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Aircraft Photography Tips Part 2 – Camera Metering Modes, Exposure Modes And Exposure Compensation
Aircraft Photography Tips – Choosing Camera Metering Modes, Exposure Modes And Exposure Compensation
In my first post on aircraft photography, called aircraft photography tips part 1, I discussed essential camera modes and looked at some of the currently available lenses.
Specifically, I mentioned the importance of control over certain camera modes of your chosen camera.
Those camera modes were –
- metering mode – centre weighted and spot
- manual control of exposure compensation
- auto modes – aperture priority and shutter priority
Lets look at these camera modes to understand how and why they affect the finished image.
The article will talk in depth about the technical aspects of camera exposure. My aim is to make the article interesting enough for those with some knowledge of the subject without being too complex for beginners. Please let me know if I was successful in this approach!
Camera Metering Modes
One of the most important factors in any type of photography is to understand and interpret the varying light levels in your chosen scene. The photographer then needs to understand how the selected metering mode will affect the camera in achieving the final exposure.
In general photography, the majority of scenes will consist of evenly lit subjects.
Multi area matrix metering, which evaluates the relative brightness of subjects in the whole scene, is usually very good at selecting an exposure that will render the colours and brightness levels in a very authentic manner.
I am sure we have all experienced scenes that have more sky or shadow and see that the resultant image has either nice shadow detail and a burnt out sky or a nice sky and dark shadows.
This is because the matrix metering is trying to evaluate an unevenly lit scene. Whichever element, bright sky or dark shadows, forms the majority of the scene will be judged to be the most important and the camera exposes accordingly.
It is extremely important to remember that aircraft in the air are comparatively small and dark against a big bright (hopefully blue!) background.
If you choose wide area matrix metering modes you are going to quickly run into underexposed shots.
With multi area matrix metering, the camera sees a large bright expanse of sky dominating the scene and exposes for an overall bright image. Typically you will get a nice blue sky and a black or dark grey aircraft.
Because the aircraft are relatively small compared to the whole scene, you must compensate against this by selecting centre weighted or spot metering mode.
These two camera modes reduce the amount of the overall scene that the camera measures when computing exposure.
Centre Weighted Metering
Centre weighted metering simply means that the exposure calculations made by the camera put more emphasis on the readings detected in the centre of the image.
Typically, centre weighted metering will put the emphasis on about 8-15% of the scene. The brightness levels of the whole scene are still evaluated, but the camera adjusts the exposure so that the readings taken from that 8-15% are given the greatest emphasis in its calculations.
One thing to remember is that each brand implements their metering modes slightly differently, and the sophistication of weighting calculations vary as well.
Lower end models may have a fixed value of emphasis and have the centre weighting fixed to the centre of the focusing area.
With the more expensive cameras in any given range, you will find the sophistication of the systems increase.
You will find that you can control the size of the centre weighting in steps somewhere between 8-15% and that this weighting is not fixed but follows the selected focusing point.
Spot Metering
Spot metering is simply a more extreme version of centre weighted metering. The emphasis is now placed on an area as low as 1 or 2% of the scene. Again, each brand implements the feature slightly differently and the sophistication increases as you move higher into the brand range.
Spot metering is a key feature and is not always included in the lower end models so make sure any model of camera you look at has spot metering.
It is extremely important to remember that aircraft in the air are comparatively small and dark against a big bright (hopefully blue!) background
So, by understanding how cameras evaluate a scene, and how the user can select a weighting mode, you should be able to see how a more accurate exposure of our aircraft against a bright sky can be achieved.
Although cameras metering modes are becoming extremely sophisticated and competent, they are still not fool-proof in getting that well-exposed aircraft photo.
This is where the next important camera feature – exposure compensation, comes in to help.
Exposure Compensation
So far we have looked at how we can choose a metering mode that will help the camera to interpret the scene as we want it to.
Exposure compensation allows you to directly adjust the calculated exposure value by a set amount of either over or under exposure.
By manually controlling exposure compensation, you are further controlling the final calculated exposure.
Most modern DSLR cameras allow you to manually ‘dial-in’ a fixed adjustment to the calculated exposure value.
Depending on your camera, you can usually add in between +2 and -2 stops of exposure in steps of either 1/3 or 1/2 stop increments.
I like to dial in up to +0.7 exposure for small aircraft and +0.3 exposure for larger aircraft, but you will find that the exact compensation is a matter of trial and error depending on the light encountered on the day.
I do this because a smaller aircraft means more bright sky affecting the calculation so I want the camera to overexpose slightly more on its calculation. A larger aircraft means less bright sky so the camera is more likely to calculate a more pleasing exposure so only a small adjustment is needed.
Don’t be afraid to take test images – review the histogram and fine tune your adjustments. As the light changes during the day, you will probably need to make adjustments anyway.
In the example below, a single F-16 trails vapour at an airshow. The camera sees a large tract of bright blue sky as the dominant feature in the scene.
white vapour trails during an airshow display
By selecting either spot or centre-weighted metering, adding exposure compensation and framing your target aircraft in the area of emphasis, you can increase the chances of a good exposure.
In this example I had +0.3 dialled in and used spot metering exposure mode.
Lets look at the next features – aperture priority and shutter priority modes
Auto Exposure Modes – Aperture Priority and Shutter Priority
We use the camera as a tool to calculate that ‘x’ amount of light needs to get to the sensor to produce a ‘good exposure’.
The previous section looked at how we help the camera calculate a good exposure, now its time to look at how the camera executes that exposure.
Camera exposure basics
Exposure is controlling the amount of light hitting the camera sensor.
