Any idea whats wrong with this?


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yehosaphat

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Oct 28, 2005
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#1
Any idea whats wrong with this pic using a CPL? Find the blue too blotchy... why is this so??

 

roygoh

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Jan 18, 2002
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#2
Polarizer is not effective over the entire sky. When you shoot in ultra wide angle you include a wide area of the sky and the polarizer can only darken part if it.

In the shot above, a graduated ND is probably a better filter to use. Alternatively, bracket the exposures and then blend the shots in post processing.
 

yehosaphat

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#4
This was achieved by rotating the CPL. My concern is shouldn't the blue be uniform instead of being patchy?? Is it something wrong with the CPL?
 

roygoh

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#5
This was achieved by rotating the CPL. My concern is shouldn't the blue be uniform instead of being patchy?? Is it something wrong with the CPL?
First of all, why did you want to use a polarizer? To darken the sky?

If so, then as I have explained, a polarizer can only darken part of the sky...not the entire sky. That's why the blue is darker at the area where the polarizer is most effective and brighter where the polarizer is not as effective.

Do a thumbs up gesture with you hand and point your thumb at the sun. Then open and close your fingers...the parts of the sky that your fingers sweep across is where a polarizer is most effective in darkening (when the angle is right)...because most of the scattered light from that direction is polarized, and can be blocked by the polarizer. Light coming from other parts of the sky is not polarized, so a polarizer only gives the same amount of dimming regardless of the rotation angle.

There is nothing wrong with your polarizer...but I think I can spot some sensor dust...:)
 

MaZaCA

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Dec 22, 2007
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#6
Polarizer is not effective over the entire sky. When you shoot in ultra wide angle you include a wide area of the sky and the polarizer can only darken part if it.

In the shot above, a graduated ND is probably a better filter to use. Alternatively, bracket the exposures and then blend the shots in post processing.
Sorry, hijack the thread…. so is GND the solution? any other method or solution if I were to use wide angle, say 12-24? thanks in advance.
 

yehosaphat

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#7
First of all, why did you want to use a polarizer? To darken the sky?

If so, then as I have explained, a polarizer can only darken part of the sky...not the entire sky. That's why the blue is darker at the area where the polarizer is most effective and brighter where the polarizer is not as effective.

Do a thumbs up gesture with you hand and point your thumb at the sun. Then open and close your fingers...the parts of the sky that your fingers sweep across is where a polarizer is most effective in darkening (when the angle is right)...because most of the scattered light from that direction is polarized, and can be blocked by the polarizer. Light coming from other parts of the sky is not polarized, so a polarizer only gives the same amount of dimming regardless of the rotation angle.

There is nothing wrong with your polarizer...but I think I can spot some sensor dust...:)
Yes I am aware of how CPL is to be angled with the sun and i wanted to darken the sky. I am refering to the patch where is blue... is it supposed to be that patchy? I thought it should be a gradual deepening of the blue?
 

icebox

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Do you mean the banding of blue colors, as they get darker? Either you've pulled the histogram wider using levels in Photoshop, or it's simply a limitation of our monitors, particularly LCDs. They cannot display the differences between very close colors, leading to banding.
 

roygoh

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#9
Yes I am aware of how CPL is to be angled with the sun and i wanted to darken the sky. I am refering to the patch where is blue... is it supposed to be that patchy? I thought it should be a gradual deepening of the blue?
Sorry for misunderstanding your question...If you are referring then to the banding in the area where the brighter sky transitions into the darker blue, then as icebox has explained, it could be due to monitor not able to display the very gradual transition.

Also, JPEG compression can create that effect...if you lower the quality setting.
 

giantcanopy

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Feb 11, 2007
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#10
Sorry, hijack the thread…. so is GND the solution? any other method or solution if I were to use wide angle, say 12-24? thanks in advance.
You can use a GND to darken the sky as well but it works by darkening everything under the area it covers compared to how a polariser works. A polariser can bring punchy contrast between the clouds and the skies

Ryan
 

yehosaphat

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#11
Sorry for misunderstanding your question...If you are referring then to the banding in the area where the brighter sky transitions into the darker blue, then as icebox has explained, it could be due to monitor not able to display the very gradual transition.

Also, JPEG compression can create that effect...if you lower the quality setting.
No worries. But but I use the highest quality... so in your opinion, this pic is ok? in terms of its blue hues?
 

#12
This is why a CPL doesn't work on wide angle lenses. It is actually an excellent example picture. At any rate, everyone's advice is pretty much spot on. a GND is your solution. :) Still, take heart in your nice composition. :)
 

calebk

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Jul 25, 2006
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#13
No worries. But but I use the highest quality... so in your opinion, this pic is ok? in terms of its blue hues?
In terms of blues, it's okay, but the uneven polarisation spoils it any way, so no point. Go with a GND if you want to darken skies; it's usually a better solution on the ultrawide.
 

yehosaphat

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#14
Ok... thanks for your comments. At least some learning pts, CPL is working fine :p and CPLs doesnt work well with ultrawides ;)
 

calebk

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#15
Ok... thanks for your comments. At least some learning pts, CPL is working fine :p and CPLs doesnt work well with ultrawides ;)
As additional content, you may want to have a look at this thread. There are some examples and explanations on uneven polarisation, even though the thread is more on slim filters

http://www.clubsnap.com/forums/showthread.php?p=3845061

Also check out this website:

http://www.great-landscape-photography.com/polarizing-filter.html

Look for the paragraph titled "are there any pitfalls to using one?" for some info on uneven polarisation.

Hope these help.
 

yehosaphat

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#16
Ahh.... thanks. So its a common prob... so does that mean using a slim CPL will help avoid this uneven banding?
 

Beethoven

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Jul 25, 2005
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#17
Ahh.... thanks. So its a common prob... so does that mean using a slim CPL will help avoid this uneven banding?
The thickness of the polarizer has nothing to do with the uneven-ness of the effect it has on the sky. I haven't read the links, but what Roy and the others are trying to say is that the polarizer affects light coming in one plane.

When it is used with a normal to tele lens the light coming into the lens are similar in angle/direction, hence the polarizing effect is similar throughout the photo, but when a wide and esp ultrawide lens is used different angles of light come from different parts of the sky, and it is this dissimilarity that results in the uneven darkening.
 

calebk

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#18
Ahh.... thanks. So its a common prob... so does that mean using a slim CPL will help avoid this uneven banding?
No it doesn't. It has to do with polarisation of light, not at all the physical width of the polariser.
 

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