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Guys I have a Canon 7D aps-c with 1.6x crop, and I have a Samyang 8mm for Canon cameras.

Here is my question. As the lens does not have electronic contacts on it to connect to the camera, there is no EXIF data. When I wanna use programs like PTGui, it asks me for the focal length and multiplier, which I assume is 8 mm and 1.6. But what about the other programs like Autopano Giga?? In APG you can only define the focal length. So shall I write the 8 mm or shall I multiply the 8mm by 1.6 and then the result would be my actual focal length?

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    Why not try both and see what happens? – ElendilTheTall Oct 7 '16 at 10:59
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    Also, although it seems counterintuitive, you'll probably have better luck using longer focal length lenses that demonstrate less geometric distortion. Of course you'll also need to take more shots. – Michael C Oct 7 '16 at 12:59
  • My question is more about the photography knowledge behind of it – Amir Nassajian Oct 7 '16 at 13:25
  • But yes of course i can try both to see what will happend, oh by the way, lenses with less distortion, means many many more pictures than just 8-20 what usually needed for a full 360 degree panorama, and not to forget, if you have fisheye lens like this, u wont really need a pano head tripod and rotator and so on. – Amir Nassajian Oct 7 '16 at 13:27
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According to their documentation, use 8mm, the actual focal length of the lens. Autopano uses the camera model information from the camera EXIF to determine your crop factor, and will calculate the 35mm-film equivalency of your lens automatically.

Also, your actual focal length is always what's printed on the front of the lens. The focal length of a lens is a physical property that does not change just because you change the size of the sensor behind it. Equivalency is really only about field of view. See: What is crop factor and how does it relate to focal length?

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