To Garry Edwards - follow on from a previous Q

[susan_smith5]

With reference to this thread<br><br>

 

<a href="http://www.photo.net/bboard/q-and-a-fetch-msg?

msg_id=008XxW"target="_new">question/replies</a><br><br>

 

 

 

and to Garry's response.<br><br>

 

Garry, if your (separate) exposure readings are correct for each

light source, won't you be overexposing once you <u>combine</u> the

two sources for the shot? I'm obviously a bit muddled.

[guy ronkar]

Obviously I'm not Garry, but maybe I can answer the question :-)

<p>You will not overexpose in this case (mixing continous light and flash). By setting the aperture to the indicated f-stop, you expose for the flash. By setting the shutter speed, you expose for the continous light. The duration of the flash is so short that it won't make any difference what shutter speed you use, only the aperture is important. So by setting your aperture, you expose correctly for the flash, which is the most prominent light source. Setting the shutter speed doesn't make a difference for the total exposure, but it ensures that you can actually see the light from the continous light source in the final shot.

<p>Of course, I'm waiting for Garry to correct me if I'm wrong (I'm sure no expert on these things)

<p>Hope this helps

<p>Guy

[garry edwards]

Susan,

 

Guy is right. He has explained how using a combination of shutter speed and aperture is used to get the correct exposure when using tungsten light sources. This has also been explained, in detail in a couple of the Lighting Themes filed under administration in this forum (this one for example) http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=009bC3

 

But if I understand your Q correctly, you are wondering not about how to use both flash and continuous light but about whether using both lights together will cause overexposure because the subject is receiving lights from both sources?

 

Yes and no.

 

Let's assume, just as an example, that you are photographing a face and the flash is the key light. Because of it's angle, it causes areas of shadow and so you use the tungsten light to fill the shadows to some extent. The tungsten fill light should only illuminate the areas not illuminated by the flash, in which case there would be no over-exposure, but in practical terms there would be some theoretical overexposure where some of the tungsten light spilled into areas also lit by the flash, and vice versa - but this happens with all lighting and not just with a combination of different types of lighting.

 

A meter reading would give you an acceptable answer, and most flash meters are capable of reading both flash and continuous light.

 

But that's a lousy example, because I wouldn't combine flash and continuous light on a face because of the different colour temperature of the 2 light sources. Normally, the face would be lit say with flash and the background or the hair would be lit with the tungsten light.

 

In this situation, if the flash exposure of the face is f8 and the required exposure for the background at f8 with the tungsten light is, say, 1/15th @ f8, you would set the shutter speed to 1/15th and the aperture to f8. Assuming that there was no light spill from the flash to the background then each part of the subject would have its own separate light source and its own separate exposure.

 

Hope this helps.

[susan_smith5]

Thanks to you both.

 

I understood the shutter and aperture settings etc but was worried about the additive effects of the two light sources.