Advantages of manual exposure?

Started Feb 17, 2012 | Discussions thread
Graystar
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A Description of Auto Mode Techniques - Part III
In reply to petermc45, Feb 20, 2012

(Continued from Part II. Link below...)
http://forums.dpreview.com/forums/read.asp?forum=1039&message=40674399

Exposure lock is easy. In Spot metering mode, you simply meter a known reference (like clear blue sky or sunny side of grass) and lock exposure. If you metered a reference with a known EC adjustment (like evergreens, -1, light skin, +1, snow, +2.7, etc.) then you apply that EC. That's it...metering is done. Now you simply select your desired aperture and start shooting. Here's one of the reason Nikons are better than others. You can change the shooting mode and your exposure lock will remain (actually, you can change nearly any setting on the camera and the AE Lock will remain.) With most other cameras, if you change the shooting mode you lose your AE Lock. Dunno why...bad programming, I guess. But not with Nikon. So you can control your aperture for a while, and if you decide you now want to control your shutter, you just switch shooting modes. And all the while that you're changing aperture or shutter, the camera is adjusting the settings under its control to maintain your desired exposure level. Once again, your mind is freed from having to constantly deal with exposure changes, allowing unbroken concentration on your subject.

The spot-metering/focus-point-shifting is actually a variation of exposure lock. But instead of actually locking the exposure, you "lock" exposure by tying exposure to your subject. So...you have a subject that you're shooting and the light is changing. Why is the light changing? Because you're outdoors and the sky is full of small puffy clouds that keep passing in front of the sun. So you set spot metering and then pick one spot on the subject that with be the "focus" of your focusing and metering. You spot meter and adjust your EC for the subject tone. You might even take a shot or two just to fine tune the EC. Once you have your exposure compensated the way you want, you can now shoot. As you take your shots and recompose (landscape, portrait, centered, off-centered, etc.) what you're going to do is to move the focus point over the same spot for every shot.

So what does this do for you? Well, another wonderful thing about Nikon cameras is that Spot metering follows the focus point. By moving the focus point to the same location on your subject, you will get consistent exposure shot after shot, as well as consistent focus. By default, Nikon doesn't lock exposure when you half-press the shutter. You can set that if you want (dunno why you'd want it) but it's better to leave it as is. What this means is that a Nikon doesn't set exposure until the last instant before taking the shot. So if clouds are rolling by and changing the light on you, the camera will be able to produce the same exposure over and over.

There are other techniques and uses for the AE Lock and EC functions. You can use AE Lock in M mode. If you want to control both aperture and shutter, you can meter a reference, lock exposure, and now point at your subject. regardless of the tone of your subject, the Exposure Indicator doesn't move. It only moves when you change aperture or shutter. That's because the center of the Exposure Display now represents your locked exposure...not the current exposure that the subject would produce. Why would you do this? It makes changing aperture and shutter easier. You can change your aperture and you KNOW with absolute certainty that adjusting shutter until the Exposure Indicator is centered will give you the same exposure. If you had not locked exposure, you would need to count clicks of the dial to make sure you adjust shutter the same amount that you adjust aperture.

You can use EC with ND filters. If you meter landscape with a waterfall, take a shot, and now want to catch the water in motion, you pop on your +3 ND filter, and just apply +3 EC...exposure is done. And there are other very specific uses for these functions. And you won't find any of this in any book. The reason is based on functionality. While the basic operation of the auto modes is the same across cameras, the operation of the supporting functions (EC, AE Lock, Spot metering and focus points) is not the same across cameras. As far as I know, only Sony and Nikon will keep an AE Lock for more than one frame without user intervention. Canons require you to push a button after every shot (though, the top of the line Canon does have a meter timeout extension, and Canon has a page describing how to use that function for AE Lock across multiple images.) Only Nikon has a properly designed Auto-ISO where you always know what your exposure will be. Only Nikon allows EC in M mode, which is necessary if you use Auto-ISO in M mode (it's the only way to control exposure.) Some cameras disable Auto-ISO in M mode. Only Nikon cameras have a Spot metering function that follows the selected focus point.

Because of this, it's difficult to write a book on how to utilize auto modes when every camera make is a little different in their implementation. I suspect that in time, the functionality of other cameras will expand and eventually the behavior will become more consistent across makes. Then books can be written that will apply to any camera. Until then, you'll just have to bookmark these posts!

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