In basic terms, every lens has an adjustable opening, called its aperture, that controls how much light entering the front of the lens is passed through to the sensor.
The shutter speed controls how long the sensor is exposed to the light coming through the lenses aperture.
The exposure calculation simply means the camera needs to let ‘x’ amount of light get to the sensor.
To get ‘x’ amount of light onto the sensor, the camera selects an appropriate combination of aperture and shutter speed.
In pure ‘auto’ or commonly ‘P’ mode, the camera will select both values and operate the shutter.
Essentially, Aperture Priority and Shutter Priority are still camera ‘auto’ modes, but importantly execute that exposure based on the user choosing to directly control either the aperture value or shutter speed.
By using Aperture Priority or Shutter Priority modes, we are taking more direct control on how the camera is generating the image.
So what does that all this mean in simpler terms?
Differences between Shutter Priority and Aperture Priority camera modes
In shutter priority mode, the user can select an exact shutter speed and the camera will choose an appropriate aperture to ensure the exposure corresponds to our ‘x’ amount of light.
Conversely in aperture priority mode, the user selects an aperture and the camera will calculate the appropriate shutter speed for our ‘x’ amount of light.
So, if aperture priority and shutter priority both do a similar thing, why bother differentiating between them – why not just use whatever mode you are comfortable with?
Unfortunately, it isn’t that simple if you want the best results. You will find to get the best photos, you will be regularly swapping between both modes depending on the type of aircraft, lighting conditions and mood you want to create.
So, if aperture priority and shutter priority both do a similar thing, why bother differentiating between them – why not just use whatever mode you are comfortable with? Unfortunately it isn’t that simple if you want the best results.
Benefits of Aperture Priority mode
Lets look at a couple of environmental issues you will likely face when out and about –
- you are using a telephoto (and probably heavy) lens
- your subject could be moving extremely fast (military jets) or painfully slow (older prop aircraft)
- the wind is probably going to be blowing you about
- the lens hood will be acting as a sail increasing the effects of any wind
Very quickly you are going to run into the problem of camera shake and blurred images. The aim is sharp images so you want the fastest shutter speed obtainable.
In aperture priority mode, you can select an aperture of f2.8 or f4 (on more expensive lenses), f5.6 ( most common on cheaper telephotos), f8, f11, f16, f22 and maybe f32.
You choose an aperture and the camera automatically chooses an appropriate shutter speed to give a good exposure. That amounts to 7 options (slightly more if including intermediate apertures between each major ‘stop’).
The aperture options for you to select are restricted to the physical quality and abilities of the lens.
Hidden dangers of Shutter Priority Mode
In shutter priority mode, you can select a shutter speed anywhere from 30 seconds through to 1/4000th of a second. That is a lot of options.
This is where you need to be really careful and understand the concepts of exposure.
Starting with aperture priority, let’s consider an average bright day with ISO set to 200.
The table below shows examples of typical shutter speeds your camera will generate for a given aperture.
- f5.6 1/1600
- f8 1/800
- f11 1/400
- f16 1/200
- f22 1/100
From this you can see the suitable shutter speeds for good exposure range from 1/1600th to 1/100th of a second.
Herein lies a trap for the unwary.
In shutter priority mode, you can select any shutter speed you want. If you choose a faster shutter speed, the camera will need to select a wider aperture to let more light in. If the lens doesn’t support a wide enough aperture to allow enough light in for a balanced exposure, you will get an underexposed image.
Conversely, you can select a 1 second exposure, but if the lens doesn’t have a small enough aperture to automatically restrict the light sufficiently you will create an overexposed image.
If you are using shutter priority mode, you need to be conscious of this. In the heat of the action, you might want to get a faster shutter speed and not realise you are already at the limit of the available apertures.
How I use shutter priority and aperture priority camera modes
To manage shutter speeds I use aperture priority mode to obtain the fastest possible shutter speed while safely staying within acceptable exposure values.
I do this because, in aperture priority mode, once you get to the widest aperture, you cannot make any further adjustments. The camera will have selected the fastest possible shutter speed for that aperture and ISO setting.
This is why you should use aperture priority mode to select your fastest possible shutter speed.
Herein lies a trap for the unwary. You can select a faster shutter speed, but because the lens doesn’t support a wide enough aperture to allow enough light in for a balanced exposure, you will get an underexposed image.
When starting out in aviation photography, you want to aim for 1/1000th of a second shutter speed as a minimum – if you see lower speeds than say 1/320th, you really need consider turning up your ISO setting.
If you find you are still seeing lower shutter speeds and are approaching ISO 640 or higher, you need to see part 4 where I will discuss some techniques to help you through this problem.
There is an awful lot more to choosing appropriate apertures, shutter speeds and photographing aircraft, but the above lays out the basics for those starting out in aviation photography. If followed, with a little practice, you should be on the road to getting some acceptable images. Once you are getting a good hit rate using these basics you can look into some of the more advanced techniques and aspects of aviation photography in the upcoming parts 3 and 4 of my series.
So in summary
- use either centre or spot metering modes to reduce the effects of a bright background on your subject
- use exposure compensation to further control exposure
- use aperture priority mode to get the fastest shutter speed whilst staying within a band of appropriate exposure values
- beware of incorrect exposure by relying on shutter priority mode
By now you might be asking why bother mentioning shutter priority mode at all – why not stop in aperture priority mode?
Check Aircraft Photography Tips Part 3 to see the answer.
That’s all for now folks, thanks for reading and I hope you have learnt something useful from this article. Please don’t be afraid to leave your own tips or question on what I have discussed above.
Gary
