Testing mods

[erick]

I'm just about to go outside and test a couple of mods to my little 8" reflector on EQ5.

1) The JMI focusser I swapped in to replace the original GSO

2) The secondary collimation. I have just replaced one of the three screws with a small robust spring so the other two push against it rather than a rigid screw.

I'll let you know how it goes.

[erick]

OK, started to cloud over so I packed up.

Secondary collimation is easier. I just have to watch for rotation around the central screw. It held collimation as I moved the scope from horizon to zenith. I pulled out the E and F stars in the Trapezium no problem (lovely sky tonight!). I got down to the 5mm TMB/Burgess Planetary eyepiece - magnification 240 or so (still haven't worked out the focal length of this 8" reflector. I reckon collimation was easy to achieve, was quite good and held up well.

JMI focusser was nice and smooth. I just need to get the electric focusser connected since the scope wobbles on the EQ5 - too much for 240x!

Happy, Jan! :)

[Waxing_Gibbous]

Hi Erick,
Info on the spring? I was contemplating this but couldn't find anything locally to fit the bill. Grateful for your input.
Thanks,
Peter

[erick]

I was heading to Bunnings to look at their compression springs when I used a stapler and thought - there is a spring in here :). I pulled the springs out of several staplers and one seemed fine. (I have had to buy my wife a new stapler today!). I removed one of the Bob's knobs and have replaced it with an M4 screw (the original I think) with a couple of nuts so that the end of the screw sat about 2mm above the back of the secondary mirror holder when fully screwed in. Retracted it, and forced the spring into position, then reinserted the screw. That will prevent the spring from going AWOL! (and hitting the mirror(s) on its way!!)

Obviously, the Secondary needs to be in its correct position up/down the optical axis when the mod is made - well it cannot be several mm out, anyway.

No guarantees as yet that this will work well. I think I still want to put a slightly flexible pad under each of the two remaining screws. A piece of plastic milk bottle as per a thread in Cloudy Nights. And maybe polish off the ends of the screws to a nice surface with rounded smooth edges to stop the bite that they have been getting into the existing metal washer.