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SAMYANG 8 mm - configuration: 7,8, 9 or 10 mm ????

PostPosted: Sat May 12, 2012 12:49 pm
by samycanon
Hi all

I have a big question with my Samyang 8 mm.

What parameter configured in Autopano Giga focal lenght?

I have read many post on this forum and there is much confusion.

Some photographers say 7 mm, 8 mm, other 9 and 10 mm in the options.

Which is correct?

Thank you.

PostPosted: Sat May 12, 2012 2:17 pm
by mediavets
samycanon wrote:Hi all

I have a big question with my Samyang 8 mm.

What parameter configured in Autopano Giga focal lenght?

I have read many post on this forum and there is much confusion.

Some photographers say 7 mm, 8 mm, other 9 and 10 mm in the options.

Which is correct?

Thank you.

Welcome to the forum...

Try 9mm.

In APP/APG I'm not sure it matters that much because, as I understand it, the software calculates the focal length when using fisheye lenses and uses the declared focal length just as a guide - but you should check that the crop circle is placed accurately.

PostPosted: Sat May 12, 2012 3:51 pm
by hermer-blr
Try PTGUI Pro:

I mean, use PTGUI pro to let it define the focal length. I did it and it gave 8.67 (Samyang Fisheye used with a Nikon D5100). I have now set this value in APG to perform a new panorama optimization and I am waitng for the result.

The achieved RMS is cat. 3.5 (not wonderful), but, compared with my previous tests with 8 mm, the images seem now to match correctly : When I walk the mouse over the panorama (in "image mode"), I do not see anymore the features change from one image to the adjoining one...

I am confident...

PostPosted: Sat May 12, 2012 4:02 pm
by mediavets
hermer-blr wrote:The achieved RMS is cat. 3.5 (not wonderful)..

As I'm sure you are aware the RMS value is not a simple thing to 'interpret'. Working to reduce the value of RMS using the Control Point Editor does not necessarily result in a better stitch.

I believe that typical RMS values have risen with recent versions of APP/APG without that implying a poorer stitch.

As I understand it, RMS is not at all the same thing as what appears to be a similar indicator of stitch quality used in PTGui where a lower value is definitely indicative of a better stitch.

PostPosted: Sat May 12, 2012 10:24 pm
by hermer-blr
OK - Panorama successful !

And the distortion correction was good enough so that I could go to ghost hunting through .png files without creating artefact or misalignments in the panorama. The pano will now be definitive after tripod removal (by image processing) !

PostPosted: Mon May 14, 2012 12:06 pm
by hermer-blr
It is interesting to note that this review has suggested a focal length of 8.7 mm for the Samyang fisheye, perfectly matching the calculation made by PTGUI (I have made a PTGUI test on an other set of images and reached the same value) !!!

http://michel.thoby.free.fr/SAMYANG/Early test report.htm

PostPosted: Tue May 15, 2012 12:22 pm
by AlexandreJ
In autopano, setting the right value of the focal length is not really needed ( this needs is typical from ptgui ).
So 8, 9 or 10 mm should all work.

PostPosted: Tue May 15, 2012 8:09 pm
by hermer-blr
Alexandre,

This is however not my (very limited sofar) experience.

I am a new Samyang user, but my first experience with it was a mess. This is why I made a test with PTGui to get confirmation (and I got it) that my pectures could result in a correct panorama. PTGUI calculated a focal length of 8.7 (for 8 mm proposed through the MMI) that I forced into APG (instead of 7.7 set by the SWare at image detection). And, then, the result was excellent !

Since then, I have made other tests and the result has systematically been good: for all these tests, not wanting to waste time, I have forced 8.7 mm

PostPosted: Wed May 16, 2012 8:43 am
by AlexandreJ
Interesting. I have to check that.

PostPosted: Sun Jun 03, 2012 7:38 pm
by HansKeesom
OMG OMG OMG OMG, is this for real? You guys made my day.

PostPosted: Sun Jun 03, 2012 9:20 pm
by hermer-blr
To Hans: And your conclusion is ......... ?

I continue to be happy with 8.7

But I have not tried anymore to take the risk of an other focal length. I may have been unlucky once; I will never know !

PostPosted: Mon Jun 04, 2012 12:59 pm
by HansKeesom
Hi, not yet a conclusion as I have not used it enough yet. Will try do redo some difficult to stitch project and see if it helps.

It made me also try out the samyang on my old 1D, which is FF. Cool. No bracketing but 4 shots wil give 360*160, better then a girocam ;-)