Red Dot Finder Alignment help!

[tibbz2]

Hey guys, my first post here and i'm already asking for help!

Anyway, I've recently got into Astronomy in the past half-year or so, and got bought a simple telescope as a gift in September, nothing special, but it does the job (Pretty sure it's a Sky-hawk 114 reflector). However now i'm trying to use the telescope and equ. mount properly, and I tried aligning the RDF on the side the other day, but it won't go far enough! I have the dial screwed all the way in to make the dot move left, but when I look through it's still a far way out! I've tried pushing, re-arranging and everything, but nothing helps. Any advice on how I could fix it?

I'm just glad it's so cloudy at the moment so i'm not missing out on much while I fiddle with it!

Thanks!

[Twiggles]

May sound silly, but are you sure its going the right way? Try moving the other way. If it definitely is reaching end of travel then the only thing that I could think of would be to look at the mounting screws and see if you can loosen those then shift the finder a little bit before retightening them.

[tibbz2]

Yeah i've checked that I wasn't doing that, unfortunately it was going the right way so it's kinda stuck as far as it can go! I've tried the mount too, however it doesn't move or help much in this case.

[Twiggles]

Strange.. I can only tell you what I would do, as I really don't know how much you have tried so far and I'm a beginner myself so apologies if I'm teaching you to suck eggs!

What I would do now is go back to the beginning, and get the red dot centralised. By that I mean set both alignment wheels so it appears to be roughly in the middle of length of travel. Line up on a distant object and then move left and right then back to center, now move up and down and back to center, this is just to make sure you get full travel along the sight glass window. Remember to get it back to 'neutral' in the center.

Now sight it on a distant object (the further away the better) and see how much of the view finder window shows of what you can see in the scope, ignore the red dot for now. If it is like mine, you really need to get in the right position to see the red dot anyway, and by the sounds of it for now you just want to see if the view finder window looks as if its pointing somewhere close to what the scope sees. If that looks ok then turn the red dot on, if not you may have to loosen all mounting screws to try and get it closer then tighten them again. Once that is roughly where you need it, put red dot on and then adjust that one in. The further away your aiming target the better, especially once it comes to aligning with stars.

Good luck!

[Carbon Brush]

I have seen this problem with certain finders and used packing between the finder foot and scope tube.

There is another possibility.

Have you checked if the telescope optical and mechanical axes are aligned?

What I mean here is the the main mirror might be pointing off to one side of the tube, instead of straight down.

This makes it possible for the finder adjustment to run out of travel before aligning with the mirror.

You can check this easily in daylight.

Set the tube horizontal and walk a few yards away from the open end.

Look back and move your head until you see your reflection in the main mirror.

At this point the scope sides should be invisible to you. If the side is visible, then you have a mirror/tube alignment issue.

Hope this helps.

[tibbz2]

Ok thanks for the advice, i'll give that a try when I can, and get back to here with the results!

[tibbz2]

I have seen this problem with certain finders and used packing between the finder foot and scope tube.

There is another possibility.

Have you checked if the telescope optical and mechanical axes are aligned?

What I mean here is the the main mirror might be pointing off to one side of the tube, instead of straight down.

This makes it possible for the finder adjustment to run out of travel before aligning with the mirror.

You can check this easily in daylight.

Set the tube horizontal and walk a few yards away from the open end.

Look back and move your head until you see your reflection in the main mirror.

At this point the scope sides should be invisible to you. If the side is visible, then you have a mirror/tube alignment issue.

Hope this helps.

Sorry I don't quite get what you mean by see my reflection in the main mirror, and the sides should be visible?

I tried this and all i can see when looking down is the reflection of the wall from the smaller mirror through the eyepiece, that's been projected onto the main mirror, I can only see myself around the edges of this.

[Carbon Brush]

A picture says a thousand words and alll that.

I will post photos later to show what i mean.

David.

[tibbz2]

A picture says a thousand words and alll that.

I will post photos later to show what i mean.

David.

Ok thanks

[Carbon Brush]

OK here are some (poor quality) pictures.

I have used a TAL200K, but the principle applies to your scope.

I have also had to take the pictures from close up, rather than being a few yards away.

Scope 1 shows what you see when you look at the scope from the front. Eyes focus on the front of the tube and (in your case) the secondary mirror holder. The primary mirror being much further away is out of focus. You are though on the mechanical axis of the scope. The tube outer, blackened interior and primary mirror form concentric circles.

Scope 2 shows what you see when you focus your eyes on the view of the primary mirror. In my case the camera body staring back, in your case your face.

By seeing yourself, and the scope features being concentric, you know the mechanical and optical axes are aligned.

Scope 3 shows a view when moving away from the mechanical axis. You start to see the outside of the tube. In this case the mirror is well away from showing the camera. But if you see your face from this sort of view, then you have an alignment problem.

Some years ago I bought a brand new scope from a UK manufacturer (not an importer). The optical and mechanical axes were well off.

After sorting this, and other things, it worked a lot better.

Hope this is useful.

[tibbz2]

Thanks a lot, that was certainly very helpful!

I just tried this and it seems they are aligned well, so it's just my RDF playing up! I have managed to get it in line vertically, it's just a bit off to the right of what I can see in the scope, so I guess i'll just have to remember to aim the dot to the right of what I want to see by about a cm and hopefully that works until I can sort it out somehow!

Thanks for the help both of you though It's much better than it was before, and I have peace of mind that my mirrors are aligned