Re: [MF 3D] MF viewer lighting

[Greg Erker <erker@xxxxxxxxxxxxxx>]

>Hewlett Packard has recently introduced white LEDs with
>color-temperature grading:  http://www.hp.com/pressrel/mar99/15mar99.htm
>
>These lamps have a color temperature of 6500K and a Color Rendering
>Index (CRI) of 75 (i.e., a reasonably continuous spectrum).

  Nice. I believe the Nichia (sp?) ones are CRI of
85.

>LEDs are pretty close to ideal light sources - very bright, long-lived,
>energy efficient.  If it weren't for that #%&! collimating lens that
>restricts angle of view (enhancing apparent brightness)!  A modification
>I've made to LEDs used in backlights is to cut off the lens (using a
>Dremel emery cutting wheel - and being careful not to nick the embedded
>thin wire connecting the chip to one of the leads).  The cut surface is
>then sanded with #400 wetted sandpaper (very little sanding is needed as
>the Dremel wheel makes a smooth cut) and polished  with "Blue Magic"
>polishing compound (available from Micro-Mark).

  Would scuffing the lens to diffuse the
light work as well or would you lose too much
light internally.

>These modified LEDs have a very wide illumination pattern.  Mount them
>in a reflective chamber with a decent diffuser and voila - instant
>backlight.  I've made a twin 35mm viewer this way, using 4 LEDs per side
>for increased brightness and uniformity of illumination.

  So you have 8 LEDs at about 3V and 25mA (guessing).
So this is 0.6W (ignoring losses in the dropping
resistors or regulator). Quite a bit lower that say
the Redbutton with 2.5V 0.8A halogen.

  How would you compare the brightness? Do have
any way to measure the EV into the eyepiece to
compare to my viewer brightness measurments?

Greg E.