NON-circular polarizer for lenses?

[2005GLI]

Ok i had a cic. polarizer that i pickedup when i got my xt. I forget what brand but it really didn't do much. I then picked up a multicoated hoya cic.polarizer for my sigma 70-300 and kit lens. Its a lil better but the part that makes the blue sky actually appear blue does not seem right. It barely covers the part of the sky or does only half of it. I tried it numerous times and i got the same results.

I had a tiffen on my g2 lens tube adapter and it worked great. I mean i saw the sky change dramatically and all reflections gone when i used it. Im thinking i may get a tiffen in 58mm, but not sure yet. Do they make a non circular polarizer for digi lens? Is there a disadvantage or any advantage?

[robertwgross]

For any EOS camera, you want to use a circular polarizer, not a linear polarizer (or else you may get odd autofocus results).

---Bob Gross---

[2005GLI]

Thanks for info. I'll check into a tiffen like i had on my old camera. Maybe the filter i got didnt make it through quality control.

[SkipD]

Are you aware that you don't just screw on a polarizer filter and expect it to give you the maximum effect? You need to rotate the filter while looking through it (preferably while it is attached to the lens so you can look through the camera) and select the rotational position that does the best job for your situation.

[2005GLI]

Are you aware that you don't just screw on a polarizer filter and expect it to give you the maximum effect? You need to rotate the filter while looking through it (preferably while it is attached to the lens so you can look through the camera) and select the rotational position that does the best job for your situation.


of course im aware of that, why else would it be called a circular polarizer? I did that, rotated it in both directions and barely saw if any change thru the viewfinder.

[robertwgross]

of course im aware of that, why else would it be called a circular polarizer? I did that, rotated it in both directions and barely saw if any change thru the viewfinder.

I think you are missing the point.

First of all, all polarizers have to be rotated to work right, no matter whether they are the circular type or the linear type.

Second, the effect of a polarizer will vary dramatically depending on your shooting angle to the sun. A polarizer can get its maximum effect if aimed 90 degrees from the sun. By the same token, if you shoot toward the sun or directly away from the sun, you are likely to get zero effect other than you have lost a couple of stops of light.

---Bob Gross---

[SkipD]

of course im aware of that, why else would it be called a circular polarizer? I did that, rotated it in both directions and barely saw if any change thru the viewfinder.Don't sound so miffed. There are quite a few folks who try to use polarizers and don't understand that it has to be adjusted for the situation.

Like Bob said, though most polarizing filters are physically round, some are linear polarizers (anything made in the 60's and possibly in the 70's is almost sure to be a linear polarizer) and some are circular polarizers. Circular polarizers are required for cameras with autofocus systems.

The easiest way to be absolutely sure that a polarizer is circular vs linear is to hold the filter up between you and a mirror. You want to be holding the filter so that, in the mirror, it covers the eye that you'd be using to look through the filter. Thus, you are looking through the filter twice to see your eye in the mirror. Then flip-flop the filter so you are looking at the other side of it. If you have a linear polarizer, you will be able to see your eye in the mirror with the filter held both ways. If it's a circular polarizer, you will see it blacked out in one direction and the other direction you'll be able to see your eye in the mirror.

[RAitch]

You can still use linear with some AF systems... I think the newer systems can handle it.
I had a linear pol for my old Fugi S5000 and it worked fine.

[KennyG]

You can still use linear with some AF systems... I think the newer systems can handle it.
I had a linear pol for my old Fugi S5000 and it worked fine.

No, you can't use linear CPLs with EOS AF systems, period. The Fuji is a very different animal, not the same thing at all. It has nothing to do with the age of AF systems, simply how they work.

I find that a lot of people just can't understand how a polarizer works and expect to suddenly see the sky go a deep blue when they put it on a lens. Sorry, it does not work like that. A polarizer either works or it is in broken bits, they don't go faulty. There are good and bad polarizers, the main difference being the glass, coatings and build quality.

[RAitch]

No, you can't use linear CPLs with EOS AF systems, period. The Fuji is a very different animal, not the same thing at all. It has nothing to do with the age of AF systems, simply how they work.

