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Re: [OM] IMG: another panorama, this time BIG

Subject: Re: [OM] IMG: another panorama, this time BIG
From: Nathan Wajsman <photo@xxxxxxxxxxxxxx>
Date: Thu, 4 Jun 2009 06:48:51 +0200
Thanks for looking, Moose. There was no barrel distortion on the  
individual images, the cigar distortion in the picture must therefore  
be the result of the tripod not being perfectly level (and the degree  
of un-levelness changing as I rotated the tripod head). I need to get  
a dedicated panorama head which will allow me to align things more  
precisely and to ensure that the camera rotates around the optical node.

Nathan

Nathan Wajsman
Alicante, Spain
http://www.frozenlight.eu
http://www.greatpix.eu
http://www.nathanfoto.com

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On Jun 3, 2009, at 9:18 PM, Moose wrote:

> Nathan Wajsman wrote:
>> When I posted the golf course panorama the other day, many of you  
>> asked for a larger size. So, here is one I made this afternoon at  
>> our beach. It covers about 200 degrees. I took 15 pictures with the  
>> 35mm lens. Unfortunately I did not level the tripod completely, so  
>> there is what appears to be some barrel distortion.
>>
>
> I haven't looked at the full size image, so can't speak to any
> repetitive barrel distortion within individual parts. The overall
> distortion you see is sometimes called "cigar" distortion. Think about
> the optical/mechanical situation for a moment.
>
> As the angle varies from straight ahead, the focal distance increases
> and the image gets smaller. The effect is not particularly obvious  
> with
> many subjects. With a small, even, linear band like the sea in this
> image, it becomes very obvious, appearing larger in the middle and
> tapering off in both directions.
>
> It's very common with panorama cameras using rotating lenses, like the
> Widelux, Horizant, etc., where the whole sweep is on one film image.  
> It
> is much less commonly seen in stitched panoramas simply because most
> stitching software compensates for it in at least one mode.The  
> stitched
> image gets taller as you go out from the middle. You then crop off the
> spreading wings at the height of the central frame.
>
> Linear distortion within individual frames is another issue that can
> indeed detract from the result. If I am doing a panorama at 35 mm  
> focal
> length, I use the long end of my 17-35, which is almost distortion  
> free,
> rather than the short end of the 28-300, which has modest visible
> distortion @ 35 mm.
> <http://galleries.moosemystic.net/MooseFoto/index.php?gallery=Miscellaneous&image=MossBraeP116laz.jpg
>  
> >
>
>
> Even modest distortion can cause problems matching across frames.  
> Taking
> many, highly overlapping frames, as you did with the golf course,  
> gives
> the stitching program a way around such problems. Correcting each  
> frame
> with something like PTLens or DXO before stitching also works quite
> well, in my experience.
>
> Moose
> -- 
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