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01-03-2020, 08:03 AM   #1
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Use of a CPL on an Irix 15mm Lens

I've just purchased an Irix 15mm lens for landscape use on my K-1. I frequently use a polarizing filter on my other lenses for landscapes but my understanding is they often do not work well on ultra wide angle lenses, problems such as banding occurring. I don't have a CPL large enough (95mm and expensive) for the Irix and wonder if there is any point purchasing one specifically for landscape use. Thanks for any suggestions.

01-03-2020, 08:18 AM   #2
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I have never experienced "banding", others can chime in... vignetting is more often the problem with extreme WA lenses. For this I use a larger Polarizer and a step-up ring. But at 95mm as the starting filter size, that will be one LARGE polarizer to get!
01-03-2020, 08:21 AM - 1 Like   #3
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The issue with UWA lenses and polarizing filters is that the sky has different amounts and directions of polarization across the sky. Thus, there's no setting of the polarizer than gets nice uniform results. In a UWA image with a polarizer, some parts of the sky will be darkened but some will not. The result is a strange look with dark blue sky in one part of the image and light blue sky in the other.

So if you want a more intense sky, a polarizing filter isn't going to do it.

That said, a polarizer can still reduce or enhance reflections off of water and other reflective surfaces, even on a UWA.
01-03-2020, 09:17 AM - 1 Like   #4
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QuoteOriginally posted by photoptimist Quote
The issue with UWA lenses and polarizing filters is that the sky has different amounts and directions of polarization across the sky. Thus, there's no setting of the polarizer than gets nice uniform results. In a UWA image with a polarizer, some parts of the sky will be darkened but some will not. The result is a strange look with dark blue sky in one part of the image and light blue sky in the other.
Correct, but why is this so? Lemme tell ya:

The polarized light in the sky comes from scattered sun light. The polarization effect on scattered light is strongest for light scattered at a 90 degree angle from the source (= the sun). So, the sky viewed roughly towards the sun shows very little polarization (as does looking in the opposite direction from the sun). If you look at the sky that is 90 degrees away from the sun, there will be the maximum polarization, and the maximum effect due to any polarizing filter.

So, if the sun happens to be nearly overhead, the sky along the horizon - in all directions - will show a substantial polarization effect. If your wide angle lens covers from the horizon to the zenith in this case, the polarization can vary considerably over the frame, depending on the angle the polarizer is set to.

This is physics - there's no way around it!!

01-03-2020, 09:44 AM   #5
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I would reconsider purchasing CPL If you often use gradual filters as well. Irix 15mm on full frame will show big vignetting (completely black corners) when you mount IFH100 holder even on dedicated slim UV filter.
01-03-2020, 10:37 AM   #6
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I use a polarizer on my DFA 15-30, and that includes the 15mm end. It can be tricky, but it also can yield good results. Banding can certainly be an issue, and I often find that dialing it back a hair still gives a benefit without making the sky looking weird. It really gets down to angles and subject matter, and taking a few shots without the polarizer is a good idea to make sure you have something to work with. They can be pricey, so I'd say the way to go at it is knowing it's going to be tricky, and be ready to accept results that are less than you hoped for. That way, you can be pleasantly surprised when you use it more than you thought versus upset when less than you had wanted.
01-03-2020, 12:50 PM - 1 Like   #7
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QuoteOriginally posted by wanderer2 Quote
I've just purchased an Irix 15mm lens for landscape use on my K-1. I frequently use a polarizing filter on my other lenses for landscapes but my understanding is they often do not work well on ultra wide angle lenses, problems such as banding occurring. I don't have a CPL large enough (95mm and expensive) for the Irix and wonder if there is any point purchasing one specifically for landscape use. Thanks for any suggestions.
If you use ND filters, the filter holder that Irix makes is excellent. It’s very well made.
01-03-2020, 03:54 PM   #8
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You should be able to build a small retaining mount to place a filter behind the lens (stick it to the rear of the lens but not in contact with the rear lens element), but that is more prone to any defects in the polarizing material (optically). If you get material of adequate quality, that's the better way to go and far less expensive. Another downside is that you can't conveniently rotate it so you have to adjust it by trial and error until it has the proper rotation for what you're after.

01-05-2020, 05:51 AM   #9
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Thanks for the replies. It seems that a CPL in this situation can be quite problematic and given the expense of a quality 95 mm CPL I think I will hold off purchasing one, at least at this time. My early shots with the Irix show an exceptionally blue sky rendering, or perhaps that's at least partly due to the landscape setting on my K-1. Thanks again for all the help.
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