[Tfug] Way OT: optics mumbo jumbo

[Bexley Hall]

Hi,

--- erich <erich1 at copper.net> wrote:

> Bexley Hall wrote:
> 
> >But, I don't waste a lot of time thinking about
> >*how* I do this -- I just keep dicking around
> >with where I am standing, ambient lighting,
> >camera angle, etc. until I get something that
> >more-or-less shows what I want/need to show.
> >(much easier when you can click a dozen frames
> >"for free" instead of having to use Polariods!!)
> >
> >Dealing with the flash is almost always a PITA
> >for me.  It's always "too hot" and too much
> >reflected glare, etc.  Granted, I can change the
> >camera angle to eliminate this to some extent.
> >But, at other times, it just moves the reflection
> >to another surface, etc.
> >
> >Often, my solution is to back away from the item
> >(light falls off as the square -- or cube? -- of
> >the distance) until the reflections are manageable.
>
> Inverse 4th power (x^(-4)), because the light makes
> a round trip
> from a light-dispersing object.

OK.
 
> >Of course, this means the image is smaller  :-/
>
> The aparture is constant. So, the light gathering
> ability doesn't
> increase unless you physically move closer to the
> subject.

OK.  Though presumably the camera can adjust the
(electronic equivalent of the) iris?
 
> >So, I crank up the (optical) zoom to make the
> >image large enough to be useful.
> >
> >Now, my naive question:  by doing this, am I,
> >to some extent, counteracting the effect of
> >"moving away" from the target?  I.e., does
> >the magnification I am bringing in to play
> >*increase* the amount of light that strikes
> >the (digital) film?
> >  
> Is a thought experiment so necessary? Why not just
> test it for
> real? Choose a subject and chalk off distances from
> it. Use
> the same camera. Then view images on the same
> monitor screen.

I would have to mount the camera to ensure it
doesn't move (orientation wrt the target and
light sources) between shots, etc.  I.e., this
would be more than a "simple experiment".  :<
THen, trying to *objectively* decide what differences
there are in the results.

I'd much prefer understanding what those results
*should* be and then correlating them with my
observations ex post facto.

> ><sheepish grin>  I've tried to construct a
> >"thought experiment" to convince myself one way
> >or the other but seem to just be thinking myself
> >in circles...
> >
> ><shrug>  I definitely won't lose any sleep over
> >this but it *is* amusing (to me) to think about
> >what's really going on...



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