Problems with CPL.

Dewman · 08-23-2015, 01:34 PM

When shooting using a CPL, it seems as if my K-50 is not adjusting for the loss of light and my images are constantly dark. Any suggestions? I would think, that it being a TTL metering system, it would compensate.... right?

Aaron28 · 08-23-2015, 01:39 PM

curious as I am learning how/when to use a cpl (acquired by my aunts old camera bag)........maybe an ev comp?

Dewman · 08-23-2015, 03:30 PM

Originally posted by Aaron28

curious as I am learning how/when to use a cpl (acquired by my aunts old camera bag)........maybe an ev comp?

Hmmm, Aaron.... maybe we can both learn something about this subject. That would be a good thing. I'm wondering if it would have anything to do with the regular old polarizing filter and the ones designed specifically for digital photography? Geez.... I'm dumb as a post about such things. But, where better to get educated than PF, eh?

promacjoe · 08-23-2015, 04:01 PM

Maybe you have a bad circular polarizer. A circular polarizer that does not randomize the light properly, can affect your exposure meter and focusing system. hold your polarizer up to your flatscreen Computer monitor with a white background. rotated about 90°, it should lighten and darken the screen. Now flip it over, And perform the same test. You should see no change. If during either test, you see a color change, Red, green or blue. Then you have a cheap polarizer. The change in color cast can affect your image. Throw it away and buy a good one.

Aaron28 · 08-23-2015, 04:16 PM

no color change for me although I will say 1 appears a dark blue whereas the other is quite black when completely darkened

LeDave · 08-23-2015, 04:29 PM

Don't photograph using a CPL against or behind the sun. Position yourself so the sunlight is either on the left or right of you and then use the CPL. At least that's what I think, may or may not be true but some other's input would help.

Aaron28 · 08-23-2015, 04:33 PM

Originally posted by LeDave

the left or right

that's sounds good from what I have read 90deg to it........

**MJSfoto1956** · 08-23-2015, 05:32 PM

IMHO, the best use for a CPL is to make your foliage "pop" -- the rich vibrant greens will impress you.
The sky darkening is just "so so" compared to how a CPL improves landscapes overall.

YMMV

Michael

promacjoe · 08-23-2015, 05:42 PM

Originally posted by Aaron28

no color change for me although I will say 1 appears a dark blue whereas the other is quite black when completely darkened

the main test is when you flip it backwards, is there any change in Brightness or color. When turned backwards, You should not see any change in brightness on a good filter.

When in the normal orientation, changing from light to Dark gray and black is good. That means that all colors are being darkened equally. Dark blue is not so good. It means that the colors are not being darkened equally. What kind of filter is it, and how old is it.

This test works because all LCD TVs and monitors has a built-in Fixed polarizer. the LCD panel itself is a variable polarizer. when the screen is white, both polarizers are in the same orientation. When you add a third polarizer and rotate it, it acts the same as stacking two standard polarizers together, And rotating one 90° from the other.

Note: you will not get the same effect if you stack two circular polarizers together, or stack one circular polarizer on top of a standard polarizer.

A circular polarizer has a second layer called a quarter wave plate. This causes the light rays to spin, Which randomize is the light rays. When you flip a circular polarizer over In front of a LCD Monitor, the quarter wave plate randomizes the light before it hits the polarizer layer. then this randomized light is re-polarized. This leaves the light in basically the same orientation that it was from the LCD Monitor.

the basic function of the polarizer is, to reduce reflections at 90° from the light source, Darken the sky, and reduce glare. Reflections from a metal surface are not affected by a polarizer, since these reflections are not polarized light. reflections off of painted surfaces, glass surfaces or water, Have a polarized element. By placing the second polarizer in the right orientation, you can remove most of these reflections.

Aaron28 · 08-23-2015, 05:49 PM

Originally posted by promacjoe

What kind of filter is it, and how old is it

both hoya's 1 from aunt(pentax user) 1 from cousin(canon user & 'dark blue' one).......assuming sometime in the 80s.......the 'dark blue' only at max effect but its difficult to tell whilst getting darker

promacjoe · 08-23-2015, 05:59 PM

I believe the first autofocus cameras appeared in the 80s. And the concept of the circular polarizer was new. The first ones were not very good. There have been many improvements however. some of the new ones are very good, but there are still some out there that are pure garbage. Find yourself a good new circular polarizer and try it on your camera. See if that fixes the problem.

