Circular Polarizer focus problem - P4K

The place for questions about shooting with Blackmagic Cameras.
  • Author
  • Message
Offline
User avatar

dondidnod

  • Posts: 228
  • Joined: Sun Nov 25, 2018 7:52 am
  • Location: Castro Valley, CA
  • Real Name: Donald Keller

Circular Polarizer focus problem - P4K

PostTue Aug 06, 2019 9:53 am

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:
NoCPLL&CPLOutRMir1Tree1.jpg
No Circular Polarizer - L Misadjusted Circular Polarizer - R
NoCPLL&CPLOutRMir1Tree1.jpg (418.1 KiB) Viewed 5539 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:
CPLOutL&CPLInRMir1Tree2.jpg
Misadjusted Circular Polarizer - L Adjusted Circular Polarizer - R
CPLOutL&CPLInRMir1Tree2.jpg (471.83 KiB) Viewed 5539 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:
NoCPLL&CPLInRMir1Tree.jpg
No Circular Polarizer - L Adjusted Circular Polarizer - R
NoCPLL&CPLInRMir1Tree.jpg (463.65 KiB) Viewed 5539 times
Last edited by dondidnod on Wed Aug 07, 2019 2:21 am, edited 4 times in total.
Offline
User avatar

dondidnod

  • Posts: 228
  • Joined: Sun Nov 25, 2018 7:52 am
  • Location: Castro Valley, CA
  • Real Name: Donald Keller

Re: Circular Polarizer focus problem - P4K

PostTue Aug 06, 2019 10:26 am

Another example of the Circular Polarizer problem. All shots at ISO 100. Picture 4 of 7.
On a lens with a MC filter the out of focus effect is less pronounced. Here is a cropped picture from a Helios 44M-7 58mm F/2.0 1993 lens and a Hoya Circular Polarizer Super-HMC Thin Filter through a M42 to MFT adapter on a BMPCC 4K. Both were shot at F3.5, 1/200 and 1/200 shutter, facing South at around 4:30 PM:
CPLOutL&CPLInR44M7Tree.jpg
Misadjusted Circular Polarizer - L Adjusted Circular Polarizer - R
CPLOutL&CPLInR44M7Tree.jpg (469.96 KiB) Viewed 5450 times


Another example, picture 5 of 7 with the Helios 44M-7. Both were shot at F3.5, 1/200 and 1/200 shutter, facing South at around 5:20 PM:
CPLOutL&CPLInR44M7Bridge.jpg
Misadjusted Circular Polarizer - L adjusted Circular Polarizer - R
CPLOutL&CPLInR44M7Bridge.jpg (576.12 KiB) Viewed 5450 times


Another example of the Circular Polarizer problem. Picture 6 of 7.
On a later design lens the misadjusted Circular Polarizer increases the amount of chromatic aberration. Here is a cropped picture from a Voightlander 17.5mm F/0.95 and B + W XS-Pro Kaesemann High Transmission Circular Polarizer on a BMPCC 4K with it out of adjustment and with it adjusted. These were shot facing East in dappled light, at 5 PM near wide open for bokeh at 1/60 shutter:
CPL&NoCPLCA769&770.jpg
Misadjusted Circular Polarizer - L adjusted Circular Polarizer - R
CPL&NoCPLCA769&770.jpg (476.54 KiB) Viewed 5450 times
Last edited by dondidnod on Tue Aug 06, 2019 9:38 pm, edited 2 times in total.
Offline
User avatar

dondidnod

  • Posts: 228
  • Joined: Sun Nov 25, 2018 7:52 am
  • Location: Castro Valley, CA
  • Real Name: Donald Keller

Re: Circular Polarizer focus problem - P4K

PostTue Aug 06, 2019 10:32 am

Another example of the Circular Polarizer problem. Picture 7 of 7.
When a Circular Polarizer is used on a wide-angle lens from across the street, is is difficult to focus properly as I suspect that the focus peaking is compromised by it. I always use the high setting for focus peaking.

