Flare, and “veiling glare” is arguably the most destructive effect of the transmission of light through glass elements. Every place where a light wave moves from one medium to another, generally from air to glass and back, gives the light the opportunity to scatter. Consequently, we have the potential for flare at the edge of each additional lens element.

Flare is controlled though a few strategies. Multicoating of lenses is probably the single most powerful process to control flare, along with the addition of various materials in the manufacturing of the glass. Ironically, one of the most effective devices for reducing flare is to eliminate stray light from hitting the lens, by use of a simple lens hood. A good lens will suffer the effects of stray light less than a poor lens, but both benefit dramatically from the use of a hood.

In these tests we’re seeing some fairly insignificant differences. The first set of charts represents the local contrast and density results, and is probably the easiest to use to represent the visible effects of flare on the image. Flare, or “veiling glare”, reduces contrast. The higher the curve, the less flare.

The first set of charts are from the Canon EF f/1.2L USM, shot at f/1.2 and f/1.8, and we’re seeing very little variation.

Canon EF 85mm f/1.2L II USM @ f/1.2

Canon EF 85mm f/1.2L II USM @ f/1.8

Canon EF 85mm f/1.8 USM @ f/1.8

Note, the curve for the f/1.8 lens is on axes with a slightly different scale; although they appear to be a different value and slope, a quick reference of the values confirms the results are almost identical.

At f/7.1, we’re getting a similar result between the two prime lenses.

Canon EF 85mm f/1.2L II USM @ f/7.1

Canon EF 85mm f/1.8 USM @ f/7.1

While we may expect enhanced flare performance from the more pricey lens, these results really aren’t too surprising considering that the coating processes are shared by the two lenses. If we saw a significant difference in the amount of groups or elements, perhaps we could expect to see some dramatic variations here, but the ens designs, in terms of elements and groups, are very close: 9 elements in 7 groups in the f/1.8 compared to 8 elements in 7 groups in the f/1.2.

Since it’s not a significant expense to use a standard glass formula and coating method, it’s not a shock to see these two lenses handle flare in much the same way.