Author Topic: reference of camera zoom-settings  (Read 11030 times)

Frank

    Reputation: 29
reference of camera zoom-settings
« on: January 13, 2012, 11:57:12 am »
January 13, 2012, 11:57:12 am
A customer asked for the reference of the zoom-settings of the camera.
Did you use a special camera as reference?

I noticed, that if i use a 35mm-zoom on my Canon EOS 300D the foto nearly matches with the still rendered in Lumion.

Re: reference of camera zoom-settings
« Reply #1 on: January 13, 2012, 02:35:55 pm »
January 13, 2012, 02:35:55 pm
Hi Frank, is this rendered with a Zoom angle of 35 in Lumion?

Frank

    Reputation: 29
Re: reference of camera zoom-settings
« Reply #2 on: January 13, 2012, 03:39:32 pm »
January 13, 2012, 03:39:32 pm
Yes, zoom 35.

Re: reference of camera zoom-settings
« Reply #3 on: January 13, 2012, 04:38:52 pm »
January 13, 2012, 04:38:52 pm
I'm sure Remko knows the answer to this question :)

Re: reference of camera zoom-settings
« Reply #4 on: January 16, 2012, 10:46:34 pm »
January 16, 2012, 10:46:34 pm
I'm sure Remko knows the answer to this question :)
We used 35mm so for your eos you should use 35mm equivalent zoom factor. Because of the sensor i believe there is conversion ratio of 1.6. If you just use 35mm film as reference the angle should match.

Re: reference of camera zoom-settings
« Reply #5 on: January 16, 2012, 10:59:20 pm »
January 16, 2012, 10:59:20 pm
I think that there is a small error though. We use 35mm vertical fov equivalent angle while the common convention is to take horizontal fov angle.

See it like this: in our convention we add extra image info to the sides to turn a 3:2 ratio into 16:9. I think we should change it so our 16:9 image is a crop of the 3:2 image and not an expansion.

Re: reference of camera zoom-settings
« Reply #6 on: January 18, 2012, 12:44:00 pm »
January 18, 2012, 12:44:00 pm
OK I did some tests and I fixed it for the next release. We convert the focal length to a fov and use that as the horizontal fov for the image. In camera's though you get a circular image with a certain fov and then the final image is cut out. With a 35mm film the crop factor is 1.0 so the biggest square that fits inside the fov cirle is cut out and from this image and then the resulting image is cropped to get a 16:9 ratio. Look at the image below for an explanation.

stucki

    Reputation: 32
Re: reference of camera zoom-settings
« Reply #7 on: January 18, 2012, 12:49:35 pm »
January 18, 2012, 12:49:35 pm
does that mean all movies we have done before and want to rerender will look different now ?

Frank

    Reputation: 29
Re: reference of camera zoom-settings
« Reply #8 on: January 18, 2012, 03:00:59 pm »
January 18, 2012, 03:00:59 pm
Thank you Remko for your detailed answer!
Regards,
Frank

Re: reference of camera zoom-settings
« Reply #9 on: January 18, 2012, 05:54:02 pm »
January 18, 2012, 05:54:02 pm
Thank you Remko for your detailed answer!
Regards,
Frank


Hmm I did some more testing and looking on the internet and as it seems we DO use the right formula's.

If you look at this calculator you can see that for a 50mm focal length the 35mm film equivalent horizontal fov is exacly 39.6 degrees. This matches with the angles I get in Lumion.

We then crop the top and bottom to get a 16:9 image. So, as it turns out we did have it right the first time. No worries! Everything will stay as it is!

http://www.frankvanderpol.nl/fov_pan_calc.htm

All the cunfusion comes from the fact that there are many places where we can find the conversion between focal length and field of view but they do not explain which field of view is meant. The diagonal of the uncropped image would seem the most logical angle to me but as it turns out it's the uncropped size (horizontal or vertical) of the image.

This calculator for example uses the diagonal: http://kmp.bdimitrov.de/technology/fov.html
Which explains the difference with the fisrt calculator (note that they also show the diagonal fov in the first calculator)

Re: reference of camera zoom-settings
« Reply #10 on: January 19, 2012, 06:02:08 pm »
January 19, 2012, 06:02:08 pm
So, just to be sure I did some additional testing because I had the feeling the camera was always too much zoomed in.

As it turns out the results in Lumion are 100% correct. For a 'natural' camera angle I suggest you you use 50mm as the zoom factor because this matches the perspective distortion of human sight. Anything lower can be considered zoomed out and anything higher can be considered zoomed in.

If you want Lumion to match your digital camera then please use the 35mm equivalent zoom factor and it will match the lumion perspective. If you do not have 35mm equivalent settings on your zoom lens you can always look online to get the conversion for your camera. Very often you will need to provide the crop factor of your camera and you can calculate the 35mm equivalent zoom factor.

RAD

    Reputation: 32
Re: reference of camera zoom-settings
« Reply #11 on: January 20, 2012, 12:19:16 am »
January 20, 2012, 12:19:16 am
"50mm....matches the perspective distortion of human sight"

 8)

Re: reference of camera zoom-settings
« Reply #12 on: January 20, 2012, 10:18:53 am »
January 20, 2012, 10:18:53 am
"50mm....matches the perspective distortion of human sight"

 8)

Isn't it weird by the way how zoomed in it is? We crop the image to get a 16:9 aspect ratio. Wouldn't it make more sense to expand the image instead of cropping it? Does anyone know how real camera's handle this?

Do they just cut off the top and bottom to get 16:9? If this is the case then human vision distortion is not 50mm it should be smaller to account for the extra panorama you get of the 16:9 ratio opposed to the 3:2 aspect used for photo's.

I did some calculations and if you use a focal length of 41.5 with an aspect ratio of 16:9 you get the same verticlal fov as a standard 3:2 photo at 50mm. In short I can conclude that a 'normal' and natural focal lenth in Lumion is 41.5mm. Anything smaller will make things look bigger and further apart and anything bigger will make things closer together and smaller.

Re: reference of camera zoom-settings
« Reply #13 on: January 20, 2012, 10:49:47 am »
January 20, 2012, 10:49:47 am
Ok, here are some practical tests. I made two walls in sketchup with an exact angle between them of 39.6 degrees. This is the angle of a 50mm lens on 35mm film.

The first image shows a focal length of 27mm. As you can see the fov is much too large because the view of the camera goes much beyond the walls.

The second image shows a focal length of 50mm. You can no barely see a small edge of the walls. This confirms that at 50mm the angle is indeed the same as what we would expect.

In the last image I used a focal length of 41.5. As you can see the fov is now just a bit larger than the 39.6 degrees because of the 16:9 aspect ratio. This means we still get the same distortion but we do benefit from the extra space on the sides given by the 16:9 aspec as opposed to the 3:2 aspect used on classic photograps.

Frank

    Reputation: 29
Re: reference of camera zoom-settings
« Reply #14 on: January 20, 2012, 12:03:23 pm »
January 20, 2012, 12:03:23 pm
Is this the right way to match rendered still and photo?

1) taking the photo with focal length=41.5mm (EOS 300D).
2) rendering still in lumion with focal length = 41.5mm.