So, when I packed the camera bag for vacation, I grabbed an old polarizing filter. By old, I mean “linear”. But it’s also 30+ years old. (Does that make it old old?
(Hint: if you’re buying a filter, buy the best filter you can afford. They don’t go bad. Indeed, they usually meet their maker by being dropped. Or being sat on and bent. Not that I know anything about that – I’ve just heard… Seriously though, if a filter’s price seems too good to be true, it probably is.)
Anyway, what’s the big deal about a linear polarizing filter? Well, linear filters were just fine back in the days when autofocus cameras were a fantasy and Kodachrome ruled. You rotated the filter to get your desired effect, pressed the shutter release, and went on about your business.
These days, with autofocus cameras, one needs to think and buy a circular polarizing filters Why? Your contemporary autofocus – autoexposure camera’s meter likes circular polarizers. It’s all about physics, and I’m not a physicist, so I’m not even going to try to explain it here. However, Bob Atkins does a pretty good job of explaining things, so if my word isn’t good enough, you can click here and read his article about linear and circular polarizing filters.
So why am I talking about this and why are you reading this? Well, there’s one other problem that you can have besides the meter producing bad exposures, and I encountered it.
If this image looks fuzzy, it’s not you.
On the other hand, if this image looks in focus, it’s you! Please visit your eye care professional immediately.
So… what’s going on here?
A linear polarizer can confuse a multi-point autofocus system, and this is proof positive of that.
I was shooting using the linear polarizing filter to remove glare on the water without a problem, perhaps because the sun was behind me. However, I found my camera not focusing on two subjects the next day in situations where the sun was at a 60-90 degree angle to me. Being totally relaxed on vacation, I didn’t think about the filter being the problem. Instead, I was annoyed / mad / worried thinking my lens had decided to break. I tuned the camera off, removed the lens, put the lens back on, turned the camera on, and same problem….! After repeating that twice (which usually resets everything), I’d given up on the lens for the rest of the trip.
The Frog was not laughing.
And then, later in the day, I looked at the lens. And saw the filter. And realized that I’d had that filter since the early 1980’s…
I took the filter off. I turned the camera on. It focused.
And, I said to myself, “it’s the filter, stupid…!”
Don’t forget to visit your local camera store when you go to get your polarizing filter!