Polarizers - the good, the bad, and the ugly

Just wanted some opinions/recommendations :

I need (I think) to pick up a polarizer... (I have a Sigma 18 - 200 - I know it's not the fastest lens available, but since I have some older Pentax glass, and since I blew my whole budget on the body.... and I guessed that after I got a little more accustomed to the camera, I'd have a better idea of what I wanted...) I used PL's all the time on my MF lenses, but 49mm just wont cut it anymore...

So, in checking a couple local camera shops, I can get a few different 62mm filters, ranging from an Optex CPL for $30 that's at least a centimeter thick, or a Nikon one (if that wouldn't be a terrible heresy) for about $130 that looks 3 or 4 mm thick. Am I going to have problems with vignetting at the short end if I get a thicker filter, and also, since I believe you pay for what you get, the $20 one can't be very good, right ?

Any ideas or sage advice for a novice...

Don't have an answer, just my experience. I tried a Hoya circular polarizer with the DA50-200 and found vignetting quite noticeable at 50mm, but not at longer focal lengths. I not sure of the benefits of these filters with DSLRs since you can do so much pp. I too would be interested in others experiences here.

Alan

Probably the only useful filter on digital is the polariser as polarisation is one of the few effects that can't be achieved after the shot is taken.

On film I used to use polarisers, 81A for colour and the usual colours for monochrome, particularly orange and red. All these things can be done in Photoshop with the exception of the polariser.

As regards protection of the lens I don't bother. It can only reduce quality, albeit only very slightly, and I have never ever damaged a filter, never mind a lens. There will be a first time, no doubt, but that's life. And that's what insurance is for.

Pretty much what I thought - I have a bag full of various size screw-on and cokin filters that my digital body and PC have just made obselete...

So is it worth spending more money for a good PL, or is the difference not going to be noticeable anyway, to an amateurs like myself...?

Just because we're amateurs doesn't mean that we can't have professional standards. Always strive for the best. I'm sure that a cheap polariser, like anything else, can only disappoint in the long run.

It needs to be thin to avoid vignetting, be a circular polariser to avoid confusing the AF system and be optically and mechanically sound.

I would go for the best you can afford, without breaking the bank. eBay could be a good place to save some money.

I used circular polarizers quite regularly with film, but when I'm out and about with the K10D I tend to have the DA16-45 (67mm filter size, don't have it!) and the DA50-200 (52mm filter size) I will make some more tests with the DA50-200 when the atmospheric conditions are more appropriate. As for filters in general, I don't keep them on these lenses - they have good lenshoods to protect the front element. I would only get a cp filter for the 16-45 if I thought it would be useful - a top quality 67mm cp filter costs a few bucks!

Alan

I use a Kood circular polariser (Cokin P size) a lot, on my istD. Has exactly the same effect on digital as it does on film, and it's something, as John rightly says, that can't be reproduced after the event.

I tend to use the cheaper ones as I seem to have butter fingers when it comes to filters - but I've been perfectly happy with the quality of them. I've not noticed a difference in image quality between images taken with and without the filter, but I am careful to avoid sunlight hitting the filter, as it's obviously not got SMC!

Dan

One thing to do is buy a filter that has a larger thread size than the lens. Use a step-up ring to attach it to the lens and the vignetting problem should be minimized or removed.

You can also use it on all your other lenses by purchasing some step-up rings for the other thread sizes.

When I get the chance (or change), I'll get a 77mm CP and step-up ring from 67mm to 77mm for my 16-45mm DA. That's a lens that deserves it.

The reason the OPtex filter is so thick is that the glass is primarily intended for use in the film industry - its designed to keep camera noise in! They are of the highest quality and the price you quote is a bargain but I'm sure you would get vignetting. I use a Jessops own brand 'Pro' filter which is extremely thin and causes no problems at all, I'm just about certain that this is a re-badged Hoya because the spec is exactly the same.

So called Pro Circular Polarisers have a slim mount and also have anti-reflection coating. Check out: Hoya Pro, B&W Pro, Sigma EX and Marumi DHG. All the Pro filters are expensive, but cheap circular polarisers do not have anti-reflection coating.

I'm happy with my 72mm B+W slim circular polarizer....

I tried a step up ring on the FA35/2 (49mm to 52mm), but using a step up ring and the lens hood is a real pain. Because the hood will not fit over the ring, the hood has to be in place first. Trying to fit the CP filter with the hood in place for someone like me with arthritic fingers is not really practical, so I've abandoned this idea. Have decided now to bite the bullet and get a 67mm CP filter for the 16-45.

Alan[/quote]

Just a word of caution about using polarisers with ultra-wide lenses. You will find there can be large variations in the depth of blue in a sky, for example, because the degree of polarisation varies depending on the angle with the sun. With an ultra-wide (even a 24mm equivalent such as the wide end of the 16-45mm) this effect can be quite odd and it does little to enhance the photograph.

I find that the ultra-wide angle tends to darken the sky anyway, partly because of natural vignetting in the lens designs and partly because of the oblique angle of the light.

John:

Would I be correct then in assuming that if a couple miillimetres difference in filter width vignettes the picture, then I'm probably too wide to avoid the variable polarization issues you're talking about...?

(Since the thin ones (5mm) are double the money of the thick ones (7mm) with the same coatings...)

From B&W there is either a slim version or an EW (extra wide) version.
What for what?