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 Post subject: Working without Exif
PostPosted: Mon Dec 09, 2013 11:51 am 
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Joined: Tue Sep 01, 2009 9:34 pm
Posts: 27
Hi,

I am starting to use a new camera without any EXIF information transmitted from the lens to the body (and therefore to the image EXIF data). Since I am an avid APG user, I'd like to understand the consequences of this into my workflow. All the lenses will be rectilinear, with the widest equivalent to a ~21mm on a full frame, longest about 70mm.

The few tests I have made show that if I leave the standard option "use 50mm with a crop of 1.0 when no exif" works in a few test cases (the final HFOV was not very large though).

However, in one case (using my other camera, a Canon FF body and 14mm prime, also no focal length transmission to the camera), I noticed that APG detected a completely funky panorama - totally unuseable. Putting the 14mm focal length into APG solved that problem.

So it seems that sometimes, 50mm as a baseline works fine and some other times, the software really needs a focal length. Is it so that the larger the final HFOV, the more important the FL is ? Do you think that if the problem appears, putting a "fake" focal length (say 21mm) would allow a good detection ? Or should I really be careful, and write down the exact focal length for each pano, and input that into the software before detecting ?

Thanks for your thoughts !


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 Post subject: Re: Working without Exif
PostPosted: Mon Dec 09, 2013 1:14 pm 
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Joined: Wed Nov 14, 2007 2:12 pm
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Location: Isleham, Cambridgeshire, UK.
miska wrote:
Or should I really be careful, and write down the exact focal length for each pano, and input that into the software before detecting ?

Thanks for your thoughts !


Yes.


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 Post subject: Re: Working without Exif
PostPosted: Mon Dec 09, 2013 1:23 pm 
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Joined: Tue Sep 01, 2009 9:34 pm
Posts: 27
Well, since I am technically interested, could you explain how the HFOV of the lens in the EXIF is used to build the panorama and what precision is required ?
I would have thought that in the fitting process, a more accurate value than the one reported by the lens could be calculated and used. Isn't it the case that a lens advertized to be 14mm could be 14.87 or 13.8 ? But maybe its order of magnitude is used to start the fit ? And if it's too far from reality, things go bananas ?
What precision does the focal length have to be input to not influence the final panorama ? I guess 50mm vs 14mm is too crude.

Thanks again!


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 Post subject: Re: Working without Exif
PostPosted: Sat Jan 04, 2014 3:57 pm 
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Joined: Tue Sep 01, 2009 9:34 pm
Posts: 27
I'm happy to see that in the APG 3.5 public beta, they specifically mention: "Better detection and stitching of images that don’t have EXIF data".

Yay ! Now hopefully the new version also improves working with (very slightly) vignetted images. Right now, Microsoft ICE (yikes !) does a better job (out of the box, without parameter fiddling) at producing smooth skies when there is a tiny bit of vignetting in the images...


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