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I have an Olympus EPL1 with two lenses: the micro 4/3rds 14-42mm and the 4/3rds 40-150mm. At the beach today, I could see the sea creatures in the rock pools but couldn't take a picture of them. The reason I could see them was because I was wearing polarised sunglasses. Sticking the sunglasses in front of the lens didn't work. A passing professor of physics told me that it was because my sunglasses are prescription glasses!

So I'm considering getting a polarising filter, but have absolutely no idea what to get or what to look for (I've never even used filters before, let alone thought about buying one). Reading around on the internet, I see that there are two types: circular and linear. How do I decide which to get?

I've also read that I probably shouldn't bother with a filter for the 14-42mm because the front of the lens rotates when it focusses. (This isn't true of the 40-150mm, I just checked.) As a first foray into the realm of filters, would I be really hampering myself by only getting a filter for the 40-150mm lens?

What's a reasonable price to pay for a filter? Given that I'm only dipping a toe in this particular water, I don't want to pay a great deal for something that might turn out to be not as useful as I thought, but I do want to give it a fair go. Looking on a certain website, named for a South American river, I see a circular polariser filter of the right size for my lens (\phi 58) with a RRP of 70UKP but on sale for 14UKP. Don't touch with a bargepole? Or reasonable for the experiment?

My most likely use would be shots through water, and scenery shots with the sun low on the horizon (happens a lot in Norway).

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PS: I'm confused as to what "circular" and "linear" mean when referring to polarising filters. Can anyone link to a good guide that explains it? –  Loop Space Aug 13 '11 at 21:15
    
Linear polarizes light and leaves it polarized. Circular is actually a linear polarizer followed by a quarter-wave plate which turns the polarized light that went through into unpolarized light. –  Itai Aug 13 '11 at 21:57
    
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possible duplicate of How do I choose a polarizer? –  mattdm Aug 13 '11 at 23:47
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@mattdm: Possibly: at the time of asking I wasn't sure if the camera had any bearing on the matter. Now that I know otherwise, then it is pretty much a duplicate. I leave it to your discretion as to whether to close it or not. –  Loop Space Aug 14 '11 at 19:38

2 Answers 2

up vote 4 down vote accepted

A circular polarizer is what you want. Those are the ones that are broadly compatible with modern autofocus and metering tools built-in to cameras.

As for quality, if you're just trying out the effect, sure, go for the cheap one. But watch out for the usual problems with cheap filters: they are probably more prone to flare and ghosting than more expensive filters, they might degrade image quality to an unacceptable degree, and they might be less efficient at letting light through (so you'll need more exposure).

If you find you're using it often, then upgrade to a nice, multi-coated one from one of the brand names (Tiffen, Hoya, etc.) that's large enough to cover any other lenses you're planning on getting. A circular polarizer is one of the few things you can't fake in Photoshop, so it's still broadly useful to have around.

You would want to get one that fits the largest thread mount you have. In your case, that'd be 58mm on the 40-150 lens. Get a 37mm-58mm step-up ring to use it on your 14-42mm.

You can use it on your 14-42mm, but if the front element rotates you'll have to constantly readjust the filter, which is annoying. What I'd do in that situation is leave the filter off; then, compose, focus, switch it to manual focus so the front element won't move, put the filter on, adjust the filter and exposure, and then (finally) shoot. Again, sort of a pain, but it's certainly possible.

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Thanks for the answer. One query on your first point: the Olympus isn't a DSLR and focusses by contrast. Is a circular polariser still going to work with that? –  Loop Space Aug 13 '11 at 21:16
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Yes, anything can focus through a circular polarizer since light exits it in a non-polarized state. The E-PL1 will focus through it and most likely with a linear polarizer as well (didn't try it though). –  Itai Aug 13 '11 at 21:55
    
Yeah, circular polarizers let the light through in a way that any camera's metering and focus systems can still work. In some cameras (not sure if the E-PL1 is one) a linear polarizer can cause problems. Circular is the safe choice. –  unexplainedBacn Aug 13 '11 at 22:05
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The light which exits a circular polarizer is still polarized, just differently. –  mattdm Aug 13 '11 at 23:50
    
@itai: My friendly neighbourhood physicist agrees with mattdm on this: the light is still polarised, but has components in all linear directions. –  Loop Space Aug 14 '11 at 19:39

These considerations:

  1. Linear or circular? For an SLR, you'd need circular, but for a m43 camera like yours, either will work. All else being equal, linear will be less expensive. So unless you plan to use your filter on an SLR as well, pick linear.
  2. What size? As unexplainedBacn says, big enough for your largest diameter lens. Use step-up adapters as necessary for smaller diameter lenses.
  3. Coating? Broadly speaking: multi-coated > single-coated > uncoated.
  4. Which make and model? Set yourself a budget, and within that, shop around and pick the best (read some reviews!) you can find.
  5. Know their limitations. Using them with wide-angle lenses or with severe step-up adapters can cause vignetting. Using them to shoot panoramas can cause uneven results. Don't stop learning
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