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View Full Version : Circular Polarising filter use...?


theMusicMan
25th April 2008, 08:48 AM
Hey All

OK, I know, I know... this is a "dollard noobie to filters" question, but heck, if you don't ask you'll never learn eh!

My Cokin P filter set arrived this morning nicely in time for our weekend away in Bude, one of the filters I purchased was the circular polariser filter.

Now... the sky isn't reslly blue today, but how on earth does one know which way to align the filter when it's on the holder and lens? I can't see a mark on the filter that enables me to see which way the polariser is set to.

How do I know...? or have I totally missed the point and perhaps I should be able to see this if I have a decent image in the viewfinder instead of my back garden...:)

j.baker
25th April 2008, 09:38 AM
I dont think it matters. You rotate one element in order to adjust the polarisation effect.

theMusicMan
25th April 2008, 09:52 AM
Thats what I mean John - do I see the polarising effect through the viewfinder? If so, then fine, but if I don't then how can I see what the effect will be as it would be guesswork.

j.baker
25th April 2008, 10:06 AM
If you can see it then the camera can see it.

HughofBardfield
25th April 2008, 10:25 AM
It is entirely trial and error with a CP, I'm afraid. The amount of polarisation varies depending on the angle of the light. Generally speaking, the greatest effect is obtained when the sun is roughly at right angles to the lens. There's a useful summary here: http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/filter/polarizer.html

it also explores the other main use of polariser - controlling surface reflections.

One other point. Using a polariser with an very wide lens (like the 11-22 at the wide end) has to be done with caution, as the extremely large field of view will include light at different angles and may cause "banding" in the sky (eg, dark in the middle and lighter at the sides). If you have the standard P holder, you will also need to watch out for vignetting at 11mm. Cokin do a special wide angle version of the P holder - or you can do what I did and buy a Kood P holder (£2.99 + P&P from CrookedImaging on eBay) and chop the front slots off with a Dremmel! :-)

shenstone
25th April 2008, 04:47 PM
It is entirely trial and error with a CP, I'm afraid. The amount of polarisation varies depending on the angle of the light. Generally speaking, the greatest effect is obtained when the sun is roughly at right angles to the lens. There's a useful summary here: http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/filter/polarizer.html

it also explores the other main use of polariser - controlling surface reflections.

One other point. Using a polariser with an very wide lens (like the 11-22 at the wide end) has to be done with caution, as the extremely large field of view will include light at different angles and may cause "banding" in the sky (eg, dark in the middle and lighter at the sides). If you have the standard P holder, you will also need to watch out for vignetting at 11mm. Cokin do a special wide angle version of the P holder - or you can do what I did and buy a Kood P holder (2.99 + P&P from CrookedImaging on eBay) and chop the front slots off with a Dremmel! :-)

Graham is right in his description. You use it visually and decide the level and effect that you wish to get. The rule of thumb is that skies should be as dark as you can get them, but it's fun to break the rule at times. When looking to reduce reflections then you typically turn the filter until you get the balance you want.

In this shot in my gallery you can see the banding effect that Graham describes in the 11-22 @ 11. I liked it in this picture so left it.

http://e-group.uk.net/gallery/data/500/ny1.jpg (http://e-group.uk.net/gallery/showphoto.php/photo/1101)

The vignetting does happen with this lens. When I want to retain the full view and still use the filter I have to manually adjust the corners in post processing. To minimise this problem especially whenusing a screw in filter, remove any other filters before adding your cpl filter and buy one that is thin in construction.

BTW Your idea of a pointer would be no-use with lenses where the front of the lens rotates during focussing - you need to readjust after every focus event on such lenses

Hope that helps
Regards
Andy

theMusicMan
27th April 2008, 08:33 PM
Well, back now from an excellent weekend away. Not processed many images yet, but here's one I took with the polariser filter - my first with this filter type.

Thoughts... (be kind... it's a first with ANY filter, let alone a polariser!!)

http://www.reflectingme.com/img/v1/p754041787.jpg

Ray Shotter
27th April 2008, 08:48 PM
I think it is a well composed shot and the colour contrast (especially in the sky) is excellent. I shall have to use my polarising filter more. I have tended to use it only when I have wanted to avoid excessive reflection of light off water etc..

Ray.

HughofBardfield
28th April 2008, 10:23 AM
Very nice colours - very punchy!

Ian
28th April 2008, 01:05 PM
It is entirely trial and error with a CP, I'm afraid. The amount of polarisation varies depending on the angle of the light. Generally speaking, the greatest effect is obtained when the sun is roughly at right angles to the lens. There's a useful summary here: http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/filter/polarizer.html

it also explores the other main use of polariser - controlling surface reflections.

One other point. Using a polariser with an very wide lens (like the 11-22 at the wide end) has to be done with caution, as the extremely large field of view will include light at different angles and may cause "banding" in the sky (eg, dark in the middle and lighter at the sides). If you have the standard P holder, you will also need to watch out for vignetting at 11mm. Cokin do a special wide angle version of the P holder - or you can do what I did and buy a Kood P holder (2.99 + P&P from CrookedImaging on eBay) and chop the front slots off with a Dremmel! :-)

I've used the wide-angle Cokin P-holder with the 12-60 at 12mm without vignetting.

Ian