Friday, 9 April 2010

Checking Image Sharpness - Don't Be Fooled By The Small Screen

How many of you have previewed an image on the screen of your camera only to be disappointed when you download your images to your computer? We've all done it! In the excitement of getting the shot, we forget to preview and check sharpness, correct focus etc.

What may look pin sharp on your DSLR screen may in fact be blurred or out of focus. On first inspection the image of this FlyBe airliner may look sharp to the unaided eye, but when you magnify it you may see a distinct difference.

If you look carefully at the image above, you'll see that the text on the fuselage of the airliner is blurred - this is caused by two things: 1. Bad panning technique on the part of the photographer i.e. ME and 2. A shutter speed that was too low thus allowing subject movement.

When out shooting it's well worth examining your images on your DSLR screen at regular intervals just to make sure your images are sharp and in focus - if that's the look you're going for! Make sure that you use the cameras facility to magnify the screen preview image and if possible exclude any extraneous light using a screen shade or in my case a Hoodman Hoodloupe 3. On the back of your camera will be a Magnify (Canon) or Zoom In (Nikon) button. Use the controls to check the whole image for sharpness at high magnification. If an image is not sharp, you can always reshoot to avoid disappointment on you return home.

You can see in the image above that the letters are now much sharper. This is because my panning technique was smoother and matched the speed of the airliner. Both frames were exposed at 100 ISO, f8 at 1/500 th second with a Canon 100 - 400 mm L IS zoom lens, which probably had the IS (Image Stabilisation) switched on. This goes to show that even a high shutter speed and using IS there's no guarantee of a sharp frame. What I should have done was increase my ISO to 200 or higher, which would have given me a shutter speed of 1/1000 th second or faster - increasing your ISO sensitivity allows you to increase your shutter speed or use a smaller aperture. A smaller or slower stop or aperture is one with a larger number i.e. f11 is smaller than f8.

Needless to say, I recommend that you ALWAYS shoot multiple frames.

Have a good weekend.

Ian

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