Here is a cropped picture from a Voightlander 17.5mm F/0.95 without a filter and with a B + W XS-Pro Kaesemann High Transmission Circular Polarizer on a BMPCC 4K that may be misadjusted. Notice the chromatic aberration on the roofline. These were shot facing South at around 6 PM, ISO 100. The one on the left is about F11 with a shutter speed of 1/200 and the one on the right was open more than F2.8 (for flare) with a shutter speed of 1/500:
NoCPLL&CPLOutRVoight17.jpg
No Circular Polarizer - L misadjusted Circular Polarizer - R
NoCPLL&CPLOutRVoight17.jpg (456.81 KiB) Viewed 5449 times


Here is the un-cropped version of the out of focus picture indicating a flare from an open iris:
Union&AugustLady1742_3Full.jpg
North Beach Painted Lady - CPL
Union&AugustLady1742_3Full.jpg (831.15 KiB) Viewed 5313 times
Last edited by dondidnod on Tue Aug 06, 2019 10:47 pm, edited 3 times in total.
Offline
User avatar

carlomacchiavello

  • Posts: 1037
  • Joined: Tue Aug 28, 2012 6:04 pm
  • Location: italy

Re: Circular Polarizer focus problem - P4K

PostTue Aug 06, 2019 12:50 pm

Australian Image wrote:I'd say it's to do with the filter/lens combination. I've never seen anything like that with any of my lenses.


Me too. I used circular Polar from many years, with m4/3 from 2011 lumix gh2, and then gh3, gh4, pocket, pocke4k and many other cameras without this kind of problems.
Offline

Chris Whitten

  • Posts: 506
  • Joined: Mon Jul 22, 2013 10:10 pm

Re: Circular Polarizer focus problem - P4K

PostTue Aug 06, 2019 1:23 pm

I have used a polariser on occasion. Not sure if it is 'circular', but probably it is.
I turn it until my picture looks good - darker skies, or clearer water etc. Why would you use false colour?

I focus manually. Once the polariser is in the right spot, I check the focus on my lens and adjust of needed.
Never had anything out of focus after that.
Chris Whitten
Offline

Brad Hurley

  • Posts: 1526
  • Joined: Wed Jan 17, 2018 7:42 pm
  • Location: Montréal

Re: Circular Polarizer focus problem - P4K

PostTue Aug 06, 2019 1:37 pm

Chris Whitten wrote:I Why would you use false colour?


It can help you nail exposure more accurately -- it's good for properly exposing skin tones, for example, and also to avoid crushing shadows or clipping highlights. For example, see below for the false colour spectrum for the Blackmagic Video Assist. The polarizer affects exposure: standard circular polarizers reduce the amount of light entering the camera by 1.5-2.5 stops; HRT filters have a smaller effect.

Screen Shot 2019-08-06 at 9.36.14 AM.png
Screen Shot 2019-08-06 at 9.36.14 AM.png (24.66 KiB) Viewed 5409 times
Resolve 16.1.2 Studio, Mac Pro 3.0 GHz 8-core, 32 gigs RAM, dual AMD D700 GPU.
Audio I/O: Sound Devices USBPre-2
Offline
User avatar

carlomacchiavello

  • Posts: 1037
  • Joined: Tue Aug 28, 2012 6:04 pm
  • Location: italy

Re: Circular Polarizer focus problem - P4K

PostTue Aug 06, 2019 1:58 pm

Brad Hurley wrote:
Chris Whitten wrote:I Why would you use false colour?


It can help you nail exposure more accurately -- it's good for properly exposing skin tones, for example, and also to avoid crushing shadows or clipping highlights. For example, see below for the false colour spectrum for the Blackmagic Video Assist. The polarizer affects exposure: standard circular polarizers reduce the amount of light entering the camera by 1.5-2.5 stops; HRT filters have a smaller effect.

Screen Shot 2019-08-06 at 9.36.14 AM.png

circular help you often cut upper light (sky) and often give you a 1/2 stop of latitude more.
false color help you to be linear to expose correctly and shot by shot keep same exposure on skin and other important things. If you work with too much light often false color help you to understand when you clip highlights that often seems just clipped before, and for correct exposure of low light, to avoid crushing shadow when you need more infos.

https://translate.google.com/translate? ... -colori%2F

here my post (italian translated to english by google), see the last picture where correct exposure give you better picture.
Offline

Cooper

  • Posts: 145
  • Joined: Sat Sep 29, 2018 9:46 am
  • Real Name: Jari Keskisalo

Re: Circular Polarizer focus problem - P4K

PostTue Aug 06, 2019 2:41 pm

Finally got all required pieces for my shoulder rig ... final piece a 2kg counter weight isnt quite enough need to move pieces closer together a bit, but time to start doing test soon.. some power wire soldering incoming first.

I have hot ir cut 715 and true pol circular polarizer 4mm filters 10x10 schneider mptv filters, and nisi 4mm nd ir cut filters 3 and 5 stops if I remember right. The normal version of the polarizer believe is 1 2/3 stops (box is somewhere), so my 2 filter trays should be enough for my needs. Then theres some cheaper screw in filters: hoya ir cut, kenko pl variable nd and circular polarizer for more handheld shots... tiny rig to build/gimbal.

