Canon 580ex's Manual mode

[kevinbriggs]

I'm currently using the Canon 5D with the 580ex as the on-camera flash (as well

as 2 480ex's as slaves). I have a question in relation to the "Manual flash

mode" of the 580ex.

 

On page 22 of the 580ex manual it states: "You can set the flash output from

1/128 power to 1/1 full power in 1/3-stop increments. Use a hand-held flash

meter to determine the required flash output to obtain a correct flash exposure."

 

I have just recently acquired a flash meter (Sekonic L-308s). Having never used

a flash meter before, what is confusing about the instructions in the 580ex

manual (page 22 and 23) are that I do not know how to translate the vernacular

of the Manual flash mode with the readings produced by the flash meter.

 

In other words, when you get back values of shutter speeds and aperture settings

(from the meter) how is that supposed to translate to the Manual flash settings

of everything between 1/1 and 1/128?

 

Any and all comments would be most appreciated!

 

K.

[jimstrutz]

Most flash meters don't respond with a shutter speed, just the aperture. However, many of the better flash meters will adjust the shutter speed for the ambient lighting as a component with the flash lighting. If the ambient lighting is dim, the shutter speed (within reason) will have no effect on flash lighting or flash metering. You can ignore the above paragraph if it seems confusing. It's late and my mind is wandering. Can't think of a simpler way to word it.

 

Anyway, the flash meter will report an aperture it suggests for use with the flash when the flash is set to a specific power setting. You can set the lens aperture to that and call it good, or if you don't want to use that aperture (or can't), reset the flash to a different power and re-meter it.

 

There are two basic ways to go about this whole process. You can do as above and set the aperture to what the flash and flash meter indictate, or you can choose an aperture first and keep adjusting the flash until it meters correctly for the chosen aperture.

[michael j hoffman]

Attach flash to camera and turn both on.

Set camera and flash to manual mode.

Check ISO setting on camera and meter.

Set meter to flash mode.

Set camera shutter speed to x-synch or slower.

Set desired aperture on camera.

Test fire the flash to get your 1/1 reading.

Repeat above as necessary decreasing flash power as needed.

When your desired aperture is indicated on the meter you're there.

 

You could also select a specific amount of flash power (1/1, 1/4, 1/32, et al) and meter for the aperture, but I can't see that being useful outside of a tricky fill-flash situation which may still be a bit ahead of your position on the learning curve. Flash is tricky, but indispensable once you know what you - and your equipment - are doing. There is no direct "translation" between the manual flash output power setting and the aperture and shutter speed. Shutter speed is essentially irrelevant so long as it is set to flash synch or slower. Aperture is directly affected by the flash, but not only by output power. Aperture is also affected by the distance between the flash and the subject. Flash output power settings are arbitrary; 1/2 power setting could produce just the right amount of flash or too little or too much. Again, this is largely dependent upon flash to subject distance, and also the effect you are striving to achieve.

 

Have fun!

 

Michael J Hoffman

[kevinbriggs]

Thanks very much for these responses. They have proven to be exceptionally heleful. I think I now have a much better understanding of what Manual flash is all about.

 

Given that Manual flash settings control the power output of the flash, can you now explain to me what the difference is between this Manual control and Flash Exposure Compensation?

 

My original understanding of this flash output control was that it was similarly controlling the power output of the flash. But maybe I am mistaken...?

 

Thanks again,

 

K.

[kin_lau]

Manual Flash... you make _all_ the decisions and calculations.

 

Flash Exposure Compensation... the camera & flash work together to provide the proper exposure, and you just _tweak_ it (brighter or darker). Eg FEC of -1 means you want exposure to be 1 stop less than what the camera+flash calculates it should be.

[ruben leal]

Kevin,

The difference between Manual Mode (M) and Flash Exposure Compensation (FEC), is:

on M, the Flash will allways deliver the same amount of power, when set at the same value;

but, when on FEC, it will deliver an amount of power proportional to that required by the camera's (TTL) exposure meter.

 

Say your camera needs an amount of power to illuminate an scene, but you want to use the flash just as a fill (particulary needed when disabling the auto fill reduction via a custom function in you 5D, and perhaps using Av in the camera), then you adjust your flash's FEC to somwhere around -2. Then the camera will adjust it's own exposition to take the picture, and the flash will set the needed amount of power to deliver 2 stops less of light than that needed to illuminate the scene. Hope the explanation is better than the sample, as I'm having trouble understanding myself!

[keith_lubow]

The setting the flash meter gives you is an aperture based on the test fire of the strobe. Say it gives you F/16 with your flash at full power. You decide you want to use F/2.0, however, and you decide to expose one stop over what the meter says, just because you know your meter and what using its recommended settings will give you, and for this instance you think that a one stop overexposure will look best for the picture you want. You can use the settings you want by controlling flash power. You can lower flash power 5 stops to get to F/2.0 and back up one to overexpose. So, just lower flash power 4 stops to 1/16 power.

 

Since you have digital, you can adjust the additional flashes based on your test shots rather than Polaroids.

 

keith