linear vs. circular polarizer : LUSENET : Konica 35mm SLRs : One Thread

hi folks---

i would like to take advantage of the effects of a polarizer. i have been told that there is no need to get a circular polarizer with my TC because it is not autofocus. all i need is a linear one. is this true? i am only confused because someone else told me the opposite: even though the camera is not AF, the linear one will throw off the meter to the point where it does not work.

i am confused....??


-- Paul Trunfio

-- Anonymous, January 20, 2000




You can use a linear polarizer with your konica lenses. Circular polarizers are a must if you want to maintain autofocus capability (with cameras that employ it), but they're not necessary for manual focus cameras.

The polarizer will reduce the amount of light getting to the film, but since the exposure meter is on the film side of the filter it will compensate properly.

-- Anonymous, January 20, 2000

linear vs circular polarizer

Paul, There is a lot of confusion caused by folks who are versed only in relatively new equipment. Almost all cameras made today require a circular polarizer because of the metering systems employed, not just simply because they are autofocus. The polarizer does not affect the autofocus except to the extent that the light it has to work with is reduced.

Jon from Deepinaharta, Georgia

-- Anonymous, January 20, 2000

Re: linear vs circular polarizer

Now I am confused. I thought that one of the primary purposes of a polarizer was to eliminate glare. It works because ideal flat surfaces reflect only the component of light linearly polarized in the plane of the surface. So, if you look at a lake through polarizing glasses that pass only vertically polarized light you can see through the surface more easily. The horizontally polarized glare reflecting from the surface is stopped by the polarizer before it reaches your eyes. A polarizing filter that passes light circularly polarized in one direction but not the other would not have this benefit. (Note: I may have switched horizontal and vertical here.)

Unless what what I wrote above is wrong, I don't see why a light meter would be designed to be sensitive to the polarization of the light.

Am I missing something?


-- Anonymous, January 21, 2000

Re:linear vs circular polarizer

William, I can't remember the exact reason for the screwing up of the metering (I'm in the process of looking it up), or why a meter would be affected in a deleterious manner by a polarizer, but I do remember that the photo press and rags wrote prolifically about it. The auto-focus may be affected as well, but I really can't say, as I am not into such equipment except for my Canon point-and-shoots. As I recall, when a linear polarizer is used in newer cameras, the metering can be off by as much as 2 stops. As I said, I am in the process of looking it up and I will post a response on what I find. Probably the mind (always the first to go) taking a short vacation.:-) In other words, I could be entirely wrong, so please bear with me.

Jon from Deepinaharta, Georgia

-- Anonymous, January 21, 2000

Re: why linear vs circular polarizer

William, I have (finally!!) got it together to answer your earlier question. The way a polarizer works is to interdict unpolarized light that causes the glare. The linear polarizer does this by filtering the usually scattered light we see and allows only light rays of a certain orientation to pass through. The only thing it doesn't work on is metal specular reflections. Now, (and this is the tricky part, for me, at least) both polarizers perform the same functions, however, the circular polarizers work on auto-focus cameras because auto-focus cameras use beam-splitters to siphon off some light to the meter cell and the rest to the viewfinder. This light that is siphoned off is already polarized and if a linear polarizer is used, it will act as a second polarizer and block off the light. You can achieve the same effect by using polarized material over spotlights and then turn the ring on a second polarizer attached to the lens. Also, if wearing polarized sunglasses, try using a polarizer on your SLR. The viewfinder will go black. This trick I have pulled on myself inadvertently on a few occasions. This can screw up auto-focus systems that use beam-splitter modules in them, also. So, it appears, in theory, at least, we were both correct, but for differing reasons. BTW, circular polarizers work by using a 1/4 wave retarder foil to convert the incoming light so that it appears unpolarized to the meter, hence, exposures end up correct. I hope this clears it up for everyone. If not, e-mail me off-list and we'll see what we can come up with.

Jon from Deepiinaharta, Georgia

-- Anonymous, January 29, 2000

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