Easy polarizer questions

[JMWallace]

In regard to my 50 1.4 and 85 1.8

My understanding is that circular polarizers are for zoom lenses or lenses that have a rotating outer element.

#1) as I am sure you will (probably Don ;) ) correct me if I'm wrong.

(if I am wrong, no need to see #2)

#2) Is it a linear polarizer I am suppose to get for those lenses??

Thanks

[cdifoto]

In regard to my 50 1.4 and 85 1.8

My understanding is that circular polarizers are for zoom lenses or lenses that have a rotating outer element.

#1) as I am sure you will (probably Don ;) ) correct me if I'm wrong.

(if I am wrong, no need to see #2)

#2) Is it a linear polarizer I am suppose to get for those lenses??

Thanks

1) Wrong. You want a lens that does NOT rotate. The filter rotates, so you want a lens that stays in place so you don't have to keep adjusting the filter as you focus/zoom.

2) Circular, regardless of lens type.

[BBPhoto]

You need to worry about which type of polarizer you require based on your camera, not your lens. Linear polarizers are usually better and more cost effective but you'll most likely only be able to use one if your camera is pre 1970's.

Both types use semi-silvered mirrors to syphon off some of the light coming though the lens. If that light is linearly polarized it renders either the metering or the auto focus ineffective. So, if your camera has auto focus or a TTL metering system, you'll need a circular polarizer.

Another word on the subject - avoid cheap polarizers. It is really worth it to get a good one like B+H.

[Sungrazer]

Actually, rotating front elements make it more difficult to use filters, as you have to reposition them every time you change the focal length. You probably want a circular polarizer, not a linear one. From what I understand, linear polarizers can interfere with autofocus and metering. Polarizers can be used on any type of lens.

[coldrain]

Actually, rotating front elements make it more difficult to use filters, as you have to reposition them every time you change the focal length. You probably want a circular polarizer, not a linear one. From what I understand, linear polarizers can interfere with autofocus and metering. Polarizers can be used on any type of lens.
Almost true this time. But, rotating front elements rotate with focussing, this is the real problem. If it was with zooming, it sort of would be usable still. But lenses with rotating front elements will rotate the filter while focussing, and since rotating the filter makes the polarized light more or less effective, this is totally unwanted.

As to linear vs. circular, AF sensors rely on light that has different polarizations, with a linear polarizer it can happen that the AF sensor will not "see" anything anymore. So a circular polarizer filters polarized light, but then twists some of the light that comes through so the AF sensor always can "see". Or something.

Linear polarizers can be used by compact digital cameras. DSLRs with AF sensors need circular pol. filters.

[Sungrazer]

Almost true this time. But, rotating front elements rotate with focussing, this is the real problem. If it was with zooming, it sort of would be usable still. But lenses with rotating front elements will rotate the filter while focussing, and since rotating the filter makes the polarized light more or less effective, this is totally unwanted.

Thanks for the clarification.

[Mark_48]

As noted, most all (D)SLR type cameras today will need a circular polarizer for auto focus and metering to work correctly.
Are you planning on using a hood with the lens? This makes it slightly more difficult to adjust the polarizer, if at all.
If you can afford it, buy a quality ($$) polarizer such as B&W or Heliopan.

Here's a link to some additional info on polarizers....

http://www.camerapedia.org/wiki/Polarizer