Re: [MF 3D] MF viewer lighting

[Greg Erker <erker@xxxxxxxxxxxxxx>]

>You do lose more light if the lens is just roughened, how much is "too much"
>is tough to say.  If the LEDs are in a perfectly reflecting chamber where the
>only way for light to escape is through a scattering but non-absorbing
>diffuser, it wouldn't matter.  Real mirrors, on the other hand, reflect ~90%
>if you're lucky, and diffusers also absorb, so getting as much light as
>possible from the LED chip directly to the diffuser is important.

  Understood. Do you have a photo or drawing
showing the configuration of your LEDs and
reflector?

>The current through the LEDs is a little less than 20mA (total current for
>all 8 is 150mA, power is about 0.45W).  Aiming an exposure meter (set at ISO
>100) into the eyepiece of the viewer gives me a reading of about 10EV.  I
>have a Realist Red Button viewer with the original yellowed reflector
>replaced by white matte photographic paper that has been "fixed" (probably
>the whitest paper you can find with optical brightners), and a halogen bulb
>rated 600mA @ 2.33V.  I use alkaline "D" cells with a [switchable] series
>diode to drop the voltage to about the right range when the batteries are
>fresh, extending the bulb life.  With slightly used batteries, I measure
>585mA @ 2.15V, and the exposure meter sees 9.6EV.
>
>This is something of an apples/oranges comparison, but basically I'm getting
>about the same brightness with a lot less power using LEDs for the
>backlight.  Given the price of white LEDs, you get more brightness/$ with
>CCFL - the reason I went that route for the MF viewer.

  Very interesting results. I have some brightness
measurements on my web page at:
http://www.angelfire.com/ca/erker/brightness.html

  Basically I measure about EV12 on my Dr T's
Red Button viewer (2.5V 0.8A clear bulb). And
in my MF viewer with Cabin Light panel measure
between EV11 and EV12.5 depending on input
voltage.

  Do you have an EV measurement for your
CCFL lit MF viewer?

  Regarding power consumption: my RB is 2.0W
and my Cabin Light panel is 1.3W on low setting
and 2.7W on high. So your 8 LED solution is
a definite winner in the power consumption
battle.

Greg E.