Curious to see if theres some issues with focusing/tint, leaving my current speed boosters unwanted limitations out. Now these all issues seem to be manual focus releted, so is the issue of camera not detecting in focus points so the helping overlays are incorrect? Theres the angle to sun for polarization effect etc.
Offline

Chris Whitten

  • Posts: 506
  • Joined: Mon Jul 22, 2013 10:10 pm

Re: Circular Polarizer focus problem - P4K

PostTue Aug 06, 2019 5:35 pm

Yes, I know why everyone uses False Colour, I use it myself. It was more the method I was questioning.
I would personally use False Colour to help me correctly expose, then adjust my Polariser to bring out a bit more detail in the sky, or reflections off water or glass.
I wouldn't use False Colour to adjust the polariser.
Correct exposure first, then adjust polariser, then slightly adjust exposure (without False Colour) if the polarising effect has made the exposure more dark - or maybe check it with False Colour.
Chris Whitten
Offline
User avatar

dondidnod

  • Posts: 228
  • Joined: Sun Nov 25, 2018 7:52 am
  • Location: Castro Valley, CA
  • Real Name: Donald Keller

Re: Circular Polarizer focus problem - P4K

PostTue Aug 06, 2019 6:45 pm

I live in the San Francisco Bay area and frequently the humidity produces haze that frustrates my ability to see when the Circular Polarizer is spot on. If I don't see a blue sky, how can I see when it gets darker? I'm sure that people who live in smoggy areas have the same problem.

I close the aperture down to f16 and then check the false color display and turn the polarizer ring looking for the blue section where it shows blacks clipping. It may not always work depending on the available light.

The lenses I use have character and frequently have lower contrast that may contribute to the focus assist colored lines not doing it's job to help me focus. I usually pull the dehaze up in post and am rewarded with a lot more control over the image with these lenses.
Last edited by dondidnod on Sat Sep 14, 2019 2:00 am, edited 1 time in total.
Offline

Brad Hurley

  • Posts: 1526
  • Joined: Wed Jan 17, 2018 7:42 pm
  • Location: Montréal

Re: Circular Polarizer focus problem - P4K

PostTue Aug 06, 2019 7:06 pm

dondidnod wrote:I close the aperture down to f16


This might be the issue -- could it be diffraction causing the softness? Were your polarizer shots taken at f16? There would be a significant amount of diffraction there, even on the P4K (more so on the original Pocket). Were the other shots also taken at f16?
Resolve 16.1.2 Studio, Mac Pro 3.0 GHz 8-core, 32 gigs RAM, dual AMD D700 GPU.
Audio I/O: Sound Devices USBPre-2
Offline
User avatar

dondidnod

  • Posts: 228
  • Joined: Sun Nov 25, 2018 7:52 am
  • Location: Castro Valley, CA
  • Real Name: Donald Keller

Re: Circular Polarizer focus problem - P4K

PostTue Aug 06, 2019 9:20 pm

Maybe diffraction has something to do with it on the Zenit Mir-1 37mm F/2.8 lens with it's single blue coating that is known for it's warm vintage look from 1966 and earlier. I used F16 on the Mir-1 shots. I thought that closing down the iris was supposed to widen the depth of field and make focusing easier however.

The Helios 44M-7 was the 7th generation of this series which was the sharpest and it benefited from a MC coating. Since I was considering getting another one with the Anamorfake string modification with a non-adjustable oval aperture of f3.5 for it's pseudo JJ Abrams signature horizontal line flare in every one of his films, I wanted to experiment with this setting. JJ hints at "hey, look what I can do with the $100,000 plus Anamorphic lens used on Ben-Hur in 1959!". All my Helios 44M-7 shots that day were at F3.5, including shots 4 and 5 I posted.

Shot 7 with the Voightlander 17.5 F/0.95 MFT lens was shot at f11 without the CPL and f2.8 or wider for the CPL one with the focus problem.

I have edited my previous posts with more information on each shot.

