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07-22-2009, 05:38 PM   #16
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B+W Kaesemann Polarizers are very good.

Some info from the Schneider Optics web site:

The “high-end” polarizing foils of the Käsemann-type filters are neutral in color, they have a higher efficiency than conventional polarizing foils and they are cemented between high-grade plano-parallel optical glass. The resulting sandwich is then precision-polished again to achieve highly accurate plano-parallel surfaces. Subsequently they are edge-sealed to protect the foil against humidity. Brass mounts made on CNC-controlled machines ensure precise seating on the lens. Discriminating photographers regard the B+W Käsemann-Type Polarizing Filter to be the very best of all polarizing filters. They are well suited for applications that require the highest possible imaging quality, especially with high-speed telephoto lenses and apochromatic lenses.

07-22-2009, 05:54 PM   #17
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I don't claim to be an expert in these matters, but I don't think any filter will make the sky bluer..... I think only Mother Nature can accomplish this feat. You can, however, have the sky APPEAR bluer with a Polarizer filter taken at the correct angle.
07-22-2009, 09:35 PM   #18
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QuoteOriginally posted by raymeedc Quote
I don't claim to be an expert in these matters, but I don't think any filter will make the sky bluer..... I think only Mother Nature can accomplish this feat. You can, however, have the sky APPEAR bluer with a Polarizer filter taken at the correct angle.
Very true, you are just removing light reflections with a Polarizer. The sky is still the same blue as it has always been.
07-23-2009, 10:38 AM   #19
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QuoteOriginally posted by vmax84 Quote
Any suggestions for my 49mm manual focus lens and 52mm for my autofocus kit lens? I've looked around, and there are just so many choices.

vmax84
Get a good quality Hoya Pro or B&W 52mm polarizing filter and a "49mm to 52mm" adapter ring.

07-23-2009, 03:15 PM   #20
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Amazon.com: Tiffen 52mm Circular Polarizer: Electronics

I ended up ordering this one yesterday. I really appreciate the good advice and input, and thought for the time being, I'd try it "on the cheap" and see how it goes.

Like most things I do, why "measure twice and cut once", when you can just get the chainsaw out and start cutting.

Thanks again and I'll keep you posted on how things go. Should get the polarizer Friday or Saturday.

vmax84
07-23-2009, 03:43 PM   #21
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QuoteOriginally posted by geauxpez Quote
Playing with effects? Here's a neat trick: If you are shooting a relatively close subject against a blue sky, you can change your white balance setting to tungsten -- that will make the skay an electric blue. Then use a flash with a CTO gel (orange filter) to light your subject. Your subject will be colored normally and your background will be VERY blue.
I tried switching over to tungsten........you're right, very cool and very fun!! These cameras have SO much capability in the right hands.

vmax84
07-23-2009, 05:57 PM   #22
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QuoteOriginally posted by gofour3 Quote
Very true, you are just removing light reflections with a Polarizer. The sky is still the same blue as it has always been.
Well, of course, you are not having an effec ton the actual sky as seen by the rest of the world. But a polarizer *does* effect the appearance of the sky in a photo (or can, anyhow, depending on how it is used). The standard explanation is that the sky consists of polarized reflections, so a polarizer at the right angle cuts out a lot of those light rays just as it does for other reflections, yielding a darker sky.
07-24-2009, 03:49 AM   #23
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In my experience a gradient neutral density filter yields more uniform results than a polarizer regarding making the sky's blue color deeper.

The polarizer only helps when the sun is at your side.

I think the polarizer's effect actually does make the sky bluer...

QuoteOriginally posted by http://www.polarization.com/sky/sky.html:
The blue lineage is more likely to have been scattered multiple times than does the red part of the spectrum. As multiple scatterings destroy the polarization of light, blue light is less polarized than other colors in skylight.

Thus, by aligning a polarizer so it blocks the polarization of the sky its blue color is enhanced (but darkened). Photographers frequently use polarized filters on their cameras to capture skies that look more saturated than to the unaided eye.
The above says that more non-blue light is removed by the polarizer; less "non-blue" means "more blue" ie. "bluer". I'll try to measure this & let you know the results.

Dave in Iowa


Last edited by newarts; 07-24-2009 at 04:13 AM.
07-24-2009, 04:11 AM   #24
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Do it during post processing with a software like Photoshop or Lightroom... dead easy, infinitely variable, repeatable and free
07-24-2009, 04:14 AM   #25
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Others have mentioned it, but circular polarizers work best when used perpendicular to the sun's rays. If the sun is high in the sky or you are shooting into the sun, you won't have much difference. However, they can give some amazing results.
07-24-2009, 04:43 AM   #26
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Here's a brief analysis of the effect of a polarizer on the "blueness" of the sky. The fisheye photo was taken pointing straight up at susnset (sun on the right.) A polarizing filter was used with the polarizer aligned along the east-west axis (horizontal diameter).

The ImageJ graphs to the right of the photo are the red, green, and blue components of the light across the diameter of the photo (ie. from east to west). Compare the relative red, green & blue intensities at the peak on the left with that in the valley; there's a greater fraction of blue in the valley - ie. the sky is about 20% "bluer" as well as darker.

Dave

PS This fisheye photograph (hi-res) of the full sky at sunset was kindly provided by Forrest Mims of electronics authoring fame. He took it from his South-Central Texas Observatory using a polarizing filter aligned East-West. The roughly North-South line of dark blue sky shows where polarization was at its maximum. As the title of that country-western song not yet written says: "the skies of Texas are bluest for the cowboy with sunglasses and no blues to sing."

Mims will grant use of this picture for noncommercial use by students and individuals so long as acknowledgment is given. If you are interested in computers, you should read his first-hand account of the history of Altair, the first commercial personal computer, at his site Forrest M. Mims III.


see: The polarization of the sky

Disclaimer I am no expert on these topics and the conclusions I offer are just observations based on ad-hoc measurements of data drawn from whatever sources are handy. I avoid saying things I can't justify with actual measurements, but that doesn't guarantee correctness.

I've learned an awful lot doing these measurements/analyses; before this morning, I thought a polarizer's effect was to darken some of the sky, not to change its color! Amazing what can be discovered when one measures rather than assumes.

Last edited by newarts; 07-24-2009 at 07:51 AM. Reason: Added quantitative estimate of "bluer" & Disclaimer
07-24-2009, 04:53 AM   #27
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In my experience a gradient neutral density filter yields more uniform results than a polarizer regarding making the sky's blue color deeper.

The polarizer only helps when the sun is at your side.
07-24-2009, 04:27 PM   #28
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A graduated Blue filter works too. I have one. But it is limited in use.
.
07-25-2009, 03:18 AM   #29
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Besides a filter, think about the time of day. Don't shoot at high noon.
07-25-2009, 05:24 AM   #30
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Polarizer makes sky a little bit bluer

I took a photo of the sky's spectrum in the direction of maximum polarization (90 degrees with respect to the sun) with a polarizer in both crossed and uncrossed positions. Here's the result:


The graphs to the right of the spectra are plots of the light intensity across the spectra. Blue is towards the left. Look at the intensity near the 800 marker on both graphs. It is lower for the polarizer in the crossed position. This means there's less green light; therefore a slightly greater fraction of blue.

Supposedly this is because a little more polarized blue light is re-scattered by the atmosphere, hence depolarized and can make it through the polarizing filter.

But the effect is small compared to the overall darkening caused by the polarizer; I'd say no more than a few percent.

Dave

PS pay no attention to the splotches of color in the spectra, they are an artifact of the Bayer Filter.

Last edited by newarts; 07-25-2009 at 05:41 AM.
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