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Fri Aug 12, 2016 9:48 am

Joined: Fri Aug 12, 2016 9:43 am
Posts: 1

Maybe I am misunderstanding the purpose of the modeling lamp on my AB400.
I use it to set exposure and have it set to TRACK with the flash.
I set the exposure based upon the modeling lamp lighting, then fire.
Every shot is blown completely out to white. :shock:
What am I missing?
Nikon D5300
thanks,
jph




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Fri Aug 12, 2016 2:39 pm

Site Admin
Joined: Tue Dec 08, 2009 10:43 am
Posts: 5266

The model lamps are there to show the relative brightness between then (ideally) and to show how the shadows will fall and if there will be any reflections in shiny surfaces, etc.

The model lamp would not be used to determine exposure, as there will inherently be a different exposure. If the difference in exposure was not there, then there would be no reason to have two light sources, as one would do the same job as the other.

Additionally, the continuous light from the model lamp is affected by the exposure time (shutter speed), whereas the flash is generally not affected by shutter speed (below x-sync).

So, lets pretend we have a model lamp exposure of 1/250 and f/11 at ISO 100. If we changed to 1/125 and f/16 at ISO100, you would maintain the same exposure.

Let's now pretend the flash exposure is the same: 1/250 and f/11 (with no model lamp present). Like with continuous light, if we raise the aperture to f/11, we get one stop less light. But unlike continuous light, if we slow the shutter down by one stop, we do not let any more flash in, because all flash that was available was emitted in the 1/250 exposure time, and there is no more to acquire. This leaves us with less light. So this goes to show that even if the light levels could be the same, the exposures could be different without changing the amount of light.

In reality, the disparity of the two is generally very very large in a practical application. You are looking at a 250W light at full power to be noticeable with 5Ws of flash power (at about 1/200s).




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