I have a Sekonic light meter (478 DR I think) and I use my off-camera flashes in TTL mode. So I was wondering if using a light meter even makes sense in this case?

up vote 4 down vote accepted

If you are using your flashes in full auto TTL, then there is no point in having a LightMeter, however, if you wish to have better control and more accurate tone, colour, brightness, contrast, shadows and highlights, then manual is the way to go and the Sekonic Lightmeter is a great tool to have.

Apologies if I happen to go over anything too basic with my answer, but the metering systems are measuring light differently.

TTL is measuring the light that is reflecting off the subject An external light meter is measuring light that is directly hitting the subject, thus the reason for the above mentioned points

In general, both sets of metering will result in different exposure settings and ultimately, different results.

A good example of seeing the difference will be to expose for a subject that has both, high levels of white and high levels of Black. Lets say, two friends, one wearing all black and one wearing all white. If you spot for white, the black will be too dark and if you expose for black, then vice versa; the white will be blown.

You can compensate for that by ensuring that you are using Evaluate metering, but at the end of the day, it is only evaluative.

With the Sekonic light meter, the white invercone when held near the subject and facing towards the direction of the camera, will break up the direct light inside this cone hitting the reflector behind the cone to provide correct exposure settings.

  • 1
    It depends on the external meter and how it is used. You may measure either incident or reflected light with an external meter. – Michael C Aug 13 '15 at 23:43
  • thanks, @MichaelClark so you guys suggest I meter with that cone pushed in? instead of it being out? I am using a Sekonic 478DR and I ask the model to hold it next to her face pointing the cone to where the flash is pointing to...Am I doing it wrong? – user1899082 Aug 18 '15 at 14:34

Probably no, it has no sense.

The point in long term will be learning how to use a lightmeter and not using the TTL.

But it can help you to compensate the ev+-. If the TTL gives you a f/11 aperture on a situation, and the lightmeter reads f/8 try to compensate a 1+ ev and compare the results.

  • 2
    TTL cannot "give you f/11". TTL automation cannot change aperture, it uses whatever necessary flash power level to match the aperture that you or the ambient automation selected. But to the OP, the camera TTL system uses the cameras meter, regardless. You cannot use a different meter with TTL. You can control TTL automation by using Flash Compensation. – WayneF Aug 13 '15 at 17:16

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