I was at an aircraft / car show today and taking photographs of aircraft against a sometimes cloudy, sometimes blue sky. I used the viewfinder for accurate framing and increased exposure compensation to improve the exposure. But, having got home and reviewed the photos, so many are over-exposed. Also I think on my Canon 550d it has slowed the shutter speed as there is some blurring. My estimated ec value is clearly too much. But sitting in a field with only the camera's lcd screen to check, what should I have done to get the shutter speed and exposure right at the time? Thanks!
When you increase exposure compensation, often the shutter speed is lengthened to give the additional exposure. This is almost certainly true when you are using Av exposure mode. That may be why you think the camera has slowed the shutter speed - because it has slowed the shutter speed.
If you are shooting against a clear sky you can pan the camera with the plane to keep it at the same spot in the frame as the photo is being taken. That's the way to get a prop driven plane with a long enough shutter time (usually around 1/125 second or so) to get a nicely blurred circle for the propellor(s) instead of making it look like the engine has stopped!
Sometimes you have to choose whether to expose for the sky or to expose for the other things in the scene. There is often too great a difference between the two to be able to properly expose both. This is particularly true if the sun is high in the sky or otherwise not behind your shooting position. By shooting raw files you can do a lot in post processing to pull back the highlights and push the shadows a bit, but only within the total dynamic range capability of your particular camera.
Using a narrower metering circle, such as your EOS 550D's Partial metering or Spot metering that measure the center 9% or 4% of your camera's field of view respectively, will allow you to more precisely meter what you most wish to expose properly. Just remember that the meter wants everything to be medium gray halfway between white and black. If the plane you are metering is white or bare aluminum, allow for about one stop of positive EC. If the plane is dark navy or black, allow for about a stop or more of negative EC.
Rather than trying to judge exposure by the image on your camera's LCD, use the histogram to see where the highlights and shadows fall. The histogram displayed on your camera's LCD screen is based on a jpeg created in camera. Even when you are saving only the raw data, the histogram is based on a jpeg preview image processed in camera and attached to the raw file. If you're saving all of the raw data, you have about 1-2 stops of headroom in the highlights before they completely lose any detail in the raw data. If you're saving in JPEG format the histogram shows what you've got.
Of course you can always just wait until Matt Younkin shows up in his Beech-18 for a moonlight show!
But sitting in a field with only the camera's lcd screen to check, what should I have done to get the shutter speed and exposure right at the time?
- Check your histogram: It will tell you the distribution of light and dark pixels (very basically speaking, check histogram) if you have only one peak at the highlights, you know that the image is overexposed without looking at the image.
- Auto Exposure Bracketing (AEB): Just take 3 exposures each time you take an image. This gives you the choice to pick the right one when you are back at home.
- Spot metering: let you meter determine the exposure on a very limited part of the image. This reduces the influence of a possibly bright or dark background on the exposure. Point the spot metering area at the subject, recompose and click. If I'm not mistaken, the 550D does have spot metering. If you have a camera that doesn't or you don't want to switch metering modes, you could also fill the frame with something that's roughly as bright as the subject is. This way, you don't have to guess a hard number for the compensation. Is this +1? or +2? You can visually determine what the camera should automatically expose for. yeah, that aircraft next to me is as bright as the one I want to photograph over there, but this one is so close, I can fill the frame without any sky in the background that throws the meter reading off
- Post processing: Don't try to make perfect images in camera, just make sure you remain within the bounds of what you can fix in post. Even in film days people tweaked the hell out of their negatives. Changing lighting environments can be a demanding challenge. Don't get too upset about exposures that aren't perfect. You're there to enjoy the show, too.