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-   -   What is AE shift actually doing? (http://www.dvinfo.net/forum/canon-xl-gl-series-dv-camcorders/74676-what-ae-shift-actually-doing.html)

Jarrod Whaley September 1st, 2006 12:43 PM

What is AE shift actually doing?
 
I've manually adjusted exposure almost 100% of the time in the past, but I'm currently finding myself in more situations where it makes sense to go with Tv mode. Because of this, I've really never used the AE shift control before, but I'm running into rare situations now where it might be helpful.

The problem is, I'm not sure what it's actually doing to the image in a technical sense. If it isn't just gain, then what it is it? Some kind of gamma adjustment?

I can't find a technical explanation anywhere.

Nate Weaver September 1st, 2006 01:05 PM

It just manipulates the iris (or, shutter, sometimes).

If Tv mode gives you an exposure of 1/48th and F4, and you move the AE dial to +1, it will leave the shutter at 1/48th and open up the auto iris a stop to 2.8.

If you did the same in Av mode, with the same initial settings, it would bump the shutter speed to 1/24th.

If you were on auto-everything, and were at the end of your rope on shutter and iris, it would probably THEN manipulate the gain.

It doesn't, however, do anything to gamma, ever.

Jarrod Whaley September 1st, 2006 01:10 PM

I see. Should've guessed that. Thanks.

Greg Boston September 1st, 2006 01:22 PM

Quote:

Originally Posted by Jarrod Whaley
I've manually adjusted exposure almost 100% of the time in the past, but I'm currently finding myself in more situations where it makes sense to go with Tv mode. Because of this, I've really never used the AE shift control before, but I'm running into rare situations now where it might be helpful.

The problem is, I'm not sure what it's actually doing to the image in a technical sense. If it isn't just gain, then what it is it? Some kind of gamma adjustment?

I can't find a technical explanation anywhere.


Jarrod,

Think of AE shift as a 'bias' adjustment. What the camera thinks is appropriate auto exposure may not always be dead on. Therefore, using AE shift, you can tell the camera that you want it to think darker or lighter.

It's a lot like the buttons on a photocopier for darker and lighter copies.

-gb-

Jarrod Whaley September 1st, 2006 02:23 PM

Thanks, Greg. For some reason I just couldn't figure out what was really going on in there. Makes operfect sense to me now however.

Ash Greyson September 1st, 2006 08:10 PM

This can also be useful for timelapse stuff or odd framings. AE will adjust for the entire picture and in many cases, overlight an area you want to be darkened. The only time I got near any auto features is when the camera is unmanned.



ash =o)

Jarrod Whaley September 1st, 2006 08:48 PM

Quote:

Originally Posted by Ash Greyson
The only time I got near any auto features is when the camera is unmanned.

I've always felt the same way until recently, when a project I've been working on has called for on-the-fly aperture adjustments in mid-shot. The incremental stepping of the iris dial looks like such crap in these situations; the only way that I've found to do a smooth opening or closing of the iris is to shoot in Tv mode and let the AE handle the iris. It's clearly a pretty flawed way of handling the problem, but it seems like the only solution.

Now that this thread is meandering in an unintended direction, any better ideas?

Ash Greyson September 1st, 2006 10:50 PM

I frame things rather cinematically and extreme and auto iris just never works. The problem with the electronic iris is that is does step. This can be fixed in post but if you have to do it a lot...obviously that is impractical. Just one of the compromises for using a smaller form camera.




ash =o)

Jarrod Whaley September 2nd, 2006 12:58 AM

Auto-iris is very unpredictable. But it will open/close the iris without steps. You may have to shoot something 7 or 8 times before you get what you want, but this strikes me less tedious than trying to smooth stepped iris adjustments in post. No?

Obviously if you're shooting docs, then 7 or 8 takes isn't an option. But I'm not shooting docs. I have the time and the patience to do those takes if I have to. I just wish there were something I could do to manually adjust the iris on the fly without the steps. Like you say, that's the price you pay for using consumer gear. But I'm not at all a "fix it in post" kind of guy, and if there's any way at all to get something done in the camera, I'm going to do it, even if I end up pulling out my hair after 15 tries because some automatic camera function won't bend to my will. I try to do everything optically if at all possible, even if doing so is a major pain in the a**. SD video just isn't that forgiving of most forms of post processing, in my opinion.

Anyway, thanks.

Tony Davies-Patrick September 2nd, 2006 11:32 AM

I use the AE shift button quite a lot when in AV mode, but my most often-used button is the Exposure Lock Button. Manual exposure will change during a pan or shift in framing across an unevenly lit background with the XL2, but will maintain even exposure if the Exp.Lock is pressed first.

For decades I've used Aperture-Priority Exposure mode + Exposure Lock for Stills photography, and so tend to work better and faster with the XL2 in AE mode, rather than Manual, especially when I'm outdoors and working fast in unpredictable and drastically changing light conditions.


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