Calibrate lens GUI

[Oskar Sander]

I've played around with it and this is a really nice application, thanks guys!

Can I use it also when focal length/fov is not quite known, or must I get that in some other way? (Hugin for example)

The thing is ´my camera has a focal length of 5.1mm  eqv to 24 mm on 35mm film, alright. But then I add a housing an a wet-lens and dive with it.  The lens have a stated angle of view of 85° (106.5° on land) and magnification of 0.65x. 

Should I just try to calculate a focal length like this which would suggest something slightly wider than 24mm eqv?  (http://en.wikipedia.org/wiki/Angle_of_view)

cheers
//O

[Carlos Eduardo G. Carvalho (Cartola)]

Hi, have you already seen this tutorial?

http://hugin.sourceforge.net/tutorials/calibration/en.shtml

Cheers,

Carlos E G Carvalho (Cartola)
http://cartola.org/360

2011/9/1 Oskar Sander <oskar....@gmail.com>

--
You received this message because you are subscribed to the Google Groups "Hugin and other free panoramic software" group.
A list of frequently asked questions is available at: http://wiki.panotools.org/Hugin_FAQ
To post to this group, send email to hugi...@googlegroups.com
To unsubscribe from this group, send email to hugin-ptx+...@googlegroups.com
For more options, visit this group at http://groups.google.com/group/hugin-ptx

[Oskar Sander]

Hi yes I have thanks.

My question really is, how important is an accurate  focal lengt/hfov for a useful result from the calibrate lens GUI?

If I approximate the focal length to about 24 when it's probably around 23 something, does it matter for the lens distorsion figures, and does the slightly off focal lengt matter for a panorama or mosaic project?

/O

2011/9/1 Carlos Eduardo G. Carvalho (Cartola) <cart...@gmail.com>

--
/O

[Carlos Eduardo G. Carvalho (Cartola)]

Well, I don't know exactly. I would say you can use approximate values and it wont be a problem. Just try to use spread control points and think about optimizing fov. If you optimize V then the lens will change anyway, so I think the accuracy of the initial value is not so important.

Hope it helps. I don't do mosaics very much. I usually do fullsphere panos.

[Bruno Postle]

On Thu 01-Sep-2011 at 19:59 +0200, Oskar Sander wrote:
>
>My question really is, how important is an accurate focal lengt/hfov for a
>useful result from the calibrate lens GUI?

I'm not 100% sure.

Barrel distortion is purely a function of distance from the centre
of the photo - At least this is true for rectilinear images - i.e.
you can straighten straight lines and will get the same a,b,c values
whatever value you enter for field of view.

The Calibrate Lens GUI did originally have an option to optimise
field of view, but Thomas removed this on my suggestion for the
above reason.

..but with fisheye photos it isn't so clear that the situation is
the same, you definitely do need to feed the right focal length into
the Calibrate Lens tool. What I don't know is whether it should be
possible to optimise field of view at the same time as barrel
distortion (with fisheye images).

>If I approximate the focal length to about 24 when it's probably around 23
>something, does it matter for the lens distorsion figures, and does the
>slightly off focal lengt matter for a panorama or mosaic project?

--
Bruno