[ismaelg]

Hello,

Not sure if this is the right place for this question:
How critical is coating on circular polarizer filters? I see a big price difference between non coated and multicoated. Among other things coating prevents glare, but that's part of the idea of the polarizer in the first place. Is that correct?
I have a multicoated UV filter in my lens mostly for protection. Is it advisable to use the Cir Pol on top of it?


Thanks,

[jmbradd]

coating is a big deal on any filter for me personally. Adding a filter is another exposed element that can pick up stray light and affect your image. Coating doesn't improve the effect of a circular polarizer but it certainly helps eliminate stray light. Uncoated filters are like attaching a mirror to the front of your lens (ok thats dramatic but i've seen the difference).

As for cost, someone posted in the thread I made about a brand of cpl I liked (marumi) a place called Welcome to WestCoastCameras! that had the best prices on filters I had seen.

[Digitalis]

as soon as you attach a filter to a lens the glass that the filter is made of becomes a part of the optical system of the lens. I wouldn't be caught dead using a $10 piece of glass in front of a $2000 lens. I have seen filters reduce image quality quite substantially on otherwise superb lenses.

But I do use filters in situations where my lenses are going to be exposed to the elements, and the filters I use are the best money can buy. Schneider MRC filters that DO cost quite a bit but they are worth it.

polarisers are expensive, but getting a good (multi coated, of course for the very good reasons that have been explained above) one is very important because polarisers there are so many things that can go wrong with them. so it pays to get one that is made by a manufacturer that uses quality components. Hoya makes reasonably well made filters, I have had some come apart on me. caveat emptor.

[newarts]

It is possible that a low cost multicoated, optically flat circular polarizer exists; I don't know how to find it.

I use an inexpensive"Sonia" circular polarizer and am well satisfied with its performance. I have never seen it contribute flare or distortion to an image.

[Lodewijk]

Stacking a polarizing filter with an uv filter has no advantages, and can only lead to more vignetting, flare and/or ghosting.
Coating on polarizing filters is a big deal especially on the rear (facing the front element) to minimize light "bouncing" between the rear of the filter and the front element causing ghosting.
Furthermore it is advisable to always use a lens hood when using a polarizer. Since I always have a lens hood on my lenses I never use an UV/protection filter as I think the lens hood protects them enough.

[Wheatfield]

Stacking filters is a bad thing, unless you actually need the effect that two particular filters will give.
I've never bought into the hype about circular polarizers. I think they are a waste of money.
A good multicoated linear polarizer can be had for more or less the same $$ as a cheap, poor quality circular, and will do a better job at what it is supposed to do.
They will not affect light metering on any but a very few cameras (the LX is the only Pentax that might be affected by a linear, and then, only in manual exposure mode), and the use of a polarizer obviates much of the reason for using auto focus, although I've never had an AF go blind enough to become inoperable from using a linear polarizer.
To me, circular polarizers are a solution to a non existent problem.

[Canada_Rockies]

Your polarizer should be the best you can possibly afford. The very best will not come cheap, but anything less will ultimately leave you in the lurch. The ideal polarizer is the ultra thin top of the line polarizer. The thin reduces the vignetting and the top of the line will be the best optical coatings you can buy.

A polarizer can darken a blue sky to make the clouds stand out or the sky to be a deeper blue. Using that on a very wide lens is at times detracting to the image because the sky will come out almost black at 90 degrees to the sun, fading to nothing as you move away. That creates an image that just does not look real. The sky is the palest of blue on the left and almost black on the right.

The best use of a polarizer, I find, is to remove reflections. When taking a picture of a car, a polarizer can reduce or remove reflections in the windows of other patrons at the car show. Shortly after a rain fall, colours of leaves and scenery will have reflections from the water that hide the underlying foliage. A polarizer in this instance can really bring out the colours.

[Squier]

So what are the optical differences in Linear and Circular PL's ? And why do so many folk use a Circular on a DSLR rather than a linear - i dont actually know anyone that uses a Linear

[Wheatfield]

So what are the optical differences in Linear and Circular PL's ? And why do so many folk use a Circular on a DSLR rather than a linear - i dont actually know anyone that uses a Linear

Without getting into the physics, which is beyond me anyway, a circular polarizer somehow depolarizes the light after going through the polarizing screen. This allows the light to go through the camera's optical path without cross polarizing on whatever sub mirrors are present (the AF mirror, for example).
As far as I can tell, people use circular polarizers because they have been told that is what they need by people who are in the market to sell more expensive equipment.
To be fair though, there may well be cameras out there who's exposures can be thrown off by a linear polarizer, it's just that Pentax isn't among them (with the one exception being the LX under certain usages).
We started getting circular polarizers in with the first wave of AF slr's back inthe 1980s, and we were told that this was all that would work, so that is what we sold. I think that it has elevated to urban legend status at this point.
Anyway, a linear polarizer may affect AF, causing it to hunt due to light loss if cross polarization occurs at the sub mirror, but with Pentax, it won't affect the exposure meter, which reads directly off the focusing screen.
Given that polarizers tend to be used in fairly static picture taking situations where AF can be turned off in favour of manual focus, I'm not seeing any advantage to circular polarizers

[Squier]

Nice

I dont have any filters for my lenses at all, but am seriously thinking of 1 or 2 in the future, and a Polarizer is one of them.

I managed to read up about them , and rightly or wrongly ( i wouldnt know ) that CPL's were for DSLR's and Linear were for Film

[Canada_Rockies]

Nice

I dont have any filters for my lenses at all, but am seriously thinking of 1 or 2 in the future, and a Polarizer is one of them.

I managed to read up about them , and rightly or wrongly ( i wouldnt know ) that CPL's were for DSLR's and Linear were for Film

Not quite. Circular polarizers are for any camera with a split mirror feed to exposure (LX) and/or AF (all Pentax AF cameras). The split polarizes the light that is sent to the AF sensor. If everything is lined up just right, the AF goes crazy. So 90 or 99 or 99 44/100 percent of the time a linear will work just fine. Knowing my luck, it will be the things that happens when I have exactly the wrong circumstances and 1.376 seconds to take the shot. At my age the reaction time is around .75 seconds, which would leave me with a bit over half a second to realize that my polarizer was going to screw up my AF, refocus manually and shoot. I bought circular.

[Squier]

A linear may suit me then, as i dont use AF at all

[Canada_Rockies]

A linear may suit me then, as i dont use AF at all

You can save a lot of money on an equivalent filter that way. Keep in mind that if you use the in focus indicator when manually focusing, you will have the occasional glitch. I tend to use the matte screen to focus my M and A lenses and ignore the little hexagon, so if you work the same way I do with them, no problem with linear polarizers. However, I do use AF with the DA lenses, and so I sprang the extra gelt for the ciruclar polarizers.

[Squier]

I'm about to change my matte screen for a focusing.com split image / microprism / grid screen.

I dont know whether this affects things like filters , CR ?

[Canada_Rockies]

I'm about to change my matte screen for a focusing.com split image / microprism / grid screen.

I dont know whether this affects things like filters , CR ?

I have heard that the split may upset the meter with slow lenses.