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Hi all,
I have been experimenting with my brand new NN5L at home, and it seems that I cannot get the rail settings right, I've used those from the NN website, but there remain parallax/stitching errors (used PTGui).
Anybody who has the same camera/lens and the same problem, or maybe does not have the problem...
I have added a sample picture. Camera was tilted -10 degrees for smaller nadir footprint.
Like to here your opinion.
Thanks and have a nice day!
Wim.
Here you can see my lower rail settings when the 'cross' is in the middle. 63-64 mm...
Line were accurately drawn from image corners (and then cropped).
I have two suggestions:
1) The settings from the Nodal Ninja site may or may not be reliable. Verify the upper rail setting by specifically checking for parallax, as described in http://www.johnhpanos.com/epcalib.htm.
2) Shoot a test panorama in a reasonably large venue that has plenty of nice features for control points in all directions. In your panorama at home, the canvas above is very revealing of stitching errors, yet it's not easy to find matching features beween adjacent images for assigning control points in that large area. (Try assigning points there manually yourself). Moreover - being flexible, the canvas may flap about in the wind between shots.
When you have done a successful stitch, you can then use the saved project file as a template, which can be applied to future similar sets of images to greatly help the stitching process when control points might be scarce as in this one.
John
John,
I use exactly the same setup as you (D300 / 10.5 / Nodal Ninja 5L). I think the problem that you are seeing could be caused by the camera sensor being off center. This would mean it would look like everything is centered but things would still be off. These are the setting that I use. Lower rail 59.5mm (well somewhere between 59mm and 60mm). Upper rail 81mm. When I shoot I also use a -15 degree tilt. If you upgrade to the full Nodal Ninja 5 then this angle will have a stop to lock at that position too.
A HDR example of this setup in action is here http://www.bilsland.co.uk/greatwitleychurch/
I hope this sorts things out for you. If anything isn't clear enough let us know.
Bob Bilsland.
Hi Bob,
Thanks for the reply!
I hope it's not my camera's sensor that is off centre... will be spending an awful lot of thime then finding the entrance pupil settings.
Do you shoot your zenith at 90degrees? I have made another pano just now and it seems that the parallax is mostly (if not only) apparent on the top and bottom of the pano (I do not shoot the nadir).
I use a -10 degree tilt, otherwise the tripod legs are in view.
Thank you all!
Wim.
Originally Posted by MrB
Don't automatically assume that stitching errors are due to parallax errors. They are frequently due to other causes - e.g. inadequate optimization and poor control point placement and distribution. Note that an offset of the lens axis with respect to the centre of the sensor is quite common. PTGui can make allowance for this if the lens shift parameters (d & e) are included in the optimization process. This is always recommended when a fisheye lens is used.
John
Wim,
Yes a sensor offset is nothing to worry about. Just think how many pixels they fit into the size of the sensor. The D300 sensor is only 23.6mm x 15.8mm and in that size Nikon fit 4288 pixels x 2848 pixels. Now just think if that sensor is just 0.1mm out that equates to just under 20 pixels!
When I shoot my panoramas I shoot 6 photos round tilted 15 degrees down and a single zenith shot at 90 degrees up. I shoot at 15 degrees down because I don't open my tripod out fully, I have the legs spread as little as possible, just enough to be stable. This combination produces a very small hole to patch below.
Bob Bilsland.
Dear Bob,
Ok?©, an off-center sensor sounded like some kind of bad camera-disease, but I guess it's not that big of a disaster, ??f it is the case.
I do the -10/-15 degrees trick as well, it's saves you a whole lot of photoshop work or it just eliminates the nadir shot if a nadir cap is used, thanks.
I have stitched my photo's now with Realviz and I have to say I get far better results that with PTGui... not p?©rfect, but close to, so I'm getting confidence it's software-dependent (well... it's depending on my skills configuring the software I guess :-) ). The problem persists so maybe I have to tweak the panohead some more too.
About the zenith shot, I have now tried and angle of 60 degrees instead of 90 and the results are great. When you stitch the images without the zenith shot, the zenith hole is relatively small, so not that much info was gathered from the zenith shot. A 60 degrees photo gives you far more control points with the other photo's, certainly when photographing a while ceiling or so.
I'll keep on trying...
Have a fine day!
Wim.
