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Do I need a circular polarizer?


brian hanson

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Do I need a circular polarizer? I know that they are mostly for auto

focus cameras, but I have read that they need to be used for proper

metering as well. I use T-90s, A-1s, and an F-1 and I am going to

buy some new filters because I just got a 20mm 2.8, old style, and I

need ND, Polarizer, and UV filters for it. Do I need the thin type

for this lens? I plan to buy B+W, but I am open to suggestions,

especially if they are cheaper! Thanks, Brian.

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Thanks Dan. I have been using linear polarizers for a long time with my FTb and A-1, and with no problems. But from what I can see on the web is that it may be a problem with my T-90. Does anybody know for sure? Also, Should I buy thin filters to use with this 20mm 2.8 lens? Thanks.
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A linear polarizer will very definitely cause exposure reading errors with the FTb and with the F-1. I don't know how the A-1 meter works, but the angled beam splitter in the F-1 and FTb focusing screens polarize light. So light entering the lens must be de-polarized with a circular polarizer.
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<ol><li> I've never had a problem with metering using my linear polarizer on my AE-1P with 50mm and 28mm lenses.

 

</li><li>Using 3 filters on a wide angle lens might not be a good idea (due to vigneting).

 

</li><li>Why do you need a neutral density filter? Wouldn't a faster shutter speed or slower film give better results? (I'm assuming you're not talking about a <i>graduated</i> neutral density filter.)

</li></ol>

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I'm fairly sure the T-90 needs a circular polarizer if you want to meter through the filter. It's generally recommended with most later Canon bodies that use a beamsplitting prism in the focusing screen to direct light to the meter.

 

I wouldn't bother with a polarizer on a 20mm lens. In certain scenes it can work, but in general, particularly for landscapes, you'll get uneven polarization with a lens that wide. In that situation a graduated ND is more effective.

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It's very easy to know if you need a circular polarizer. And it may not be obvious whether you have a linear or circular polarizer. I'd suggest taking a pair of polarized sunglasses and holding them in front of your lens. The sunglasses are virtually guaranteed to be linear polarizers. Rotate the eyeglass lens while metering a white painted wall. If the meter reading changes, you need a circular polarizer.

 

People may have no problem with a polarizer they assume to be linear when in fact it's circular.

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b+w filters are definetely have slimmer rings to start with but i would get a slim circular

polarizer anyway. You can always put your pola on top of the first filter that way you don't

need one with threads. You won't be able to stack 2 or more on your 20mm though

unless you get some step up rings and larger filters like 72mm or 77mm which aren't

cheap.

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Yes, for your T90. I'm using a regular Hoya filter on my new 20mm f2.8 with no drama. It may be true that you'll get uneven skies with a polariser on the 20 mm (anything wider than ~28 mm will ensure this), polarisers have other uses for removing reflections in rainforest shots and other non metallic refelecting surfaces.
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For Peter:

 

http://f4.grp.yahoofs.com/v1/8H4SQg78WvKduj5r0WjVoXYnk-wn-A5FeQk15A2WPQzhNfm639BdMWUPNYPfj6sKpWuZn7mvYuBxAyanop1VKtQyHwIuDYo/polarizing%20filters%20and%20canon%20bodies.jpg

 

good luck cutting and pasting

 

Here's the info from the chart

 

These bodies can use a Linear Polarizer:

 

EF

 

AE-1

 

AV-1

 

AE-1P

 

AT-1

 

A-1

 

T50

 

T70

 

And these bodies need a Circular polarizer:

 

F-1

 

F-1n

 

F-1N

 

FTb

 

FTb-n

 

TLb

 

AL-1

 

T80

 

T90

 

The FTb FTb-n and TLb bodies I added to the Circular Polarizer list based on their metering system

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Hmmm,

 

I had an AT-1. And as I recall, it had the same rectangular metering pattern as the FTb I used before it, and the F-1 (stock screen, immediately replaced by a spot screen) I replaced it with in 1986. I thought it used the same beam splitter design as both the FTb and the F-1. Am I not remembering correctly?

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Peter the AT-1 does have center weighted metering the same as the AE-1 AV-1 A-1 and AE-1P the reason the AL-1 needs the circular polarizer is due to it's focusing assist system.

 

The AT-1 uses the smae focusing screens as the AE-1 a non interchangable screen that would require the prism to be taken out of the camera to change the screen.

 

The Chart is accurate as I typed it this info has been checked back and forth a bunch of times on the Canon group on Yahoo where it is posted.

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Yeah. I must be getting old. Just can't remember much of anything any more. ;-)

 

But I do remember now how happy I was when I got the F-1 and again had some control over what I was metering. I had bought the AT-1 because it was lighter, not thinking about the different metering pattern. I was very used to the center rectangle on the FTb. And of course the spot metering screens for the F-1 were even better.

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