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Viewpoints

Exposure Part I - Metering for a Midpoint

Modern electronics are a wonderful thing. The matrix metering systems in modern DSLRs are extremely sophisticated and will do a good job the majority of times. But that’s just it – not always. Leaving the camera on automatic is giving up control to a machine of one of the most critical and creative aspects of your photography.

DSLR metering systems work by taking multiple readings from the scene and then 'averaging' out the result.

But average is not necessarily right. How can a machine know how you really want the image to come out? How often is the shot just a little too dark or light? Have you noticed that a preponderance of a dark colour like blue or too much white (e.g. snow) causes the camera to over or under expose dramatically? How do you avoid the highlights blowing? How do you get white whites? How do you guarantee detail in the shadows?

Or what if you have a desire to try out a view camera which has no automated metering support at all? What do you do?

The objective of this series of articles is to encourage you to get off the automatic modes and pick up one of the most important of photographic skills – getting exposure right using a spot meter.

If you have a DSLR to practice these skills with you are at a massive advantage. Why? Because the histogram on a DSLR allows you to review the results without waiting for days for the film to come back from the developers. The feedback loop is instantaneous. What is more, many DSLRs have a spot meter. So put the camera on manual spot metering and give it a go.

The first skill to acquire is fixing a midpoint. This is simple once mastered but not quite as straightforward as it might seem. Why? Because the spot meter treats every colour as if it is a mid grey – regardless of whether it is white, red, green, yellow or black. In practice, each colour needs either slightly more or slightly less exposure. If you spot off an object, you have to adjust for its colour.

So how do you fix a good mid point? Well, in the majority of cases, it is not too difficult. Landscape photographers have it easy - green. 9 times out of 10 you can spot meter straight off a patch of sunlit green grass or vegetation and be confident you have got it right. For example, if the spot reading on a patch of sunlit grass reads 1/125 at F11 that’s what you use. Similarly mid grey rocks or a grey road make a good mid point. An example of this is my picture 'Dawn over Loch Cleat' - this was metered from the sunlit grass (I was also using a graduated filter, but that is to come in a later article.)

Try this approach next time you are taking a portrait of someone outdoors – spot meter on the grass in the same light as your subject. You will get perfect exposures every time, regardless of whether they are wearing a dark blue jumper or a white top.

A light rock or marble building is usually best placed one stop above. To do this you need to take a spot meter reading and add one stop of exposure. For example, if you get a reading of 1/125 at f11, you expose at either 1/60 at f11 or 1/125 at f8. On 35mm, I tend to adjust the shutter speed. On large format, I adjust the aperture.

A dark rock or darkish blue jumper is best placed one stop below. To do this, take a spot reading and reduce the exposure by one stop. For example, 1/500 at f5.6 becomes 1/1000 at f5.6.

Picking a good subject and adjusting for the colour accurately comes from practice and experience. Here are my common targets and adjustments:

  • Sunlit grass = no adjustment
  • Grey road or roof or mid grey rock = no adjustment
  • Light rock or marble building = +1 stop
  • White skin tone +1/3 stop
  • Yellow foliage +2/3 stop

I tend to avoid darker objects because they are harder to judge accurately. What you go with is ultimately a matter of personal choice and experience, so you may disagree with my adjustments. Thats fine. The thing is to be consistent and to practice so that you can do it without thinking.

Give it a go next time you are out with a DSLR. With practice you will find the process becomes intuitive quite quickly.

So far so good. But what if there isn’t an obvious mid tone? What if it is critical to ensure you have highlight detail? What if you want white to look white but retain detail? What if you want to ensure sufficient shadow detail on film?

In Exposure Part II, I will discuss how to get the highlights and shadows right.

© Jon Brock 2007