el, PTN, if you have a 21ohm res. in parallel, then it's connected the wrong way. The resistor should be in series & be about 300 ohm. I have a 3 mm *normal*,(not hi-brite), red LED with a 2k7 resistor in series, inside facing the objective, & it just illuminates the X hairs nicely. But then I'm running off 12 volts. (as long as you don't exceed 20 mA, but at that current, it will be bright).Try using a 5k/10k pot. in the circuit with a 150 ohm resistor in series with it to adjust the brightness, then measure the pot. value & sub a fixed resistor. How about velcro/rubber bands to hold the 2 x AA holder on the finder? This would make it self contained. HTH.
L.