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Does anyone know of any good comparisons for linear polarizers, similar to the excellent circular polarizer test done by LensTip?

Unfortunately, a number of those manufacturers don't offer the same coatings and whatnot on their Linear Polarizers.

I want a Linear Polarizer over circular for a couple reasons:

  • Pentaxians claim it does not affect their AF or metering system
  • I want at least one linear polarizer so I can get the cheap variable ND filter to play with
  • They are much cheaper

EDIT: I did some comparison of cheap CPLs and cheap LPLs. Difference was surprising. See here.

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Do you have a link to Pentax's claims that a Linear Polarizer is OK? – Mark Ransom Oct 18 '10 at 0:38
Sorry, I can't find the link, but it was second hand from someone talking to support. While looking for it, I found another claim that they said it "may" affect AF. Anyways, many others, including myself, have used linear polarizers without problems. – Eruditass Oct 18 '10 at 1:44
I thought the problems with linear polarizers had to do with the meter, and whether it was beam splitting. From what I understand, beam-splitting meters also polarize the light, which would double-polarize if you used a linear polarizer, and give you incorrect meter readings. – jrista Oct 18 '10 at 3:03
Yes, I've heard figures of up to +/- 2 stops incorrect metering, but had not noticed any issues. I will carry out a non-reflective wall test soon, but I still want at least one. AF will only be affected if the lenses in the AF system are polarization sensitive (birefringent), which can include plastic lenses under stress. – Eruditass Oct 21 '10 at 1:00
From what I've read (I've never experienced this myself), beam-splitting meters/AF sensors may be susceptible to total blackout if the polarizer is oriented 90 degrees to their own polarization, effectively eliminating the possibility of metering. I gather that AF sensors are not susceptible to total blackout, but AF speed can definitely be affected by a LPL. It would really boil down to how the meter works. If it does not use any polarizing filters, then it would probably be fine, but if it does, there is always the chance of blackout if you align your LPL 90 degrees to the meter filters. – jrista Oct 22 '10 at 1:30

As I noted in comments, I think that you can generally expect that a company that makes a good circular polarizer will like also make a good linear one. However, if the purpose is to reduce cost, because of different lenses (now and in the future), then there is an alternative option: Lee Filters or the Cokin P Series.

In a nutshell, these are square/rectangular filter systems that you purchase an inexpensive filter holder that slides onto diameter adapters (also quite inexpensive) and then slide filters into the adapter. Most, as I noted, are rectangular except for the polarizers. These are round and fit into a special slot on the holder and then you adjust as normal. The polarizer is large enough to handle lens diameters specified by the chosen system and so you can get quite a range (I'm ranging from 49mm to 77mm with one polarizer).

In terms of quality, Lee is generally regarded to be better than Cokin, but is also more expensive. Cokin is, however, decent and may not only cover your needs well, but may be easier to find. Either way, I literally saved close to a $1000 on circular polarizers and other filters by going this route.

The final upside is that you can get a lot of other filters, such as ND, graduated ND, and more and use them on your lens collection. Saves a lot of dough and there are third party makers of these filters for the two systems.

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Can you elaborate on the pro's versus one 77mm linear polarizer ($30) and step-up adapters from 49mm to 77mm ($10)? Two will act as a variable ND, and I can still stack a grad ND as long as the filters have threads on the front. Ease of use? – Eruditass Oct 26 '10 at 15:53
You can certainly go that route, but a rectangular graduated ND is much more flexible than one that screws onto the lens because it is much easier to adjust the graduation point for the composition. With one that screws onto the lens, you're likely going to need to adjust your composition instead, which is not as ideal. In any case, either system is dead simple to use, no harder than any other filter option. There are also other forms of graduated filters that may be of interest as you go along. – John Cavan Oct 26 '10 at 16:04
So what I've gathered: is that it's more of a pain with polarizers because you can't rotate it as easily, but useful for split filters and grad ND's because you can slide it out. And they have a hood system (and other accessories) system. – Eruditass Oct 26 '10 at 16:05
I haven't found it to be especially a pain, but that probably varies by individual more than anything. But yes, they have lots of accessories and other filter options that are harder to do with a screw in type. That's a plus that attracted me to the system, that and it would seem that many of the drop in filters are cheaper than their cousins, so as I accumulate, I save a little bit. – John Cavan Oct 26 '10 at 16:09
Yep, getting oversize filters and using a holder or step up rings is a very good way to "future proof" your filter investment! – Matt Grum Oct 26 '10 at 16:16

Some quick searches for "[brand] linear polarizer" returns some pretty bland results. Each brand generally has just one linear polarizer. Some offer multi-coated ones, while others offer them in a glass variant. Tiffen offered some "warm" versions (linear polarization seems to cool light, in contrast with circular polarization, which may warm, cool, or tint light depending on orientation an coating), B+W and Heliopan offer "Kaeseman", or a fully "encased", filters that are edge sealed (might be useful to guarantee full weather sealing on lenses+bodies that support weather sealing), etc.

They seem to come in three general price ranges: Around $20, around $60-80, and $120-$160. Between all the price ranges, the $60-80 range seems to be the best deal, as they seem to be multi-coated glass linear polarizers. The really expensive ones don't really seem to have anything particularly compelling outside of fancy terms like "Kaeseman edge-sealed" or "slim edge mount" and whatnot.

From what I can tell, a glass, multi-coated, linear polarizer is a very simple optical device, and there are generally one or two lines from each filter maker: the basic version, and the "uber" version that is super thin, kaeseman sealed, better-multi-coated, etc.

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DSLRs use phase detection autofocus. This takes a bit of the light through a semi silvered mirror and reflects it through a variety of prisms and mirrors into the AF sensor - all these components are polarization sensitive, and so need circular polarized light (*).

Compact cameras use contrast AF where the sharpness of several images is measured as the lens is tracked through focus - this needs a live view type sensor and is much slower and less accurate.

(*) In theory you could use phase preserving coatings on the prisms as in very high end binocular prisms but iv'e never heard of a DSLR implementing this

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I just tested out my low-end linear polarizer and it's autofocus still seems fast and accurate. Regardless, this doesn't even address my original question. – Eruditass Oct 22 '10 at 4:48

Bob Atkins has a great article covering polarizers in which he explains the differences between linear and circular.

In the end, the extra cost of a circular filter is probably justified... however if you are really sure that you want a linear filter, your best bet is probably going to be to look through the review for circular polarizers that you referenced and pick a brand based on the ratings there.

I don't think you're going to find a good review out there, simply because there isn't much demand. Most people want circular polarizers, because they work better with AF on most camera bodies.

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