PTGui Pro and stereographic lenses ?

[Roel de Wit]

Hi,

I've recently bought PTGui Pro and a Samyang 12mm f2.8 (stereographic) lens. I've done my best to adjust my panoramic head for the no-paralax point at the angles I intend to shoot at (following instructions on how to best do this with fisheye lenses). Still somehow this doesn't ensure that a created panorama is stitched perfectly (when using a decent overlap). The camera is remotely triggered and I'm not incidentally moving my tripod. I can get rid of the stitching errors by setting the feather slider to the far right (well I can still see that something is slightly different at those points by really looking for it, but others probably will not notice at all). Using smartblend always gives worse results (tried it just in case). As I'm trying to figure out how to solve this I'd like to ask a few questions.

- When making panorama's in rooms (not outside), do you require setting the feather slider (almost completely) to the right to completely avoid stitching errors ?

- My lens is a stereographic lens, instead of a normal fisheye lens. Am I correct that PTGui should automatically detect it's distortion characteristics or would I still need to provide manual lens values somehow ?

- Also assuming that PTGui should detect (reasonably) correct values in a 360 panorama with at least 30% overlap. What is the advantage of storing this information in the lens database ? Will it result in better stitching when using a minimal amount of images to create a panorama with ?

- It's possible to set the maximum control points per pair and project. Is there any common-sense value to use and does using extreme values add any benefit over the default settings ?

Thanks,

Roel

[PTGui Support]

Hi Roel,

Sounds like you may have parallax in your setup. If the panohead is set
up perfectly, PTGui should generally stitch your images without
misalignments using the default settings.

Have you done a parallax test, like here:

http://www.johnhpanos.com/epcalib.htm

https://www.youtube.com/watch?v=zEgLgReARxs&feature=youtu.be


If you can't solve the problem please make a set of images available for
download so we can take a look:

Please do not add attachments to your posts; instead upload your files
at a file sharing site (for example http://ge.tt/ ) and include a link
in your message.


Kind regards,

New House Internet Services BV
Joost Nieuwenhuijse

-----------------------------------------------
PTGui - Photo Stitching Software

www.ptgui.com
For support see: http://www.ptgui.com/faq/
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[John Houghton]

Roel, This lens is fairly new and as Joost suggested,  it would be useful if you could upload a set of images (jpeg) somewhere for investigation.

You should also check that the lens type is correctly specified on the Lens Settings tab (available in Advanced mode, selected via the button on the Project Assistant).  PTGui will automatically set this using rules defined at Tools->Options->EXIF.  You will probably want to amend these so that the correct choice is made for your lens, but of course you can also enter the lens details manually.

Storing lens parameters in the lens database enables them to be inserted into a project to get the optimizer off to a flying start and is particularly useful in projects that are starved of features for control points.  You need a wide spread of control points to enable the optimizer to evaluate the lens distortion correction parameters accurately.  Few points mean that the optimizer may be hard pressed to do this effectively, but if you already have the parameters to hand, then the stored values can be used to ensure good distortion correction.  In this case you can prevent the optimizer from updating these parameters via selections made on the Optimizer tab (turn off Minimize lens distortion).

John

[Erik Krause]

Am 24.07.2015 um 01:27 schrieb Roel de Wit:
> - My lens is a stereographic lens, instead of a normal fisheye lens. Am I
> correct that PTGui should automatically detect it's distortion
> characteristics or would I still need to provide manual lens values somehow?

This should pose no problem. The samyang 8mm fisheye is stereographic as
well and widely used on APS-C sized sensors (I have one, too). According
to some users stereographic stitches easier than classical fisheye, due
to lower distortion in the outer regions.

You could check whether there are many control points in the corners of
the images. Since those corners form horns in equirectangular
projection, they might have control points in common with non-adjacent
yet overlapping images, which almost always gives worse results.
Additionally the deviation of the NPP is worse in the corners. To avoid
the corners I load full frame fisheye images as circular fisheye. This
cuts the horns (without affecting result resolution or number of images
needed) and no control points are created in the corners.

Erik

[JPS]

Hi !

I have also just received a Samyang 12mm. f/2.8 that I ordered, in order to take advantage of the FULL FRAME on my Nikon D800, instead of the Nikon 10.5 f/2.8 (shaved) tht I have been using for years ! Apparently, the equirectangular image from the Samyang is about 17000x8800 pixels, as compared to the 11500x5750 pixels I had with the 10.5 ! Quite a few pixels more indeed !

I rapidly tried a spherical pano, taking 6 images, tilting the lens 15 degrees up, plus one shot for the Nadir ! At first, PTGui assume -wrongly- that the lens is a circular fisheye, but it does aligns the images -almost- correctly, except that it leaves a litle band at the top of the equirectangle !?!

In "Lens Settings", it shows a FL of 14.26mm., HFOV of 146 degrees and theoretical 180 degrees (as found in the EXIFs).