I am not using an external monitor. Sometimes I use a loupe over the screen when I'm not in the shade. Maybe I depend too much on focus peaking and need a larger, brighter, cooler monitor. Till then I might leave my CPL in the bag and use it only for emergencies.
Last edited by dondidnod on Tue Aug 06, 2019 9:28 pm, edited 1 time in total.
Offline

Brad Hurley

  • Posts: 1526
  • Joined: Wed Jan 17, 2018 7:42 pm
  • Location: Montréal

Re: Circular Polarizer focus problem - P4K

PostTue Aug 06, 2019 9:36 pm

Diffraction is a function of your camera's sensor and the lens's aperture. This article is useful:

https://www.cambridgeincolour.com/tutor ... graphy.htm

Stopping down to f16 or f22 on a MFT-size sensor is going to soften the image due to diffraction. It's even more of a problem on the original Pocket; I never go smaller than f8 or at most f11 on mine, otherwise the softening due to diffraction is very noticeable.

It's counterintuitive to what you may have learned with stills photography -- when I was shooting 35mm film, landscapes, Elliot-Porter style stuff, I was almost always at f22. Now doing video with smaller-than-MFT sensors, I never go above f8 or f11.
Resolve 16.1.2 Studio, Mac Pro 3.0 GHz 8-core, 32 gigs RAM, dual AMD D700 GPU.
Audio I/O: Sound Devices USBPre-2
Offline

John Brawley

  • Posts: 2362
  • Joined: Tue Aug 21, 2012 7:57 am
  • Location: London UK

Re: Circular Polarizer focus problem - P4K

PostTue Aug 06, 2019 10:17 pm

Is it a circular polarizer or just a polariser problem ? I think you need to test both to make sure it's only that thats the issue.

A polariser is basically a form of a diffraction grate. A very small tiny version of an egg crate over your image that only let's light enter from a certain wavelength / angle.

In a circular polariser, which is usually only necessary for some AF functions to work correctly, an extra 1/4 wave plate (grid) is added.

You're basically shooting through kind of a tiny tiny version of a chain link fence...actually two fences when you make it a circular polariser.

Variable ND's are actually usually two polarisers and it's well known this causes resolution problems (the downside of the convenience.)

In theory they shouldn't affect your resolution. But. This is where the quality of the filter and consistency og the manufacturing might affect things.

And anytime you add more glass in front or behind of your lens you have a chance to mess with the optical path. (including speed boosters)

The image from any BMD camera tends to be very very sharp because they don't have OLPFS so they're also sensitive to when things aren't 100%.

Some more reading
https://ascmag.com/blog/shot-craft/unde ... ng-filters

JB
John Brawley
Cinematographer
London UK
Offline
User avatar

dondidnod

  • Posts: 228
  • Joined: Sun Nov 25, 2018 7:52 am
  • Location: Castro Valley, CA
  • Real Name: Donald Keller

Re: Circular Polarizer focus problem - P4K

PostWed Aug 07, 2019 1:58 am

Was diffraction from shooting at f16 the culprit in the softness of the Circular Polarizer? Does using a Circular Polarizer make an image more prone to diffraction softness at closed apertures?

Here are the same images as in my first post of Picture 3 of 7 with the Mir-1 lens, but this is without even simple "auto" processing in Adobe Lightroom:
NoCPLL&CPLInRMir1TreeRaw.jpg
No Circular Polarizer - L adjusted Circular Polarizer - R
NoCPLL&CPLInRMir1TreeRaw.jpg (515.15 KiB) Viewed 5296 times


After applying full full color correction to the image without a Circular Polarizer and then to the one with the adjusted Circular Polarizer, I found that I have a more detailed image that is less "plasticy" and lacking the unrealistic sky hue without the Hoya Circular Polarizer Super-HMC:
NoCPLL&CPLInRMir1TreeA.jpg
No Circular Polarizer corrected - L adjusted Circular Polarizer corrected - R
NoCPLL&CPLInRMir1TreeA.jpg (716.75 KiB) Viewed 5296 times


Here are the same corrected pictures without the crop:
NoCPLL&CPLInRMir1TreeAFull.jpg
No Circular Polarizer corrected - L adjusted Circular Polarizer corrected - R
NoCPLL&CPLInRMir1TreeAFull.jpg (893.82 KiB) Viewed 5296 times
Last edited by dondidnod on Thu Aug 08, 2019 5:01 am, edited 1 time in total.
Offline
User avatar

dondidnod

  • Posts: 228
  • Joined: Sun Nov 25, 2018 7:52 am
  • Location: Castro Valley, CA
  • Real Name: Donald Keller

Re: Circular Polarizer focus problem - P4K

PostThu Aug 08, 2019 4:57 am

I found this on the internet to explain this:

https://www.cambridgeincolour.com/tutor ... ilters.htm
"...Since polarizers reduce direct reflections, this often has the consequence of also reducing image contrast.
...In general, using a polarizer on clouds and skies will almost always increase contrast, but if the subject itself is highly relfective then a polarizer will instead likely decrease contrast.
...Furthermore, sometimes reflections are essential to a photograph. Two key examples include sunsets and rainbows*; use a polarizer on either and the colorful, reflected light may disappear if the polarizer is rotated for maximum effect."

