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Old Jul 31, 2003, 6:28 PM   #1
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Default Circular or Linear Polarizer Filter for 7i?

I have a Dimage 7i and want to use a polarizer filter and have been unsuccessful with Minolta to determine if a linear polarizer filter would work just as well as a circular one, given the circular filter is almost 2x the cost. Anyone knows the answer?

Also, I hear that using a step-up ring and 62mm filter, I can avoid vignetting. I've heard mixed reviews on this. Would going with something like 67mm insure eliminating vignetting at wide angles?

Finally, I'm thinking of getting either Hoya or Tiffen filers (the low end price range - OK so I'm cheap). Anyone know if there is any appreciable differences between them?
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Old Jul 31, 2003, 10:18 PM   #2
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You'll need a circular polarizer... a linear will interfere with the camera AF! Also you'll need a slim-line, ie 4-5mm or less @ 49mm, Hoya, B+W, or Heliopan all make them. The thickness of the polarizer is what make it vignette, a slim-line with no front filter thread will work just fine and won't interfere with the camera's tulip lens shade...
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Old Jul 31, 2003, 11:38 PM   #3
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I have a D7i and use a Cokin A system, which offers a circular polarizer and have not experienced any vignetting. Cokin is very affordable and once you've got the basic filter holder (which screws onto th 7i lens) you can add additional filters and expand your collection for not too big investments.

You can read about cokin filters here : http://www.geocities.com/cokinfiltersystem/

And I bought my filters here: http://www.bhphotovideo.com/bh2.sph/...ID=F2913751F40

Cheers
Albert
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Old Aug 1, 2003, 1:01 PM   #4
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Default Now I'm really confused

I just read an old response to the question of filters for the Dimage 7 that reads:

"You won't need a circular polarizing filter, a cheaper linear will be OK if you can find one (all slim filters I've found have been circular polarizing ones)." -MarkoB on 10/7/02 to topic "Filters"

I understand the reason a linear polarizer can interfer with the AF systems with SLR cameras is because they employ light-splitting technique via prisms, mirrors, etc. that causes some internal polarizing that a linear polarizer could interfer with causing the AF problems. However, on most digital cameras which do not have light-splitting techniques, this problem does not exist. Without knowing for sure if the Dimage series of cameras does or does emply this light-splitting technique, I'm not sure if I need a circular polarizer or not. Also the response from MarkoB and the above 2 does not help settle this question.

Does anyone know for sure if a polarizer is needed or not? Please advise if your response is just your opinion, or fact based on actual experience and/or knowledge. Has anyone actually used a linear polarizer and found that indeed the AF system failed?
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Old Aug 1, 2003, 7:40 PM   #5
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Oops, in the last paragraph in the above response, I meant to say,

"Does anyone know for sure if a CIRCULAR polarizer is needed or not? Please advise if your response is just your opinion, or fact based on actual experience and/or knowledge. Has anyone actually used a linear polarizer and found that indeed the AF system failed?"
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Old Aug 2, 2003, 7:25 AM   #6
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Quote:
I understand the reason a linear polarizer can interfer with the AF systems with SLR cameras is because they employ light-splitting technique via prisms, mirrors, etc. that causes some internal polarizing that a linear polarizer could interfer with causing the AF problems. However, on most digital cameras which do not have light-splitting techniques, this problem does not exist. Without knowing for sure if the Dimage series of cameras does or does emply this light-splitting technique, I'm not sure if I need a circular polarizer or not. Also the response from MarkoB and the above 2 does not help settle this question.
... You're probably correct here, since the D7's use no prism or beam splitting, but other cameras might (like my 10D). Most people would just buy the one that will work with both systems, ie a circular one. I haven't try it on my D7 since I don't have a linear one, but I see no technical reason why it should not work here, but make sure to get a very slim one (4-5 mm or less or it will surely vignette otherwise)!
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Old Aug 2, 2003, 3:57 PM   #7
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think of the future
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Old Aug 2, 2003, 4:31 PM   #8
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Quote:
Originally Posted by BobE
Oops, in the last paragraph in the above response, I meant to say,

"Does anyone know for sure if a CIRCULAR polarizer is needed or not? Please advise if your response is just your opinion, or fact based on actual experience and/or knowledge. Has anyone actually used a linear polarizer and found that indeed the AF system failed?"
You asked this some time ago, but I don't get out much. :-) I have a Cokin linear polarizer, and it works just fine with my 7i. A circular polarizer is not needed. And, BTW, the Cokin "A" system does not vignette. It also has other advantages, like a graduated neutral density filter that makes it easy to adjust the point where it fades from grey to clear.
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Old Aug 6, 2003, 1:55 PM   #9
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here is my 2 cents. i might be wrong

as far as i know, linear polarizer will not work with any digital camera because of ccd or image senser. color filters (If any) on ccd will misread linear polarized light. it will give u wrong exposure rather than not focusing.
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Old Aug 6, 2003, 8:04 PM   #10
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Quote:
Originally Posted by zhu001
here is my 2 cents. i might be wrong

as far as i know, linear polarizer will not work with any digital camera because of ccd or image senser. color filters (If any) on ccd will misread linear polarized light. it will give u wrong exposure rather than not focusing.
You are wrong.

As I said in my message, "I have a Cokin linear polarizer, and it works just fine with my 7i". It does not cause any problems with focusing or with exposure. Some cameras do have a problem focussing with a linear polarizer in place. The 7/i/Hi is not one of them. Others on the dpreview forum and Bryan's forum have reported that they also have had no problem with linear polarizers.
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