Now if in "Lens Type", I click on "Full Frame Fisheye", then it shows a FL of 10.09mm. and HFOV of 146 degrees !!

If then I click again on "Align Images", I get a clean equirectangle (with the Nadir part blank of course, as I haven't yet loaded the Nadir image) !

So... I'd like to make a template for the Samyang, but I need to know the exact FOV angle (not the diagonal one) ! Anyone has a clue on that ?

...and how shall I set the "Lens Setting" part, as neither the "Circular Fisheye" not the "Full Frame Fisheye" give correct FL values ???

Looking forward for any help...

Thanks in advance,

J-P.

[John Houghton]

J-P, All that PTGui cares about is the HFOV.  The focal length and crop factor values are irrelevant, and are only used to estimate the HFOV at the outset.  You can initialize the focal length to 12mm and the crop factor as 1.  The estimate for the HFOV from these values depends on whether you specify the lens type as circular or fullframe.  Some people like to specify circular even for fullframe images and adjust the crop circle to cut off the corners, which are usually of poor quality and generally not needed.  For a circular crop, the HFOV value is the width of the full crop circle specified.  For fullframe, the HFOV is the width of the full image frame, as opened by PTGui.  An accurate value for the HFOV will be evaluated by the optimizer when stitching a full 360 panorama project (e.g. the template project).

John

[JPS]

Thanks for the comments, John !

Still when -before to "Align Images"- I go to "Lens Settings", chose "Full Frame" and change the FL to 12mm., when I go back to "Align Images", PTGui stitches them alright !

BUT, when I check in "Lens Settings", the FL has been changed to 13.35.., the HFOW became 106.9 degrees and the "B" parametre -the only one who's not 0- is 0.041358451 !

Is that normal ? Shouldn't the REAL FL be taken into account ? ...and I suppose the HFOV is much larger than 106.9 degrees...

[John Houghton]

J-P, Do not be too concerned about the focal length parameter value after optimization.  The Samyang 8mm fisheye optimizes to 9mm.  I'm not familiar with the 12mm lens so I don't know what's normal for that.  However, I suggest that on the optimizer tab you try selecting "Heavy + lens shift" for the Minimize lens distortion" option.  That will result in non-zero lens parameters after running the optimizer - not just B.  If the resulting stitch is good then be happy.

John

[JPS]

OK, I will try again, John ! Thanks a lot for the time and efforts !

...in any case, I won't be able to shoot anything soon: I lent my D800 to a friend and he'll only be back in 2 weeks !

Have a pleasant week-end !

[Erik Krause]

Am 24.07.2015 um 18:21 schrieb JPS:
> Is that normal ? Shouldn't the REAL FL be taken into account ? ...and I
> suppose the HFOV is much larger than 106.9 degrees...

It's normal that PTGui changes the field of view such that the images
fit best (if optimization of FoV is allowed, which is the case for all
(except "No") presets in Simple mode on Optimizer tab. The focal length
is just calculated back from the FoV, but according to ideal fisheye
mapping, which naturally gives a different result.

If you chose "Heavy + lens shift" as John suggests, you might get even
different values and a better fit.

--
Erik Krause
http://www.erik-krause.de

[JPS]

Thanks Erik ! I will do that !

:-)
J-P.

[Roel de Wit]

Hi,

Thanks for all the feedback. When I'll have time to try all the suggestions some time in the coming week I'll report back on the results and if needed will upload some pictures in case the issue still exists.

Thanks,

Roel

[jose de queiroz]

Hello Erik

maybe you can help me
I have sony alpha 7 s + samyang 12 mm fisheye
where can find a option to chose  the 12 mm samyang in the preset conf ptgui 11 beta ?
thx

[PTGui Support]

Hi Jose,

If the image has EXIF data the lens profile is applied automatically
when you load the image in PTGui.

Otherwise the 'Focal length' window will pop up. Enter 12mm and you can
select it from the drop down list.

Kind regards,

New House Internet Services BV
Joost Nieuwenhuijse

-----------------------------------------------
PTGui - Photo Stitching Software

www.ptgui.com
For support see: http://www.ptgui.com/faq/
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[Tom Sharpless]

I have been using Samyang's stereographic fisheyes, both 8mm and 12mm, for years and find them "easy stitching" compared to other lenses with comparable fields of view.  So your problems must be due to set-up.  First, be sure the lens pupil is centered left-right as well as front-back, that is, parallax is cancelled equally with rotation in both directions.  This is sometimes overlooked.  Inside PTGui, be sure the lens is recognized as a full-frame fisheye, and enable optimization of all 5 lens parameters (fov, a, b, c, hshift, vshift).  

For the most consistent results (once your rig is adjusted right), you should  calibrate the lens: shoot a 360 series with 70% overlap (no need for up/down shots), take lots of control points, optimize fully as suggested, save to the lens database and use those settings for stitching future panos. However many of us (self included) don't routinely use prior calibration.  I find it essential for stitching stereo, but otherwise I generally let PTGui assign ad-hoc lens parameters.