[Tfug] Way OT: optics mumbo jumbo

Bexley Hall bexley401 at yahoo.com
Sun Mar 23 18:16:30 MST 2008


--- TR <trexx at pobox.com> wrote:

> On Tue, Mar 18, 2008 at 8:11 PM, Bexley Hall
> <bexley401 at yahoo.com> wrote:
> >  I often take photos of things that I have built
> >  (etc.) to show clients problems that I have
> >  encountered (picture, 1000 words, etc.).
> >
> >  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!!)
> Ah the fallicy of digital, keep shooting till I get
> it right.

When moving the camera a few inches and pressing the
shutter release 10 seconds later has a good chance
of "fixing" the problem, why spend two hours at
a library researching the phenomenon of light and
optics?  :>  I'm not trying to be a world-class
photographer.  Rather, I'm trying to show that:
"the diameter of capacitor C215 is larger than
planned in the PCB layout and, as such, it overhangs
he cathode lead of diode D27".  While that text
describes the problem, showing a real board with
those two devices populated and interfering is
far more descriptive!

> don't take the time to analyze the mistake just keep
> shooting.

That was the point behind this post  :-(

> >  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.don't change the camera
> change the flash. . for small object bounce it off a
> white card so the light falls over the subject at a
> different plain the the lens.

Like most digital cameras, the flash is built in.
So, bouncing it off a white card would mean bouncing
the target image off that same card (since the
lens points in the same direction as the flash
and is separated from it by only an inch or so)

> >  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.
> the fall off is the sqare og the distance.
> >
> >  Of course, this means the image is smaller  :-/
>  change the focal length of the  lens but that  in
> turrn chages the perspective

Cheap digital camera.  Note the cheap POLAROID
camera worked much better!

> >  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?
> Yes and no. as you move away the light returning
> from the subject
> lessens.  But the camera is always trying to make
> the average light on
> the film plane the same.  So it either it pumps more
> light to the
> flash. opens the appeture to let in more light.

So, in plain English, "am I counteracting the
effect of moving away from the target"?

> >  <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...
> >
> >  We now return you to your regularly scheduled
> >  program...



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