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How do you balance flash w/ambient light?
I am confused on how you go about trying to calculate how to set your flash (Canon 580EX and 430EX) to a specific F-stop without using a hand held flash meter?
I have read on the Strobist webpage and also the book the "Minimalist Lighting" that for example if you manually set your camera for the ambient light reading of say 1/60 F 8.0 then set your flash to F 5.6
I understand that your aperature controls (has a greater effect) of the quantity of light via flash and the shutter speed will control (greater effect) of the quantity the ambient light. But how can you tell what aperature/F-stop the flash output actually is?
The flash or flashes including the camera would all be in manual mode with the flashes being trigger via wireless remote (flashwaves). I have used the flashes with the off camera cord (OC-3?) and I have set various ratios (580EX set as master / 430EX set as slave) using E-TTL the cord is really too short and really limits where I can place the 530EX flash with respect to the camera and if you move to far flash and light stand moves or threatens to fall... a real pain in the backside to say the least. I think I am ready to have more control.
Is there a given starting point as far as the setting for the flash which gets you close then you just fine tune with a couple of test shots? I've read there is but how do you know where to set your flash without know what aperature it is outputing for?
Help!!! Thnx
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I have read on the Strobist webpage and also the book the "Minimalist Lighting" that for example if you manually set your camera for the ambient light reading of say 1/60 F 8.0 then set your flash to F 5.6
I understand that your aperature controls (has a greater effect) of the quantity of light via flash and the shutter speed will control (greater effect) of the quantity the ambient light. But how can you tell what aperature/F-stop the flash output actually is?
The flash or flashes including the camera would all be in manual mode with the flashes being trigger via wireless remote (flashwaves). I have used the flashes with the off camera cord (OC-3?) and I have set various ratios (580EX set as master / 430EX set as slave) using E-TTL the cord is really too short and really limits where I can place the 530EX flash with respect to the camera and if you move to far flash and light stand moves or threatens to fall... a real pain in the backside to say the least. I think I am ready to have more control.
Is there a given starting point as far as the setting for the flash which gets you close then you just fine tune with a couple of test shots? I've read there is but how do you know where to set your flash without know what aperature it is outputing for?
Help!!! Thnx
--
J. Murph
0
Comments
There are two things that you need to keep separate I think.
First, shooting with ETTL in the EOS system - If you set your camera for Av or Manual Mode YOU set your aperture to the aperture of your choice. You can shoot with the flash on the camera, or via an off shoe cord, or via a wireless connection with a master and a slave, but they are all still ETTL. The system will determine the amount of light output needed and quench the strobe after it has been emitted.
If you shoot with your FLASH set to Manual Mode ( NOT YOUR CAMERA )- the flash is now just a dumb fast light bulb, which will emit exactly the same amount of light each time it fires. Setting the proper exposure is entirely up to you. And yes, a flashmeter is one way to do it. But an older method was to use a guide number.
If the flash is set to full output, then the guide number for your flash ( for a specific ISO ) will help you figure out what aperture to set for your specific flash to subject distance. The guide number for your flash will be in the manual that came with it. Or these days you can just google it, as I did. According to Bob Atkins the guide number in feet for the 580ex at ISO 100, is 191 ( for feet ) and 58 ( for meters ). At ISO 200 the guide numbers will double of course.
Here is the equation GN = distance × f-number, so if you know your guide number for your flash and the aperture you want, then GN/f number = distance
For example, if the guide # of your flash is 191 ( for measurement in feet - some GNs are for meters ), and your desired aperture is f8, 191/8 = 23.9 feet.
The lighting ratios for a flash that does not vary is output, is that if it will properly expose the subject at 16 feet, then cutting its power by 1/2 will mean a distance of 11 feet. If you halve the power again, then the distance is 8 feet. Cut the power by half again and the distance is 5.6 feet. Guess what distance is needed if you halve the power one more time. 4 feet. Have you seen these numbers somewhere else previously? Of course you have, it is on your lens barrel as aperture numbers also.
I will tell you a little secret here though - I don't believe that guide number ( 191 for a 580ex ), I think it is overly optimistic.
Do this - set your flash on your camera with a medium range lens 50mm, or 100mm, set you camera to Manual mode at f8, 1/160th and your flash to manual mode full output, pick a neutral target about 10 -15 feet away and shoot some frames from 8 to 20 feet, and find out exactly what distance gives you a perfect histogram with an spike in the middle of you histogram.
That distance x 8 ( your aperture ) will equal your guide number for that ISO. Now you will know how to set up your flash to shoot at f8. Set it at the proper distance for the ISO you are using.
Once you have determined exactly what flash to subject distance provides the proper exposure at ISO 100 for f8. The rest is just ratios.
To to set your flash up for f5.6 , simply cut the power of your flash from full to 1/2, and you will now have the proper amount of light for f5.6 without changing the flash to subject distance.
Or you could move your flash farther ( 1.4x times) from the subject, without changing the power.
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Thank you very much for taking your time to explain. I will do some testing as soon as I can.
If you have any questions after my wordy post, I'll try to make them clearer
Moderator of the Technique Forum and Finishing School on Dgrin