Metering

I'm going to start with a deeper dive into the camera's metering system.  Metering is one of the last things I think of when going out to shoot.  And in photo review when I get back to base, if I missed nailing the setting correctly it shows.  And a lot of times I'm left to ask myself what was the camera thinking?

One advantage of a DSLR over a 35 mm is the DSLR can measure the amount of light that is on the subject and relay that information in some form to the camera operator.  35 mm?  Not so much. 
As light makes its way through the lens and is collected by the meter, the information is is used to set the important stuff, like you know, speed, aperture and ISO in the automatic modes or displaying the information on the exposure gage when in Manual Mode.  The camera is trying its best to make you look smart.  But the camera is technical, not artistic.  So technically the light settings are correct, but.....  If we were going for just technically correct, there would be only one mode to shoot in, AUTO.  Enough said.

To help us along, we need to understand the concept of middle grey.  (Or is it gray?)  Grey is what happens when you mix equal amounts of absolute white (0, 0, 0) and absolute black (255, 255, 255).  There are many thoughts as to assigning some number to middle grey, anywhere between 10% and 20%.  Most articles I've read settle on 18%.  (I ask myself why not 50%?  Well, it has to do with concepts like reflective values and higher math.  Means versus averages.  I saw one equation with a square root symbol.  WTF?  Photography is supposed to be fun, so I'm going with the overall concept and damn the details.)

FYI: 18% grey comes from the world of print and is based on reflection. An 18% grey card reflects back 18% of the light that hits it. And it is actually the geometric mean between white paper (95% reflective) and black ink (3.5% reflective).  Wasn't that fun?

What we do need to take away from this is every camera manufacturer has it's own shade of grey that it wants to meter to.  Proprietary.  And what metering mode we choose to use plays a great part in how the camera's light meter thinks of a shot.

The camera's metering system wants to make every shot middle grey.  Understand this, grasshopper, and the rest is (relatively) easy.

Why are all my snow shots dark?  A snow shot will trick the camera to an underexposure.  The camera sees all that light throughout the photo - and tries to make it middle grey.  The meter takes light away.  Poof.  #Trash.  And the opposite occurs as well.  I've come back from a sunny day at an airshow and all the military aircraft shots were a bit overexposed.  I was metering on a flat gray paint scheme, under a wing in the shade.  The camera tried to help me.  Thanks.

The simple fix of course is becoming friends with exposure compensation and knowing how much to dial in.  Too light - dial in a -1.  Take those highlights right out.  Need a little light, dial in +1.  Bring out those colors.

The real fix of course is knowing which mode gets you in the best position to succeed.   Practice, practice, practice.

The Nikon basic metering modes: 
Center weighted (Most used, been around for ever.)
Spot
Matrix
Matrix* - Matrix on highlight.

Center weighted mode is the place to start.  Center weighted metering would look at the entire frame and give most attention to the center.  Extreme close ups would be a good use for this mode.  I usually don't shoot center weighted mode.  Most of my shots are never close ups, and after I figured out why the military aircraft shots didn't come out as I expected - I've stayed away.  It is important to note that exposure lock doesn't work in this mode.  It is the center of the view.  On my Nikons, the center can be defined through the menu system.  You can increase the center area.  Or not.

Spot metering.  Name says it all.  In my opinion, this is the most difficult to master.  In Nikons, the 'spot' is tied to the center AF spot.  If the center AF spot moves, so will the focus point.  If the subject moves and 'spot' drops off the subject, you guessed it.  The subject isn't the subject anymore.  Could be frustrating.  I have better things to do with my time that get frustrated because I missed the metering point.  Spot metering would be good if you have a somewhat larger mid toned object in the middle of our shot, or what will be primarily in focus.  This would ignore other influences.

Matrix metering.  This is why we have electronics.  Multiple sensors in the camera, fast computing and for fun, adding color inputs.  And lets not forget about talking to the lens.  All this and more in Matrix metering.  Essentially the process involves breaking up the view into segments.  In the beginning there were a few segments, like five.  Now, there are over 100.  All of the segments are evaluated and the exposure process begins.  There are inputs from the AF mode and point.  The mode will take information from the lens, if capable, from focal distance and length.  And there's more!  There are also color considerations.  All this in 1/3200 second!  Or faster.  With all this information, the Nikon computer goes to work does the computing hocus pocus and sends the information where needed.

What to use and when?  Personally, I use matrix by default.  The mode works best with a wide spectrum of tones and colors.  I'm generally in the sunshine and targeting flashy colors.  If I'm shooting in the shade, real shade like heavy canopy, I'd start looking for other options.  

There is a lot going on with metering.  If you are using an AUTO mode and shooting JPG format, this is an element that can really help your photos - or cause you to wonder what happened?  there are a lot of articles available on the web.  Most are a lot more technical, such as the placement of the sensors. 

Hopefully we'll be able to meet again as a club and chat about stuff like this.  Soon.