Circular and linear what's the difference?

[pmrud]

I recently bought a Cokin adapter ring for my 50mm lens, it came with a holder and a couple of filters one of which was a polariser. Great I thought, until it arrived and I realised it is a linear and not a circular polariser. From what I recall a circular is needed for autofocus ...or was that for digital?
I took a couple of test shots and it seems to work fine, camera focuses, filter kills reflections, exposure seemed OK using the camera's meter.
So what's the difference? Why use one over the other?

 

[Nod]

SOME cameras' meters can be confused by linear polarisers while others seem to work fine. If your linear and camera work well together - result!

 

[pmrud]

Thanks Nod, I guess a few more test shots are required just to confirm all is good.

 

[madmardle]

Hi Peter,
I used a Cokin linear polariser for a number of years on a Nikon D50 with no issues at all, I know they are not supposed to work as the autofocus may be affected, but there's no harn in trying it, I'm sure it will be fine.
Ken