A 35mm film camera represented in Python object

[Eli the Bearded]

In comp.lang.python,
D.M. Procida <real-not-anti-spam-address at apple-juice.co.uk> wrote:
> Hi everyone, I've created <https://github.com/evildmp/C-is-for-Camera> -
> a representation of a Canonet G-III QL17 in Python.
> 
> There's also documentation: <https://c-is-for-camera.readthedocs.io>.

This is interesting. Some feedback.

> It's a pure Python model of the physical sub-systems of a camera and
> their interactions. So far it's at a fairly high level - I haven't yet
> got down to the level of individual springs and levers yet.

There's a wealth of specifics for that camera above individual springs
and levers. Notably how the light meter performs with different
batteries and how it works with other films. This much is clear from
just a few minutes research on the Canonet G-III QL17 (what a mouthful
of a name).

I'm guessing you plan to deal light meter quirks because of the battery
voltage setting. I see you don't even attempt to tackle ISO outside of
supported range (and I have no idea how the camera itself deals with
that). Is the camera sensing the ISO from the film roll (so won't work
with hand rolled film cartridges)? Is there a setting on the camera to
manually specify that? (I don't think so.)

> You can do things like advance the film, release the shutter, meter the
> scene with the built-in light meter (if the camera has a battery of
> course) and even spoil your film if you make the mistake of opening the
> back in daylight.

Film spoilage isn't boolean in real life. If I rewind most, but not all
of the way, before I open the back, I've only ruined a few frames. If I
open it in a lightproof camera bag, I can take the roll out without
rewinding.

(I've done such things with pin hole cameras.)

> But you can also do things that you shouldn't do, like opening the back
> of the camera in daylight with a partially-exposed roll of film inside -
> which will spoil the film::
> 
>     >>> c.back.open()
>     Opening back
>     Resetting frame counter to 0
>     'Film is ruined'

If luminosity is set to zero, that could emulate the lightproof bag.
Frame by frame "film is ruined" might be a better choice for boolean.

On this camera, there's no manual double exposure setting, right? So
partial rewind would be the way to do that. But I can make double
exposures with this code:

>>> c.shutter.trip()
Shutter openening for 1/128 seconds
Shutter closes
Shutter uncocked
'Tripped'
>>> c.shutter.cock()
Cocking shutter
Cocked
'Cocked'
>>> c.shutter_speed = 1/512
>>> c.shutter.trip()
Shutter openening for 1/512 seconds
Shutter closes
Shutter uncocked
'Tripped'
>>>

In general, I never used simple cameras with light meters. Advanced SLR
or dumb cameras. My personal favorite film camera is a Universal Mercury
II, a half frame 35mm from mid 1940s with hot and cold shoes (intended
for flash and film meter attachments), bulb to 1/1000 shutter range,
mechanical exposure calculator on the back, and a dial for reminding you
what film you have in it.

Does a camera like the one you have modelled that actively stop you from
using a ISO/shutter speed/F-stop that will vastly over- or under- expose
things? Or is it just a warning light in the viewfinder?

Certainly my c.shutter.trip() calls give me no advice from the meter.

A useful thing your camera-as-code model could provide, but doesn't, is
some measure of how exposed each frame is. This will be a function of
film speed, iris setting, cumulative exposure time from zero or more
shutter openings, and scene luminosity. (You could extend this to
include opened back over exposure conditions.)

Elijah
------
can see how this might get integrated with an image generation tool