Polarizing Filters

Hi.
Polarizing filters are best used at righ angles to the sun for dark blue skys
if you use them with the sun in front or back of you there is not much
effect.
Phil.

Legends 06, just a polarizer not PS.

This is what happens if your not at right angles to the sun, the upper right hand side of the pic is Polarized the left side is not.

Wow thanks for all your help, one last question though I also have a skylight filter which was bought for me as a present, could I use them both at the same time or is that pointless or is one better than the other?

Mr A,How does this change in effect of the filter occur? – It’s a long time since I was at school, but somewhere deep in my memory of A-level physics is the fact that polarising lenses/filters block out light waves that have anything other than a fairly narrow plane of orientation of their wave form (normal light sources produce light in which the waves oscillate in all possible planes about the axis as they travel between source and viewer). By reducing the orientation of the plane of the waves, different results can be seen.

That’s why if you get a pair of polarised lenses (or filters), hold them in front of each other like an ad hoc telescope but a few inches apart, then view a light source through them both, by rotating one of the lenses/filters you can actually reduce the amount of light getting through, and even end up with almost no light at all, i.e. the light source is shut off. This occurs because the first lense restrict the passage of all light except that in a narrow plane of wave form. The now-planar light waves allowed through the first lense then reach the second lens which is orientated at right angles to the first, thus effectively preventing transmission of the planar waves that are at right angles to it’s permissible range, so very little light gets through the second lens. (Its akin to trying to post a letter through a letter box when the letter is held at 90 degrees to the letter box slot.).

Incidentally this is always a quick way to check if cheap “polarising” sunglasses on the local market stall are indeed polarised, hold two pairs up one in front of one another, and rotate one pair – at some point in the rotation the lenses should appear to go very dark. If they do not , then at least on set of the sunglasses is not actually polarised.

Here endeth the lesson….No doubt someone else can explain it properly, but it does prove that orientation of a polarising filter may change the effect it produces.

Paul F

Yes, absolutely. The light emitted from LCD computer monitors is polarised, so if you rotate a polarising filter in front of your monitor, when it hits 90 degrees from your screen, it disappears!

Paul

Polarising filters, a tip…

Mr A,

One thing to look out for is finding the optimum “orientation” of the filter in any situation, assuming it can be rotated once fitted to the lens/holder.

I’ve used a polarising filter occasionally with 35mm SLRs for years, and by rotating the filter itself within it’s mount (my set up is/was a Cokin filter system if that means anything to you) I found I could vary the degree of “effect” of the same polarising filter.

While this may be a marginal benefit/effect, it does make a difference to the degree of enhanced “blueness” of the sky etc, and might have a similar effect in terms of degree of reduction of glare highlights off perspex etc.

If the “lens” of the filter cannot be rotated once in place on the camera/lens, you can always try rotating the whole camera and lens itself between “landscape” and “portrait” positions, this may change the effect obtained with the filter. Later processing in Photoshop (or similar) can always allow you to “re-crop” back into the preferred image shape/orientation.

How does this change in effect of the filter occur? – It’s a long time since I was at school, but somewhere deep in my memory of A-level physics is the fact that polarising lenses/filters block out light waves that have anything other than a fairly narrow plane of orientation of their wave form (normal light sources produce light in which the waves oscillate in all possible planes about the axis as they travel between source and viewer). By reducing the orientation of the plane of the waves, different results can be seen.

That’s why if you get a pair of polarised lenses (or filters), hold them in front of each other like an ad hoc telescope but a few inches apart, then view a light source through them both, by rotating one of the lenses/filters you can actually reduce the amount of light getting through, and even end up with almost no light at all, i.e. the light source is shut off. This occurs because the first lense restrict the passage of all light except that in a narrow plane of wave form. The now-planar light waves allowed through the first lense then reach the second lens which is orientated at right angles to the first, thus effectively preventing transmission of the planar waves that are at right angles to it’s permissible range, so very little light gets through the second lens. (Its akin to trying to post a letter through a letter box when the letter is held at 90 degrees to the letter box slot.).

Incidentally this is always a quick way to check if cheap “polarising” sunglasses on the local market stall are indeed polarised, hold two pairs up one in front of one another, and rotate one pair – at some point in the rotation the lenses should appear to go very dark. If they do not , then at least on set of the sunglasses is not actually polarised.

Here endeth the lesson….No doubt someone else can explain it properly, but it does prove that orientation of a polarising filter may change the effect it produces.

Paul F

A polarizer is also useful in cutting down unwanted reflections, eg sun glinting of canopies. Best thing to do is just try it in as many different positions and see what the results are like. At least with a digital you can get instant feedback, and you’re not using up film on test shots. Just go out and have some fun!

William

im guessing the rule of thumb is nice bright day use it, dull day dont. is that about right?

Pretty much. All a polarising filter will do on a dull day is make things even duller! You’ll have fun with it on those wonderful sunny days though. 🙂

Paul

It only cost me 3 quid on ebay so even if its crap its no biggy, thanks for your answers im guessing the rule of thumb is nice bright day use it, dull day dont. is that about right?

If the 5600 only goes down to 200 asa like its predecessors then you’ll find anything that cuts down the light entering the camera very useful on bright days.

The 5600 goes down to ISO 64. 🙂

Paul

Polarising filters are wonderful, but are only really of any use under certain conditions, those generally being when it’s sunny! Essentially a polarising filter darkens blue skies increasing contrast between clouds and the sky itself, and increases colour saturation. I’ve never used one for aviation photography because my main lens has an 86mm thread and filters that size cost a fortune, but I’ve used one a lot for landscape-type photography and it can really bring your images to life.

A word of warning though… Because it is basically allowing only a part of the light hitting your camera to get through to the lens you’ll lose around 2 stops, but as polarising filters are generally most beneficial in good, bright light this shouldn’t be a problem as long as whatever you’re shooting doesn’t move too fast!

Paul