Tips for aligning an RDF?

[smithcorp (Brian)]

Hi all, I am trying to get my RDF better aligned on my little scope with a dobsonian mount. My problem is that the process of adjusting it also moves the scope tube. How do the experts do it? What's a good way to hold the mount from moving while tinkering with the RDF?

Any advice appreciated, thanks!

[mental4astro (Alexander)]

Hi Brian,

First, do it during the day.

2, use something in the distance to aim at, & note the one spot on that landmark you'll focus on.

3, do your first sighting through the RDF & then through the scope. Resight through the RDF & turn the first knob to realign. If the scope moves don't worry about it, resight the SCOPE & then see how you've done with the RDF.

4, readjust as needed.

This happens to me two with my own scopes too. If the movement is too touchy, you can tighten the Nyloc nut in the base of the little dobbie to firm up the action, just remember to back it off again. The altitude movement, up and down movement, it's a little trickier. Just be patient with the process. Doing it during the day helps reduce the frustration if done at night when you can have all sorts of pressures put on you to get going!

[Honest_Gaza (Garry)]

Brian, as an absolute beginner, here is what I did.....the absolute reverse of how you will use it.

Get the Moon centrally within your eyepiece (which is relatively easy), and then adjust the Scope Finder to show the cross in the centre of the Moon (that will then align the Scope and the Eyepiece). Of course this may take several attempts while the Moon "moves" across the Eyepiece.

Once this is completed, then use the Scope Finder to centrally locate the Moon and then set the RDF to do the same....again, this will take several attempts.

Once completed, you should be able to do the following :

• Point RDF to centre of the Moon
• Use Scope Finder to fine tune the point selected
• View via the Eyepiece

The Full Moon should make the perfect target for doing this (as long as the Clouds disappear)

[smithcorp (Brian)]

Gaza - you have a scope finder and an RDF! Luxury! We just have cardboard box on motorway!

Thanks all for the tips. My main problem is I have nothing in view during the day from my house that would be far enough away to centre on, so unless I take the scope for a trip somewhere else, i may have to try using the Moon.

Alex, thanks for the tip about tightening up the mount base, so I only have to try to stop it from traversing. I will attempt again and report back.

We are heading out to Parkes for a weekend soon and staying on an isolated farm - hope to get that starry sky!

smith

[ZeroID (Brent)]

Someone posted earlier a method for aligning a finder\RDF etc without requiring along distance object.
He basically drew a target with two points to aim at spaced the distance between the finder centre axis and the scopes centre axis, eg 200mm or whatever it may be. He pinned the double target on a fence as far away as possible and oriented the target rotation so it matched the scope\finder configuration. Lined up the scope and checked that the finder saw the second target spot. Adjusted to suit.
Probably not quite as accurate as a good long distance target but should get it at least within a usable range.
My RDF and finder are never bang on target, a close approximation is good enough in most cases.