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Old Jan 3, 2010, 1:31 AM   #1
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Default Linear polarizers on my E-520

OK, I know linear type polarizer filters are not supposed to be compatible with digital photography. However I used one fine on my old Fuji S6500FD, no issues, got good blue skys and water shots all the time.
On my Olympus E-520 it's a different story now, but it depends which lens I fit as to how bad the linear polarizer messes up the shots.
On a short lens it gives poor sharpness/focus, and on a long lens it's hopeless. Auto focus AND manual focus is never sharp, and that was a surprise, I thought it would just mess up AF on a dSLR!

OK, I guess I 'DO' need a Circular Polarizer for the E-520. Nothing like your own empirical testing to find out for sure.

I have below two 640x480 cropped test shots. One with no filter, one with a Japanese Fujiyama polarizer.

It's obvious the linear polarizer is ruining the shot, and even doing a manual focus does not get a better one.

Question.
Has anybody got a linear type AND a circular type polarizer in their kit, and could they take a test shot with each to demonstrate the difference on an Olympus dSLR ?

Just curious,
Martin
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Old Jan 3, 2010, 3:51 AM   #2
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The issue is the fact dSLRs use a semi-silvered mirror...look at the red line and follow it through the mirror in this image, and onto the focus/exposure sensor:


When you use a linear polarizer, the polarized light doesn't travel through the mirror and the camera can't focus (and may also have issues with exposure depending on what mode you're in).

Your S6500FD wasn't an SLR, so there was no mirror, so therefore no problem using a linear polarizer on that camera. Same goes for the new Micro FourThirds cameras.

I admit I do use linear polarizers (two together to create a variable ND filter) with my E-3xx cameras, but then I use manual focus and manual exposure, so no problem...although if I did it with a linear and a circular I could probably still do auto exposure and autofocus (if there's enough light).

To sum up quickly, the circular polarizer is a linear polarizer with a 1/4 wave plate which circularizes the light, after it has been linearly polarized.

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Old Jan 3, 2010, 7:24 AM   #3
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........this was interesting to learn. Thanks for the question AND the explanation, I've wondered (why) about this from time to time.
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Old Jan 4, 2010, 6:20 AM   #4
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Default Manual focus ?

Thanks Mike, that's a fantastic cutaway image there. Great reply and info.
OK, I follow the lack of light getting to the AF sensor, no problem with that part.
My next query on the subject is this. Why can't I use manual focus either ?

I tried, and tried, with two lenses, and it will not manual focus to a normal level of sharpness. Using a long lens (50-200mm, zoomed) it's a real joke actually. See my next image, it's the BEST I could do via the view finder on the E-520.
Is there some weird effect on the light going to the view finder also, the 'direct' path if you like ?

I went and saw a pal with a Pentax tonight, the linear polarizer has the same effect on his too. He also is puzzled why the direct view finder path is unfocusable...

very curious,
Martin
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Old Feb 11, 2010, 6:41 PM   #5
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Default Hoya HD

I bought a Hoya HD CPL filter yesterday from the LHS, I'd had small windfall in cash that was burning a hole in my credit card...

At $140AU (normally I'd never consider spending that much on a filter), I hope it works well. I'll post a test image when I get time.
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Old Feb 11, 2010, 8:15 PM   #6
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Quote:
Originally Posted by mr.sneezy View Post
I tried, and tried, with two lenses, and it will not manual focus to a normal level of sharpness. Using a long lens (50-200mm, zoomed) it's a real joke actually. See my next image, it's the BEST I could do via the view finder on the E-520.
Some of that may be blur from camera shake. It looks like your shutter speed was only 1/125 second for that photo.

Since you were at a 35mm equivalent focal length of 400mm (actual focal length of 200mm, giving you the same angle of view you'd have using a 400mm lens on a 35mm camera), the "rule of thumb" for a hand held camera would mean that you'd need shutter speeds of at least 1/400 second to reduce blur from camera shake.

Now, that's only a rule of thumb. But, given higher density sensors, with larger viewing sizes when looking at 100% crops, there is some evidence to suggest that the older rule of thumb may not be good enough in some cases (depending on how steady someone can hold a camera and squeeze the shutter button).

I understand that the E-520 is stabilized. But, that's only going to help so much, and your shutter speeds may have been "borderline" trying to shoot at 1/125 second at a focal length that long, depending on how steady you can hold a camera and squeeze the shutter button.

Keep in mind that you'll have significant loss of light using a polarizer, too. That could be one of the contributing factors when you and your friend are having difficulty getting sharp shots using one, even with manual focus (because of slower shutter speeds if you don't increase your ISO speed to compensate for light loss through a polarizer).

It can also be tough to judge focus accuracy in a smaller viewfinder unless you're using a split prism type focus screen.
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Old Feb 12, 2010, 3:58 AM   #7
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Quote:
Originally Posted by JimC View Post
Some of that may be blur from camera shake. It looks like your shutter speed was only 1/125 second for that photo.
Sorry Jim, perhaps I should have stated originally I used a tripod and IR remote trigger for all shots so shake was minimal, if not zero. I also turned off IS as suggested in the manual.
I also used Live View's magnifier to help manual focus when I tried MF. Tried to avoid the common pitfalls I knew about when testing lenses.

Will try a new test with the Hoya HD soon.

Thanks,
Martin
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Old Feb 12, 2010, 7:45 AM   #8
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If you're using Live View to focus, the you're using the main imaging sensor with your E-520 (so, it's going to see the image in the same way you were focusing when the photo is taken).

IOW, unless camera shake is a factor, it sounds like your focus was off (i.e, the image should have already been soft on your Live View display, since it's using the camera's main imaging sensor to provide that display), unless the filter itself was degrading the image quality due to it's optics (but, again, that degradation should have been visible in the Live View display, too). Are you sure that tripod is steady (no ground vibration from vehicles, or perhaps high winds that could have been causing an issue)?
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