Aaron28 · 08-23-2015, 06:07 PM

Originally posted by promacjoe

See if that fixes the problem.

i'm not having the problem.....following thread to learn......dewman is the one having the exposure issue.......I haven't really started my trial and many errors yet........just prepping for when I force myself to use one.......but good to know I prolly do have a faulty filter......so I can be aware when I actually use it

DeadJohn · 08-24-2015, 08:00 AM

Originally posted by Dewman

When shooting using a CPL, it seems as if my K-50 is not adjusting for the loss of light and my images are constantly dark. Any suggestions? I would think, that it being a TTL metering system, it would compensate.... right?

I often but not always get slightly dark images with a CPL on my K-5. My CPL is designed for digital metering and doesn't create color casts, so I think the CPL isn't faulty.

I've noticed that the histogram for CPL images looks compressed; the extreme black and white ends are lower and shifted a little bit towards the middle of the image. This wasn't a scientific test just an observation. I suspect that the CPL effect knocks down highlights more than it does darker areas, and that skews metering. (a uniform ND filter meters okay)

Since I always shoot in DNG I don't worry about it much; I can adjust exposure or the white point in Lightroom later.

promacjoe · 08-24-2015, 09:23 AM

since there is no way for your camera to tell if a CPL is on or not, I suspect that something is messed up in your settings. go through your camera settings and make sure nothing is set wrong, that can affect your exposure. Pay special attention to your histogram and white balance settings. reset everything to default if necessary, Then test your exposure. After that you can manually reset your settings to what you need, one page at a time. this way you can identify any problems if something comes up. see if the problem comes up with another lens and CPL combination.

If the problem persists after resetting your camera settings to default, there may be something wrong with your camera. You may need to send it in for repair.

08-23-2015, 01:34 PM	#1
Dewman Veteran Member Join Date: May 2012 Location: Idaho Posts: 5,492	Problems with CPL. When shooting using a CPL, it seems as if my K-50 is not adjusting for the loss of light and my images are constantly dark. Any suggestions? I would think, that it being a TTL metering system, it would compensate.... right?

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08-23-2015, 01:39 PM	#2
Aaron28 Pentaxian Join Date: Jan 2015 Location: Huntsville, Al Posts: 7,131	curious as I am learning how/when to use a cpl (acquired by my aunts old camera bag)........maybe an ev comp?

08-23-2015, 03:30 PM	#3
Dewman Veteran Member Join Date: May 2012 Location: Idaho Posts: 5,492 Original Poster	Originally posted by Aaron28 curious as I am learning how/when to use a cpl (acquired by my aunts old camera bag)........maybe an ev comp? Hmmm, Aaron.... maybe we can both learn something about this subject. That would be a good thing. I'm wondering if it would have anything to do with the regular old polarizing filter and the ones designed specifically for digital photography? Geez.... I'm dumb as a post about such things. But, where better to get educated than PF, eh?

08-23-2015, 04:01 PM	#4
promacjoe Veteran Member Join Date: Jun 2014 Posts: 340	Maybe you have a bad circular polarizer. A circular polarizer that does not randomize the light properly, can affect your exposure meter and focusing system. hold your polarizer up to your flatscreen Computer monitor with a white background. rotated about 90°, it should lighten and darken the screen. Now flip it over, And perform the same test. You should see no change. If during either test, you see a color change, Red, green or blue. Then you have a cheap polarizer. The change in color cast can affect your image. Throw it away and buy a good one.

08-23-2015, 04:16 PM	#5
Aaron28 Pentaxian Join Date: Jan 2015 Location: Huntsville, Al Posts: 7,131	no color change for me although I will say 1 appears a dark blue whereas the other is quite black when completely darkened

08-23-2015, 04:29 PM	#6
LeDave Veteran Member Join Date: Jun 2009 Location: Minneapolis - St. Paul Photos: Gallery Posts: 3,067	Don't photograph using a CPL against or behind the sun. Position yourself so the sunlight is either on the left or right of you and then use the CPL. At least that's what I think, may or may not be true but some other's input would help.

08-23-2015, 04:33 PM	#7
Aaron28 Pentaxian Join Date: Jan 2015 Location: Huntsville, Al Posts: 7,131	Originally posted by LeDave the left or right that's sounds good from what I have read 90deg to it........