I have been collecting vintage lenses for their ability to display colorful flares of reflected light. They lack contrast by design. If I shoot reflective subjects then adding a polarizer to the combination is only defeating the ability of a mirrorless camera to focus, since it relies on contrast detection to do its job, resulting in a soft image.

It would appear from the result of processing the images, that the Circular Polarizer baked in a view that cheated the sensor of the data it needed to deliver a sharp, contrasty final image.
Offline
User avatar

dondidnod

  • Posts: 228
  • Joined: Sun Nov 25, 2018 7:52 am
  • Location: Castro Valley, CA
  • Real Name: Donald Keller

Re: Circular Polarizer focus problem - P4K

PostThu Aug 08, 2019 7:29 pm

To prove the previous statement about how a Circular Polarizer affects the image, here is another comparison with a different polarized shot. Notice that the light is a little stronger on the polarized image due to the width of it on the curved Windows. The highlights are crushed along with the flare though due go the decreased contrast in the well lit area. The graduation of the shading in the tan area below the roof is compromised in the polarized image. The shaded area below the roof overhang has greater contrast however in the polarized image. In this area we see a slight increase in sharpness. This is like what happens to clouds with a polarizer.

The un-polarized picture is wet and the polarized picture is dry.

I'm still puzzled as to what is responsible for the chromatic aberration on the roof. The aperture was not closed down which might rule out diffraction. Maybe it was the misadjustment of the polarizer.

Here is another cropped picture from a Voightlander 17.5mm F/0.95 without a filter and with a B + W XS-Pro Kaesemann High Transmission Circular Polarizer on a BMPCC 4K that may be misadjusted. Notice the chromatic aberration on the roofline. These were shot facing South at around 6 PM, ISO 100. Although they were shot a week apart, they were only 8 minutes apart, so the angles to the sun are the same. The one on the left is about F11 with a shutter speed of 1/200 and the one on the right was open more than F2.8 (for flare) with a shutter speed of 1/500:
Attachments
NoCPLL&CPLOutRVoight17A.jpg
No Circular Polarizer Voightlander 17.5mm - L misadjusted Circular Polarizer Voightlander 17.5mm - R
NoCPLL&CPLOutRVoight17A.jpg (831.37 KiB) Viewed 5213 times
Offline
User avatar

dondidnod

  • Posts: 228
  • Joined: Sun Nov 25, 2018 7:52 am
  • Location: Castro Valley, CA
  • Real Name: Donald Keller

Re: Circular Polarizer focus problem - P4K

PostThu Aug 15, 2019 7:06 am

The lack of focus in the polarized picture in previous post of the Voigtländer 17.5mm F/0.95 lens was partly due to the difficulty in seeing the colored lines of the focus assist on the monitor and the subject having different distances at each end of the frame. It was also possible that the contrast focus system has trouble showing it's colored lines of the focus assist at this distance from across the street. This was also aggravated by this lenses tendency to be soft as you get to F/2 and below.

Here are fairer comparisons of this lens which has greater contrast than the old Soviet era lenses that I am having polarizer problems with. These were taken facing South at around 7:15 PM. Although the increased contrast of the well lit cracked seam next to the smooth surface makes it sharper, both the surface of the ball and the background trees are slightly grainier on the polarized image.

The first one is at F/2.8 at 1/500 of a sec. It is a sculpture, Rotante Dal Foro Centrale by Arnaldo Pomodoro, near the West gate of the campus at the University of California at Berkeley, shot from about 4 meters away. It originally had a gold finish, but the weather has taken it's toll on it since 1971. Both images have had auto processing only in Adobe Lightroom. There was no filter on the left with reflections from the trees. On the right it was taken with a B + W XS-Pro Kaesemann Circular Polarizer Multi-Coated Glass Filter.
V17NCp&CpInF2_8_500UCBBall.jpg
Voigtländer 17.5mm F/2.8 - Left Voigtländer 17.5mm F/2.8 & Circular Polarizer - Right
V17NCp&CpInF2_8_500UCBBall.jpg (912.32 KiB) Viewed 4855 times


