Help! D90 commander settings

beyond the blue

beyond the blue

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Neil
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Can anyone explain (in a language that a thicko can understand) what the compensation settings do in the flash commander screen on a Nikon D90.
I am using the built in flash to fire an off camera flash, I have set group "A" (which is correct for my particular off camera flash) to TTL but what would I achieve by altering the "comp" setting of group "A" being as though the built in flash has no bearing on the exposure, and only being used only to fire the other flash. I hope I've explained that well enough!
 
The camera calculates how much light the flash should output to give what the camera thinks will be a correct exposure. Of course the camera is not always right or you might want a different effect so by adjusting the compensation setting you are telling the camera that you want it to tell the flash to give out either more or less light (I think!).
 
f1charlie said:
The camera calculates how much light the flash should output to give what the camera thinks will be a correct exposure. Of course the camera is not always right or you might want a different effect so by adjusting the compensation setting you are telling the camera that you want it to tell the flash to give out either more or less light (I think!).
Click to expand...

Thanks for that, however I am still struggling to get my head around how the camera can get the off camera flash to fire more light when it is controlled only by a flash of light and not by a cable. I can only see that it is the camera that compensates, and not the flash. Totally confused now.:thinking:
 
This is how I explain it to myself, someone who knows what they are talking about might be able to explain it better:

It's all done by the pixies in the camera and the flash...

You set the flash up where you want it and press the shutter. The pixies in the camera send a morse message, using the cameras pop up flash, to your external flash. The message says: "we're taking a picture and need to test the exposure".

The pixies in the flash say OK, and fire the flash at a set amount, this is a preflash. The pixies in the camera measure the amount of light coming into the lens from this preflash. They then use the pop up flash to send another morse message to the external flash to say if it needs to be brighter or dimmer, then they open the shutter. The external flash pixies then fire the flash at the required level and you get a beautiful picture.

If you have put in flash compensation the pixies will include that in their morse message.

This of course happens really quickly so it looks like just one flash, but it is in fact multiple pixie morse messages.

So that's your answer... pixies. :p

Pretty damned clever :D

John
 
JohnL said:
This is how I explain it to myself, someone who knows what they are talking about might be able to explain it better:

It's all done by the pixies in the camera and the flash...

You set the flash up where you want it and press the shutter. The pixies in the camera send a morse message, using the cameras pop up flash, to your external flash. The message says: "we're taking a picture and need to test the exposure".

The pixies in the flash say OK, and fire the flash at a set amount, this is a preflash. The pixies in the camera measure the amount of light coming into the lens from this preflash. They then use the pop up flash to send another morse message to the external flash to say if it needs to be brighter or dimmer, then they open the shutter. The external flash pixies then fire the flash at the required level and you get a beautiful picture.

If you have put in flash compensation the pixies will include that in their morse message.

This of course happens really quickly so it looks like just one flash, but it is in fact multiple pixie morse messages.

So that's your answer... pixies. :p

Pretty damned clever :D

John
Click to expand...

Brilliant:lol::lol::lol: Now on a serious note, is that how it works or are you pulling my pl****r;). If you are, I'm not offended in the slightest cause it was very funny, but I would like to believe it's true, or am I indeed a pl****r:D
 
This is a really good guide:

nikonclspracticalguide.blogspot.co.uk

Good luck!
 
Someone told me it some clever Japanese electronics but I think it's the pixies. :bonk:

In all seriousness, I believe it basically does work like that. To see the pixies in action try the following:

Set the pop up flash to commander mode.

Set the flash to slow, rear curtain sync.

Set the shutter speed to a few seconds (exposure doesn't matter as you're just watching the pixies not actually taking a picture).

Press the shutter. You will see the pop up flash give a very short burst of pixie morse, and the external flash will give a little pre flash. A few seconds later the pop up flash will give another very short burst of pixie morse and the external flash will fire to the correct exposure.

John
 
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The pixies are even cleverer by using only the infra-red part of light to send the signal, so if you don't want the light from your pop-up flash getting into your photo you can fit a special filter in front of the pop-up which will block visible light but let infra-red through.
 
I was under the impression if the pop up is set to off, it still pre flashes but is not in the actual thoto, a delayed reaction so to speak
 
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