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Question about camera moving vs. focal length
Posted: 24 June 2014 06:06 PM   [ Ignore ]   [ # 16 ]
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I’m guessing that its somehow a fundamental mistake and won’t be fixed before V5.0.

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Posted: 25 June 2014 12:55 AM   [ Ignore ]   [ # 17 ]
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I’m not seeing what you are in DS4.6 at 50mm but my focal distance is not set to 200 something either.

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Exile, Drows Walk: A Tale of Jaderail starts here. Free pulp fiction at its Fantasy best, Updated 2/3/14.
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Posted: 25 June 2014 03:49 AM   [ Ignore ]   [ # 18 ]
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This is what I get with Render Dimension set to 10:1 with 50mm Focal Length camera. 

Note that the 10:1 render dimension setting has effectively reduced camera focal length to 5.53mm. 

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50mm_from_3m_10x1.JPG
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Posted: 25 June 2014 03:59 AM   [ Ignore ]   [ # 19 ]
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And this with Render dimension set to 1:1 with 5.53mm Focal Length camera (extreme wide angle).

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5.53mm_from_3m_1x1_.JPG
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Posted: 25 June 2014 04:23 AM   [ Ignore ]   [ # 20 ]
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Jaderail - 25 June 2014 12:55 AM

I’m not seeing what you are in DS4.6 at 50mm but my focal distance is not set to 200 something either.

Focal distance is not part of the problem.  In the scene above,  the camera focal distance is set to 300 (focused on corner of small blue cube).

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Posted: 25 June 2014 09:27 AM   [ Ignore ]   [ # 21 ]
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Render dimension set to 1:1 with 50mm Focal Length camera.

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50mm_from_3m_1x1_.JPG
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Posted: 25 June 2014 02:20 PM   [ Ignore ]   [ # 22 ]
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I can confirm the observation of Rayman29.

If you have some knowledge of real world photography, focal lenght and aspect ratios you should immediately notice that whatever happens in the DS viewport at an aspect ratio of 10:1 is not in any way based on real world camera values at a focal lenght of 50mm.

In a realistic simulation there should be no interaction between aspect ratio and focal lenght at all. excaim

- - -

I also set focual lenght to 50mm and the render aspect ratio to 10:1.
Focus is set on the cube front surface.

Result:

The cube in the scene AND the wireframe ground plane are completly distorted in the DS viewport.

If focal lenght is at 50mm there should be NO DISTORTION what so ever.

In this specific example the lower side of the cube seems to be smaller than the upper side.
There is NO logical reason why this should happen at a focal lenght of 50mm.

In the OctaneRender viewport you can also see that this distortion is affecting the OctaneRender plugin as well.

- - -

So I believe it may be as Rayman29 explained.

For some reason the aspect ratio is distorting the focal lenght in a way that the viewport is showing an image with a much lower focal lenght.  excaim

As pointed out by Rayman29 the actual (!) focal lenght of the viewport seems to be around 5mm or even lower.

At a focal lenght of around 8mm also with real world camera lenses you can observe such extreme distortions of the image.

- - -

Admited an aspect ratio of 10:1 is very well unusual.
It would be interesting to do further testing.

Is the “apsect ratio bug” behaving in a linear way?

OR

Is there some kind of treshold after which extreme aspect ratio values cause unrealistic distortions by affecting the focal lenght.
- - -

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render_aspect_size_distorting_image.jpg
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Posted: 25 June 2014 03:09 PM   [ Ignore ]   [ # 23 ]
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linvanchene, at last a photographer.  The bug seems to effect all focal lengths.  The 10:1 render dimension was an extreme example, with render dimension set to 2:1, 50mm focal length is effectively reduced to 31.59mm.

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2x1_50mm.JPG1x1_31.59mm_.JPG
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Posted: 25 June 2014 05:49 PM   [ Ignore ]   [ # 24 ]
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Rayman29 - 25 June 2014 03:09 PM

linvanchene, at last a photographer.  The bug seems to effect all focal lengths.  The 10:1 render dimension was an extreme example, with render dimension set to 2:1, 50mm focal length is effectively reduced to 31.59mm.

It seems the situation is worse than I originally thought.

I am also a bit embarrased that I did not notice this before.   red face

The question is: Was this bug introduced in one of the last updates or did we all just not notice for a very long time?

- - -

This will lead to major issues when compositing different CG images created with different CG software.
This will lead to major issues when compositing real life footage from real photo and video cameras with CG images.

The basic rule of any compositing work is: The focal lenght of all images needs to be exactly the same. excaim

Example:
If I have a photograph at focal lenght of 50mm I need to be able to rely that if I enter the value of 50mm in any render software that the resulting image of the viewport also is at a focal lenght of 50mm.

- - -

True in DAZ studio most people may use focal lenghts of either 35 or 50mm. Most people may use aspect ratios of 2:3, or 16:9.
Most people have difficulties telling the difference between 85mm and 50mm lenses in real life as well.

Nevertheless the lower the focal lenght gets the more obvious distortions will get!!!

If you want to composite landscape images at 16mm with computer graphic images you will run into serious issues if the actual focal lenght is downscaled to below 5mm. A lot of edges will be slanted and the images will just not match at all and be unusable for any compositing.

If I have a street photography shot at a focal lenght of 35mm things will just not look right if the computer graphic image has a focal lenght of 24mm or even lower.

- - -

I opened up a ticket with support

and hope that

- we can get some feedback in this thread what is happening here and why it is happening
- the issue will be fixed as quickly as possible

 

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Posted: 25 June 2014 06:25 PM   [ Ignore ]   [ # 25 ]
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linvanchene - 25 June 2014 05:49 PM

The question is: Was this bug introduced in one of the last updates or did we all just not notice for a very long time?

Looking back I thought that it might have first appeared with the 4.6 release.  But I’m now thinking it was the 4.5 release. 

 

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Posted: 27 June 2014 06:37 AM   [ Ignore ]   [ # 26 ]
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Here’s a list of render dimensions with the approximative focal length correction.

2:1 multiply focal length by 1.579
3:1…........................................2.370
4:1…....................................... 3.172
5:1…....................................... 3.971
6:1…....................................... 4.770
7:1…....................................... 5.561
8:1…........................................6.329
9:1…....................................... 7.142
10:1…..................................... 7.936

Most of the error is removed at any reasonable focal length (8mm to 800mm).  As linvanchene pointed out though, for composite work focal length needs to be precisely matched.

Edit:- The above only works between focal lengths of 40 to 50mm.

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