 It was my birthday yesterday (now 22!), and my brother came home from holland with my present; a Hoya cir-polarizing filter, ooh!
I wasnt sure what one does, then I tried it out, and my god, its amazing! For everyone else that doesnt know what it does, it basically eliminates reflections from certain surfaces, like glass and water when you rotate the filter (so you can adjust how 'dimmed' the reflections are), so its great for getting more accurate exposure without burnt out highlights from reflections.
I just couldnt believe what I was seeing, how does a filter get rid of reflections? Is it to do with light wave lengths or something? if anyone could shed some light on this apparent magic (in relatively simple terms), I would be very grateful.
Thanks,
James.
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 It's a 2 stage thing. Firstly you have a polariser. This takes 'busy' multiple frequency light and simplifies it, essentially keeps it simple. If you think about it, your camera is capturing light from all sorts of refractions. A polariser just selectively limits those. Now circular polarisation is basically splitting the selected frequency further by further splitting the light. It's a series of slight incidences that divides the light - that's why you have to rotate the filter, it selects what will fall off.
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Alternatively you can go to wikipedia's explanation:
"In electrodynamics, circular polarization (also circular polarisation) of electromagnetic radiation is a polarization such that the tip of the electric field vector, at a fixed point in space, describes a circle as time progresses. The name is derived from this fact. The electric vector, at one point in time, describes a helix along the direction of wave propagation (see the polarization article for pictures). The magnitude of the electric field vector is constant as it rotates. Circular polarization is a limiting case of the more general condition of elliptical polarization. The other special case is the easier-to-understand linear polarization.
Circular (and elliptical) polarization is possible because the propagating electric (and magnetic) fields can have two orthogonal components with independent amplitudes and phases (and the same frequency).
A circularly polarized wave may be resolved into two linearly polarized waves, of equal amplitude, in phase quadrature (90 degrees apart) and with their planes of polarization at right angles to each other."
- which sounds bloody confusing! :-)
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Thanks for that Mike, I much prefer the first 'simple' answer though, with the nice picture! :-)
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that initial picture is just a polarising diagram... circular polariser would show a different diagram...but depends on this polariser in the first instance
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The thing about a polariser is that it is basically the only filter that you cannot replicate in photoshop
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| Edited: 01/06/07 13:45 |
Mike, i guess the technology / theory behind both is quite similar though.
Chas, good point! I hadnt thought of it like that.
I haven't really had a chance to get out and use it yet though (only in the garden), as ive been too busy with uni work and still am for the next few weeks :-(
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 Just got a circular polerizer myself, well - I had a couple of others but they wouldn't fit any of my current lenses! Been wanting to get a new one for years as a result, and finally bit the bullet, destroyed the bank account and my Cokin Z Pro job arrived a few days ago!
Can't wait to use it
Just need something to use it on!!!!
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.jpg) Got one on my 'wish list' for my 400D !
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 Yes, I want one too. Have just bought a Nikon 18-200mm vr lens for my D40 (yep, the lens is bigger and cost more than the camera), so I'm planning to use this lens for just about everything, so - here it comes - I can now buy one filter; rather than filters for many different lenses. I'm going to check ebay for a circ polarizer soon, but should probably leave it until my wife has forgiven me for buying the new lens. Any advice on the pros and cons of different types of polarizing filters is welcome. It's going to be expensive I suppose, especially because the end of my lens is quite wide, 72mm. An aside. The sun came out today. Whooo! And, I've found there's a family of kingfishers at a lake just down the road from where I live. Watch this space.....
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| Edited: 19/01/08 14:38 |
 The Hoya ones were always good, I have one for my standard Rokkor lenses, but I've just bought a Vivitar one (S/H) and that seems OK too. I think any of the old recognised makes will do a good job.
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http://www.amazon.co.uk/Hama-Circular-Polarizer-Filter-72mm/dp/B00005K4A5 There's a £20 72mm one on Amazon from Hama... Rated 3/5 stars... But it's £20, not £80. 
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I just received my Hoya one from 7dayshop.com for £17.99 albeit a 58mm and I notice the 72s are about double the price, although Hama still only £17ish. It's a great website, though, for satisfying that need to buy something photographic without breaking the bank. I also notice that the Amazon link (sorry Mike) said '2-5' weeks - that usually means better try elsewhere, in my experience. So, as soon as we get some daylight, there's going to be a cornucopia of polarized piccies in the galleries, by the looks of it ....
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Most filters come from Germany... Stocks in the UK are a lot lower, so sometimes there will be delays. May be worth searching in Euros and seeing what you come up with. There's other places I found earlier around the same price as Amazon - including eBay (if you trust it).
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Thanks all. I've just ordered a 72mm Hama Circ Polarizer filter, from Aspen of Hereford (on ebay). I think it was £16.99, so will be approx £20 with postage. Looking forward to taking landscapes with it. Maybe it will work well on dragonflies, as the wings can reflect a lot. We'll see..... Should arrive tomorrow or Tuesday.
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A polarizer will also remove reflections from water so you can see right into it instead of just the reflections on the surface- same with windows, used at the correct angle. They usually work best at or around 90 degrees to the Sun.
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