I’ve been reading up on long zooms because I’m considering buying one (something that goes up to 300mm or so.) I found one discussion thread comparing the Sigma 70-300 APO and the Tamron 70-300 Di, which kept talking about PF.

Now, I’ve been around camera discussions for a while, but somehow never encountered PF in any reviews before. It took a fair amount of Googling to find the answer, so I’ll just post it here in case that helps anyone else.

PF is just Purple Fringing. CA (chromatic aberration) is the more common term for that in lens reviews, but purple fringing is certainly descriptive, since that’s what you’ll see. It’s probably more accurate as well, since chromatic aberration should really encompass all kinds of image problems, even if the term is now pretty synonymous with purple fringing.

For the record, it sounds like the Tamron lens has more purple issues than the Sigma, although people seem to be fairly evenly distributed between which lens they prefer. Some find the Tamron sharper, others find the Sigma sharper. My reading of that is that, for my uses, I’m probably fine with either of them, and it probably depends more on the individual copy of the lens than on consistent differences between the two brands.

I think I’m slowly moving up the price ladder. I noticed that the Canon 75-300 III (USM or not) was available pretty cheaply used, and thought about it. But the Sigma APO version isn’t much more, and apparently gives you a pretty big bump in quality. Just in case anyone else was wondering, or was trying to research the Canon, or just trying to figure out PF.