[Tfug] Way OT: optics mumbo jumbo

[erich]

Bexley Hall 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!!)
>
>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.

>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.

>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.

><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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>  
>