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[OM] Re: 7-14 digital zoom / polarizing effect

Subject: [OM] Re: 7-14 digital zoom / polarizing effect
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxx>
Date: Fri, 11 Aug 2006 17:49:11 -0400
Funny this "wide angle appears polarized" subject should come up just 
now since I noticed it for the first time yesterday when building this 
pano shot with the A1.
<http://www.chucknorcutt.com/chatham/>
It obviously doesn't take a super wide.  This image is made from 5 
images shot at 7mm (28mm equivalent) and overlapped by about 50%.  The 
pano was constructed by PTGUI.  When it showed me the intermediate image 
before blending all togheter I was astounded to see what looked like a 
polarizing effect from the edge of one image blending into the next. 
The right side of one image was a much different blue than the left side 
of its partner but it hadn't really been noticeable until the images 
were overlaid.  It was so pronounced that I actually went and inspected 
the camera to see if I had accidentally left the polarizer on.  I 
hadn't.   I was even more astounded when PTGUI gracefully blended all 
the various shades of sky blue together to give me what you see here.

This image was taken in Chatham, Massachusett which is at the bend in 
the elbow of Cape Cod.  The water in the foreground is Oyster Pond River 
and the water in the far background is Nantucket Sound.  On this map
<http://maps.yahoo.com/maps_result?addr=&csz=chatham%2C+MA&country=us&new=1&name=&qty=>
you can see Stage Harbor and it's the Oyster Pond River that's flowing 
into the Harbor from the north west.  The photo is taken looking south 
on the north side of the bend in the river.  Perhaps the polarizing 
effect was due to the clear air over the water.  The weather was cool 
and very dry for August.

My wife and I had been invited to spend a few days with friends who had 
rented a house on the Cape.  Based on a previous trip to visit these 
friends (at a much less spectular house) I really didn't think there'd 
be any opportunity for photography so didn't pack anything but the A1 
and a 256MB card.  Shooting the pano was a spur of the moment decision 
when I walked out into the back yard in the morning after arriving the 
night before.  Then I wished I'd brought the 5D and a tripod and shot 
everything in raw.

There is some more shadow detail in the JPEG's but I haven't attempted 
to tease it out.

Chuck Norcutt

Garth wrote:
> Winsor Crosby wrote:
> 
>>You are such a lucky guy. It is a clear air effect.
>>
>>  I used to be accused of using a polarizer with my hiking shots  
>>because people had never seen blue skied unbleached by dust and  
>>moisture. This picture obviously has the sun behind the shadowed  
>>hill. The other one you posted shows lightening near the horizon  
>>where the thick atmosphere is. Of course the wide angle exaggerates  
>>the effect.
> 
> 
> 
> I believe Winsor's bang on the money.  This is quite common in wide 
> angle shots in Western Canada, where we have lots and lots of clear air 
> -- I see it in every few shots I take of landscapes.  It also shows up 
> when you're doing panos.
> 
> Basically, as you look toward the sun, you're also looking through water 
> vapour, low-level ozone, etc.  Most of these particulates/molecules do 
> *not* scatter light widely; for example, it's unusual that sunlight 
> would be reflected 90 degrees off-axis.  But, say, 20 degrees?  Sure, no 
> problem.  The sky near the sun tends to seem "washed out" by this 
> effect, because scattered sunlight's coming at you from a "halo" around 
> the sun.
> 
> Turn 90 degrees away from the sun in either direction, and you'll see 
> less of this effect in the sky.  (Polarized light from other effects may 
> be greater, though.)
> 
> I've tried playing with a polarizer to reduce this effect.  It works 
> *slightly*, but not enough to really float my boat.  I assume that the 
> scattered light near the sunlight's axis of origin (WRT the observer) is 
> either not strongly polarized or there's something else going on that 
> I'm too scientifically illiterate to comprehend.  (Probably the latter 
> -- I expect many replies by Listees ready to pounce on my simplistic 
> explanation.)
> 
> But there's nothing "odd" about your lens (other than it captures a 
> HOOGE HONKING ANGLE OF VIEW, an "oddness" I dearly covet).  ;-)
> 
> 
> Garth
> 
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