Truncated panorama  

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hermer-blr
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Truncated panorama

by hermer-blr » Sat Apr 14, 2012 8:51 pm

I have been lent a Samyang fisheye lens and just shot my first panorama with it.

This pano is made of 6 images

The 6 images (portrait mode) are shot alternatively with 0° and 5° vertical orientation. Surprisingly the panorama is irregularly truncated in its upper part, not covering the full 180°.

Anybody who could help me understand the issue and resolve it ?
Nikon D5100 (formerly Nikon D60) - Sigma 10-20 - 24 shots Panoramas in 3 raws
Windows 32 bits - APG
website htt://jmh.trp.free.fr

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by mediavets » Sat Apr 14, 2012 9:21 pm

hermer-blr wrote:I have been lent a Samyang fisheye lens and just shot my first panorama with it.

This pano is made of 6 images

The 6 images (portrait mode) are shot alternatively with 0° and 5° vertical orientation. Surprisingly the panorama is irregularly truncated in its upper part, not covering the full 180°.

Is that so surprising? The Samyang provides something like a 180 degree diagonal FOV I think, not a 180 degree vertical FOV.

I would suggest a shooting pattern something like 6-around at -10 degrees and one up at about +60 degrees.
Last edited by mediavets on Sat Apr 14, 2012 9:23 pm, edited 1 time in total.
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by hermer-blr » Sat Apr 14, 2012 9:53 pm

Thanks ! You are right !

This is my first test with a fisheye and I had not realized up to now that the 180° angle was not vertical but diagonal. Surprisingly, there is no website to give the horizontal and vertical FOV for such lenses.
Nikon D5100 (formerly Nikon D60) - Sigma 10-20 - 24 shots Panoramas in 3 raws
Windows 32 bits - APG
website htt://jmh.trp.free.fr

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by lumelix » Sun Apr 15, 2012 1:07 am

Hi jmh
You can easily calculate this, when you know the diagonal angle:
Normal sensor ratio is somewhat like 24x36mm (FX) or 16x24mm (DX, D5100), so the diagonal is 43.3mm (FX) or 28.8 mm (DX).
This equals to the diagonal FOV.
With a 180° diagonal FOV you have about 100 x 150° on the sides.
If you shoot portrait orientated, you need minimal 4 shoots around, but then there is not enough overlapping. So 6 shoots like Andrew says is the best, every 60° one image. Most panoheads have this scale.
Regards
Martin

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by hermer-blr » Sun Apr 15, 2012 7:43 am

Thanks for the calculation.

I had not realized that the vertical FOV was only 150°. Hence, my surprise !

I have just ordered a panoramic head and I know that it will have click stops every 60°; so, fine !

But, in general (daily conditions), I shoot handheld to save time : I however use my tripod as a mean to locate the nodal point and turn around it handheld. Even with my sigma 10 mm lens and 24 shots, I achieved perfect stitching by proceeding that way. The panoramic head will be for dark conditions where I need long exposure time.
Nikon D5100 (formerly Nikon D60) - Sigma 10-20 - 24 shots Panoramas in 3 raws
Windows 32 bits - APG
website htt://jmh.trp.free.fr

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by lumelix » Sun Apr 15, 2012 9:00 am

Hi jmh
When you have objects fare away and some really close to you, then shooting with a panohead avoid you from having strong parallaxes.
These are sometimes really hard to edit. For example, when you have a chain link fence in front :)
So if you have set up the tripod anyway, use the new panohead as often as possible.
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Martin

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by hermer-blr » Sun Apr 15, 2012 10:29 am

Thanks

I know that, but really, just using the tripod and knowing where your nodal pont is, is sufficient. I made some trigonometry calculations in order to define how to shoot my upper and lower rows with minimal nodal point error... Now, with the fisheye, and only one row, it will be much easier... My first trial, except for the missing part, was perfect; there were however short range trees and branches and leaves...

I think that, handheld, I keep my nodal point within a, say, 1 cm radius sphere. That's enough with APG and the multiple viewpoint setting. If, by chance, there is a short range ghost due to parallax error, I remove it from one of the pictures (alpha channel, .png file) prior to final panorama assembly.

My worry, with the pano head, is to spend too much time in preparation : my wife may not like it !
Last edited by hermer-blr on Sun Apr 15, 2012 10:30 am, edited 1 time in total.
Nikon D5100 (formerly Nikon D60) - Sigma 10-20 - 24 shots Panoramas in 3 raws
Windows 32 bits - APG
website htt://jmh.trp.free.fr


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