- Posts: 637
- Joined: Sun Nov 25, 2018 7:52 am
- Location: Castro Valley, CA
- Real Name: Donald Keller
I think that there is a problem with using a Circular Polarizer on a BMPCC 4K. I have been using false color to adjust a Circular Polarizer with the aperture closed down to force the sky closer to black clipping to get the false color blue for the darker sky. I then readjust the aperture for the image. Any suggestions on how to do it properly would be appreciated.
Although I use manual focus lenses, I found this on dpreview.com by Jonathan Usher in 2012 regarding autofocus:
"...I've noticed a pretty big - but variable - loss of sharpness when using the CPL filters. I've used two now - a slim B&W filter as well as a brand new Kaesemann B&W filter. I can manually focus the lenses with the CPL filter on and get almost all the sharpness I noticed when not using the filter. However it seems that autofocus accuracy is degraded by quite a bit - many images are now quite soft when using AF.
Seeing as the OM-D (and other mirrorless cameras) operate with contrast detection, and a CPL filter reduces light by (say) a couple of stops, I'm wondering if this light loss could be reducing contrast to such a point that autofocus has some real challenges."
Cameron2 posted:
"...I was looking at polarizers for my first m43 camera, I found some information that explained that circular polarizers were necessary for PDAF (Phase Detect Auto Focus - DSLR), but degrade the quality of pictures with mirrorless (CDAF - Contrast Detection Auto Focus) cameras, and thus you should prefer the cheaper linear polarizers."
On an early vintage lens with a single coating and low contrast the out of focus effect of a Circular Polarizer is more pronounced. All the shots in this post were at ISO 100. Here are cropped pictures from a Soviet era Mir-1 37mm F/2.8 1966 lens and a Hoya Circular Polarizer Super-HMC Thin Filter through a DEC Lensregain focal reducer on a BMPCC 4K.
This lens is much sharper without a Circular Polarizer compared to using one that is misadjusted. Both were shot at F16, 1/240 and 1/72 shutter, facing South at around 4:30 PM:
Adjusting the Circular Polarizer helps to sharpen it slightly by increasing the contrast. Both were shot at F16, 1/72 and 1/240 shutter, facing South at around 4:30 PM:
Even with a properly adjusted Circular Polarizer the picture is sharper without it. Both were shot at F16 and 1/240 shutter, facing South at around 4:30 PM:
Although I use manual focus lenses, I found this on dpreview.com by Jonathan Usher in 2012 regarding autofocus:
"...I've noticed a pretty big - but variable - loss of sharpness when using the CPL filters. I've used two now - a slim B&W filter as well as a brand new Kaesemann B&W filter. I can manually focus the lenses with the CPL filter on and get almost all the sharpness I noticed when not using the filter. However it seems that autofocus accuracy is degraded by quite a bit - many images are now quite soft when using AF.
Seeing as the OM-D (and other mirrorless cameras) operate with contrast detection, and a CPL filter reduces light by (say) a couple of stops, I'm wondering if this light loss could be reducing contrast to such a point that autofocus has some real challenges."
Cameron2 posted:
"...I was looking at polarizers for my first m43 camera, I found some information that explained that circular polarizers were necessary for PDAF (Phase Detect Auto Focus - DSLR), but degrade the quality of pictures with mirrorless (CDAF - Contrast Detection Auto Focus) cameras, and thus you should prefer the cheaper linear polarizers."
On an early vintage lens with a single coating and low contrast the out of focus effect of a Circular Polarizer is more pronounced. All the shots in this post were at ISO 100. Here are cropped pictures from a Soviet era Mir-1 37mm F/2.8 1966 lens and a Hoya Circular Polarizer Super-HMC Thin Filter through a DEC Lensregain focal reducer on a BMPCC 4K.
This lens is much sharper without a Circular Polarizer compared to using one that is misadjusted. Both were shot at F16, 1/240 and 1/72 shutter, facing South at around 4:30 PM:
- No Circular Polarizer - L Misadjusted Circular Polarizer - R
- NoCPLL&CPLOutRMir1Tree1.jpg (418.1 KiB) Viewed 10597 times
Adjusting the Circular Polarizer helps to sharpen it slightly by increasing the contrast. Both were shot at F16, 1/72 and 1/240 shutter, facing South at around 4:30 PM:
- Misadjusted Circular Polarizer - L Adjusted Circular Polarizer - R
- CPLOutL&CPLInRMir1Tree2.jpg (471.83 KiB) Viewed 10597 times
Even with a properly adjusted Circular Polarizer the picture is sharper without it. Both were shot at F16 and 1/240 shutter, facing South at around 4:30 PM:
- No Circular Polarizer - L Adjusted Circular Polarizer - R
- NoCPLL&CPLInRMir1Tree.jpg (463.65 KiB) Viewed 10597 times
Last edited by dondidnod on Wed Aug 07, 2019 2:21 am, edited 4 times in total.