Very very and I mean VERY silly question about Circular Polarizing Filters

D.S.

D.S.

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I bought a Hoya Circular Polarizing Filter for these bright sunny days, on fitting and playing a bit I noticed the glass turns independently of the body. It has a white mark at a position.

What do I do with this? Point it towards the sun, or up, or down?

DO'H :bonk::bang::thinking:
 
No such thing as a silly question :)

You point the white mark at the sun. The filter works best when you shoot at 90 degrees to the sun i.e. with the sun in the 3 or 9 o'clock position if the lens is pointing at 12 o'clock.
 
If you look through the viewfinder and twist the CPL you'll notice the "effect" changes. No idea what the technical in and outs are exactly but I'm sure someone will be along soon to explain.......

One thing worth noting, as the AF turns the filter round it changes the "effect" so it's best to lock the focus first, then turn the CPL to how you want it. I think that's how it works anyway........
 
You rotate it until it gives you the effect you want.

Two simple ways to try it out:

1. On a bright day with a blue sky and fluffy white clouds, point the camera at a scene including plenty of sky and with the sun to your left or right.
Rotate the polariser. As you rotate it, you will notice the sky gets dark then light again.
The point at which the sky is darkest is at it's fully polarised point. If you take a picture you will get saturated blue sky with nice white, well defined clouds. Take a picture with the polariser showing a light sky and you will get a pale blue sky. Compare the two images to see what I mean.

2. Polariser can also be used to remove reflections. Find a shiny surface such as a car windscreen or a shop window. Look at it through the camera and rotate the polariser. You will see that the reflections disapear and return again depending on the polariser's position. This will also work on reflections on water and bright reflections on foliage.


Steve.
 
Here's a good one with a polariser...

Point it at a laptop screen (has to be LCD I think) and turn it around...
Then turn it around (so it's facing toward you) and do the same thing.....
 
Slimbert said:
One thing worth noting, as the AF turns the filter round it changes the "effect" so it's best to lock the focus first, then turn the CPL to how you want it. I think that's how it works anyway........
Click to expand...

end of my lenses don't spin with AF :/
 
So how do you use one of these with a lens with a rear filter. Is it still the same or is the effect different?

Kev
 
Kev said:
So how do you use one of these with a lens with a rear filter. Is it still the same or is the effect different?

Kev
Click to expand...

Now that's a good question - how would you rotate it? :thinking:

And from my limited knowledge, they work by blocking light from certain angles, so if it's at the back of the lens, the majority of light is coming in at the same angle, right?
 
OutLore said:
And from my limited knowledge, they work by blocking light from certain angles, so if it's at the back of the lens, the majority of light is coming in at the same angle, right?
Click to expand...

That's my reasoning also, but not as eloquently thought through though :thinking: , hence the question about if the effect is different, or even any effect at all?

Kev
 
would you get away with a linear polariser with a rear filter lens?
 
Slimbert said:
I thought it was linear for film and circular for digital? Could be talking out of my rear again.......:shrug:
Click to expand...

no not talking out of your rear i read up on it only yesterday lol some digital can take linear from what i read so i wondered reading this thread if a linear would work on a rear filter lens
 
Kev said:
So how do you use one of these with a lens with a rear filter. Is it still the same or is the effect different?

Kev
Click to expand...

The effect is the same. The rear filters for long Canon lenses, (and I assume Nikon) come with a knurled wheel to rotate them. Not sure of current price
but were well over £200.
C
 
It doesn't matter if the filter is on the front or the rear as far as polarising is concerned. The direction of polarisation rotates around the centre line of the lens. e.g. vertical would be top to bottom, horizontal would be left to right.

A linear polariser is the simplest form. Circular polarisers cut out the polarised light then 'randomise' it again. The reason for this is that some cameras use integral polarisers for the lightmeter (and possibly focus) systems so the circular polariser ensures there is always some light to work with.

Nothing to do with film/digital as some newer and current film cameras also need the circular polariser.


Steve.
 
OutLore said:
And from my limited knowledge, they work by blocking light from certain angles, so if it's at the back of the lens, the majority of light is coming in at the same angle, right?
Click to expand...


The polariser works by blocking light at certain wavelengths, not certain angles.

Colour is created by a surface and the light wavelengths that it reflects and absorbs. A polariser works by absorbing the light wavelengths that are creating the glare and letting through the remaining wavelengths of light. Hence you can minimise the shine on water and then see the reflected image on the water surface.
 
Glad you asked this... I've just picked one up. Sorry MG TF 135... polarisers block angles of light, not wavelenghts. I can't get my head around how a CPL actually works though... but it doesn't really matter, it's the end result that counts. Having had a quick play.. cheers for the LCD screen tip I can see the effect and what a difference on blue skies...
 
jgs001 said:
I can't get my head around how a CPL actually works though....
Click to expand...

I know what they do but I haven't looked into how they do it.

It doesn't really matter though as as far as the image is concerned, a linear or circular polariser has the same effect.


Steve.
 
Am I the only person to have had Polaroid ( polarised) sunglasses. I leant how they work by looking at rivers and tipping my head from side to side to see the fish under the surface!
They used to play havoc with the old "Zebrazone" windscreens too........

Allan
 
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