How to adjust a circular polarizer?

NeilL

I have a Hoya CP. It has a white dot on the adjusting ring, but no reference mark to show what the position of the mark means. Can anyone explain where to set this mark for getting most, to none, polarizing?

Thanks.
Neil

Mr. 2H2O

Here's something I read for the ones with the dot:

"The outer ring should have a white mark on it. When this is at the top (when filter fitted to lens) it is at max polarisation. 1/4 turn in either direction will put it to minimum pol."

I have a Heliopan and it has numbers - since I have P&S type with EVF, I look through my CPL in my hand and adjust the outer ring to find what I want as the effect, look at the orientation (specifically, which number is at the "12 o'clock" position), mount it, then turn the ring to match what I had done off camera. With a regular SLR, you should be able to do it with the CPL just mounted on the lens.

- Mike

NeilL

Mr. 2H2O wrote:

Here's something I read for the ones with the dot:

"The outer ring should have a white mark on it. When this is at the top (when filter fitted to lens) it is at max polarisation. 1/4 turn in either direction will put it to minimum pol."

I have a Heliopan and it has numbers - since I have P&S type with EVF, I look through my CPL in my hand and adjust the outer ring to find what I want as the effect, look at the orientation (specifically, which number is at the "12 o'clock" position), mount it, then turn the ring to match what I had done off camera. With a regular SLR, you should be able to do it with the CPL just mounted on the lens.

- Mike

Thanks for your reply!

Yes, I had a hunch that was how to do it. But you know, when I look through the CP on or off lens and turn it I don't see anything happening, ie everything looks the same. Should I be able to the effect of the CP?

cmason

NeilL wrote:

Thanks for your reply!

Yes, I had a hunch that was how to do it. But you know, when I look through the CP on or off lens and turn it I don't see anything happening, ie everything looks the same. Should I be able to the effect of the CP?

You doing this indoors? You won't see as much effect indoors, especially if there are multiple lights in the room. Go outside, and stand 90 degrees to sun. You will see it

NeilL

cmason wrote:

You doing this indoors? You won't see as much effect indoors, especially if there are multiple lights in the room. Go outside, and stand 90 degrees to sun. You will see it

Ah! So... I should be standing 90deg to the sun/light source?

It's night time here now, so I'll put your advice into practice tomorrow. Thanks!

Mr. 2H2O

cmason wrote:

You doing this indoors? You won't see as much effect indoors, especially if there are multiple lights in the room. Go outside, and stand 90 degrees to sun. You will see it

Yup - what he said. The polarizer will change the angle of light entering the lens. For instance, if you are trying to use it early morning or dusk, the light is pretty linear with your line of sight so it will have little effect - the light "waves" are bouncing off of stuff (reflected light) pretty much into your lens straight.

Toward late morning through mid afternoon, the sun is at a higher angle and the light "bounces" incidental to your lens so you want to use a polarizer to change that angle so become more "linear" coming into your lens. One of the biggest benefits shows up on reflections - you can change the angle of light coming into your lens and eliminate the reflections off a surface.

- Mike

Robinivich

If you have an LCD screen on a computer, camera, etc, it ought to show the effect as well, it's actually very pronounced, because LCDs use built in polarization to help control the light they emit.

NeilL

Fascinating stuff! Thanks!

I'm in Saudi Arabia, so plenty of sand and not much surface water with reflections. Wonder what a CP would do with a mirage?

But seriously, I've seen examples of how a CP can beautify the sky etc in landscapes, so I'm hoping it might improve those kinds of shots here.

mr peas

Hold the filter in place with your left hand, then rotate the camera around the filter with your right.

Haha. jk. Take the lens+polarizer outdoors like everyone else says, check out the sky while rotating the filter, then take a look at some reflection on water or glass and check out the difference when you adjust the filter.

Its almost like its voodoo!

Tanuki

NeilL wrote:

I have a Hoya CP. It has a white dot on the adjusting ring, but no reference mark to show what the position of the mark means. Can anyone explain where to set this mark for getting most, to none, polarizing?

