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09-16-2011, 04:22 PM   #16
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QuoteOriginally posted by wizofoz Quote
One thing I noticed is there is not a lot of difference when rotating the filter through 90deg's and taking another shot. Maybe the disadvantage is that the polarisation is not as nuanced as with a CPL? Someone much more educated than I may have the answer.
If the light source itself is not polarized (like maybe an incandescent lamp) and scatters off perpendicular or matte surfaces then which way you turn the polarizer won't have any effect.

09-16-2011, 04:23 PM   #17
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QuoteOriginally posted by newarts Quote
If the light source itself is not polarized (like maybe an incandescent lamp) and scatters off perpendicular or matte surfaces then which way you turn the polarizer won't have any effect.
Thanks Newarts, but I was just shooting in sunlight. Not sure if that makes a difference.
09-16-2011, 04:24 PM   #18
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QuoteOriginally posted by wizofoz Quote
Thanks Newarts, but I was just shooting in sunlight. Not sure if that makes a difference.
No effect for direct sunlight.
09-16-2011, 04:31 PM   #19
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Ok, taking on board the comment about polarised light, I just went outside and took a shot of the beautiful early spring sunshine reflecting off my pool using the LPL.

Shot directly at the sun's reflection and used the pool edge as a contrasty focus point. There was a significant difference when turning the polariser through 45' .Exposure without polarisation was 1/3200 F5.6 iso 400. Exposure with polarisation was 1/320 F5.6 iso 400. Very interesting.

09-16-2011, 04:37 PM   #20
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the trick would be a CPL that fits all your lenses , I have a Cokin P which fits them all, (if i was starting over i'd just invest in Cokin Xpro which didn't exist back when i bought all mine)
09-16-2011, 04:41 PM   #21
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QuoteOriginally posted by eddie1960 Quote
the trick would be a CPL that fits all your lenses , I have a Cokin P which fits them all, (if i was starting over i'd just invest in Cokin Xpro which didn't exist back when i bought all mine)
I agree Eddie, but I would probably give the Cokin's a miss and go straight to Lee filters or maybe B&W. P series Cokin's have a reputation of adding a magenta tint to exposures.
09-16-2011, 06:22 PM   #22
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at half the price of lee's (b/w doesn't have a system like lee and Cokin)
Cokin gets a worse rap than it should (or the quality has gone down since I bought mine admittedly a good 20 years ago)
09-16-2011, 06:38 PM   #23
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QuoteOriginally posted by eddie1960 Quote
Cokin gets a worse rap than it should (or the quality has gone down since I bought mine admittedly a good 20 years ago)
Eddie, sadly, the quality has gone down in the past 20 years.
I was never happy with my P-series grads (blurry and wavy) and then got some old ones in a package deal from another forum-er. Yes, the old ones (I think he said from 1988) were much better!

The Z-Pro system I replaced it with was even better, but then I started using Schneider/Schott filters. Glass is the way to go! No color casts when combining filters, no increase in aberrations, and no easy scratching...

(BTW Eddie, I was tromping in your docklands today by the old power station... got some nice shots!)

09-16-2011, 07:30 PM   #24
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QuoteOriginally posted by eddie1960 Quote
the trick would be a CPL that fits all your lenses , I have a Cokin P which fits them all, (if i was starting over i'd just invest in Cokin Xpro which didn't exist back when i bought all mine)
the problem is that the only option for a CPL that fits all of your lenses is the square filter system. I'm not interested in a 49 to 67 (or 77mm) step up ring on a small prime. Or tbh I have zero interest in a square filter on a small prime. One of the reasons that I want a small prime is portability.

imo you either restrict yourself to lenses with the same filter size or invest in multiple filter collections (costly). For example a 49mm filter set and a large square filter set for the 67-77mm filter zooms. And this is another reason that I'm not interested in adding a WA zoom in the near future.
09-17-2011, 05:06 AM   #25
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QuoteOriginally posted by wizofoz Quote
Ok, taking on board the comment about polarised light, I just went outside and took a shot of the beautiful early spring sunshine reflecting off my pool using the LPL.

Shot directly at the sun's reflection and used the pool edge as a contrasty focus point. There was a significant difference when turning the polariser through 45' .Exposure without polarisation was 1/3200 F5.6 iso 400. Exposure with polarisation was 1/320 F5.6 iso 400. Very interesting.
That's consistent with a reflection off a shiny, non metallic surface. Here's how polarization varies with reflection angle for water:


If the angle between the camera's optic axis and the water surface was anywhere close to 50- 60 degrees there can easily be a tenfold brightness difference depending on how the polarizer is turned.

