On 10-7-2015 7:19, Pekka Aho wrote:
> Alain <kua### [at] videotronca> wrote:
>>
>> It's usualy best, and recomended, to use the same value for look_at and
>> focal_point.
>
> I admit it wouldn't be the first time for me having a rather obscure way of
> seeing and understanding common things, but personally I've just always found it
> important for the scene to fine-tune look_at and focal_point independently to
> get the camera angle as desired and furthermore to have the blur in the correct
> point. My own recommendation would thus be that it certainly depends on what you
> are having in the scene and what you want to emphasize. :)
>

I agree with this. It is identical to the use of a traditional camera: 
focus on a certain object (aka focal_point), half-press the shutter, 
then compose the scene (aka look_at), finally press the shutter completely.


-- 
Thomas

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On 2015-07-10 03:06 AM (-4), Thomas de Groot wrote:
> I agree with this. It is identical to the use of a traditional camera:
> focus on a certain object (aka focal_point), half-press the shutter,
> then compose the scene (aka look_at), finally press the shutter completely.

Digital cameras are now considered "traditional"?

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Le 10/07/2015 11:25, Cousin Ricky a écrit :
> On 2015-07-10 03:06 AM (-4), Thomas de Groot wrote:
>> I agree with this. It is identical to the use of a traditional camera:
>> focus on a certain object (aka focal_point), half-press the shutter,
>> then compose the scene (aka look_at), finally press the shutter
>> completely.
>
> Digital cameras are now considered "traditional"?
>
It worked already like that on auto-focus film-based camera.

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On 10-7-2015 12:30, Le_Forgeron wrote:
> Le 10/07/2015 11:25, Cousin Ricky a écrit :
>> On 2015-07-10 03:06 AM (-4), Thomas de Groot wrote:
>>> I agree with this. It is identical to the use of a traditional camera:
>>> focus on a certain object (aka focal_point), half-press the shutter,
>>> then compose the scene (aka look_at), finally press the shutter
>>> completely.
>>
>> Digital cameras are now considered "traditional"?
>>
> It worked already like that on auto-focus film-based camera.

And that is what I was referring to. Before auto-focus it was even nicer 
(for those who did not experience that golden age): just the manual 
combination of distance setting, diaphragm opening / exposure time. You 
can simulate this on digital cameras, sure, but that was not the same 
feeling.

-- 
Thomas

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> And that is what I was referring to. Before auto-focus it was even nicer
> (for those who did not experience that golden age): just the manual
> combination of distance setting, diaphragm opening / exposure time.

It was the real golden age because you had to actually figure out the 
right combination to get the image you want. And you wouldn't know if 
you succeeded or not until you processed the film.

Nowadays you get a real-time preview (with histograms if you want) 
whilst you adjust the settings.

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Problem.
The camera in the Blender has no look_at parameter.
Therefore from a matrix take the parameters "rotate", "translate".
All this well works, if not Blur.
For Blur it is necessary to enter the translate parameter into "location", and
to remove with "rotate".
But, how to calculate the look_at parameter????

image 1
camera {
    perspective
    location  <0, 0, 0>
    look_at  <0, 0, -1>
    right <-1.7777777777777777, 0, 0>
    up <0, 1, 0>
    angle  49.134343
    rotate  <-21.713552, 91.172234, 0.000124>
    translate <27.149088, 10.813705, -0.555530>
    blur_samples 25, 100
    aperture 0.04
    confidence 0
    variance 1
    focal_point <0,0,0>
}

image 2
camera {
    perspective
    location  <27.149088, 10.813705, -0.555530>
    look_at  <0, 0, -1>
    right <-1.7777777777777777, 0, 0>
    up <0, 1, 0>
    angle  49.134343
    blur_samples 25, 100
    aperture 4
    confidence 0
    variance 1
    focal_point <0,0,0>
}

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Attachments:
Download 'blur.jpg' (13 KB)

Preview of image 'blur.jpg'

I found solution.
Thanks!

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Attachments:
Download 'blur.blend.jpg' (148 KB)

Preview of image 'blur.blend.jpg'

> Alain <kua### [at] videotronca> wrote:
>>
>> It's usualy best, and recomended, to use the same value for look_at and
>> focal_point.
>
> I admit it wouldn't be the first time for me having a rather obscure way of
> seeing and understanding common things, but personally I've just always found it
> important for the scene to fine-tune look_at and focal_point independently to
> get the camera angle as desired and furthermore to have the blur in the correct
> point. My own recommendation would thus be that it certainly depends on what you
> are having in the scene and what you want to emphasize. :)

Right. But, initialy, having the two been identical is simpler and less 
error prone. Nothing can prevent you from changing the focal_point for 
the final render.

>
>> To match the original, you only need to negate the value for right:
>> right -x*image_width/image_height
>
> Ah, of course, forgot about that one completely. I should sleep more. Or drink
> more tea. %-)
>
>

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Alain <kua### [at] videotronca> wrote:
> Right. But, initialy, having the two been identical is simpler and less
> error prone.

Look_at defines the direction where the camera itself points at, nothing more.
Focal_point defines the sharpest spot/axis for the focal blur effect. They are
definitely two different things and you certainly want to define them separately
depending on what you're having in the scene and what you want to bring out from
the image. There is no such thing as "recommendation" for the two values ever
being identical, and it has nothing to do with being "simplier" either, as you
surely know at all times what there is in your scene, where and in what kind of
scale. If all else fails for some weird reason, the last means to avoid "errors"
is to use for example a small colored sphere to find the exactly desired spot
for the focal_point. There's nothing difficult in this really. The whole idea of
a separate focal_point value is the freedom to put it where you want it to be.

> Nothing can prevent you from changing the focal_point for the final render.

Of course you also do test renders with lesser settings to fine-tune everything
before the final render. Obvious and self-evident matters.

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It is possible to use focal_point vector unequal look_at in animation.
It is more interesting to create animation, than photorealistic pictures.
For photorealistic pictures there are photorealistic cameras. :)

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Attachments:
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Preview of image 'blur_anim.jpg'