Chaos Corona for 3ds Max > [Max] I need help!

How to translate real drone camera specs to CoronaCamera?

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juninholiveira:
Hello guys. I'm trying to do some matching with real drone footage, but before trying to do the alignment, I want to match the CoronaCamera sensor and lens settings to the real camera, which I already have the specs. It's the following:

DJI Mavic Pro

* Sensor   1/2.3” (CMOS), Effective pixels:12.35 M (Total pixels:12.71M)
* Lens   FOV 78.8° 26 mm (35 mm format equivalent) f/2.2
* Distortion < 1.5% Focus from 0.5 m to ∞
* ISO Range   video: 100-3200
* photo: 100-1600
* Electronic Shutter Speed   8s -1/8000 s
* Image Size   4000×3000
In 3DS Max we have thos options for the CoronaCamera:

Field of View OR Focal Length [mm]
Film Width [mm]
Zoom Factor
ISO
F-Stop

How should I translate those camera specs to my CoronaCamera. Other thing, I can do a predefined Lens Correction in photoshop. Should I do it before the matching?

pokoy:
This seems to be a 6.4 x 4.8 mms sensor, so it's 6.4 mms for film width. When you use 26mm as focal width it should produce the given fov.
However, if you want to be on the safe side use 78.8 degs for fov instead of focal width since this is what the lens effectively sees.

As for matching... not sure but I guess matching apps should be able to use exif data correctly nowadays and have a lens database to correct for any distortion. In any case, don't use Photoshop's correction, it crops images (changing the effective fov) and produces wrong results if the lens is not included in their database. I would go without any lens correction and only try if the match is obviously wrong.

juninholiveira:

--- Quote from: pokoy on 2022-09-05, 16:49:43 ---This seems to be a 6.4 x 4.8 mms sensor, so it's 6.4 mms for film width. When you use 26mm as focal width it should produce the given fov.
However, if you want to be on the safe side use 78.8 degs for fov instead of focal width since this is what the lens effectively sees.

As for matching... not sure but I guess matching apps should be able to use exif data correctly nowadays and have a lens database to correct for any distortion. In any case, don't use Photoshop's correction, it crops images (changing the effective fov) and produces wrong results if the lens is not included in their database. I would go without any lens correction and only try if the match is obviously wrong.

--- End quote ---

Thank you! Well, so now I know that this 1/2.3" sensor should go into the Filmd Width slot. But I still don't understand the relation of it with the other values (FOV and Focal Length). At first, I inserted the 78.8° in the FOV of my CoronaCamera, like the drone specs told me, but the matching was wrong. So with a little help of the Perspective Match tool in 3DS Max I was able to get a very good matching. But the surprise is that the resulting FOV was around 65°.

But then I inserted the Filmd Width of 6.4mm like you told, based on the sensor. I know this will only affect the DoF, not the projection, so it makes no difference for me now, but somehow, when I modify the Film Width with my FOV selected and setted, the greyed out Focal Length changes to around 5mm. I don't understando very well the relation between those values, how one affects the others. And if I'm using the FOV option, the greyed out Focal Length has no influence in the camera, right?

If you can point me to some docs or tutorials that explain this better, I would appreciete. Been getting a lot of jobs lately that require real footage matching, for stills and animations.

pokoy:
I answered your post yesterday without trying the values in Max and you're right, they're producing confusing results...

From my knowledge, using the FOV should give you a match as this is the deciding factor of what area the lens actually sees, with whatever values you use for focal length and sensor size. With a different sensor size your DOF result will not be able to match, though. But, as this is a wide lens, DOF will be deep throughout almost all distances, blurriness will be negligible.

This may be a different lens design... then again they are stating that its 26mm are 35mm equivalent. I'm confused, too.

A note on the Perspective Match tool - watch out for its side effects: it sometimes (always?) produces non-uniformly scaled cameras to match the source, this might be a problem in rendering and other post prod matching tools you might want to use (such as exporting camera to AE etc).

When you use the Perspective Match tool, what do you get for focal length / fov on the camera the tool creates?

Juraj:
There is problem with nomenclature being incompletely used in photography (and CGI) field. It's almost never specified if they talk about Horizontal or Diagonal FOV.

But, we also know:

1) Camera&Lens companies almost always advertise diagonal FOV. It's simply bigger number ;- ).
2) 3dsMax for some reason implement Horizontal FOV (and CoronaCam likewise thus).

We also know majority of devices never use the full sensor width, so ignore the specified 1/2.2 nonsense. It can just as well crop to 1/2.5 physically or software side. But the FOV is probably accurate before distortion correction. (which can automatically be applied and baked into file format of said device).

Since DJI crop to 4:3 ratio, 79 DEG diagonally, corresponds to +/- 67 DEG horizontally. So your 3dsMax camera match got it pretty good :- ).

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