Polar Illuminator - LED Position?

[Nomad Z]

I'm making an illuminator for the polar scope in my EQ3. The construction and electronics aspects are fine, but I'm not sure about the position of the LED.

When I first made the thing, the wires to the LED were a bit short such that the LED couldn't be placed in the centre, but was quite close. What I got was a reticule that was mostly dull but had a brighter patch where the LED was partially visible (or some of the emission from the LED was spilling into the scope's objective). I assumed at first that the LED was supposed to be out of the way, so I bent it back a bit, but the reticule was very dark - in a dark room, it was very hard to see the engravings even with the LED at high brightness (and allowing some time for my eyes to become dark adapted).

Now, I'm wondering if the LED should be in the centre, with the brightness set to give a balance between reticule readability and being able to see Polaris. If that's the case, am I right in thinking that the scope will still see the star because only a small area in the middle is obscured by the LED? It's a 3mm LED and the illuminator has a variable brightness control.

Should the LED be placed on the scope's axis?

[steppenwolf]

I have built a couple of these (one for an EQ3 and one for a Polarie) and I set my LED bang in the centre at the top end of the polarscope. Here is a link to what I did and below a photograph of it..

[wookie1965]

http://www.365astronomy.com/Skywatcher-Polar-Scope-Illuminator-for-EQ3-2-EQ5-and-Star-Adventurer-Telescope-Mounts.html

This is the illuminator for the EQ3-2 and EQ5 perhaps from the picture you can glean where to put it. 

[Nomad Z]

Thanks folks - looks like the centre is the place to put it.

Just been extending the wires to the LED and finishing it off, and here it is...

3D printed in three parts - the ring, the main case,  and the cover. It runs on a PP3 battery. There's a little bit of vero inside, which has a 1K resistor in series with a 10K linear preset pot for setting brightness. The switch and pot are recessed.

The other side...

The ring is a nice, snug fit into the opening in the mount (which seems to be 35mm diameter nominal). The LED is within the edge of the ring rather than sticking out. The idea is for the bits to not get bumped when it's in the bag (particularly the switch).

Here it is on the mount...

 

 

Haven't had a chance to try it outside yet, but the reticule illumination is now nice and even and it's easy to read. Shining a small, relatively weak, torch at the ceiling washed out the pinkish-red colouring (at the fairly bright setting shown in the photos), so I'm reasonably confident that it can be adjusted for balance with Polaris.