This picture is at F/1.4 at 1/500 of a sec. Both images have had minimal processing in Adobe Lightroom. There was no filter on the left and the softness of this lens with the aperture near fully open is evident. On the right it was taken with an adjusted B + W XS-Pro Kaesemann Circular Polarizer Multi-Coated Glass Filter and this is a fix for the softness at this level of correction since it is sharper.
V17NCp&CpInF1_4_500UCBBall.jpg
Voigtländer 17.5mm F/1.4 - Left Voigtländer 17.5mm F/1.4 & Circular Polarizer - Right
V17NCp&CpInF1_4_500UCBBall.jpg (760.4 KiB) Viewed 4855 times


This is a comparison of the same two pictures as before, but after further processing of the unfiltered image. I increased clarity, dehaze and contrast. On both pictures I added the removal of chromatic aberration and applied the corrected profile for the lens. The sharpness advantage of using the Circular Polarizer is gone thanks to the adjustment range of the 12 bit dng image. The distant tree has greater sharpness without the polarizer. The only advantage of the polarizer is the reduction of the reflection.
V17NCp&CpInF1_4_500UCBBallA.jpg
processed Voigtländer 17.5mm F/1.4 - Left Voigtländer 17.5mm F/1.4 & Circular Polarizer - Right
V17NCp&CpInF1_4_500UCBBallA.jpg (956.22 KiB) Viewed 4855 times
Last edited by dondidnod on Sat Sep 14, 2019 2:52 am, edited 3 times in total.
Offline
User avatar

dondidnod

  • Posts: 228
  • Joined: Sun Nov 25, 2018 7:52 am
  • Location: Castro Valley, CA
  • Real Name: Donald Keller

Re: Circular Polarizer focus problem - P4K

PostThu Aug 15, 2019 7:16 am

To put it in perspective, here are the uncropped images of the spheres.
V17NCp&CpInF1_4_500UCBBallB.jpg
processed Voigtländer 17.5mm F/1.4 - Left Voigtländer 17.5mm F/1.4 & Circular Polarizer - Right
V17NCp&CpInF1_4_500UCBBallB.jpg (928.36 KiB) Viewed 4852 times


With more light from the sun at 75 degrees with the further distance of 15 meters at around 7:35 PM, the same adjusted Circular Polarizer seems to behave differently. Again, this is the University of California ay Berkeley. Both images have had minimal processing in Adobe Lightroom and were shot at F/2.8 at 1/200 of a sec. The highlights are greater on the unpolarized picture. On the polarized picture shadow detail is lost with more noise. I did have a harder time adjusting the polarizer at this angle however.
V17NCp&CpInF2_8_200UCBClTree.jpg
Voigtländer 17.5mm F/2.8 - Left Voigtländer 17.5mm F/2.8 & Circular Polarizer - Right
V17NCp&CpInF2_8_200UCBClTree.jpg (724.65 KiB) Viewed 4852 times


This is a comparison of the same two pictures as before, but after further processing of the unfiltered image. I increased clarity, dehaze and contrast. On both pictures I added dehaze, noise reduction, removed chromatic aberration and applied the corrected profile for the lens. The sharpness advantage of using the Circular Polarizer is gone and there is a slight loss of dynamic range.
V17NCp&CpInF2_8_200UCBClTreeA.jpg
processed Voigtländer 17.5mm F/2.8 - Left Voigtländer 17.5mm F/2.8 & Circular Polarizer - Right
V17NCp&CpInF2_8_200UCBClTreeA.jpg (714.07 KiB) Viewed 4852 times
Offline
User avatar

dondidnod

  • Posts: 228
  • Joined: Sun Nov 25, 2018 7:52 am
  • Location: Castro Valley, CA
  • Real Name: Donald Keller

Re: Circular Polarizer focus problem - P4K

PostThu Aug 15, 2019 7:19 am

To put it in perspective, here are the uncropped images of the trees.
Attachments
V17NCp&CpInF2_8_200UCBClTreeWideA.jpg
processed Voigtländer 17.5mm F/2.8 - Left Voigtländer 17.5mm F/2.8 & Circular Polarizer - Right
V17NCp&CpInF2_8_200UCBClTreeWideA.jpg (961.17 KiB) Viewed 4849 times
Offline

