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05-08-2011, 12:46 AM   #1
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Some Filter Advice Please

Hi,
I am contemplating doing some equipment purchases (principally a K5) and thought that whilst I am about it and to combie shipping (I live in South Africa) I would buy a few other things as well. One of which is a wide zoom for architectural and landscape use, Correctly or incorrectly I have settled on the Sigma 10-20 f3.5 zoom which at B & H ia about $650-00. I was looking at polarising filters and was shocked at the prices for the presumably better quality filters - anything up to $300.The filter size for the lens is 82mm. Please suggest a good quality polarising filter and should I go with a circular or a linear polariser. As an aside is the 3.5mm lens worth the increase in price over the slower version??

Thanks in advance,
John

05-08-2011, 04:00 AM   #2
Ash
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Circular polarisers are easier to use - less fiddly.
The multicoated variety will leave in you in good stead to avoid aberrations and degraded image quality, but I'd highly recommend the Hoya HMC/Marumi/B+W brands as they have all been very good in this regard in my experience.
05-08-2011, 04:29 AM   #3
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QuoteOriginally posted by Ash Quote
Circular polarisers are easier to use - less fiddly.
The multicoated variety will leave in you in good stead to avoid aberrations and degraded image quality, but I'd highly recommend the Hoya HMC/Marumi/B+W brands as they have all been very good in this regard in my experience.
For most of my lenses, I bought the Hoya, Pro 1 D filters which have been fine. (Both simple UV for protection and Circular Polarizers). For my slower version Sigma 10-20, I got cheap and bought an off brand, DHG Circular Polarizer. For most shots it's OK but there are shots where I'm getting flare that shouldn't be there. Ever since, I'll recommend nothing less than the Pro 1 D series.

As to the choice of Sigma 10-20 versions, review the Sigma 10-20 Lens Club on this site. We just went through another discussion on this choice (there have been several, over time), There are also lots of fine examples by each of them.
05-08-2011, 06:00 AM   #4
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I have had good luck with inexpensive "Sonia" brand filters UV LPL & CPL. However I have not tested them critically.

CPL Filters

05-08-2011, 06:56 AM   #5
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I have the sigma 10-20 f/4-5.6 and am very happy with the pictures/colors it produces. It is my 2nd of two Sigma lens and I am also impressed with the build quality of Sigma lens. I can't say if the faster 3.5 version is worth the added cost, but it was not for me.

I use a Marumi CPL and am happy with it. I have purchased step down rings so this filer can be used on all my lens. I have since been buying Hitech 4x4 ND & NDG filters.

Marumi DHG Circular Polarizers Multicoated, UV filters atwww.2filter.com
05-08-2011, 07:43 AM   #6
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You might also try looking at used filters. My Heliopan CPL (77mm) cost me $45 on ebay not too long ago. If your photography is something you intend to make money with, it may be worthwhile not to cheap it out in this area. That's just my opinion though.


05-08-2011, 07:44 AM   #7
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With Pentax, there is no pressing reason to use a circular polarizer, and generally you can get a good linear for the price of a mediocre circular.
05-09-2011, 03:02 PM   #8
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QuoteOriginally posted by Wheatfield Quote
With Pentax, there is no pressing reason to use a circular polarizer, and generally you can get a good linear for the price of a mediocre circular.
That is interesting info to me (as I am currently contemplating buying an 82 mm polarizer and have a used linear at a fair price at hand).

You say "With Pentax, there is no pressing reason....." Is that to say that the "common wisdom" that you may have light metering issues with linear polarizers isn't so true in the case of Pentax?

05-09-2011, 04:49 PM   #9
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QuoteOriginally posted by Stone G. Quote
That is interesting info to me (as I am currently contemplating buying an 82 mm polarizer and have a used linear at a fair price at hand).

You say "With Pentax, there is no pressing reason....." Is that to say that the "common wisdom" that you may have light metering issues with linear polarizers isn't so true in the case of Pentax?
Pentax still meters off the focusing screen, which means that there is no polarization of the light that the meter reads.
The light going to the AF sensor will be (partially at least) polarized, so it is possible in some situations to cross polarize the AF sensor to the point of blinding it, but the K5 AF is also sensitive enough that this would rarely be a problem, and if it is, either focus manually or back off the polarizer a bit to focus and then rotate it back to where you want it.

I say with Pentax because I am not familiar with other manufacturers products, and so cannot say how they meter, though they all have more or less the same AF configuration with a partial mirror directing light to a sensor in the base of the mirror box.

FWIW, I do own a couple of circular polarizers, but mostly I use linear ones because I find them more effective.
05-10-2011, 12:43 AM   #10
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Thanks Wheatfield - very useful information!
05-10-2011, 05:13 AM   #11
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From Bob Atkins' "All about Polarizers - Linear and Circular" page:
"Older SLRs used fully reflecting mirrors, which reflect all polarizations with equal intensity. Newer SLRs, and particularly autofocus SLRs, often use partially reflecting mirrors. The reflected light goes to the viewfinder and metering systems, while the transmitted light goes on to the auto focus sensors. If a linear polarizer was used on such an SLR, the intensity of light sent to the metering system would depend not only on the intensity of the light, but also it's polarization angle."
Hence,
  • it is likely that a linear polariser will mess with the light metering. Canon, Nikon, Pentax DSLRs all meter through the focusing screen, no difference between brands here.
  • a linear polariser will mess with the AF. Turning the polariser so that the AF works again is a workaround and only you can decide whether it is acceptable for you.
N.B., a circular polariser is nothing but a linear polariser with an added quarter-wave plate that adds a circular spin to the linearly polarised light (by slowing down own component more than the other). Therefore, if they are differences in effectiveness, they have to do with the brand / models, but not with the difference between circular and linear polarisers. There is a reason why the quarter-wave plate is added to linear polarisers to create so-called circular polarisers, so I'd think twice before I'd settle for a linear polariser only.

Polarisers on ultra-wides are not without problems because they cover such a large FOV that they "see" the sky in large enough portions to demonstrate the phenomenon that the polarisation of the light changes with the angle you look at the sky. You'll hence have to deal with apparently darker areas in the sky (where the polarisation is effective) compared to lighter ones (where it isn't). You can only move the dark area around but rarely avoid that usually undesirable effect.

Regarding the choice between the "slower" and the constant f/3.5 version of the 10-20: I went for the constant f/3.5 because it offered the better trade-offs for me. It has an easier to correct distortion at 10mm, is faster, has HSM (-> quickshift) and had some further optical advantages that appealed to me. I'd suggest to have a look at some test, ignore the ratings (stars) but focus on particular differences and decide for yourself which lens model ticks your boxes best.

Last edited by Class A; 05-10-2011 at 05:34 AM.
05-10-2011, 10:18 PM   #12
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I have a photo of the partially reflecting mirror, but it may not be that clear unless you already know what you're looking at. First, this is the viewfinder system from the front (lens mount side). There's the mirror, reflecting light up to the pentaprism:



Now from the viewfinder side, you can see the back of the mirror, with a little opening and a secondary mirror that reflects some light to the AF sensor:


That's from a Pentax SF1, with the original SAFOX, so some of the system is different today - I don't know how the multiple points work.

I can't add anything to the polarizer discussion except that I use cheap ones that I mostly got for free, and work around limitations.
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