Polarizer Help or Advice...please!

[Paul690]

Hi everyone, i asked for help and advice about a lens a few weeks back and thanks your replies were ae, and i have a new lens, well two new lens really.

What i have a question / problem with is: i have a 70-300mm sigma lens that i have a Polarizer filter attached and work perfect at all focal lenths. But on my new Sigma 18-200mm lens as with the old Tamron 28-300mm i tried out, on the long (max) zoom wth the polarizer filter on it does not focus correct and leaves the image looking out of focus, without the lans on the picture is as clear as expected. I thought it was a problem with the Tamron untill i got my newer Sigma one
I have also now got a 170-500mm Sigma zoon and want to buy a Polariser filter for it, but dont want to waste more money if its not going to work.

My question is, is there a problem with the polariser filter or are there different ones? i think the one i bought for the 18-200 and old 28-300 is a 62mm circula polariser, if this means anything to anyone...!

I would really like any help with this as i now maybe need to buy a different 62mm one and also need to buy a 86mm one.

Thanks

[kirbinster]

Its probably an issue of not enough light caused by the polarizer on a slow lens. Try it is very bright light and see if you have better luck. I use one on my Nikon 18-200vr which is not a very fast lens with no trouble.

[Paul690]

I did try it in very bright light in the sun... Is in not somthing to do with a circular filter?

[dcclark]

Autofocus systems don't work well when there's not much light coming in. If you put a polarizer (absorbs 1-2 stops) on a slow lens (say, f/6.3 at the 200mm end), then you're barely letting in enough light to focus.

The circular part of the polarizer is just a name for how it modifies the light -- it should work fine otherwise. Have you really tried it in BRIGHT light (say, bright enough to get you a shutter speed of 1/250 or faster)?

[Paul690]

ill try t again and make sure..!

if there is a problem with the auto focus, will it be beter to focus it on manual then, or am i missing something?

[dcclark]

You could manually focus. Give it a try and see how you like the results. If your viewfinder is very dim, you may have the same problems as your camera's autofocus system, however.

The best choice, really, is either to use a faster lens, or not to use the polarizer on this lens at least.