Chris Whitten

  • Posts: 506
  • Joined: Mon Jul 22, 2013 10:10 pm

Re: Circular Polarizer focus problem - P4K

PostThu Aug 15, 2019 7:40 am

OK, I'm getting confused - it could be my issue, not yours.
Are you using the BMD Pocket4K for film or for stills?
For shooting film I have mine set to basic settings.
Shutter angle 180, Project frame rate 25fps (for Europe), shutter 1/50 (twice frame rate), dynamic range - film.
For issues of light, I use a combination of lens aperture and ND filters. So on a bright day in California I might be using ND filters as a few stops below f16 or above f1.4/f2 values are where most lenses are sharpest.
If you are trying to chase down a basic issue - like focus accuracy - why don't you go back to basics, eliminate the majority of the variables and concentrate on the focussing and the impact of that polariser?
Set the camera to BMD's advised basic settings - 180 degree shutter angle and maybe 24fps (North America) and try and focus accurately from there.
Chris Whitten
Offline
User avatar

dondidnod

  • Posts: 228
  • Joined: Sun Nov 25, 2018 7:52 am
  • Location: Castro Valley, CA
  • Real Name: Donald Keller

Re: Circular Polarizer focus problem - P4K

PostThu Aug 15, 2019 8:12 am

I'm trying to concentrate on the impact of focusing with and without the polarizer. I use the film setting and 180 degree shutter angle. I bracket a lot of shots to get the optimal image and then go to work on the best ones. Unfortunately, since the screen shows me a flat image, I have to bracket and choose the one that will maximize the camera's ability in post. I find that since I am using a lot of light and shooting raw, I don't need to use ISO for bracketing, just aperture and shutter speed.

Although I intend to use the camera for video, the most versatility in post is with the 12 bit dng image that is offered in the stills mode. I didn't want motion blur to confuse the comparison. It is also easier and faster to communicate the examples in this forum using still images that have the least amount of degradation from compression.

If I were to use ND filters it could skew the results since the filter could degrade the image and make focusing harder. I notice that the Circular Polarizer limits the dynamic range and an ND filter might also. Although I have several ND filters, I haven't invested in quality ones so far, just house brands and generics.

I'm trying to determine.If and when I should use a Circular Polarizer given the difficulties I am having with the image and getting the camera to focus properly.

Unless I need to fix a problem with refection, I'm finding that whatever the polarizer adds can be duplicated by correction when using the lenses I have. That could change if I use a more compressed codec.

Maybe others have found different results with their lenses.
Offline

Chris Whitten

  • Posts: 506
  • Joined: Mon Jul 22, 2013 10:10 pm

Re: Circular Polarizer focus problem - P4K

PostThu Aug 15, 2019 10:45 am

Just seems very confusing to me.
I think it is simpler to shoot as if in a real world situation.
Set the camera up how you want to shoot - the correct frame rate, shutter speed and shutter angle.
You say you have set shutter angle to 180, but then you are posting examples 'at 1/200 of a second' - which is now a shutter angle of 45.
Chris Whitten
Offline
User avatar

dondidnod

  • Posts: 228
  • Joined: Sun Nov 25, 2018 7:52 am
  • Location: Castro Valley, CA
  • Real Name: Donald Keller

Re: Circular Polarizer focus problem - P4K

PostThu Aug 15, 2019 10:34 pm

To show still dng images that would be closer to real world video, here are the same shots at F/2.8 at 1/60 of a sec. Since they did not match as much and the exposure is out of the sweet spot, I did not post them earlier.

A higher F Stop would have improved the image, but my goal was to find the effect on focus in the area where this lens starts to go soft when uncorrected. I like to push the boundary here to get the characteristic flare that I bought this lens for. The increased depth of field of a high F stop would have masked the focusing problem.

This is the result after processing of the images. On both pictures I added dehaze, clarity, noise reduction, contrast, removed chromatic aberration and applied the corrected profile for the lens. I changed the color temperature to make the unpolarized image slightly colder and the polarized image slightly warmer. There was no filter on the left and it has more shadow detail, but blown out highlights. On the right it was taken with a B + W XS-Pro Kaesemann Circular Polarizer Multi-Coated Glass Filter. Taken at 7:15 PM, it has greater contrast and is sharper on the well lit cracked seam next to the smooth surface, but it is colder with a bluish cast. This crack is the only place that it is noticibly sharper. This unpolarized picture might have been ideal had I used a quality ND filter. At 7:13 PM, the sun was bathing it more and the old gold plating shows through the years of grime. These are the uncropped images of the spheres.
V17NCp&CpInF2_8_60UCBBallAWide.jpg
processed Voigtländer 17.5mm F/2.8 - Left Voigtländer 17.5mm F/2.8 & Circular Polarizer - Right
V17NCp&CpInF2_8_60UCBBallAWide.jpg (986.42 KiB) Viewed 4769 times


