poor image quality on Polariser shots

[Ordessa]

On my 350D and my newer 50D running a Tamron 28-300mm superzoom - I've got circular polarisers - both purchased from 7Dayshop.

(reason for 2 was I lost the 1st - then found it)

Neither of them perform well - when I take a shot with them its as if the focusing is a fraction off each time - not blurred through camera shake - just rubbish image quality - like the lens is defoccussed.

Someone suggested they might be linear ones mis-cased... and gave me a way to test (which I've lost unfortunately)

But I'm wondering if these are really poor quality filters...and should I be investing in a better one...bearing in mind for a 62mm filter we can be moving in to £20-£50 bracket..

However I miss the saturation of the polariser ...

Any ideas..
Steve

[chris-p]

Hi Steve, welcome to the forum

There are a couple of things that might be at fault. Firstly, the 7 Day Shop filters aren't great. I've got a couple of different sized ones and frankly they don't really seem to do a lot other than make the image slightly more blue or slightly more yellow. I noticed that they don't actually seem to act properly when trying to remove reflections off water (which they just don't do!).

Focus-wise, there is one important question - does the lens focus OK (or do the shots look OK) without the polarisers? The 28-300mm isn't a particularly sharp lens at the best of times so it's worth checking that it's not just the inherent softness of these types of lenses.
It's possible (but unusual) that the polariser is throwing off the AF system. It's pretty uncommon though (for a circular polariser).

[ap4a]

All filters will reduce image quality to some extent, though some of the more expensive ones use multiple coatings to try to reduce the effects of flare and ghosting they're still an additional layer in front of your lens and that will affect how light is transmitted through the lens.

You might find this useful: http://www.clarkvision.com/articles/...ity/index.html

[Ordessa]

[QUOTE=chris-p;19021? The 28-300mm isn't a particularly sharp lens at the best of times so it's worth checking that it's not just the inherent softness of these types of lenses.
It's possible (but unusual) that the polariser is throwing off the AF system. It's pretty uncommon though (for a circular polariser).[/QUOTE]


Chris
cheers for the pointers..
yes the 28-300mm isnt pin sharp by any means...but I think the AF gets completely thrown by the &7Day polariser... as my other work with this is acceptable..

Ok..so it looks like the 7Day shop filters arent good enough (It was a test really.. as a filter probably shouldnt be that cheap!) - so can anyone recommend me a better version pls

Thanks for feeding back

[donoreo]

I plan to get a new polariser as well. I have a Camlink one that a certain magazine was giving away to new subs It is not very polarising.

[chris-p]

I haven't ever bought an expensive one, but I had a cheapie one on my old Oly and that worked fine (it was 52mm and less than £10) so it's not all cheap ones that are rubbish, just some!

Try a mid-range Hoya (or similar) - they should be pretty decent.

[donoreo]

That is what I was planning myself, a Hoya.