practical, but I'm sure it will be useful to someone.

Jul 30, 2009 at 03:10 PM

gardenvalley
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p.3 #7 · New Speedlight Softbox

Thanks for coming in on this one Carmen Miranda. I again refer you to BrianO`s formula. If anything, this thread indicates the confusion which reigns regarding the science of light. Although not entirely scientific, let`s wait and see what Scott comes up with. We`re trying to ascertain how much light is gained by using 4 flashes rather than 1. What we have to bear in mind is that light propagation is not linear but the ratio we use to measure exposure is; 2.8, 4, 5.6 etc. I`m now going to go and lie down in a dark room with my teddy bear.

Jul 30, 2009 at 03:20 PM

BrianO
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p.3 #8 · New Speedlight Softbox

gardenvalley wrote: Thanks for coming in on this one Carmen Miranda. I again refer you to BrianO`s formula.

In the interest of accuracy, "my" formula came from Light -- Science and Magic, 3rd Edition, and is found in chapter 10 on page 280.

Note that the formula is dealing with guide numbers, not f stops. So four strobes only doubles the range compared to one flash -- a demonstration of the inverse square law at work. To double the guide number requires a quadrupling of the flash output, because the area increases at the square of the distance.

The way to test this would be to measure the f stop required for a given exposure with one strobe at a given distance, and then measure the distance at which four strobes gives the same f stop.

For a refresher on guide numbers, see: http://en.wikipedia.org/wiki/Guide_number.

Jul 30, 2009 at 05:09 PM

gardenvalley
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p.3 #9 · New Speedlight Softbox

I`ve figured it out. Given that the above formula is correct;

example: GN 40, distance to subject 10 feet, f-stop would be 4
GN 80, distance to subject 10 feet, f-stop would be 8

This is a difference of 2 stops, therefore using 4 flashguns instead of 1allows for an extra 2 stops. If I`ve interpolated this right, it means that Scott`s experiment using 2 flashes will show an extra 2/3 stop difference. It`s not that bad an increase but I think it will still surprise a few people. If nothing else I`ve learned something from this. Thank goodness for TTL and histograms.

Jul 30, 2009 at 05:48 PM

Scott Clark
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p.3 #10 · New Speedlight Softbox

Had time to test this over my lunch break...results posted in their own thread

Jul 30, 2009 at 07:30 PM

CGP4
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p.3 #11 · New Speedlight Softbox

wilrobking wrote:
I wish I could get my hands on one. They're all out of stock.

FYI, as of today (8/5/09)m they're back in stock. (No affiliation with company, just a satisfied user of product!)

Aug 05, 2009 at 02:24 PM

runner301
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p.3 #12 · New Speedlight Softbox

I just wish they had polished the flute.

Aug 05, 2009 at 02:35 PM


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