Circular polarizer question

[amature]

Just purchased a circular polarizer and noticed that the outer ring has an index line on it and the outer ring turns 360 degrees. I assume turning the ring changes the polarizing effect but what direction should the index line be for min / max effect, assuming it changes something.

[kenmyers70]

The simplest answer is turn it until you get the effect you want.

[andyz]

The line is just a point of reference. In reality I'm looking through the viewfinder and selecting the view I want, not watching the line of checking it against another shot.

[lhdvies]

I also find the best way is to see what you like thru the viewfinder and not worry about right angles, guide lines etc.

[amature]

Thanks for the feedback, seems like I overlooked the obvious! Now I feel stupid.

[Dobick]

I don't know very much about polarizers, so I can't be much help on this topic, except to maybe ask a bit of a clarification on your behalf.

While the end result may very well be, look until you see what you like, my understanding is that there are a set of guidelines on how to go about starting, something like the line should point 90 degrees from the sun or light source for the strongest effect.

As I said, I haven't used one, but I have read some recommendations in the past, which might be a good starting point.

My personal preference is to at least know what the rules are before I go and decide to break them.

Maybe someone with years of experience can chime in with what the original guidance on why it is there, and then close with how it is best used (ie completely ignored)

In a world of digital, it has always helped me to start with structures and break beyond those as I get comfortable with them.

[Angelo]

Originally Posted by amature

Thanks for the feedback, seems like I overlooked the obvious! Now I feel stupid.

Never feel stupid. We are all learning.

A polarizer has other uses besides turning the sky blue. The colors are richer for one, and when you want to reduce outside light to create a special effect.

[CaptainTom]

because you are affecting a visible light spectrum you will be able to see the effect through the viewfinder. Just like putting on polarized sunglasses. It cuts down on the reflectivity depending on the angle of the source light (sun). The bezel rotates to give maximum alignment to the lenses and to let you control the amount of polarization you want. Take two sets of polarized glasses and look through one while holding the other in front of your lens. Rotate the second lens and you will notice that at a certain point the light is almost completely blocked. Voila ! polarization.

[kenw]

easy-quick method to see if it MIGHT be helpful (other than putting it on...):

make a "pistol" with your hand, index finger as barrel, thumb as hammer.

make sure the hammer and barrel are at 90 degrees to each other.

aim barrel at subject

now: can you twist your wrist to point the thumb/hammer at the sun, keeping the barrel pointing at the subject?

yes? if could help.

[kenmyers70]

OK a little physics background may be in order here.
Lets think of light as a wave in a rope. If the rope is vibrating up and down we say the polarization is up/down. Now string the rope through a picket fence. You will still be able to vibrate the rope up/down but not left/right. Rotating the fence would let more or less of the up/down vibrations through. The fence is acting as a polarizer. The cool part is that sunlight is initially unpolarized, it vibrates in all directions. Light scattered by the atmosphere (the blue light we see) tends to be more strongly polarized in one direction. So rotating the polarizer lets us choose whether we select the blue part or not. Light reflected off of surfaces is also strongly polarized into the same plane as the surface. This is how the cool fishing glasses work. The filter out the light reflected off of the surface while letting the unpolarized light from below the surface through. My guess is that the line on your CP corresponds to the direction of polarization. Test it. Look at the reflection of light off of a smooth surface. My guess is that you will see the maximum reflection when the little mark is horizontal and the minimum when it is vertical. The CP then becomes very useful for knocking down glare from surfaces. If you are careful you can tune the two light sources like I did here:

I hope this helps.

[kenmyers70]

Originally Posted by kenw

easy-quick method to see if it MIGHT be helpful (other than putting it on...):

make a "pistol" with your hand, index finger as barrel, thumb as hammer.

make sure the hammer and barrel are at 90 degrees to each other.

aim barrel at subject

now: can you twist your wrist to point the thumb/hammer at the sun, keeping the barrel pointing at the subject?

yes? if could help.

Excellent. The idea behind this is that since light coming directly from the sun is unpolarized, the polarizer would have little effect pointing directly toward or away from the sun.

[Dobick]

Originally Posted by kenmyers70

OK a little physics background may be in order here.
Lets think of light as a wave in a rope. If the rope is vibrating up and down we say the polarization is up/down. Now string the rope through a picket fence. You will still be able to vibrate the rope up/down but not left/right. Rotating the fence would let more or less of the up/down vibrations through. The fence is acting as a polarizer. The cool part is that sunlight is initially unpolarized, it vibrates in all directions. Light scattered by the atmosphere (the blue light we see) tends to be more strongly polarized in one direction. So rotating the polarizer lets us choose whether we select the blue part or not. Light reflected off of surfaces is also strongly polarized into the same plane as the surface. This is how the cool fishing glasses work. The filter out the light reflected off of the surface while letting the unpolarized light from below the surface through. My guess is that the line on your CP corresponds to the direction of polarization. Test it. Look at the reflection of light off of a smooth surface. My guess is that you will see the maximum reflection when the little mark is horizontal and the minimum when it is vertical. The CP then becomes very useful for knocking down glare from surfaces. If you are careful you can tune the two light sources like I did here:

I hope this helps.

Thank you very much for this.

I don't know if it helps the original poster or not, but it sure does help me in understanding what they do!

[Jim Victory]

Another way to check the effect is to half press the shutter while turning the pol. and observe the change in shutter speeds through the viewfinder. This lets you know how much light is being transmitted through the pol.

I use the exposure needle on old film cameras to let me know how much pol. effect was being applied. It would fluxuate depending on how much light was being transmitted through the pol.

[amature]

Thanks for all that posted. Excellent information, appreciate all the help I can get.

[rexster314]

One other thing, when shooting outdoors, don't use polarized sunglasses with the polarizing filter on the camera, you'll get all kinds of weird results.

Rex