Thanks.
Neil

If you rotate the polarizer until the dot is aiming towards a light source, the polarizer will have the maximum impact on reflections from that light source.

There is a lot more to using polarizers than this, but I think it answers your question.

Mike

Ric Grupe

Tanuki wrote:

If you rotate the polarizer until the dot is aiming towards a light source, the polarizer will have the maximum impact on reflections from that light source.

There is a lot more to using polarizers than this, but I think it answers your question.

Mike

In case you didn't know...don't wear polarized sunglasses at the same time...or you will go insane! Really.:D

claudermilk

Everyone makes it so complicated. I just rotate until the polarization effect I see in the viewfinder is what I want. I don't worry whether it's max, min, or somewhere in between. I jsut ask the question "is this the look I want for this image?" If yes, trip the shutter, if no, rotate some more. Simple.

rpcrowe

Look through your viewfinder...
Look through your viewfinder as you rotate the front ring on the CPL. You will see the difference with sky darkening and reflections reduced or eliminated if the light is at the correct angle.

A hint: When you see the maximum polarization, back off a smidgen (That's technical jargon isn't it?) That way the image will look a bit more natural. It is easy to over polarize a scene.

Additionally, I use a screw-in hood on most of my lenses and it is far easier to rotate the CPL with this type of hood than with most OEM bayonet types.

NeilL

Looks like CPs are more fun than I thought! Everything from going insane to twistin' with your gear...

Thanks to you all for an entertaining insight!

Neil

mercphoto

claudermilk wrote:

Everyone makes it so complicated. I just rotate until the polarization effect I see in the viewfinder is what I want. I don't worry whether it's max, min, or somewhere in between. I jsut ask the question "is this the look I want for this image?" If yes, trip the shutter, if no, rotate some more. Simple.

Agreed. Rotate until you get the effect you want. If you see very little change all that means is that you have relatively evenly scattered light. If you get a big change what that means is you have very polarized light.

http://en.wikipedia.org/wiki/Circular_polarizer

Polarizers are really pretty simple: they act like a filter that lets in light that is bouncing up and down in one particular direction and blocks light that is bouncing in the perpindicular direction. As you turn the ring on the CP all you are doing is changing which direction of waves you are allowing in. Its that simple.

Note that, by design, a CP blocks half the light entering the lens. No matter which direction you have the ring turned you are always allowing light in one direction and blocking light in the perpindicular direction. Half the light goes away. The other thing is that you only need to twist it 90 degrees to get the full range of effect. The effect just oscillates back and forth every 90 degrees of turn.

Usually light is randomly scattered, bouncing around in all directions. Up and down, left and right, diagonally at various angls. Some things can change that, such as reflections off metallic or shiny surfaces. Ever wonder why sunglasses are often polarized? Its because when driving your car you are often confronted with flat and reflective metallic and glass surfaces from the cars around you, and sometimes from the roadway, and diminishing those reflections makes your vision much better. And the reason why your sunglasses don't have an adjusting ring is because the direction of polarization in this situation is very predictable. Try this one day: put on your polarized sunglass while driving and then take them off, notice the difference. Now, put them on but tilt your head from side to side and notice the view change. This is analagous to rotating the ring on the CP.

One last note. The circular polarizer is probably the only filter whose effects cannot be replicated in Photoshop. Neutral density and Graduated filters are still useful, but if you don't have one you can replicate its effect in Photoshop after the effect. Not so with CPs.

Ric Grupe

mercphoto wrote:

Polarizers are really pretty simple: they act like a filter that lets in light that is bouncing up and down in one particular direction and blocks light that is bouncing in the perpindicular direction. As you turn the ring on the CP all you are doing is changing which direction of waves you are allowing in. Its that simple.

So...since it is so simple...would you say there is a general rule on how metering on the camera effects exposure with a CP attached?

mercphoto

Ric Grupe wrote:

So...since it is so simple...would you say there is a general rule on how metering on the camera effects exposure with a CP attached?