This is a comparison of shots at F/1.4 and a shutter speed of 1/60 sec., taken at 7:21 and 7:20 PM respectively. This is the result of processing of the images. On both pictures I added dehaze, clarity, noise reduction, contrast, removed chromatic aberration and applied the corrected profile for the lens. I changed the color temperature to make the unpolarized image slightly colder and the polarized image slightly warmer. Although close, the polarized picture is sharper.
V17NCp&CpInF1_4_60UCBBallA.jpg
processed Voigtländer 17.5mm F/1.4 - Left Voigtländer 17.5mm F/1.4 & Circular Polarizer - Right
V17NCp&CpInF1_4_60UCBBallA.jpg (763.38 KiB) Viewed 4769 times


To put it in perspective, here are the processed uncropped images of the spheres at F/1.4 and a shutter speed of 1/60 sec.
V17NCp&CpInF1_4_60UCBBallAWide.jpg
processed Voigtländer 17.5mm F/1.4 - Left Voigtländer 17.5mm F/1.4 & Circular Polarizer - Right
V17NCp&CpInF1_4_60UCBBallAWide.jpg (972.49 KiB) Viewed 4769 times
Online
User avatar

rick.lang

  • Posts: 13396
  • Joined: Wed Aug 22, 2012 5:41 pm
  • Location: Victoria BC Canada

Re: Circular Polarizer focus problem - P4K

PostFri Aug 16, 2019 1:44 pm

Interesting series so thanks for sharing with us. Illustrates pros and cons of using the polarizer on complex shiny objects.


Sent from my iPhone using Tapatalk
Rick Lang
Offline
User avatar

dondidnod

  • Posts: 228
  • Joined: Sun Nov 25, 2018 7:52 am
  • Location: Castro Valley, CA
  • Real Name: Donald Keller

Re: Circular Polarizer focus problem - P4K

PostSat Sep 14, 2019 1:26 pm

I went back to the Rotante Dal Foro Centrale sculpture recently with a B + W variable ND filter which has a linear polarizer in it. I had a lens that I bought recently, a modified Helios 44-2 58mm anamorfake with a fixed F/3.5 aperture. The focus is softer on this lens than the later Helios 44M designs since it is known as a bokeh king (at least on a full frame camera where you can see swirl in the edges).

Here is a cropped and corrected comparison of the anamorfake Helios 44-2 F/3.5 lens on the left with the same lens using a K&F Concept variable ND filter on the right on a BMPCC 4K camera. There is little if any difference in the soft focus.
Helios44-2NONDL&VNDR.jpg
Anamorfake Helios 44-2 F/3.5 lens no filter - L & B + W variable ND filter - R
Helios44-2NONDL&VNDR.jpg (773.93 KiB) Viewed 3497 times


A strange movement of screw ball cult Kiwibots seeking part-time labor has grown up around the sculpture. In between delivering sandwiches to overworked UC Berkeley professors and lecture notes to students in the dorms are these robots plotting something? Do they believe that the sculpture is their deity? Can it bestow some kind of grace that gives their batteries a charge? Does it's presence improve their GPS visability? What goes on in the mind of a robot anyway?
Hel442AnUCVND096_Bots.jpg
Kiwibots rally at Rotante Dal Foro Centrale - Helios 44-2 & B + W variable ND filter
Hel442AnUCVND096_Bots.jpg (739.3 KiB) Viewed 3497 times
Last edited by dondidnod on Sun Sep 15, 2019 7:45 pm, edited 1 time in total.
Online
User avatar

rick.lang

  • Posts: 13396
  • Joined: Wed Aug 22, 2012 5:41 pm
  • Location: Victoria BC Canada

Re: Circular Polarizer focus problem - P4K

PostSat Sep 14, 2019 7:23 pm

Probably asking directions to the Metaphysics department.


Sent from my iPhone using Tapatalk
Rick Lang
Offline
User avatar

dondidnod

  • Posts: 228
  • Joined: Sun Nov 25, 2018 7:52 am
  • Location: Castro Valley, CA
  • Real Name: Donald Keller

Re: Circular Polarizer focus problem - P4K

PostSun Sep 15, 2019 7:55 pm

A Kiwibot going downtown towards the train station.

This dog is contemplating his future prospects if these things aquire the skill to fetch the newspaper. Or maybe it looks like a fire plug to him.
Attachments
Hel442AnUC_109DogBot.jpg
Kiwibot at UC Berkeley going downtown
Hel442AnUC_109DogBot.jpg (777.94 KiB) Viewed 3420 times

Return to Cinematography

Who is online

Users browsing this forum: Denny Smith, Gavin_c_clark and 19 guests