PSC11: More USM Tricks

Today I’ll tell you how you can use unsharp mask to simulate the properties of expensive lenses.

The Difference

But first, let’s look at some of the differences between cheap and more expensive lenses. I recently did an experiment with a $170 sigma lens and an over $1000 canon lens. And what I did is, I compared the two. It was a bit of an unfair comparisoin, a bit like the apples/oranges thing, but I really wanted to know if it’s worth spending so much more money. Now before you start throwing away your $170 lenses and shell out tons of $$/€€/<insert_currency_of_your_choice>, let me tell you that you can get very similar results from cheaper lenses, but just under certain circumstances.

Both of the lenses were zoom lenses and what I looked for in my test were two things: the image sharpness at various focal lengths and apertures, and the local contrast of the images taken with the respective lenses.

Now this was not a scientifical test, but at least it served as a good indication as to what to expect. And the results were mostly as expected. But the surprising thing was that the cheaper lens was capable of the same image sharpness and very similar contrast under certain conditions, the so called sweet spot of the lens. The main thing that sets the more expensive lenses apart from the cheaper ones is that their sweet spot is much wider, so you can get high image sharpness and contrast with a wider range of focal lengths and apertures.

The Sweet Spot

What I call sweet spot is a specific combination of focal length, aperture and subject distance, that is different for each lens, and I usually do this kind of a test whenever I buy a new lens. I put the camera on a beanbag, and I take a series of shots at different apertures and focal lengths. I’m not doing this to find out how flawed the lens is, because there simply is no perfect lens out there, no, I do it in order to find out where the strengths of the specific lens are, so that I can make better use of the equipment I have.

But wait a minute, isn’t this supposed to be Photoshop Corner and therefore Photoshop related? Well, you’re of course right, and that’s why we’ll now explore how we can simulate some of the properties of expensive lenses during post processing.

Local Contrast

Let’s first look at what’s called local contrast, which is usually higher with expensive lenses, and it is one of the things that makes pictures more crisp and jump in your face.

And here’s where the Unsharp Mask tool comes in. Wait, back in PSC 4 you learned that Unsharp Mask is the tool of choice for image sharpening, so what does that have to do with image contrast? Well, USM increases the perceived contrast of edges by making dark areas darker and light areas lighter, but within a very small radius of action of a few pixels only. But luckily Adobe hasn’t limited the radius setting of the Unsharp Mask tool to just a few pixels, and we can use that to our advantage. Try the following Unsharp Mask settings: Choose a radius of 50 pixels or higher that's 50 – the exact setting highly depends on the resolution of your image, so you’ll have to experiment – and set the amount to something less than 10% and you should notice an increase in local image contrast.

Sharpening

Now a second property of expensive lenses is that they tend to be sharper than the cheaper ones, at least at wide open apertures or all zoomed in or out. So the second way to use USM in order to simulate the properties of expensive lenses is the actual image sharpening. By sharpening you won't really increase the amount of information in a picture, but you will increase the perceived sharpness. And I explained that in quite some detail back in Photoshop Corner #4.

Edge Sharpness

And the third thing that makes expensive lenses stand out is the fact that they have a higher edge sharpness. If you take a picture that's in focus in the middle and then zoom in to 100% on your computer, you sometimes notice that the center of the image is sharper than the edges. If your lens has that problem, you can counter it by duplicating the image to a new layer, sharpening that layer, and then applying a mask in form of a circular gradient to the sharpened layer, so that the further to the outside of your image you get, the more of the sharpening takes place.

Conclusion

Those three methods - increasing local contrast, sharpening and edge sharpening - cannot fully replace good glass, but if you have the time and patience, you can definitely give your images a higher technical quality this way.