polarisor problem ?

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albedo_0_39

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garry
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Hi Folks. I bought a circ polly a few months ago and only just had chance to use it earlier today. I took some test shots of Chesterton Mill (near Harbury). I use Pentax K10D, sigma 10-20mm, Cokin XPro filters etc. I shot at 90 degrees with the polly and a 3stop ND Grad. I adjusted the polly to accentuate the grass for colour etc and took a shot. I dont know whether it's me doing soemthing wrong or whether the polly is faulty. The resultant image does indeed have a blue sky BUT the sky has darker patches in two areas! bizarre! any suggestions of what might be the problem that is causing the darker patches in the sky? (sorry, i dont have anywhere to store and image to upload)

thanks in advance for any hlp
Gaz
 
You can upload pictures to your gallery on TP just remember Max 800px on longest side and max 200kb.
 
It would be easier if there was an image to see. I use Imageshack to link to forums, though in the past I've also used Photobucket. Alot of people use Flickr as well, but there are others, and all free too. ;)

By the sounds of it it may be the effect when using a Polariser with a 'very' wide angle lens. The angle of view is too wide for the Polariser, so you only get the effect in part of the sky. You just have to choose where you want the polarising effect, and if it suits the scene. :shrug:
 
albedo_0_39 said:
The resultant image does indeed have a blue sky BUT the sky has darker patches in two areas! bizarre! any suggestions of what might be the problem that is causing the darker patches in the sky? (sorry, i dont have anywhere to store and image to upload)

thanks in advance for any hlp
Gaz
Click to expand...

This is a common issue with ultra-wide lenses and polarisers I'm afraid. The filter isn't faulty, it's just the laws of physics!

Edit: Here's a bit more scientific detail!
 
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redhed17 said:
By the sounds of it it may be the effect when using a Polariser with a 'very' wide angle lens. The angle of view is too wide for the Polariser:
Click to expand...

I am fairly certain it has nothing to do with the ultra wide angle lens. Xpro filters are the largest cokin filters and do not present any issues with vignetting etc . You've got to admit, it does look odd though!
 
Looks like something wrong there for sure. Can you replicate it? It might just be something not lined up correctly...

(Should be easy to get rid of in PP though for that shot, at least)
 
I'm only just getting into photography, so forgive me if I'm wrong, but isn't it the effect of the ND Grad filter?

Malcolm
 
alexam said:
I'm only just getting into photography, so forgive me if I'm wrong, but isn't it the effect of the ND Grad filter?

Malcolm
Click to expand...

The effect of the ND grad should be even throughout the area it is affecting, not patchy.

(If you can't see the patches, I'd suggest having a fiddle with your monitor settings - they're pretty obvious)
 
reminds me of all the times the camera strap has dropped across the front of the lens :$


nice composition though
 
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camera strap across the lens?. no, sorry ....it was well out of the way. so finally......i have anultra wide angle lens, xpro filters that definately cope without vignetting. Ahhh, hang on.......aren't polarisors made up of TWO surfaces? if so, if these aren't aligned properly - maybe that's the problem! (just guessing). I have also ruled out any defects in the surface of the polly, there are no scratches or anything.......so, has anyone got anything I can follow up to investigate further?
 
Where was the sun in relation to you and the subject ?

You said "I shot at 90 degrees with the polly and a 3stop ND Grad"
what exactly do you mean by shooting at 90 degrees ?

Was the picture you posted cropped at all ?
 
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Suvv said:
Where was the sun in relation to you and the subject ?

You said "I shot at 90 degrees with the polly and a 3stop ND Grad"
what exactly do you mean by shooting at 90 degrees ?

Was the picture you posted cropped at all ?
Click to expand...

