Ugly Hedgehog® - Photography Forum
What Happened?
If you want to reply, then register here. Registration is free and your account is created instantly, so you can post right away.
Page: 1 2 next>>
Nov 23, 2018 18:16:11   #
Wingpilot (a regular here)
 
Sony A6300 with 15-50mm lens, with CPL. Sun was off to my right, about 120 degree. Why do I have this dark blue area at the top of the image? I figured using the CPL would result in the sky being uniformly darkened. I have to be missing something here. I'd appreciate an wisdom here.

Edit: I forgot to add that these are all unedited RAW files, right out of the camera.


(Download)


(Download)


(Download)

| Reply
Nov 23, 2018 18:27:27   #
speters (a regular here)
 
Wingpilot wrote:
Sony A6300 with 15-50mm lens, with CPL. Sun was off to my right, about 120 degree. Why do I have this dark blue area at the top of the image? I figured using the CPL would result in the sky being uniformly darkened. I have to be missing something here. I'd appreciate an wisdom here.

It is because of the CPL! That is the one issue when using a CPL, a lot of times you will get uneven polarization across a sky when using a wide lens! Using a less wide lens will avoid this phenomenon!

| Reply
Nov 23, 2018 18:31:09   #
rgrenaderphoto (a regular here)
 
speters wrote:
It is because of the CPL! That is the one issue when using a CPL, a lot of times you will get uneven polarization across a sky when using a wide lens! Using a less wide lens will avoid this phenomenon!


Exactly. This also would be very easy to adjust with a graduated filter in Lightroom.

| Reply
Nov 23, 2018 19:02:09   #
jak86094 (a regular here)
 
Agreed with prior commenters. The effect of a CPL filter on a blue sky is greatest at about 90 degrees to the sun and will reduce more and more as the angle changes to either side of 90 degree street . But the CPL will still have a good effect on highlights from leaves or water or from nonspectral reflections from glass, metal, etc. Steve Perry at Backcountry Gallery, a member of UGG, has a very clear YouTube video on using CPL filters that I highly recommend. jak

| Reply
Nov 23, 2018 19:22:21   #
Wingpilot (a regular here)
 
jak86094 wrote:
Agreed with prior commenters. The effect of a CPL filter on a blue sky is greatest at about 90 degrees to the sun and will reduce more and more as the angle changes to either side of 90 degree street . But the CPL will still have a good effect on highlights from leaves or water or from nonspectral reflections from glass, metal, etc. Steve Perry at Backcountry Gallery, a member of UGG, has a very clear YouTube video on using CPL filters that I highly recommend. jak


I need to check out that video.

| Reply
Nov 23, 2018 19:23:35   #
Wingpilot (a regular here)
 
speters wrote:
It is because of the CPL! That is the one issue when using a CPL, a lot of times you will get uneven polarization across a sky when using a wide lens! Using a less wide lens will avoid this phenomenon!


Ok, thanks very much. I was not aware of that. I've had CPL's on 50mm lenses before and not experienced this, so I will keep that in mind. My education continues.

| Reply
Nov 24, 2018 07:48:45   #
jerryc41 (a regular here)
 
Yes, a wide lens can produce strange results with a CPL.

| Reply
Nov 24, 2018 07:54:38   #
camerapapi (a regular here)
 
It is called "partial polarization." When using a wide angle to photograph the sky with a polarizer that is exactly what happens.
I seldom use a polarizer, except to eliminate reflections from non metallic surfaces.

| Reply
Nov 24, 2018 08:16:45   #
mrjcall
 
Wingpilot wrote:
Sony A6300 with 15-50mm lens, with CPL. Sun was off to my right, about 120 degree. Why do I have this dark blue area at the top of the image? I figured using the CPL would result in the sky being uniformly darkened. I have to be missing something here. I'd appreciate an wisdom here.

Edit: I forgot to add that these are all unedited RAW files, right out of the camera.


I notice you snuck an iPhone image in as the last image. No blue sky effects there, eh? 😎

| Reply
Nov 24, 2018 08:21:42   #
BebuLamar (a regular here)
 
The linear polarizer works better than a circular one as far as reducing reflection. What reason do we need the CPL? I knew but I now forgot.

| Reply
Nov 24, 2018 09:01:13   #
Woodworm65
 
CPL caused the problem

| Reply
Nov 24, 2018 09:25:53   #
DirtFarmer (a regular here)
 
BebuLamar wrote:
The linear polarizer works better than a circular one as far as reducing reflection. What reason do we need the CPL? I knew but I now forgot.


A CPL is a linear polarizer as far as the subject is concerned.

The CPL consists of a linear polarizer and a quarter wave plate. The linear polarizer is on the outside, facing the subject. The quarter wave plate is oriented at 45 degrees to the plane of polarization coming through the linear polarizer. That means it sees two orthogonal polarized components, at +/- 45 degrees to the plane of polarization coming through the linear polarizer. One of those components gets delayed in phase by 1/4 cycle. The result is circular polarization.

Circular polarization acts pretty much like unpolarized light, since it consists of two orthogonal polarized components. For that reason it is not significantly affected by reflections off dielectric surfaces, like linearly polarized light is.

| Reply
Nov 24, 2018 09:39:11   #
Rich1939 (a regular here)
 
BebuLamar wrote:
The linear polarizer works better than a circular one as far as reducing reflection. What reason do we need the CPL? I knew but I now forgot.


I too forget. At least all the specifics but our digital senors and linear polarizers don't play well together.

| Reply
Nov 24, 2018 09:41:43   #
Bipod (a regular here)
 
On cameras that work with a PL, it will cause exactly the same results as a CPL.

A CPL is a PL -- plus quarter-wave plate. The latter simply gets rid of the linearl
polarization (by converting it to ciruclar polarization) -- which otherwise would cause
problems on cameras that locate the meter and/or AF behind a partially transmissive mirror.

In every respect, a CPL is used exactly like a PL, the image will look the same.

| Reply
Nov 24, 2018 09:48:47   #
Rich1939 (a regular here)
 
For what its worth; For the last year or so I've been using either a 50mm or an 85mm lens to take multiple images then stitching them together rather then use a wide angle lens. Even then I find that a CPL can be more trouble than it is worth because of the varied angles relative to the sun. Unless there is a need for a polarizer, other than darkening the sky, that filter isn't used. I can darken shies quit effectively in post with out the hassle.

| Reply
Page: 1 2 next>>
If you want to reply, then register here. Registration is free and your account is created instantly, so you can post right away.
UglyHedgehog.com - Forum
Copyright 2011-2019 Ugly Hedgehog, Inc.