Manual flash in Program mode?

[a._valerio]

Is it true that EOS cameras and Speedlites can be used in manual flash mode AND

Program exposure mode (as well as shutter priority)?

 

If so, I can't see how this would result in a correct exposure.

 

Thanks for your help.

[thierry nguyen cuu - nomad]

Yes, you can set your flash to manual in any exposure mode.

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<i>"If so, I can't see how this would result in a correct exposure."</i>

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When one says "Manual" it means that the person is in CONTROL of the exposure/composition and effect of the shot.

[lester_wareham]

The thing to understand is that flash and ambient light exposures are metered separately.

 

An external flash in manual flash mode would require you to adjust the flash power to get the effect you want, but the camera ambient exposure could still be in one of the auto modes.

 

If you use the flash in ETTL II auto mode then the way flash and ambient light is metered depends on the ambient exposure mode and the ambient light levels, for example in Av mode the camera will try and provide fill in flash and in Tv or M you will get flash exposure and manually control the ambient balance.

 

EOS cameras with built in flash can not generally be operated in manual flash mode although the more expensive external units can. However you can get control over the flash exposure separately in ETTL II mode using the flash exposure compensation or flash exposure lock features, these are independent of ambient exposure.

 

You might find this enlightening. http://photonotes.org/articles/eos-flash/

[a._valerio]

As a Nikon user, I still can't see how this would work. I'm going to be using Canon equipment, and might even add some, so I need to understand this.

 

If I were Canon, I would make it work like this:

 

1. You're at ISO 400. Your guide number is 120 (ft) at 50mm zoom. You set the flash power (say you set 1/4).

 

2. You're at 20 feet. The flash does the guide number calculation [say: (120/(1.43^2)*(1.43^2))/20= 6].

 

3. The camera sets f/6.0. Now, the exposure is wrong, so Program AE has to meter at f/6.0 and set the corresponding shutter speed for the ambient light...say 1/30th second. So the exposure is 1/30th sec @ f/6.0.

 

Is this how it works?

 

On Nikon, you do this:

First off, it only works in aperture priority an manual modes.

Aperture Priority AE manual flash:

 

1. You're at ISO 400. Your guide number is 120 (ft) at 50mm zoom. You set the flash power (say you set 1/4).

 

2. You set any aperture you want. Say you set f/4.0. The flash does the guide number calculation [say: (120/(1.43^2)*(1.43^2))/4= 30]. The flash does not set anything for you. It simply displays the correct distance you need to be at for your power setting, ISO, and lens aperture. You move to a 30-ft. distance. This method messes up your composition.

 

3. The camera sets the corresponding shutter speed for the aperture based on the ambient light. *The exposure might might not be correct if it's dark. If you're set to slow sync mode, the camera then can use as slow a shutter speed as needed for correct exposure.

 

Alternate method on Nikon: Distance Priority manual flash:

Again, only usable in manual and Aperture Priority AE modes:

 

1. You're at ISO 400 and a 50mm zoom setting.

 

2. You're at 20 feet. You set any aperture you want. Distance, focal length, and aperture are automatically relayed from the camera to the flash unit. Say you set f/4.0. The flash does the guide number calculation in reverse (based on f/4 and 30 feet @50mm) and calculates the needed flash power [say: 4.0*20)=80. The flash unit compares 120 via a ratio to the full power output at ISO 400 and 50mm (which would be 120*(1.43)^2=245 ft*stops. 80/245=1/3. The flash sets the correct power ratio (1/3 power) for you.

 

3. The camera sets the corresponding shutter speed for the aperture based on the ambient light. *The exposure might might not be correct if it's dark. If you're set to slow sync mode, the camera then can use as slow a shutter speed as needed for correct exposure.

 

I still don't understand how the Canon method works.

[fred_c1]

>Is it true that EOS cameras and Speedlites can be used in manual flash mode AND Program exposure mode (as well as shutter priority)?

 

Why would anyone want to use that?!

 

You should do it the other way round, i.e. set shutter speed and aperture manually and let the flash does the rest.

[colinsouthern]

Possibly the best starting point for you would be http://photonotes.org/articles/eos-flash/

 

Cheers,

 

Colin

[mark u]

Even without using flash it is quite possible to set totally inappropriate exposures in manual operation - e.g. 2 seconds at f/2 and 1600 ISO on a sunny day. Arranging interlocks to try to prevent every possible stupidity is not practical and cost effective.

 

Your putative calculations can easily be totally thrown by bouncing the flash, in which case you will have to allow for the reflectivity of the bounce surface as well as the change in effective flash to subject distance. It is precisely this type of issue that gives rise to TTL flash metering and control being offered by manufacturers.

 

For those who want to have more creative control, manual settings can offer advantages. It is possible to use manual flash power with P or Tv shutter modes, especially where the ambient light and flash to subject arrangement is consistent: it simply entails adjusting the manual power level to taste, much as you might adjust the level of flash exposure compensation in an automated flash mode. Of course it is usually easier to ensure that you have manual control over ISO and aperture when using manual flash.