Windlight Contributor, Myra Wildmist, is back with another tutorial. This time on the Circul of Confusion in the SL viewer:

We’re back into the weeds of Depth of Field, today, so get your photo geek hat on.

In my last post on Depth of Field, I talked about deep (sharper) and shallow (blurrier) DoF. In Phototools, you control the depth of your DoF with the f-number – smaller numbers give you more blur; higher numbers less.

But what if you want to have even more blur? What if a small f-number doesn’t give you as much blur as you like?

What is Circle of confusion?

In Phototools (Alt+P), under the DoF/Light tab, there’s a setting called CoC. It stands for Circle of Confusion. That sounds like it might have something to do with being drunk on merry-go-round, but it’s actually an optics term, and since photography is almost all about optics, it’s also a photography term.

The circle of confusion is the largest size a point can be on our image before it’s perceived as blurred. This is dependent on visual clarity or acuity, distance from the subject, and the size of the image you’re viewing.

Using CoC

The FS Phototools tool tip for CoC says, “This is an important setting. It determines the strength of the blur itself. It does not change the depth of field, it adjusts how much those objects outside of it will be blurry. (This number can be negative, for some “odd” effects.)”

While not really telling you what CoC is, it is an accurate portrayal of what it does. When we take a photo, we’re less concerned about perceived levels of blur and more concerned about “acceptable” levels of blur.

Smaller values will give you sharper photos and larger ones will give you blurrier ones.

CoC 10 f-number2
CoC150 f-number 2. Lots of blur

Style thoughts

Set your CoC between 5-20 for sharper photos. This seems to work well with most high resolution, large format photos, in my experience.

A CoC of 0 (zero) effectively turns off DoF.

Experiment with CoC. You can get some fun effects with high CoC.

Further reading and resources used for this article

Firestorm viewer

Depth of Field and Circle of Confusion

SL Wiki

Cambridge in Color. Tutorial: Depth of Field

One thought on “SL Photography: Circle of confusion

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