90 degrees = I was facing the Mill and if that direction was 12oclock then the sun was at 3 oclock!

also, what has cropping got to do with anything?.....the patches were there before and after a slight crop! why is cropping relevant?
 
one more thing to add here.........which I apologise for not mentioning earlier......when I had the polly in the filter holder on it's own ....whsilt looking through the camera I noticed that the darker area of the polly only appeared to darken part of the sky even after successive rotations, it still happened.....so i think there's still a problem with the polly
 
Is the effect repeatable, or just on the one image?

If it is repeatable, are the darker areas in the same place?
 
I've had similar results (though not quite as bad) with a CP, and its always related to the position of the sun. The nearer to the direction of the sun you are shooting, the more pronounced the effect, so I don't think it's a fault with the filter.
 
There is nothing wrong with the filter or the lens (apart from the Sigma branding :lol:).

Ultrawide lenses cover a very large area of sky (over 90 degrees FOV). The degree of polarisation will depend on the position of light, and naturally you get the extremes.

The other way to put it don't use it on sigma 10-20 with sunlight. 24mm and longer lenses will deliver very good results in these conditions.

Now please read up the physics and / this thread.
 
daugirdas said:
There is nothing wrong with the filter or the lens (apart from the Sigma branding :lol:).

Ultrawide lenses cover a very large area of sky (over 90 degrees FOV). The degree of polarisation will depend on the position of light, and naturally you get the extremes.

The other way to put it don't use it on sigma 10-20 with sunlight. 24mm and longer lenses will deliver very good results in these conditions.

Now please read up the physics and / this thread.
Click to expand...

I wouldn't be so sure about the filter being OK, I have a CP on my lens 90% of the time (the widest focal length is 16mm), and on occasion I've borrowed a friends Sigma 10-20mm lens (with CP) and have never seen an image like the one above. :eek: I've found that when the lens is too wide the bit that is Polarised moves like a darker graduated vertical band across the top of the image as the Polariser is moved, and not patchy like the image above.

I asked if it is similar on other images, which may point to a dodgy filter if the pattern is the same. If is a one off image, then it could be something odd that was happening in the atmosphere at the time. :shrug:
 
redhed17 said:
I wouldn't be so sure about the filter being OK, I have a CP on my lens 90% of the time (the widest focal length is 16mm), and on occasion I've borrowed a friends Sigma 10-20mm lens (with CP) and have never seen an image like the one above. :eek: I've found that when the lens is too wide the bit that is Polarised moves like a darker graduated vertical band across the top of the image as the Polariser is moved, and not patchy like the image above.

I asked if it is similar on other images, which may point to a dodgy filter if the pattern is the same. If is a one off image, then it could be something odd that was happening in the atmosphere at the time. :shrug:
Click to expand...


Please don't drag this on :bang::bang::bang:! IT IS OK, if you use it at 17mm++ on crop away from the sun, etc. Try it at 10mm and then come back to tell us your results.
 
I don't think it's straightforward polarising issue either. You can tell where the sun is and project where the darker band or patch would appear, and it's not like the OP's image.

I suspect there's something going on between the two filters used for the shot, perhaps where the grad is catching the sunlight behind it. I don't know, just a wild guess really - not enough information to say anything more conclusive IMO.

Need to try and replicate the situation with and without both filters.
 
no I agree there is something else going on here. When I read the first post without pictures I assumed you were just seeing the effect of a CPL with a very wide angle. I think there is either something with the coatings on your CPL, or somehow its showing up a fault in the grad, or there is something strange going on as a result of light like round the edges of the grad and then hitting the CPL. All guesses though
 
albedo_0_39 said:
90 degrees = I was facing the Mill and if that direction was 12oclock then the sun was at 3 oclock!

also, what has cropping got to do with anything?.....the patches were there before and after a slight crop! why is cropping relevant?
Click to expand...

Cropping may have removed some of the dark banding, by seeing the whole photo it may have been easier to work out what is happening, although I do not think it would help in this case.

With a wide angle lens and a polariser you can get dark banding, however your example is very unusual.
 
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