Illuminating My Finder Scope

For about 32 years I have been bugged by not being able to see the crosshairs in my finder scope under dark skies. The finder scope that I have is the standard 8 x 50 straight through supplied with the Guan Sheng 10"/F5.

I believe it is not such a difficult job to illuminate it internally with a RED LED and I have a couple of questions in this regard.

I planned to mount the LED and a small battery in the OTA of the finder with a small switch on the side of the tube, obviously I need to keep these bits out of the light path.

My main question is will the LED provide enough internal illumination if it is mounted anywhere in the tube or does it need to be mounted very close to the crosshairs.

The 2nd question is what sized LED would do the job, I was thinking 3mm would be about right.

Are there any major foreseable problems with this that I should know about.

Thanks in Advance

Clear Skies
John Bambury

I think the hard part will be keeping the LED out
of direct view. Otherwise there will be a very
bright and distracting bunch of light. Usually
the LED is placed very near the crosshairs, and
illuminates them from a recess or hole in the
side of the tube. That way theres no direct
light path from the LED to the eye.

If the LED is up near the objective lens, it will
be really hard to keep it out of direct view.
And brightness of the crosshairs may also be a
problem if the LED is far up the tube, so it is
a doubly bad situation.

Probably best location is in the side of the tube
just foward (toward the objective lens) of the
crosshairs. That way the mounting of the crosshairs
will help block direct light.

Any LED will be bright enough; it doesn't take much
if its done right.