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04-02-2009, 03:44 PM   #1
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Circular vs. Linear Polarizer on a K100d?

Hello. I have a lab full of K100ds...upgraded from Canon P&S digital cameras (we still use our film k1000s in the Fall Semester). And I have a box full of polarizer filters that I accumulated over the years to use with the film cameras and with the Canon A85 P&S cameras. The problem is that only a couple are labeled as Circular PLs but I know some of them must be Circular.

So, 1) Does it matter to the k100d focusing & exposure system? I have heard that only some AF DSLRs need the circular. 2) How can I tell a difference between the two?

We went out shooting with the PLs today, but not to use as PLs as much as to slow down the shutters 2 stops. I will see the results tomorrow...but it didn't seem to matter with the 13 I had in use today.

Thanks for any feedback!

Drew
http://staff.beaumont.k12.tx.us/gloker/

04-02-2009, 03:57 PM   #2
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Michael Reichman has a good article on the Luminous Landscape about polarizing filters. The upshot is that you need a circular polarizing filter with TTL metering. Hope this helps.
04-02-2009, 04:40 PM   #3
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Although you will find quite a few people, myself included, have been using linear polarisers on their dSLRs quite successfully. So do some tests, it won't cost you anything.
04-02-2009, 06:40 PM   #4
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QuoteOriginally posted by lokerd Quote
1) Does it matter to the k100d focusing & exposure system? I have heard that only some AF DSLRs need the circular.
I don't know about the K100D, but I've been using linear polarizers with my K10D without any problem. I don't think the K100D is any different.

QuoteOriginally posted by lokerd Quote
2) How can I tell a difference between the two?
Standing in front of a mirror. Cover one eye with the polarizer. Can you see still see the eye in the mirror? If not, it's a circular polarizer.

If you can see the eye behind the polarizer in the mirror, flip the polarizer over so that the face facing out toward the mirror now faces in toward your eye. Can you see the eye in the mirror? If not, it's a circular polarizer.

In other words, a circular polarizer transmits refected light only one way.

It's really simple. I hope my post does not make it too confusing.

04-02-2009, 09:48 PM   #5
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Thanks for the replies. Steve, I had read that post...and several others...I was just still confused. Sounds like I just need to do a little testing. Actually, I have wanted to know this answer before. Then, today, the first couple of classes were shooting when the sun was not out...and this was good because I wanted them to have long shutters...but then the sun came out so I was scrambling to get the PLs ready to go.

QuoteOriginally posted by SOldBear Quote
In other words, a circular polarizer transmits reflected light only one way.
Thanks! This is perfect. I was wondering what the deal was...as I had noticed once before that a PL only worked one way. I did not know that this was exclusive to Circular. Very interesting tidbit there.

Thanks!
04-03-2009, 03:14 PM   #6
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There is currently another thread about exactly this topic.

You don't NEED a circular polarizer for your camera. It is only needed for expsoure meters, that receive their light via a semi-transparent mirror system, as that in itself polarizes the light. Add to that a linear polarizer and the expsoure meter sees no light at all, which leads to gross overexposure.

BUT in the K series, the expsoure meter is located in the viewfinder (as was usual for 90% of all film SLRs, too) and there are no other polarizing parts involved.

AF action is not compromised by a linear polarizer, too, as any polarization has no influence on the phase detection. The only thing (and that would be true for any polarizer, linear and circular) is, that the AF sensor gets less light, so may hunt more, with a slow lens and a polarizer.

Ben
04-03-2009, 05:24 PM   #7
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A couple other notes about a Linear Polarizer:

- They are also called a “Top” Polarizer.

- Your local camera store may not always have the filter size you are looking for in Linear, so you may have to special order it. The Circular version is more readily available.

- The Linear version will be less expensive. Example a 77mm B+W Glass (no MC) Polarizer will cost $63.50USD and the Circular version $94.95USD. If you have to buy a couple for different filter sizes you will save a lot
04-03-2009, 09:41 PM   #8
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QuoteOriginally posted by Ben_Edict Quote
There is currently another thread about exactly this topic.

You don't NEED a circular polarizer for your camera.
Thanks Ben for the reply. Sorry to ask a FAQ. I did do some searching for the answer but couldn't find it right out with the k100d...lots of similar answers about other cameras.

Good to know the k100ds are good to go.

Drew

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