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Canon XL and GL Series DV Camcorders
Canon XL2 / XL1S / XL1 and GL2 / XM2 / GL1 / XM1.


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Old June 15th, 2005, 12:14 PM   #16
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Thanks ,Marty. also, what's the difference between using the ae shift or the gain in that situation?
Bruce yarock
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Old June 15th, 2005, 12:36 PM   #17
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Quote:
Originally Posted by Bruce S. Yarock
Thanks ,Marty. also, what's the difference between using the ae shift or the gain in that situation?
Bruce yarock
To understand AE shift you need to understand the way the auto iris works. I don't know the specifics but I'd guess it goes like this.

The image is analyzed and it is determined that the scene is overexposed. So the auto iris (Tv Mode) starts to close. Your Fstop reading will inversly go up. If the scen is underexposed the iris will automatically open up to let in the proper ammount of light and inversely your fstop will go down. The camera has theoretically been calibrated to "know" how to properly expose a given scene.

This can work well for a lot of shots. But say you know for a fact that you will be shooting a brown horse standing in front of a white barn. This situation would likely cause the auto iris to properly expose for the bright wall and this would underexpose the horse. You would likely lose detail of the horse.

Where AE shift comes in is it is like your own personal way of saying "I would like for you (the XL2) to expose the way I want. I prefer to have the white wall be overexposed a little and have the details in the horse be properly exposed." You can set the AE to shift the exposue 2 stops over or 2 stops under the "XL2s" perceived proper exposure. You can shift this is 1/4 stop increments. So in this case you could set it to +1.0 so that whatever the XL2 sees as properly exposed will be increased by one stop. Oset it to 3/4 of a stop if that is better.

You are essentially biasing the auto iris in favor of overexposing or underexposing the image from the XL2's base proper exposure. Using this method is just an automatic way of controlling the iris. No artificial noise should be introduced as a result.

Gain, is essentially, a fake way of getting a few extra stops out of low light images. It artifically boosts the level of the signal to try to get an acceptable image. It is obviously more technical than that but that is the overall concept. The inherent problem is noise/grain/artifact can often be seen in the dark areas of you image. That is why I prefer opening the iris as much as I can before resorting to gain.
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Old June 15th, 2005, 02:28 PM   #18
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thanks,Marty...that's a pretty thorough explanation.Does AE shift work in manual mode, once the iris is all the way open?
Bruce Yarock
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Old June 15th, 2005, 07:55 PM   #19
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Hi Bruce. As far as I know, AE shift only works in AE modes. In manual mode the camera should expose according to your iris, shutter and gain settings, without regard for how the AE Shift is set.

By the way, if you normally like to get a narrow depth of field, setting the gain to -3dB where possible will get you another half stop of iris opening.

Richard
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Old June 15th, 2005, 10:08 PM   #20
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Thanks,Richard.
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