Linear / Circular ?

[Al Tee]

Could anyone advise please.

I've put an old (assumed), linear polarising filter on the 18-55 lens that came with my D50. It's a "Marumi" brand and it says on it "P.L". (Hence assuming the "L" stands for linear). It seems to work well although I've been told that I should only use a circular polarising filter on AF lenses.

I now want one at 62mm diameter for my 70-300 & there's a considrable difference in price between linear & circular.

What, in reasonably simplistic terms, are the benefits of a circular polarising filter over a linear?

Thanks,

Al.

[yelvertoft]

Hi Al,

If you are using autofocus with a linear polarising filter, depending on the angle of the filter, it may not allow enough light though for the AF sensors to detect when the subject is in focus.

You can use this filter, but bear in mind that the AF may not work, you almost certainly will have to switch to manual focusing, especially as the 70-300 will probably have a smaller max aperture at full zoom.

Why not get a step-up/step-down filter ring for a couple of quid and try using the existing filter you have with the bigger lens? This will let you see if it's worth getting the circular polariser. It all depends on how important AF is to you.

Hope this helps,

Duncan.

[Craftysnapper]

Contrary to popular belief most linier polarzers work OK with AF...the biggest problem is with the metering . As a general rule if you have an auto focus camera the manufacturer will recommend that you use a Circular Polarizer. Most modern SLR cameras use a polarizing half mirror system, this is called a split beam metering system. A circular type Polarizer is required for the meter to function correctly.

[Al Tee]

Thanks Duncan; thanks Craftysnapper. I use autofocus & manual focus about 50/50, & come to think of it I have been questioning the metering! Think I'm safest to go for the circular versions.
There goes another £65.00 into the Jessops funds!
Thanks again.
Al.