You should be abe to get comparable results with PTGui as you have done with Realviz. If you care to make a set of images available somewhere, I would be happy to try a stitch with PTGui and see what might be possible if that would be of interest.
John
Dear John,
Thanks a lot, that would be of great help to me!
I have uploaded the files I have been working on last, I have also included the PTGui and Realviz stitch. I have used the WIM5275 +60 degrees zenith shot, the others are for demonstration.
BTW: I have changed my NN5L back to the recommended setting from NN and this is the result.
Thanks again, I'm quite curious what you have to tell me!
Greetings, Wim.
Oh yes, the files are here: http://users.pandora.be/sijoschooltoneel2007/
Wim, I stitched the images and put the result and project file together in a zip archive at www.johnhpanos.com/ion.zip. There is some horizontal parallax visible in the images and rather more vertical parallax, so you might like to check the head adjustment specifically for that. That may account for the not very sparkling optimization report, though it's late and I haven't spent much time investigating control points. I did place a few points manually in the expanses of blank wall.
John
Hey John,
Thanks a lot for helping me out!!!
The vertical parallax, you mean I have to change the lower rail setting or am I mistaken? That would make sence since it's that one I had 'centered' on 63mm...
I wonder what happens if you buy an 'Absolute' panohead by 360precision... it's precise yes, but what if your camera is off.
Wim.
By vertical parallax, I mean image shift when the camera is roated about the horizontal axis, as when you rotate the camera upwards to take the zenith shot. This is taken from your panorama, and shows the parallax effect between the zenith shot and a horizontal shot:
However, it's virtually impossible to eliminate parallax completely when using fisheyes because the entrance pupil is not a single fixed point in the lens. Its position varies according the direction of the incident light rays. For light rays entering the lens at extreme angles like 90 degrees to the lens axis, the entrance pupil is close to the front surface of the lens. OTOH, for light rays entering directly towards the front of the lens, the entrance pupil is much further back into the lens, maybe 10-15mm. So as the light rays shift around from 0 to 90 degrees, the entrance pupil gradually moves forwards.
When you set up the pano head to avoid parallax, you therefore adjust the camera position to suit the angular position where the seam will be located. So for 6 shots around, the yaw increment is 60 degrees and centre of the overlap between two adjacent images will be at 30 degrees to the lens axis. So to eliminate parallax at the image join, you arrange for the camera to rotate about the position that the entrance pupil is in for 30 degree incident rays.
The problem with the your zenith+60 image is that the corner of it overlaps with the central part of a horizontal image. Consequently, the entrance pupil is not in the same place for each image at the join, so parallax is inevitable. There are further ramifications at http://www.panoramas.dk/panorama/fis.../parallax.html.
Parallax is only a problem with near objects in the overlap regions. It's best to avoid putting control points in such places if there is risk of significant parallax effects. The automatic cp generators won't avoid doing this, so it's best to be on your guard.
Another problem might be that the camera is not mounted on the upper rail such that the lens axis is accurately parallel to the rail. A small amount of camera tilt with respect to the rail will swing the entrance pupil away from the horizontal rotation axis at the end of the top rail.
The 360Precision head cannot eliminate the inherent parallax problems with fisheye lenses, but if you can manage to successfully stitch with templates and without control points, then you don't have to worry about where control points are placed.
John
Thanks for this info. It's quite hard figuring this all out.
>Another problem might be that the camera is not mounted on the upper rail such that the lens axis is accurately parallel to the rail. A small amount of camera tilt with respect to the rail will swing the entrance pupil away from the horizontal rotation axis at the end of the top rail.
=> Well, I have experienced this too. Actually, when you untighten the vertical arm (the lower know, to change lower rail settings) you can even 'twist' the vertical arm a little bit (around it's vertical axis) on my NN. It's really not that much but enough to swing the entrance pupil out of place like you said. So not only the lower rail setting is important but also how you tighten it, you have to make sure to press the arm firmy against the side of the rail to be sure it's parallel.
I hope you understand my explanation, I'm trying to be as precise as possible.
Wim.
Wim, I don't think you need to worry too much about the setup of your pano head. Considering how close the camera is to the nearest features, the panorama has come out very well. In larger venues and outdoors, you shouldn't have any problems. One odd thing: while I noted that the images were all given the same exposure, there are quite big variations in the brightness of the images. If they were generated from raw originals, perhaps the conversion settings weren't constant or some were set to auto.
John
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