L series lenses, which filters?

Using a polarizer in the conditions for which it was intended, you shouldn't get too much flare problem, so uncoated, single-coated or multi-coated becomes pretty much a wash for most uses. The principal concern there is the quality (optical flatness) of the glass. It's those odd times when you're trying to control a reflection hot-spot that multi-coating pays off. For an always-on filter, like an UV, then multi-coated top quality is the only way to go.

Get the SMC ones but not the ultrta thin ones

My experience is that the hoya UV filters do not clean well without smudging badly

I have a Russian 300/4.5 manual focus lens that came in a big box complete with a lot of filters (colour + UV).

When I put on the included UV filter (which was most likely made from window glass), the lens gave me awful soft images. Once I removed the filter, it was quite sharp.
So yes, cheap filters can definitely have a detrimental effect on image quality.

Best regards,
Andy

Exactly the same thing happened to me with a cheap Jessops UV filter a few years back.
Lesson learned.

Be careful using a polarizer on wide angle lenses, you get skies that look like this. That shot is at 12mm, but 17mm will probably be similar. This pic is at 20mm and you can still see the sky is graduated.

Very good point tim.
Don't even think about shooting a pano series with a CP on any lens.

I have a 77mm Canon L sharp UV Haze filter and a single Tiffen wide angle (no front thread) CP filter for all my L's and 10-22mm. But on my 24-70mmL I have noticed, that even the UV filter will produce strange effects of ghosting and such at times. So I only use the UV's if the weather is adverse, rain, sand, etc. Else I don't use a filter.

I would purchase an OK CP and ignore the other filters for now.

If you need a CP effect, then a cheap CP is better than none.
If you have crud flying in your lens, then a cheap UV is better than none.

If you're getting paid to have crud fly in your lens and the client still wants "perfect" image quality, then he should pay for an expensive filter.

Thinking about getting B+W multicoat UV filter for my 70-200.
Should I just spend the extra $$$ for a Circular Polarizer?

I'd get the polarizer. It's hard to actually scratch the front element. God knows I've tried it on some lenses.

I use CP's mainly for flora, fauna and water shots. England doesn't give that many opportunities to use a CP for deepening a blue sky

This is all food for thought and it's a big step towards buying a L series lens....which is in itself a huge step (financially).

Thanks for the views and info guys!

Wish i'd seen this when i ordered 2 hoya UV and 1 skylight 1B filter with my new lenses last night, I wasn't aware it could cause softness to an image, looks like i'll be doing a batch of tests when they get delivered

Peitolm wrote:
Wish i'd seen this when i ordered 2 hoya UV and 1 skylight 1B filter with my new lenses last night, I wasn't aware it could cause softness to an image, looks like i'll be doing a batch of tests when they get delivered

Poor quality UV filters may have an obvious impact on image quality.
Of course , in reality, all filters must have some impact.
I use Hoya HMC Pro 1 UV filters and I have done the tests and can't tell the difference between filter on and off.
That'll do for me.

They're completely different. One's for protection, one's for polarization. Decide what you want and get it.