Here’s a really good quick photo tip. I have two different zoom lenses, a Canon 15-85mm and a Canon 70-300/4.5-5.6. These two lenses give me a very broad range that I can work with. I usually never need to get any closer than the 300 can provide and if I ever need to go wider than 15mm I simply shoot a panorama. Pretty simple. But the one thing that really drives me crazy and something that I always strive for is image sharpness. So just how do you get a sharp image? And how do you know it’s as sharp as it can get?
Well there are a few things that you need to do to make your camera as sharp as possible. First, use a tripod. Whenever possible this is the first step to a sharp image. If you do use a tri-pod remember to turn OFF the Image Stabilization on the lens. Having it on can actually create some vibration if the camera is on a tri-pod. Next, use a fast shutter speed. This will cut down on any movement that is introduced to the camera even on a tripod. A cable release or using the self timer setting which is actually even better takes away the chance that you may have jiggled the camera as you pressed the shutter button. Finally you should use the lowest possible setting for ISO that your camera allows. These points will make sure that your camera is as sharp as possible. Now some of these do conflict with each other so you have to balance your settings but with a tri-pod this is rather easy to do.
So that’s it right? Well not exactly. There is one more thing you need to choose for a proper exposure and that is the proper f-stop. But did you know this? Lenses are sharper at differing f-stops. But how do you know what f-stop is the sharpest? Well you need to do a little testing. After I tested my two individual lenses I found that the 70-300 was sharpest between f11 and f16. The 15-85 was sharpest at f8.
Now sharpness and depth of field are two completely different items but they do go hand in hand. The depth of field is how much of an image will be in focus. The sharpness is just that. When it’s in focus is it sharp? So what exactly did I do to find out my sharpness settings? I shoot a lot of landscape and sky shots so I needed to take a picture of something that was at my infinity focus range. I found a building near by that has a nice field in front of it and is about 300 feet away or into my infinity zone. I manually focused the lens on a part of the building that had some nice sharp corners and angles in my viewfinder. Then I set the camera to Aperture priority and took shots from f5.6 up to f22. I also changed the zoom settings to see if that made much of a difference which in my case it did not. Thank goodness!
Then after all those shots I opened the images in Photoshop and zoomed into 100%. I lined up the images side by side and moved them around until I found a really sharp corner on the building. I also looked for good contrast on the textures of the building. That’s when the sharpness of my lens really jumped out at me. Instantly I could throw out the wide open shots and the closed down shots. Slowly I examined the remaining images until I had two I liked. The two most obvious. If they needed further examination I would slide the image around to look at different parts in the image and sometimes I would zoom into 200%. Finally I would add some sharpening to the two final images to see if that made much of a difference. On a few it helped me pull out the best of the bunch. The one thing I did to make it a little more fair was I would arrange the photos randomly so that it wasn’t just f5.6 on the left and f22 on the right. This forced me to really look at each image. Then when I had a winner I would figure out which image in the sequence it was and what the f-stop was.
This test I did was completely un-scientific but completely real world. How many times have you seen a picture of a resolution chart in the wild and do you shoot at 15 feet? Didn’t think so. My point is that you have to test YOUR equipment and evaluate it to YOUR liking. Res charts and reviews are a great starting point but you need to take it to the next level. This will save you a lot of time playing with the unsharp mask filter. Hope this helps. Mike