Sigma 18-125, Skylight filter and 20D

[alan sh]

When I have the skylight filter on my Sigma 18-125, the focussing at wide angle is very slow and it hunts for ages. Take it off, and its much better. I don't get this with my Canon 28-135.

Has anyone seen this and may know the reason ?

Filter is a Hama 1A on the Sigma and a Hoya 1B on the Canon. Whats the difference ?

Thanks for any info

Alan

[PacAce]

Have you tried it with a hood on it. If not, see if that makes a difference. I'm suspecting that you might be getting some glare from the filter that's affecting the focusing. But this is just a guess.

[alan sh]

It had the lens hood on with the filter.

This was on a tripod pointing at some trees in the distance.

Its no big deal - I was just wondering.

Alan

[RichardtheSane]

Sorry for putting this so bluntly, but Hama filters are junk.

I would get rid to be honest

[alan sh]

Interesting statement. Care to clarify it a bit. In what way ?

Alan

[roanjohn]

He probably means that you should invest your money on other brands i.e. B&W and Hoya........... :-)

Some filters does affect AF when attached to certain lenses...........It's all trial and error depending on the combo.

Ro1

[RichardtheSane]

It is an interesting statement from someone who a while ago thought 'I know, I'll save some money on filters now I've spend all my cash on camera and lenses'.

So I bought a 77mm Hama 1B and a 77mm Hama polariser to protect my new shiney lens. I posted here after a week or so because I was getting soft images and AF was not locking on every time, in fact not often at all. After many suggestions about technique, faulty hardware amongs other things someone asked about filters.
Well shortly after I proudly announced that I had filters on to protect the lens, and when I removed the filters all problems went away. Not to be deterred I tried again, and the problems came back. Poor focus accuracy and softness even stopped down (albeit slight) and this is on a lens that is well known for focusing well and being sharp.
I purchased a Canon 77mm 1b and hey presto! problems have gone. You see, hama are really cheap, and in the filter world you really do get what you pay for.

Good enough explanation? :)

[alan sh]

Good enough for me since that matches what I have seen.

However, I also get odd focussing issues with no filter - but thats for another discussion.

Thanks

Alan

[DocFrankenstein]

I have problems with my sigma focusing when I shoot with a hoya UV filter on it. Without it, works fine.