Spot Metering has a lot of power but used incorrectly often results in disastrous images. In this tutorial, we will learn to use it properly and for maximum effectiveness.
Start with an Exercise
This exercise demonstrates what spot metering does. Follow the instructions exactly and DO NOT CHIMP.
- Don’t use AUTO ISO
- Set your camera to spot metering mode
- If you shoot with Live View or an EVF, turn exposure simulation off
Let’s get started:
- Set the camera to Program mode and choose an ISO that will give you a safe hand-holdable shutter speed.
- Turn autofocus off.
- Get two targets, one non-reflective black and one non-reflective white.
- Set the black target up so it is lit indirectly. Fill the frame of the viewfinder/LCD completely.
- Make an image but do not chimp it.
- Set the white target up so it is lit indirectly. Fill the frame of the viewfinder/LCD completely.
- Make an image but do not chimp it.
- Engage playback and compare the two images.
What do you see?
This proves that the camera meter works very well to create an exposure that averages middle grey, since both images are the same exposure, although they may have slightly different tints, caused by the colour temperature of the lighting at hand.
What does this tell us?
Whatever we drop the spot on will offer an exposure that will deliver a middle grey level of luminance from the subject being metered. Awesome if the subject actually has a luminance of middle grey – 127,127,127 in RGB measurements. Bad news if it does not.
The Meter Range
Your camera light meter is based on 8-bit measurements. So while the camera sensor may have more or less dynamic range, black is always 0,0,0 and white is 254,254,254.
By dividing each section equally, we can get an RGB scale that is pretty close to accurate.
Check the metering guide to see what I mean.
What to Spot?
This question is actually one of the foundations of the Zone System created by Ansel Adams and others nearly a century ago. The presumption is that not all scenes average to a middle grey and more importantly, we might want to place the scene elsewhere on the scale.
In the perfect world, you meter off an indirectly lit grey card. This is your nominal exposure. Then you individually meter the key elements of your scene and note their exposure values. This will give you the deviance in exposure values (aka stops) from the nominal value.
Since most cameras today have at least eight stops of dynamic range, so long as no area of the scene is outside that scale, you can shoot and get a reasonably accurate rendition. If, however, your scene is mostly darker than the nominal, you may choose to shift the exposure to the right, to add more exposure in the darks to reveal detail and reduce noise. This means that everything shifts to the right, so you must also watch your lighter areas to see where they will blow out, and if they will, whether you care.
Only the spot meter gives you this level of meter control and management. You will see by now that spot metering is likely not your default metering mode because you must be cognizant of the luminosity of the spot being metered. Most people using spot metering run into trouble by not remembering this key point.
A workaround for the problem of dynamic range came about with the release of High Dynamic Range software. This software would combine multiple exposures together, to increase the relative dynamic range of the final combined image. It did this by taking the brights from an underexposed image to grab their detail, the mid-tones from a central image and the darks from an overexposed image to grab their detail. In the most basic sense, this is like using dodging and burning in the darkroom, so long as the whites and blacks are not clipped in the capture process.
Prior to there being HDR, digital artists did the same thing by combining multiple exposures of the same scene and using masks to block or pass selected areas of each individual image. This digital method is similar to that used in the chemical darkroom by black and white printing masters. Unfortunately, HDR got a bad reputation very quickly because of the capability, and then tendency, for creatives to overcook, oversaturate and overload micro-structure into images that burned viewers’ retinas. To each their own, but in my opinion, a really great HDR is not evidently an HDR.
Exercise Two
For this exercise, you will need a grey card set, consisting of a grey card, black card, and white card. These are extremely useful tools if you want to become good at using the spot meter.
- Don’t use AUTO ISO
- Set your camera to spot metering mode
- If you shoot with Live View or an EVF, turn exposure simulation off
- Put the camera in Program mode and set an ISO that lets you handhold your camera.
- Fill the frame with the black card, and make an exposure using spot metering.
- Fill the frame with the grey card, and make an exposure using spot metering.
- Fill the frame with the white card, and make an exposure using spot metering.
When you examine the images, you will discover that they look nearly identical, as they should if the meter is working properly and you have followed the instructions correctly. Next, you will determine the range of your scene.
Exercise Three
- Do not use AUTO ISO
- Set your camera to spot metering mode
- If you shoot with Live View or an EVF, turn exposure simulation off
Create 7 different exposures:
- Fill the frame with the grey card, and make an exposure using spot metering.
- Dial in -1 EV exposure compensation, and make an exposure using spot metering.
- Dial in -2 EV exposure compensation, and make an exposure using spot metering.
- Dial in -3 EV exposure compensation, and make an exposure using spot metering.
- Dial in +1 EV exposure compensation, and make an exposure using spot metering.
- Dial in +2 EV exposure compensation, and make an exposure using spot metering.
- Dial in +3 EV exposure compensation, and make an exposure using spot metering.
You now have 7 exposures at 1 EV intervals. By viewing the sample images on the LCD, you will have a very good idea how much exposure compensation is needed for this lighting to make the whites white and the blacks black. There are some guidelines in the meter guide, but this very simple exercise gives you very clear guidance for your particular situation.
Summary
By this point, you are probably exhausted from looking at swatches of grey. Fair enough, so let’s end the tutorial.
What I hope that you have gleaned is that spot metering is less a thing and more of a process. You can certainly use spot metering without following the process so long as you accept that whatever the spot is on when the exposure gets locked in is what is going to fall onto the middle grey area of the tonal range. This is great, so long as that’s what you want. But frankly, if that’s what you want, meaning you do not want to apply yourself, spot metering is not really helping you at all. Stay in matrix/evaluative, whatever your manufacturer calls the default. You’ll save time and have a higher probability of success.
However, if you want to see the full range of exposure values across your scene, and are prepared to take readings off all the areas that matter and then decide which tone you want to fall where in the tonal map, spot metering will make a huge difference in your photography. You will be more inclined to get what you wanted out of the camera, and be less likely to be moving luminosity values around in post processing. Post processing is so good, it allows many photographers to be unconsciously incompetent, which is not an insult, but a descriptor for a level of mastery. To get better, you must work, and learn from your mistakes and your successes. If you choose to do so, photography will become that much more powerful for you.
Until next time, peace.
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