On 2/12/2018 2:00 PM, Alain wrote:
> Le 18-02-10 à 19:47, Mike Horvath a écrit :
>> What effect does scaling a camera have on focal_blur?
>>
>> I have two cameras, and they should both produce the same result. But 
>> they don't.
>>
>>
>>
>> // focal blur camera
>> camera {
>>    location  <0,0,-5>
>>    look_at   <0,0,0>
>>    right     x*image_width/image_height
>>    up y
>>    aperture 1.0           // [0...N] larger is narrower depth of field 
>> (blurrier)
>>    blur_samples 10        // number of rays per pixel for sampling
>>    focal_point <0,0,0>    // point that is in focus <X,Y,Z>
>>    confidence 0.95        // [0...<1] when to move on while sampling 
>> (smaller is less accurate)
>>    variance 1/200         // [0...1] how precise to calculate (smaller 
>> is more accurate)
>>    scale 2
>> }
>>
>> /*
>> // focal blur camera
>> camera {
>>    location  <0,0,-10>
>>    look_at   <0,0,0>
>>    right     x*image_width/image_height
>>    up y
>>    aperture 1.0           // [0...N] larger is narrower depth of field 
>> (blurrier)
>>    blur_samples 10        // number of rays per pixel for sampling
>>    focal_point <0,0,0>    // point that is in focus <X,Y,Z>
>>    confidence 0.95        // [0...<1] when to move on while sampling 
>> (smaller is less accurate)
>>    variance 1/200         // [0...1] how precise to calculate (smaller 
>> is more accurate)
>> }
>> */
> 
> The amount of focal blur depends on the ratio between (1) the distance 
> between the camera's location and the focal point location and (2) the 
> actual aperture.
> 
> So, with everything else been the same, the second camera have twice the 
> focal length for the same aperture, resulting in half the focal blur or 
> twice the sharpness depth.
> 
> To get the same results, you need to scale the aperture by the same 
> amount as the rest of the camera use for the second camera :
> aperture 2.0
> 
> 
> Alain

You're wrong, and Kenneth already figured out why up-thread.


Mike

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