[libcamera-devel] [PATCH 1/1] libcamera: controls: Change LensPosition units to dioptres

[Kieran Bingham]

Hi David,

Quoting David Plowman via libcamera-devel (2022-11-17 15:45:00)
> The units for the LensPosition control, previously defined as being in
> units of 1 / hyperfocal_distance, are changed to 1 / distance (in
> metres).
> 
> Signed-off-by: David Plowman <david.plowman at raspberrypi.com>
> ---
>  src/libcamera/control_ids.yaml | 26 ++++++++++++++------------
>  1 file changed, 14 insertions(+), 12 deletions(-)
> 
> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> index a456e6c0..adea5f90 100644
> --- a/src/libcamera/control_ids.yaml
> +++ b/src/libcamera/control_ids.yaml
> @@ -591,25 +591,27 @@ controls:
>          AfModeManual, though the value is reported back unconditionally in all
>          modes.
>  
> -        The units are a reciprocal distance scale like dioptres but normalised
> -        for the hyperfocal distance. That is, for a lens with hyperfocal
> -        distance H, and setting it to a focal distance D, the lens position LP,
> -        which is generally a non-integer, is given by
> +        This value, which is generally a non-integer, is the reciprocal of the
> +        focal distance in metres, also known as dioptres. That is, to set a
> +        focal distance D, the lens position LP is given by
>  
> -        \f$LP = \frac{H}{D}\f$
> +        \f$LP = \frac{1\mathrm{m}}{D}\f$
>  
>          For example:
>  
>          0 moves the lens to infinity.
> -        0.5 moves the lens to twice the hyperfocal distance.
> -        1 moves the lens to the hyperfocal position.
> -        And larger values will focus the lens ever closer.
> +        0.5 moves the lens to focus on objects 2m away.
> +        2 moves the lens to focus on objects 50cm away.
> +        And larger values will focus the lens closer.
>  
> -        \todo Define a property to report the Hyperforcal distance of calibrated
> -        lenses.
> +        The default value of the control should indicate a good general position
> +        for the lens, often corresponding to the hyperfocal distance (the
> +        closest position for which objects at infinity are still acceptably
> +        sharp). The minimum will often be zero (meaning infinity), and the
> +        maximum value defines the closest focus position.
>  
> -        \todo Define a property to report the maximum and minimum positions of
> -        this lens. The minimum value will often be zero (meaning infinity).
> +        \todo Define a property to report the Hyperfocal distance of calibrated
> +        lenses.

Is this going to be a separate property, or the 'default' value of the
control?

In the cover letter you mentioned "we've resolved that we will be
able to read a good default position from the control info."

Presumably, that means that when lacking other information, '1' is a
good default value?


>  
>    - AfState:
>        type: int32_t
> -- 
> 2.30.2
>