If the metering is done through the lens (as they all are now) then there is zero effect on metering. Its only if you meter externally that you need to worry about a one-stop difference.

claudermilk

...and that's why TTL metering is such a boon. No filter factors to worry about any more. :ivar

pyry

Ric Grupe wrote:

In case you didn't know...don't wear polarized sunglasses at the same time...or you will go insane! Really.:D

If that doesn't do it, try looking at a mirror through a cp. Then flip it back to front (not the way you normally use it).

NeilL

mercphoto wrote:

Agreed. Rotate until you get the effect you want. If you see very little change all that means is that you have relatively evenly scattered light. If you get a big change what that means is you have very polarized light.

http://en.wikipedia.org/wiki/Circular_polarizer

Polarizers are really pretty simple: they act like a filter that lets in light that is bouncing up and down in one particular direction and blocks light that is bouncing in the perpindicular direction. As you turn the ring on the CP all you are doing is changing which direction of waves you are allowing in. Its that simple.

Note that, by design, a CP blocks half the light entering the lens. No matter which direction you have the ring turned you are always allowing light in one direction and blocking light in the perpindicular direction. Half the light goes away. The other thing is that you only need to twist it 90 degrees to get the full range of effect. The effect just oscillates back and forth every 90 degrees of turn.

Usually light is randomly scattered, bouncing around in all directions. Up and down, left and right, diagonally at various angls. Some things can change that, such as reflections off metallic or shiny surfaces. Ever wonder why sunglasses are often polarized? Its because when driving your car you are often confronted with flat and reflective metallic and glass surfaces from the cars around you, and sometimes from the roadway, and diminishing those reflections makes your vision much better. And the reason why your sunglasses don't have an adjusting ring is because the direction of polarization in this situation is very predictable. Try this one day: put on your polarized sunglass while driving and then take them off, notice the difference. Now, put them on but tilt your head from side to side and notice the view change. This is analagous to rotating the ring on the CP.

One last note. The circular polarizer is probably the only filter whose effects cannot be replicated in Photoshop. Neutral density and Graduated filters are still useful, but if you don't have one you can replicate its effect in Photoshop after the effect. Not so with CPs.

Good post. Thanks!

NeilL

pyry wrote:

If that doesn't do it, try looking at a mirror through a cp. Then flip it back to front (not the way you normally use it).

Yes, flipping back to front while looking at a mirror through a CP in a way you don't normally really does seem it would produce, if not require, a little insanity (and do awful things to your neck)! (PS I know what you mean!)

pyry

NeilL wrote:

Yes, flipping back to front while looking at a mirror through a CP in a way you don't normally really does seem it would produce, if not require, a little insanity (and do awful things to your neck)! (PS I know what you mean!)

A bit of cognitive instability does miracles for creative expression. Just ask Van Gogh's ear.

Seriously, try that mirror thing, if you haven't already. I'll bet a picture of a pie the effect catches you by surprise

NeilL

pyry wrote:

A bit of cognitive instability does miracles for creative expression. Just ask Van Gogh's ear.

Seriously, try that mirror thing, if you haven't already. I'll bet a picture of a pie the effect catches you by surprise

Yep, I guess VG would have been a bit unbalanced after losing that bit off one ear. But the adjustments necessary bear no contemplation! Better to go with creative expression, I agree!

If you don't hear more from me you'll know I've been caught by surprise (or taken away)!!

pyry

NeilL wrote:

Yep, I guess VG would have been a bit unbalanced after losing that bit off one ear. But the adjustments necessary bear no contemplation! Better to go with creative expression, I agree!

If you don't hear more from me you'll know I've been caught by surprise (or taken away)!!

You know the song don't you? :lol

They're coming to take me away, Hahaa!
They're coming to take me away, Hohoo!
To the funny farm
Where life is beautiful all the time
And I'll be happy to see
Those nice, young men
In their clean, white coats
And they're coming to take me away, Ha-haaa!

