When bad can actually be a good thing!
A CPL(or polariser) on an Ultra Wide Angle !
You may read comments by some folks that using a polariser on a very wide angle is not normally a good idea, as it causes weird blue sky effects!
like that. And of course it's true(hey I just posted an image with that weird effect didn't I? ) but many of the comments I've read from various posts(not only here but on many forums) regarding that phenomenon seem to be of the opinion that it always causes that effect, which is simply not true!
ie. the wording in the advice seems to be advocating that you will see this effect, not that you may see this effect. Two different ways of describing what should be a simple hint or tip or caveat.
So it does happen and you will almost likely see it too on your UWA , and having a higher quality polariser makes no difference.
But I sometimes put that effect to work for the common good!
Sometimes you may come across a gully or creek or valley where the dynamic range from a blue sky to the darkest shadows in the deep red earth is just too much for your camera to handle and GND's are all but useless really. You maybe able to regain 1 more DR using a good GND, but then the trees or hills or whatever that line the sides of the gully/valley will also get affected by the GND too. So another or two of range can be gained by using that ugly blue sky(UBS) phenomenon to your advantage.
As I did in this recent shot from Bendigo(actually out of Bendigo near Maldon.. but that;s not the point! )
Image links to the thread. In that thread the third image also benefited by that UBS effect, but not as much as this particular one.
Problem is that you can't rely on it. When you can't rely on it(UBS) to happen then you will almost certainly see normal polarisation, so you still get some benefit.. but UBS seems to concentrate the darker blue in that weird triangle pattern, and that seems to be maybe up to another of latitude.
How this helps is that you can overexpose the part of the sky that you'd like to make blue, and recover it later in PP.
Over expose by 1 and you should recover that colour in your editing software, but more importantly you will be a lot closer to a better value for the shadow areas.
Technically I stuffed that gully shot as I didn't over expose the sky by enough. But that's not really the issue here. I did bracket the shot though so I did get a brighter version of that scene, but this looked nicer on viewing the histogram, and the brighter version(that was +0.7Ev compared to this version) had over exposed foreground spots, and the shadows were still recoverable without losing any color info. That's all that's important.
So the point of it all ... you can maximise your dynamic range by thinking outside the square.
Where you see problems, it could actually be a solution in disguise
As for that first image example the UBS shot. That was a slightly underexposed version of a bracketed scene. Even though I bracket, I still don't HDR my images.
But with the +0.7Ev shot the UBS issue was easily manageable would have been recovered without fuss.
If it's too dark you have trouble doing so and the resultant image will have data loss/blue channel noise and a few weird mottled effects between the (now) recovered darkest part and the pulled back brighter parts of the sky.
But what I do if I can't avoid the UBS issue, is to rotate the polariser until the darkening in only on one corner, and then use the GND turned at an angle that balances out the other corner. it's simple and usually effective(if you have a GND of course! )
ie. in the upper image the I used to process I had the UBS spot nearer the upper right, and the GND turned about 15° anticlockwise to darken the left corner.
Hence, in a few of my images I stack polarisers and GND and more GNDs and maybe even another GND!.... just for the hell of it, and because I have a few of them.
That corner is the one furthest from the sun(as you'd expect ) so you you want to use GNDs in that manner just try to think about that element next time you start setting up your . ie. if you are facing the 'wrong way' then if you can turn round and face the right way.
I'm still yet to find a practical use for stacking polarisers though... but I'm working on it
I still only get a brown double v effect(at it's most extreme effectiveness and you can rotate the entire stacked set of polarisers to vary the orientation of that V within the frame.
Reality is that it looks uglier than the UBS effect... so we'll call that one the UIERBVS
I just can't think of any practical use for it
hope someone can use this hint/tip. It helps me sometimes.. not perfectly all the time and with creative use of filters(eg. I still have to stack a GND on occasion too) but as long ats the resultant image turns out with a good value(histogram) that's all that matters