Last edited by newarts; 09-17-2011 at 07:18 AM.
09-17-2011, 05:51 AM   #26
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QuoteOriginally posted by eddie1960 Quote
at half the price of lee's (b/w doesn't have a system like lee and Cokin)
Cokin gets a worse rap than it should (or the quality has gone down since I bought mine admittedly a good 20 years ago)
QuoteOriginally posted by wizofoz Quote
I agree Eddie, but I would probably give the Cokin's a miss and go straight to Lee filters or maybe B&W. P series Cokin's have a reputation of adding a magenta tint to exposures.
QuoteOriginally posted by eddie1960 Quote
the trick would be a CPL that fits all your lenses , I have a Cokin P which fits them all, (if i was starting over i'd just invest in Cokin Xpro which didn't exist back when i bought all mine)
Have used both the both the Linear and Circular Cokin Polarizers, in both A and P series, The magenta cast was present when using either Circular being a pain when trying to neutralise. As a consequence they were retired immediately.
These days I keep the Linear P for convenience when carrying other P size filters having not yet had a noticable problem with AF, otherwise it's the Marumi Super Circular and step-up rings.

Would suggest simply trying the Cokin Linear Polarizer (don't bother with A series) before heading for the more costly options as it is available (along with adapters and holders) on the usual auction site for next to nothing. You may find it fits your needs without causing any AF issues - just make sure you get it (them) inexpensively. The holder will come in useful for Graduated filters if you want to include them in your kit in the future (though that is another personal preference imposed as i don't care for screw-in grads).
09-17-2011, 06:30 AM   #27
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Polarization filter effects on exposure or AF ERROR are the issue

Originally posted by wizofoz
QuoteQuote:
Ok, taking on board the comment about polarised light, I just went outside and took a shot of the beautiful early spring sunshine reflecting off my pool using the LPL.

Shot directly at the sun's reflection and used the pool edge as a contrasty focus point. There was a significant difference when turning the polariser through 45' .Exposure without polarisation was 1/3200 F5.6 iso 400. Exposure with polarisation was 1/320 F5.6 iso 400. Very interesting.
Wizofoz and eddie1960, There should be an exposure difference in this scene caused by rotating the linear polarizing filter. Direct sunlight is essentially unpolarized, however sunlight reflecting off a pool surface (water) will be polarized to a degree (depending on angle of reflection - maximum occurs at Brewsters angle, for water, n=1.33 => Angle_Brewster~=53degrees ). Therefore Wizofoz's observation of exposure differences with different linear polarization filter orientations of this scene with sunlight reflected off pool water is consistent (but does not definitively show error).

At the "perfect" angle of reflection the sunlight reflecting off the pool's surface will have maximum polarization, and when observed through a linear polarizing filter rotated through 90 degrees will show maximum variation of the reflected light intensity. When the filter is oriented to admit vertically polarized light, the sun's reflection off the water will be filtered out and disappear to the eye and to the camera looking through that filter. Less light coming into the lens, greater exposure needed. To complicate maters more, skylight (sunlight scattered off air) is also partially polarized (maximum at 90 degrees from the sun) and if that light was also in the scene, the polarizing filter's orientation could influence its intensity as well.

From Wizofoz's comments it does not appear that there is any significant exposure error introduced by the linear polarizer.

To most sensitively test the effects of a linear polarizing filter's orientation on exposure error, shoot a scene of direct sunlight reflecting off a sanded (rough) un-coated metal surface. This light will remain unpolarized and any orientation of the linear polarizer should not affect the exposure. If it does - then the exposure metering system is sensitive to the polarization of the incoming light and it will introduce errors.

Ditto for a test of the AF system and the effects of a linear polarizer, but this might be more complicated because the K5 seems to use different focus methods in different situations.
09-18-2011, 08:20 AM   #28
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I think that the linear vs circular pola and the reasons to use one or the other have been well documented here and elsewhere on the web.

However, since the thread has drifted a bit to brands and quality, here is a good test of various pola filters from the leading manufacturers. The supplement tests two Cokin filters:


Polarizing filters test - Introduction - Lenstip.com

Polarizing filters test - supplement - Introduction - Lenstip.com

My thinking on this subject is that I own and use some of the best glass available (Pentax limiteds, for example) and scrimping to save money on a pola filter makes little sense.

I went with Marumi, which are excellent filters and also quite a value in terms of price/performance.

Ray
09-18-2011, 09:12 AM   #29
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We tested it on the PU once with a K20D, linear gave over and underexposed by one stop depending on how you turn it, the AF seemed to be fine.
09-18-2011, 09:26 AM   #30
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QuoteOriginally posted by Anvh Quote
We tested it on the PU once with a K20D, linear gave over and underexposed by one stop depending on how you turn it, the AF seemed to be fine.
"PU" ???

I just tested a K-x with a linear polarizer using a non-polarized reflection from paper. I did not observe any brightness change while rotating the polarizer and the EV indicator in the viewfinder did not change; ie. there was less than 1/3 stop in measured change.
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