Now, I'm not completely off my trolley, I'm just kickin' for more speed.

NeilL

pyry wrote:

You know the song don't you? :lol

They're coming to take me away, Hahaa!
They're coming to take me away, Hohoo!
To the funny farm
Where life is beautiful all the time
And I'll be happy to see
Those nice, young men
In their clean, white coats
And they're coming to take me away, Ha-haaa!

Now, I'm not completely off my trolley, I'm just kickin' for more speed.

Yes, this *applies* at times...!!

As far as 'hard' is concerned, as the sailor said to the doubtful lass, "Babe, it's gotta be!"

OsirisPhoto

Another use for CP filters.. place two together (one reversed) and rotate one.. voila, the mother of all light filters :ivar

Handy for taking shots of really bright things... like the sun. Not quite 'neutral density'.. but interesting light stopping ability.

pyry

Hyperbaric wrote:

Another use for CP filters.. place two together (one reversed) and rotate one.. voila, the mother of all light filters :ivar

Handy for taking shots of really bright things... like the sun. Not quite 'neutral density'.. but interesting light stopping ability.

Hey we're back on topic again! That was a fun little tangent.

Yup. You could do that with a cp and a linear polarizer, that way you don't have to fit the other filter on backwards. You still get a variable nd from nearly transparent to lots-and-then-some optical densities

NeilL

Hey, Hyperbaric & pyry - CPs are a lot more fun than I expected, as I said!

When I look through my window with the CP with the dot on top, and then rotate it 90deg, the dust on the outside of the window glass becomes less visible and the view through the window is much clearer. I would have expected the opposite if the polarizing is max with the dot on top?

mercphoto

NeilL wrote:

I would have expected the opposite if the polarizing is max with the dot on top?

Personally I think your documentation is wrong with respect to "max" and such. The CP is ALWAYS blocking 50% of the incoming light. All you change is which orientation of light is being blocked at the moment. One way to verify this is to slowly rotate the CP and see if the viewfinder grows brighter and darker.

pyry

mercphoto wrote:

Personally I think your documentation is wrong with respect to "max" and such. The CP is ALWAYS blocking 50% of the incoming light. All you change is which orientation of light is being blocked at the moment. One way to verify this is to slowly rotate the CP and see if the viewfinder grows brighter and darker.

The dot shows the direction of the polarizing whatsit. Light with a polarization axis in that direction passes through. Light with it's polarization at right angels to the filter's is blocked completely.

Therefore, incident light which has all polarizations mixed together is simply dimmed a bit regardless of how you turn the filter.

Polarized light, like what you get from the sky 90 deg away from the sun or relfected light from say, a water surface, can be passed as is or dimmed or even blocked depending on how you turn the filter.

Tanuki

NeiL wrote:

When I look through my window with the CP with the dot on top, and then rotate it 90deg, the dust on the outside of the window glass becomes less visible and the view through the window is much clearer. I would have expected the opposite if the polarizing is max with the dot on top?

The max effect is when the dot is aimed at the source of the reflected light. Not sure why your polarizing filter is having an effect on dust on the window, unless the "dust" has specular reflections. It's possible I guess, and based on your description is must be illuminated from the side.

mercphoto wrote:

Personally I think your documentation is wrong with respect to "max" and such. The CP is ALWAYS blocking 50% of the incoming light. All you change is which orientation of light is being blocked at the moment. One way to verify this is to slowly rotate the CP and see if the viewfinder grows brighter and darker.

Actually, polarizer filters block 50% of unpolarized light (not exactly, but close enough for this discussion). For polarized light, the polarizing filter can block anywhere from 0% to 100% depending on the angle of the filter to the angle of the polarization (once again, not exactly but close enough for this discussion). So the amount of light that is blocked depends on how much of the light entering your camera is polarized and what is the angle of the filter to the angle of the light polarization.

Mike