Undiscovered Features - Nikon D300 setting b4

I spent some time wandering through the menu on my Nikon D300 the other morning, and came across a feature I had missed or forgotten about when first exploring the camera.  This camera and the control UI continue to impress me.

The camera, like so many others, has 4 main modes:
  • P - Programmed auto (fully automatic)
  • S - shutter priority
  • A - Aperature priority
  • M - Manual
On the Nikon D50 (and many others) there is only a thumb dial on the back of the camera.  Depending on whether you're in S or A mode, it controls the shutter speed or the aperture.  The D300, on the other hand, has both a thumb dial on the back of the camera and a finger dial on the front.

When in Manual (M) mode, the thumb dial controls the shutter speed and the finger dial controls the aperture.  This makes sense; both controls are exposed.  The little bit of genius that seems so obvious is that the assignment of shutter speed and aperture to each dial is consistent - when in A mode, the finger dial still controls the aperture (and the thumb dial does nothing) while in S mode the thumb dial controls the shutter speed (and the finger dial does nothing).  This allows you to form a tight mental mapping of thumb=shutter, finger=aperture, and if you happen to be in the wrong mode, the wrong dial just won't work, providing additional feedback about the state of the camera.  Genius.

I nearly always stay in A mode, which means that I control the aperture and the camera will automatically adjust the shutter speed in order to maintain a correct exposure.  When that exposure isn't correct I can under or over expose the picture by holding down the exposure compensation button (right next to the 'ON' text in the picture of the front) and spinning the thumb dial.   This takes coordination, often requires looking at the body (instead of continuing to look through the viewfinder), and if I forget I've changed it, will adversely affect future shots.  But it works.  (The other method of adjusting the exposure is to use the AE-lock button on a darker part of the frame, then adjust the composition, but I find that's less predictable.)

Enter the Custom Settings Menu item b4: "Easy Exposure Compensation".

This control has three settings:
  • On (Auto Reset)
  • On
  • Off (default)
When you turn b4 to On or On (Auto Reset), it enables the other control in S and A modes.  When in S mode, the thumb dial still controls the shutter speed, and if you change it the camera will automatically change the aperture in order to maintain correct exposure.  However, if you adjust the aperture manually (still with the finger dial), it will have the same effect as the exposure compensation button - adjusting the aperture to under or over expose the picture.

Even though you are in S or A mode, you are always able to control both the shutter speed and the aperture!  If you adjust the 'right' one (shutter speed in S, aperture in A) it will keep the exposure level correct.  If you adjust the other one (aperture in S, shutter in A), it will adjust the exposure under or over.

Setting b4 to On has exactly the same effect as using the exposure compensation button.  Using the On (Auto Reset) has one additional benefit - when you turn off the camera the exposure adjustment resets to normal.  I have my camera set to On (Auto Reset).

I am in love with how this makes the process of getting your exposure just right that much easier.
  1. Frame the picture, choose the right aperture for the desired depth of field
  2. Take the picture, see that part of the subject is slightly over exposed
  3. Increase the shutter speed two notches and take the same picture (yay!  perfect!)
  4. Turn off the camera and everything resets so your next picture isn't under exposed.