My circular polarizing filter doesn't seem to have a very wide change spectrum?

[iris]

Do circular polarizing filters come in various strenghts or ranges of change?  ARe all C-polarizing filters the same?  Yes, I know how to use them. I know the 90degree angle to the sun and all that ...I feel that I should be able to rotate the filter and see through the lens excactly what the change will be...frankly I find it very difficult to see the amount of change in the blue of the sky using the filter that I have....shouldn't you be able to rotate the filter and observe the change gradations?  Shouldn't they be obvious as in a ND filter?  Should I ask for a "stronger" polarizing filter?

[Skirball · Accepted solution]

Polarizers can have different strengths.  Technically they should all be similar, since theoretcially they should eliminate all waves perpendicular to the axis.  But that's theoretical, and cheap polarizers might not be efficient.  What brand?

It's unlikely it's a complete fake, but I wouldn't be totally surprised if you bought a cheapo somewhere.  I've seen plenty of polarized sunglasses that aren't.

One thing: technically it's not 90 degrees to the sun, it's 90 degrees to a reflected surface.  The reflection has become polarized, which allows the polarizer to block it.  The effect on blue sky can vary, depending on how much reflection (haze) there is in the sky.  The best way to check that it's working is to look at sunlight reflecting off of something, like a shiny object.

[ebiggs1 · Accepted solution]

Polarizing filters do increase color saturation.  You should be able to see it in your view finder and LCD display.

A good way to visualize how this works is to aim your pointer finger at the sun while holding your thumb straight up. Everywhere your thumb points when you rotate your hand (while still pointing it at the sun) is where the polarizer will have the strongest effect. They require the camera to be pointed at a right angle to the sun for maximal effect.

The problem is all color saturation is not equal.  It can vary and not be uniform across the frame.  Another is when used on a wide angle or UWA lens the effect can be less.  Which can make it quite difficult to see the effect in a viewfinder or LCD screen.  Cheap ones can degrade IQ.

If I missed anything maybe Tim can help me out.  This is right up his alley. 

[ebiggs1 · Accepted solution]

It is easy.  Basic set up. Take three or more exposures.  One under, one correct and one over exposed.  You need a post editor.  I like and use Photomatrix Pro.  It automaticly stacks the exposures and applies the correct settings.  Plus it has other features for further adjustments.

There is a free trial version.  BTW, Photoshop can do it, too.

[kvbarkley]

No, you are not correct. It is because you need to use a circular polarizer instead of a linear polarizer. Linear polarizers interact with the phase detect auto focus. Circular polarizers don't affect focus, but they don't work as well either.

[Waddizzle]

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@kvbarkley wrote:

No, you are not correct. It is because you need to use a circular polarizer instead of a linear polarizer. Linear polarizers interact with the phase detect auto focus. Circular polarizers don't affect focus, but they don't work as well either.

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When it comes to linear vs circular, I think one is just as bad as the other.  I think both wreak havoc with AF systems.

[ebiggs1]

" I think both wreak havoc with AF systems."

Perhaps not "havoc" but you are certainly correct.  The exposure issue can be as bad or even worse. Again, for the record all polarizers are linear, otherwise they would not work at all. They just have an additional layer or filter if you will included.

[ebiggs1]

I will add with the possible exception of reflection from water or windows, etc, the ploarizer filter, as is all other filters, possible exception of the ND filter, are obsolete. Post editing and digital files have rendered them largely irrelevant.

[shawnphoto]

Filters are not obsolete. Not even close.

First of all, when you capture an image that is filtered by a real glass filter you capture the image how you want with 100% of the detail possible by the sensor. 

If you rely solely on editing, you have to crush details to get the "look" you want. 

In reality, there is usually not a lot of detail in the highlights of an image, editing that is a huge pain. And if you do go through all that trouble the end result is a lower quality image.

There's also the issue of time. With a polarizer you can greatly reduce highlights and reveal color and detail without having to take the time to edit every single picture.

Also, when using filters I tend to get a more consistent look from shot to shot vs. relying on editing alone.

Plus it's kind of fun using filters.

Anyway, hope this helps!

[ebiggs1]

"...when you capture an image that is filtered by a real glass filter you capture the image how you want with 100% of the detail possible by the sensor."..."If you rely solely on editing, you have to crush details to get the "look" you want."

Shoot Raw format, solves that issue. Second take a course in Photoshop.

"Plus it's kind of fun using filters."

Just as much or more so to watch your image develop from a good to great photo.  This is no different than our old darkroom abilities. But some folks did just drop their film off at the drug store and picked up the prints a week later?

I agree there are a few, very few, instances where certain filters can be useful but otherwise they are largely obsolete. I must have 25 or 30 filters of all kinds and types sitting on the formerly stop bath stained shelves of my old darkroom.  They have been sitting there for years and years!

[jimmy1]

What size? Any 77mm, 62mm, or 58mm? I'm always looking for cool filters. I'll pay.

" I must have 25 or 30 filters of all kinds and types sitting on the formerly stop bath stained shelves of my old darkroom. They have been sitting there for years and years!"

[ebiggs1]

DSLR cameras have a mirror which is the cause of the problem. A linear polarizer can cross polarize, causing the image to darken or go completely black. Simular to an ND filter. Our old film SLRs used fully reflecting mirrors.  Meaning they had mirrors that reflect all polarized light with equal intensity to a point. DSLRs with autofocus use partial reflecting mirrors. The reduced reflected light, the key point here, goes to the viewfinder and metering systems.  And, some light goes on to the auto focus sensors.  This reduction can cause exposure errors and/or autofocus errors.

All circular polarizer filter are linear.  They just have an additional layer that "spins" the light, so to say. This fixes the exposure and focus errors or at least reduces them to a non-critical level. Will a plain linear polarizer work on a DSLR, yes, it will since the mirror is completely out of the way of the sensor when the photo is actually taken. However, you run the risk of the exposure or auto focus errors.

Perhaps a little simplistic but that is the basic idea.