Getting one’s head around f-stops, shutter-speeds and ISO and what a ‘stops-worth’ of light actually looks like is, in my opinion, one of the fundamental foundation blocks of photography. The great benefit of digital being that you now have a reference point to work from; i.e. you can shoot a ‘test’ shot, look at it on the screen and then judge how best to expose it so that on the second attempt you can nail the exposure exactly. This is a great way to get to grips with a few things:
- how much more or less light does the camera let in when I change from one f-stop or one speed to another?
- what does a stops-worth of light actually look like?
- which metering mode on my camera should I use in each situation?
- how the hell do I get from shooting on ‘P’ all the time and get myself towards being in control?
The good news is that the answer to the last question is; ‘It’s easier than you think!’ And for those of you now thinking ‘well, that’s all very well as long as you have a decent sized screen that gives an accurate picture of the shot, so you stand a good chance of guessing how better to expose it on the next shot!’ Well, as soon as you get a hang of how much darker or brighter your screen is than how the shot looks when you get home onto your computer, you’re sorted because all of this is just relative. Plus, there’s always the histogram to look at.. which we’ll get to in a separate article.
Let’s start with getting the right metering mode on the camera because this is key to how the shot is going to come out, before even we decide which mode to be in out of manual, aperture, shutter or program.
And if you don’t know what ‘metering mode’ means either, we’re literally talking about the way in which the camera is measuring the light coming in through the lens. Typically there are about three or four choices of ‘pattern’ of metering on today’s DSLRs:
Nikon: Matrix [a clever, averaging metering system], Spot [a precise way of measuring light from a specific area of your scene], Centre-weighted [like the spot but a bit larger, with a bit more around the outside which can be good for getting readings of light from a whole face].
Canon has spot, centre-weighted and usually one called ‘centre-weighted-averaging’ which is a little bit more than the middle and it’s edges. Plus they have one called ‘Evaluative’, which is sort of like Nikon’s ‘matrix metering.
So, which metering mode is best for which occasion?
Metering modes – or patterns – which are calculating some sort of average for you [matrix, centre-weighted average] are great for occasions where the lighting is even. Spot metering is great where you do not have an ‘average’ scene in front of you. Take the two shots of Ami I took quickly just now to illustrate this: both were shot on Aperture Priority [A] mode, the first with Matrix metering and the second with Spot metering. The spot-metered scene is the clear winner, as my ‘spot’ was on Ami’s face and the camera has given me a shutter-speed to match the aperture I chose which it thought was the best average. The fact that Ami is in shade and the background is bright makes this scene not evenly lit, so Matrix has – unsurprisingly - failed to give me a decent exposure for Ami’s face. I then switched to ‘spot’, made sure the ‘spot’ from which the camera is measuring the light was over her face and, bingo, her face is properly exposed.
Obviously, if I wanted both background and Ami my only route would be to fill her with flash.
In this semi-automatic mode if I’d wanted her face exposed properly but for her not to be in the middle of the frame I could have done one of two things:
- moved the focus and metering point to the left side, placed her on the left side, made sure the spot was on her face and shot my picture.
- kept her stood on the middle, metered off of her face with the spot in the middle, pressed the AE-L [auto exposure lock] button on the back of my camera [which locks the light reading I have taken with the spot, allowing me to re-frame and not have the spot measure light from a new place.
We'll deal with the AE-L button in a separate post, as it has some eccentricities which are potentially long-winded and best dealt with in isolation.
So, just by choosing the right way of having the camera measure light we have been able to get our shot right on the first press.
How about when the camera almost gets it right but we want to change the exposure a little bit?
If you are in one of the semi-auto modes on the camera - Aperture Priority or Shutter Priority - then there are basically two ways to do this. Both are valid:
- shoot, look at the shot on the screen, check the settings the camera took it at, migrate those into manual, change them, shoot again.
- shoot, check the shot on the screen, apply exposure compensation, shoot again.
I teach the first method because I grew up shooting manual and by going manual as soon as possible in your shooting career, you stand the best chance of getting a grip on what changes in the settings mean for the picture. And, most importantly, you understand how much darker or brighter changing the values by one, two or three stops of speed, aperture or ISO actually looks like. Therefore you get an impression of what a 'stops-worth' of light actually looks like to your eye. This is very useful later on when you might want to be shooting on manual for greater control but in conditions where the light is changing. Learning what the numbers mean and how they relate to the light your eyes are seeing means you can guess the exposure very accurately. There is a post on shooting at night, here, which has at the foot of the page an excercise all to do with guessing exposure. Give it a go.
Shooting with exposure compensation is never going to develop your understanding of this properly. It doesn't mean that exp-comp is bad. It can be a quick way of adjusting your exposure. It's just that I am old-fashioned, like teaching the manual way and think it's better in the long-run to learn the rules properly and then choose or find your own way of shooting once you have all the rules down pat.
The three shots and screengrab below illustrate a little of this:
Number 1 was shot in Matrix mode, on [A]perture Priority. I chose a smallish aperture because there is plenty of light, nothing is moving [so speed is less of an issue] and the scene is deep so I want lots of depth of field. As you see, Matrix and [A] got it pretty right but for my taste it’s a little dark.
So, I checked the screen, scrolled down to where I am getting information about what speed the camera gave me at the aperture and ISO I had already set…..
.. and then I decided to shoot with the speed set to 1/160, or one stop brighter.
Then, just the for the point of illustration, I decided to shoot at 1/640 sec or one stop darker than the camera first shot the pic at.
How did I get from auto to manual? Well, I look at the first batch of settings – those you see in my screengrab of the back of the camera [1/320sec, f/5.6 and 200ISO] – then I go into Manual mode on the camera and manually set 1/320th sec against the aperture I already had selected. Why set what the camera shot it at first? So I know where to start? I do this with students and suggest you do it when you are learning. I set straight away what I want as the new speed.
The benefit of setting the speed the camera chose, when you are learning, is that you can talk your way through it to yourself:
‘This what the camera said: 1/320th sec at f/5.6″
Then change your speed to make it one stop brighter [1/160th sec]
The start talking to yourself again: “.. and this is what I want; the speed is one stop slower [smaller number] and therefore more light will come in, making the picture brighter”.
OK.. you can stop talking to yourself now.
In point form:
- Vhoose an ISO value that suits the lighting conditions [low number for bright conditions, higher for darker conditions].
- Set your semi-auto mode [Aperture of it's focus or if it's not speed/motion that is driving your picture, Shutter-speed if it's a speed or motion related image you are after].
- Set the metering mode that suits your scene.
- Shoot a test.
- Look at it on the screen in a display mode where you can see all the numbers: ISO, speed and aperture].
- Decide whether you like it or whether you want it darker or brighter.
- Go into Manual mode, remembering the recipe of numbers from the screen.
- Change the value of the parameter opposite to the mode you were first in [speed if you were in Aperture mode, aperture if you were in Shutter-priority mode]. Remember that a smaller f-number will make it brighter, as will a smaller shutter-speed number].
- Shoot the second picture.
That’s it. You are now using an automatic mode, in conjunction with the screen and data, to get to manual and thereby ween yourself off auto to take more control over the exposure of your photos.
Have a cup of tea, you deserve it…. good work.