[Tfug] Way OT: optics mumbo jumbo

[TR]

On Tue, Mar 18, 2008 at 8:11 PM, Bexley Hall <bexley401 at yahoo.com> wrote:
> Hi,
>
>  This is *way* OT but it seems there are some folks
>  with more than a casual knowledge of optics (while
>  I have *less* than a casual knowledge!) so...
>
>  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.  don't
take the time to analyze the mistake just keep shooting.
>
>  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.
>
>  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
>
>  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.
>
>  <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...
>
>
>       ____________________________________________________________________________________
>  Never miss a thing.  Make Yahoo your home page.
>  http://www.yahoo.com/r/hs
>
>  _______________________________________________
>  Tucson Free Unix Group - tfug at tfug.org
>  Subscription Options:
>  http://www.tfug.org/mailman/listinfo/tfug_tfug.org
>