How to make an illuminated reticle EP

This simple DIY illuminated reticle EP is a project for those that get satisfaction from making or improving their own equipment. While I don't claim that this simple design provides the performance of the $$$ reticle EP's currently on the market, for less then $10 and a couple of hours of your time this may be adequate for your needs, and is customisable.

For this project I chose a GSO 1.25" 15mm super plossl and a 30mm GSO wide view 2" EP, both are highly affordable and provide adequate performance for the task of achieving good tracking or matching target object size to a particular size ccd chip etc. Because the only direct modification to the EP is drilling a hole in the soft brass barrel extension, many EP types could be used. The only trick is finding the right diameter circular crosshair frame to slide up into the bottom of the extension or EP housing itself, and the mounting of the crosshairs to the frame. The inside diameter of the crosshair frame must also be slightly greater than the field stop of the bottom element, in order not to lessen the EP's field of view.

I will try to provide details by way of pictures with explanations for the steps.
Below are the basic items needed if you are interested in giving this a go.

If you are like me you might keep a bin full of useful metal, plastic and timber off cuts of all kinds. Rummaging through my lot I found a plastic tube of 23mm outside diameter and 17mm inside diameter, which slid into the inside of the 1.25" 15mm EP lense housing perfectly. Finding a suitable crosshair frame for the 2" EP was more difficult, but a trip to the hardware store yielded a 1/1/2"-1/1/4" irrigation pipe joint bushing that had a 48mm outside diameter, just perfect to fit inside any 2" barrel extension.

Below is a pic of these two items, plus the frame pieces cut from them both with a tennon saw. Frames of 5mm thickness are adequate.

With the frames now cut and scraped clean, the tricky task of fitting them with crosshairs is now in order. This is worth finding some resolve and care for, and if you find that human hair is just too difficult to work with another option is fine 4Lb 0.15mm diam fishing line, or even the fine individual strands of copper wire found in light electrical cabling. The hair used in this example was kindly donated by my good lady partner, but extraction by stealth is always an option for the keen DIY'er having trouble persuading a donor.

I drilled four 1mm holes through the outside of the frames, more by line of sight and careful guestimation than mathematics. It's more or less critical to get your crosshair alignment accurate, so marking and drilling should not be rushed.
Alternately you could elect to simply glue the hairs to the top of one side of the frame after aligning and then tensioning them (see pic below), this makes aligning them less haphazard than drilling holes, fitting and tensioning the hairs, then gluing them.

Glue to use is plastic model glue, super glue or some other.

At any rate the process can be repeated until the crosshairs are central, and checked with a set of vernier calipers, accurate ruler etc. After tensioning and gluing the hairs, the frames should be left overnight.

Keep in mind that a set of double hairs or any hair configuration can be applied to the circular frame.

With the glue well and truly set, you can slice off the loose strands of hair on the frame and inspect it again for centrepoint accuracy, if the hairs come loose from the frame it is possible to correct them with a tiny piece of bluetac.

Then carefully slide the frame into the bottom of the EP housing barrel so it's as close as possible to the inside lense element, or perhaps the top of the barrel extension in the 2" case, screw the extension back into the EP and see how the crosshairs shape up when viewed through the lenses. This is when the care we have taken becomes obvious. If the frame you have chosen for the inside of the EP housing is correct in diameter, it will neither fall out or need to be forced in.

(If you decide to use 9-15mm GSO plossls for this project, i may be able to help you with the right frame size via PM.)

Now we can consider the flashing red LED part of the project. I chose a red 3v 3mm flashing unit because it's intermitent nature gives your retina momentary relief from the soft red light, and allows you to orientate the target to the crosshairs during the short moments of darkness. These cost $1.25AU from any electronic component retailer. The power unit featured here uses two AA batteries and has an inbuilt switch in the housing, but smaller AAA units are available, they cost $2.50 with cables attatched.

Fitting a bit of heat shrink plastic tube to the power unit wires before soldering is a good idea for insulation, and so far the the wires have proven long enough for the regular range of focuser travel.

If you find the LED flash to bright, marking the LED with a black permanent marker to your liking will help to dim it's glow.

Measure how far the main EP housing screws into the barrel extension and mark the extension just below that point with a marker, this is where we need to drill a 3.5mm hole to fit the LED. The LED will be below the crosshairs. The barrels are a relatively soft metal, so lightly centrepunching a mark before drilling helps accuracy. Now might also be a good time to flock the inside of the extension if needed to help prevent glare.

*Note though that because we are fitting the LED into that hole from the outside of the barrel, the EP will not slide all the way into your focuser, but will stop at the LED. For most types of telescope setups this will have little optical consequence.

The power unit can be fastened to the scope or focuser with a rubber band or velcro, and the LED will usually just sit in the EP barrel hole by itself. When you are done with the unit you can just lift the led out, remove the EP and fit your observing EP's or CCD camera or other devices to the focuser.

This little item has been a great help in drift aligning and DSO object centering, and with another crosshair configuration it may work to organise a setup for imaging. plus i can slide the crosshair frames into other FL EP's and exchange the barrel extensions.

Its not for everyone to go to the trouble to make one, and i cant guarantee satisfaction particularly if you are accustomed to and swear by a $$$ unit.

As mentioned earlier this is for the keen DIY'ers with a flair for engineering.

by Steven McNelley