I find that a lot of people just can't understand how a polarizer works and expect to suddenly see the sky go a deep blue when they put it on a lens. Sorry, it does not work like that. A polarizer either works or it is in broken bits, they don't go faulty. There are good and bad polarizers, the main difference being the glass, coatings and build quality.
You might have a point with the AF system... depending where it is inside the camera. If light hits a mirror first, then it won't work. Metering won't work since I know it passes through 2 mirrors first.

Take it easy with the rant there buddy. I know how a polarizer works.

[2005GLI]

ok ok lets all take a deep breath. I didn't want this thread to get hostile. I may have come off that way on one of my posts, but it was just cranky that day.

I do have an understanding on how they work. It just seemed weird that it was spotty when i used it.

[chris clements]

why else would it be called a circular polarizer?
Not wishing to stoke the fire, but I trust that was a joke reply?
'Circular' describes what the filter does, not (necessarily) its physical shape

[robertwgross]

When I first studied polarized light (maybe 35 years ago), all we had was vertical-polarization or horizontal-polarization, which takes us back to linear polarizers on cameras. Much later (maybe 10-15 years ago), I learned that we had right-hand-circular polarization and left-hand-circular polarization. I'll have to go study Physics again, I guess.

---Bob Gross---

[Mercycreek]

I just bought a Tiffen 58mm CP for my 20D and used it this past weekend in the Great Smoky Mountains with no problems. The real trick to the CP filter is the angle the camera is from the sun. 90 degrees tends to be the angle of optimum control. Obviously the maximum angle doesn't have to be the right angle all the time as you can turn it ever so slightly to "loosen" the effect. I tend to do as do many here by turning the CP filter as I look at the scene through the view finder. Perhaps just re-evealuating how you use it may help.

At any rate I just purchased the Tiffen and I've had no real issue with it's use. ;)

[PacAce]

And speaking of circular polarizers and left-hand and right-hand circular polarization, anybody see "Chicken Little" in 3-D? It's interesting how they did that 3-d stuff using circular polarizers. :D

[DocFrankenstein]

When I first studied polarized light (maybe 35 years ago), all we had was vertical-polarization or horizontal-polarization, which takes us back to linear polarizers on cameras. Much later (maybe 10-15 years ago), I learned that we had right-hand-circular polarization and left-hand-circular polarization. I'll have to go study Physics again, I guess.
You're not missing much.

When you have a molecular compound and the molecules don't have a center of symmetry, you have two different kinds of molecules which are reflections of each other. Both have the same molecular mass, boiling and melting points, but they are like your hands - similar but non superimposable. If you separate the two kinds of molecules, each may rotate polarized light in a solution. One will rotate it clockwise - the other counterclockwise.

That's pretty much left/right-hand-polarization.

[robertwgross]

I was not referring to molecular compounds. I was referring to electromagnetic radiation.

---Bob Gross---

[Jon]

I was not referring to molecular compounds. I was referring to electromagnetic radiation.

---Bob Gross---
Yes, but it's the physical medium that imparts the circular (RH or LH) polarization to the EMR passing through.

[robertwgross]

Yes, but it's the physical medium that imparts the circular (RH or LH) polarization to the EMR passing through.

I guess that depends on your point of view. Microwave transmitters can employ a RH or LH circularly polarized antenna/waveguide to ship a signal through a near-empty medium. So, I don't think there is anything in the molecular makeup of the antenna that is doing it, it is the physical design of the antenna that is doing it.

Microwave energy is just sort of "slow light."

---Bob Gross---

[Jon]

I guess that depends on your point of view. Microwave transmitters can employ a RH or LH circularly polarized antenna/waveguide to ship a signal through a near-empty medium. So, I don't think there is anything in the molecular makeup of the antenna that is doing it, it is the physical design of the antenna that is doing it.

Microwave energy is just sort of "slow light."

---Bob Gross---
I'll point out that it's still the physical medium which is responsible for the polarization, which is what I said. In the case of light, passing through a polarizing medium can filter out one component of the radiation; passing a component of that through a quarter-wave plate can impart a phase shift. It's been about the same 35 years since I first studied polarized light (in optical crystallography). In the case of an antenna, use of a 1/4 wave retarding component in the antenna will result in the circular polarization.

[vixeh]

Georgia State University Physics Department has an illustrated explanation...

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/polclas.html