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Author Topic: different Fisheye distortion effect on alignment and model generation  (Read 1558 times)

JJ

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i use a FE to scan house gardens from ground level and for my use am happy with the results

right now i use a Samyang 7.5mm manual focus lens on a micro four thirds body.  i just set the lens to infinity and pretty much all images are sharp but i avoid moving in closer to the subject

i'd like to change to an auto focus lens to have more flexibility and was looking at the Panasonic 8mm

looking at this review which compares the 2 lenses, you can see that the distortion is different, so to my question - will this difference in distortion be a problem (i.e. will it have a detrimental effect on alignment and model generation) and am i better off sticking with my current lens which is tried and tested?

see here some comparison images:

https://m43photo.blogspot.com/2012/02/samyang-75mm-f35-fisheye-lens-review.html

also:

https://4.bp.blogspot.com/-di4jnTK_rNQ/ULY80ZlCMII/AAAAAAAADK4/fPNhidGu2n4/s1600/fisheye%2Bsharpness%2Bsamyang%2B7.5mm%2Bf3.5.jpg

vs

https://1.bp.blogspot.com/-jhAGnZudzoI/ULY89pHuLxI/AAAAAAAADLE/yLNcaWzuKUM/s1600/fisheye%2Bsharpness%2Blumix%2B8mm%2Bf3.5.jpg

Kiesel

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Re: different Fisheye distortion effect on alignment and model generation
« Reply #1 on: October 04, 2022, 12:02:44 PM »
Hi JJ,

Quote
right now i use a Samyang 7.5mm manual focus lens on a micro four thirds body.  i just set the lens to infinity and pretty much all images are sharp but i avoid moving in closer to the subject

i'd like to change to an auto focus lens to have more flexibility and was looking at the Panasonic 8mm

I think that's not a good idea to work with autofocus instead of fixed focus, because this way you change camera intrinsics a little bit for every shot, so your camera calibration get worse. Generally fisheyes have a very wide depth of field. I would set the focus to something like your middle distance (hyperfocal value) and tape this distance down and not to infinity b.t.w..


I don't know how well Metashape can handle different fisheye projections (stereographic, equidistant, equisolid, orthographic) and if there are any problems at all to a specific fisheye projection.


Best regards,

Kiesel
« Last Edit: October 04, 2022, 03:35:19 PM by Kiesel »

JJ

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Re: different Fisheye distortion effect on alignment and model generation
« Reply #2 on: October 05, 2022, 01:20:12 PM »
thanks Kiesel

I think that's not a good idea to work with autofocus instead of fixed focus
when the lens arrived and i was comparing the 2 i realised exactly this so returned the AF lens

in any case the little MF Samyang i have is sharper and as a bonus it looks cooler too

I would set the focus to something like your middle distance (hyperfocal value) and tape this distance down and not to infinity b.t.w..
agree again.  when i said "to infinity" i actually meant setting the focus to something suited to the site i was capturing