Saturday, July 18, 2009

Finding the Sweet Spot

In 1775 American revolutionary Patrick Henry once said “Give me critically sharp focus or give me death”. Ok, I in fact made that up, he didn’t say that at all, but had he been a photographer he would have. I am now able to tag this article with “American Revolution” thereby increasing the hits! Shameless I know.

In all seriousness though, with all that post processing can do for photos, one of the fundamental things that it cannot do is focus. If you are in the business of taking photos for print or publication, you might have experienced having a wonderful photo rejected due to “soft” focus. Now, this is not to say that great photos are always perfectly in focus, in fact some final edits are actually produced soft as an effect. However, having photos critically sharp in camera increases the ratio of how many keepers you will have and reduce throwaways.

Now there are a number of factors that go into having a photo critically sharp, and I’m just gonna touch on one of them today….aperture or F stop value. I am also not gonna bore you with charts with numbers on them, you can search for those on the internet specific for whatever lens you use.

I want to talk about the “sweet spot” that every lens has, similar to a tennis racket. The sweet spot is when the amount of light let in by the aperture setting optimizes the focus of the image. Typically this sweet spot occurs a couple stops above the maximum aperture setting of your lens. So if your lens begins at lets say, F4, your sweet spot will likely start around 5.6.

A common misconception is that buying a fast lens (i.e. 1.4) enables you to get critically sharp images at the maximum aperture. In reality a faster lens brings the sweet spot into a higher aperture value, so the sweet spot on a Canon 50 1.4 may start at F2. (Although you’d be surprised at how small the focal range is at F2, close to the size of a postage stamp)

Finding that “sweet spot” on your lens is a really good step in beginning to take control of the environment that you shoot in. If you know that you are going to get the best results at F 5.6 at ISO 100, then you can go about arranging your shoot in order to allow you to shoot at this setting, it forces you to consider things like perhaps additional lighting in a form of strobes etc.

So get out there, find the range that is your lenses sweet spot, and see if it turns you from taking photos into making photos.

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