08-23-2015, 05:32 PM	#8
MJSfoto1956 Site Supporter Join Date: Dec 2013 Location: Boston Posts: 1,305	IMHO, the best use for a CPL is to make your foliage "pop" -- the rich vibrant greens will impress you. The sky darkening is just "so so" compared to how a CPL improves landscapes overall. YMMV Michael

08-23-2015, 05:42 PM	#9
promacjoe Veteran Member Join Date: Jun 2014 Posts: 340	Originally posted by Aaron28 no color change for me although I will say 1 appears a dark blue whereas the other is quite black when completely darkened the main test is when you flip it backwards, is there any change in Brightness or color. When turned backwards, You should not see any change in brightness on a good filter. When in the normal orientation, changing from light to Dark gray and black is good. That means that all colors are being darkened equally. Dark blue is not so good. It means that the colors are not being darkened equally. What kind of filter is it, and how old is it. This test works because all LCD TVs and monitors has a built-in Fixed polarizer. the LCD panel itself is a variable polarizer. when the screen is white, both polarizers are in the same orientation. When you add a third polarizer and rotate it, it acts the same as stacking two standard polarizers together, And rotating one 90° from the other. Note: you will not get the same effect if you stack two circular polarizers together, or stack one circular polarizer on top of a standard polarizer. A circular polarizer has a second layer called a quarter wave plate. This causes the light rays to spin, Which randomize is the light rays. When you flip a circular polarizer over In front of a LCD Monitor, the quarter wave plate randomizes the light before it hits the polarizer layer. then this randomized light is re-polarized. This leaves the light in basically the same orientation that it was from the LCD Monitor. the basic function of the polarizer is, to reduce reflections at 90° from the light source, Darken the sky, and reduce glare. Reflections from a metal surface are not affected by a polarizer, since these reflections are not polarized light. reflections off of painted surfaces, glass surfaces or water, Have a polarized element. By placing the second polarizer in the right orientation, you can remove most of these reflections.

08-23-2015, 05:49 PM	#10
Aaron28 Pentaxian Join Date: Jan 2015 Location: Huntsville, Al Posts: 7,131	Originally posted by promacjoe What kind of filter is it, and how old is it both hoya's 1 from aunt(pentax user) 1 from cousin(canon user & 'dark blue' one).......assuming sometime in the 80s.......the 'dark blue' only at max effect but its difficult to tell whilst getting darker

08-23-2015, 05:59 PM	#11
promacjoe Veteran Member Join Date: Jun 2014 Posts: 340	I believe the first autofocus cameras appeared in the 80s. And the concept of the circular polarizer was new. The first ones were not very good. There have been many improvements however. some of the new ones are very good, but there are still some out there that are pure garbage. Find yourself a good new circular polarizer and try it on your camera. See if that fixes the problem.

08-23-2015, 06:07 PM	#12
Aaron28 Pentaxian Join Date: Jan 2015 Location: Huntsville, Al Posts: 7,131	Originally posted by promacjoe See if that fixes the problem. i'm not having the problem.....following thread to learn......dewman is the one having the exposure issue.......I haven't really started my trial and many errors yet........just prepping for when I force myself to use one.......but good to know I prolly do have a faulty filter......so I can be aware when I actually use it

08-24-2015, 08:00 AM	#13
DeadJohn Pentaxian Join Date: Jan 2011 Location: New York Posts: 4,834	Originally posted by Dewman When shooting using a CPL, it seems as if my K-50 is not adjusting for the loss of light and my images are constantly dark. Any suggestions? I would think, that it being a TTL metering system, it would compensate.... right? I often but not always get slightly dark images with a CPL on my K-5. My CPL is designed for digital metering and doesn't create color casts, so I think the CPL isn't faulty. I've noticed that the histogram for CPL images looks compressed; the extreme black and white ends are lower and shifted a little bit towards the middle of the image. This wasn't a scientific test just an observation. I suspect that the CPL effect knocks down highlights more than it does darker areas, and that skews metering. (a uniform ND filter meters okay) Since I always shoot in DNG I don't worry about it much; I can adjust exposure or the white point in Lightroom later.

08-24-2015, 09:23 AM	#14
promacjoe Veteran Member Join Date: Jun 2014 Posts: 340	since there is no way for your camera to tell if a CPL is on or not, I suspect that something is messed up in your settings. go through your camera settings and make sure nothing is set wrong, that can affect your exposure. Pay special attention to your histogram and white balance settings. reset everything to default if necessary, Then test your exposure. After that you can manually reset your settings to what you need, one page at a time. this way you can identify any problems if something comes up. see if the problem comes up with another lens and CPL combination. If the problem persists after resetting your camera settings to default, there may be something wrong with your camera. You may need to send it in for repair.