Collimation help

[daz]

ooo cross-post.....

Secondary looks interesting, but the 2 screws problem is solved

The 3 wingnuts - is that a cover, or the mirror cell?

[Moonshane]

ooooh, single secondary vane - very unusual and looks sturdy.

I am sure this can be sorted out. worry not.

[daz]

have you got X ray eyes Daz?

the distance down the tube from the screws is about right for the secondary mirror surely? might be an f4 as suggested but had to tell scale etc. and depends where the primary cell is.

lol!!

I can't reconcile the screws-focuser distance from the photo though. It looks a long way to me. But it is 11:30 and things are starting to blur slightly!!

And you're right Shane, tricky to tell scale. There's no visible primary bolts on the OTA...

OK, I really have to sleep, but will pick this tomorrow!

Thanks Chris, for the pictures.

[brantuk]

Yes - I'd say F4 maybe F4.5 - etension tube might just do it. Do we know the focuser diameter? Can't be more than 1.25".

[ChrisR36]

Sorry guys, this is all getting a bit technical for me, and I can't answer all of your questions. The wingnuts are actually on the mirror cell, there's no cover. The focuser diameter is about 1.25", is that standard?

[brantuk]

1.25" is standard on modern scopes - all the eyepieces are sized for that (and 2").

The wingnuts look like they are holding a cover on, so the collimation screws could be inside (beneath the cover). Are you sure they hold the mirror? You might have spent two years adjusting the cover lol.

The distance from the mirror to the center of the focuser tube looks to be around 100cm (by eye) or 1000mm. This is roughly your focal length. The f-ratio is Focal length divided by aperture diameter (250mm) so:

1000mm / 250mm = 4 (i.e f-4) simples.... eek!

If you measure from the back of the tube to the center of the focuser I could make it a more accurate guesstimate for you - it might be 1200mm giving f-4.8. Either way it's a fast scope

[John]

Trawling my memories, if this is a Wakefield scope then it will be a fairly basic (though workmanlike) design. I reckon the 3 wingnuts are the primary collimation adjustment - the mirror will be mounted either on a Y-shaped or circular plate / board - probably with silicone as I can't see mirror clips. It's similar to the design of the primary mirror cell of my Orion Optics 10" - no locking nuts, just the 3 adjustment screws.

[ChrisR36]

I'm not sure now, the mirror is kind of 'mounted' onto that disc with the wingnuts in. The whole thing comes out as one assembly, I don't take any cover off, and then the mirror, it all comes out in one piece ... hope that makes sense.

Thanks for explaining the techy stuff. You'd think I should know about these things after being in this hobby for 34 years, but all i've ever been interested in is pointing the thing at the sky and looking at the universe *blush*

[ChrisR36]

Trawling my memories, if this is a Wakefield scope then it will be a fairly basic (though workmanlike) design.

The name Wakefield does ring a bell actually ... i'm not sure, I've had the scope for about 10 years. All I can remember was the guy who made it had a big bushy beard, and he lived (or worked) in Bath, that was where I collected it from.

[John]

The name Wakefield does ring a bell actually ... i'm not sure, I've had the scope for about 10 years. All I can remember was the guy who made it had a big bushy beard, and he lived (or worked) in Bath, that was where I collected it from.

That sounds right. He is based in South Africa now I believe.

[Moonshane]

the main issue here is finding the focus point. after that the collimation will be standard and we can certainly help with that.

[daz]

Indeed. Looks like that most technical of astronomical accessories are needed..... a piece of paper and a pencil

Chris (hoping that I am not teaching grandma to suck eggs) what you need to do is point the scope at a well lit landmark, then holding a piece of paper above the focuser, move the paper up and down until you can see the landmark in sharp relief on the paper.

Measure this height.

This will tell us where the approximate focus point is. The question then is, do your eyepieces reach this height? If not, you may need an extension tube in order to reach focus - which is why you are only seeing a X and a blob.

As Shane says, once we know where your focus point is, collimation is straight forward (or should be )

[TheThing]

Great thread this - shows the real community spirit of SGL and daz is a top bloke.

For future, have a look at Andy's Shot Glass - you'll get to it via Google. I can't link as I'm on an iPhone.

This is the clearest, simplest guide on the Internet. No fancy tools needed, it teaches you how to do it by eye.

Let us now how you get on after meeting daz.

TheThing.

Sent from my iPhone using Tapatalk

[brantuk]

"i've ever been interested in is pointing the thing at the sky and looking at the universe "

Nothing wrong with that Chris - I drive everywhere in one of two cars, but open the bonnet, and I couldn't tell you where the spare tyre is, never mind the engine lol

[Moonshane]

I carry my spare tyre round my waist, then I can never forget where it is!

[daz]

LOL!!!!

[daz]

Chris, am out for the day now, but if you get a chance to check the focus postion, post up the results.

By all means speak to FLO as well, they may be able to help - and they are closer to you - but if not, will push ahead with our plan B!

Cheers

[ChrisR36]

I can't understand why I would suddenly need an extension tube when the scope worked perfectly without one before I attempted to collimate it?

I'm just about to call FLO, I'll see if they can help first, and if I get no luck there, then I'll come back and work on finding that focus point, it won't be for a few hours though, depending on whether I have to go up to Exeter or not.

Thanks guys

[John]

I can't understand why I would suddenly need an extension tube when the scope worked perfectly without one before I attempted to collimate it?....

It could be because the adjustments you made to the collimation wingnuts on the bottom of the tube have pushed the primary mirror up the tube a bit, pushing the point of focus out a bit. If the bolts that the wing nuts screw onto are quite long and are now at or near full extension (ie: very little protruding through the backplate of the tube) then this could be the case. It will all depend on the design of the mirror cell.

The solution would be to evenly tighten all 3 wing nuts as far as they will go (without any force) then just let them out enough to achieve collimation.

This web page describes how to make a simple primary mirror cell for a newtonian scope and might be something like the design that has been used on your scope (minus the centre bolt feature):

A Simple Double-Plate Mirror Cell for Your Reflector | Gary Seronik.com

As you can see from the illustrations, if you have the 3 collimation screws / wingnuts tightened up, the mirror is lower in the tube (the focus point would then move inwards a bit too) and vice versa if the screws are loosened.

I hope that makes some sense !

Edit: I've just looked at the photo you posted of the back of the tube and I can see that there is lots of collimation bolt showing so the opposite of what I have described above could be happening - ie: the mirror is right at the bottom of the travel and the focus point has moved inwards - out of the reach of an eyepiece.

[Moonshane]

hi Chris

sorry I hadn't realised that you have previously used it and it focused OK. Presumably you have the same eyepieces?

In that case, can you confirm the following please?

look down the empty focuser. can you see the bulk of the primary mirror? you should see the donut on the primary and maybe your eye's reflection.

assuming this is the case then tighten the bottom wing nuts until you feel that the play in the thread has been taken up on all nuts then back off each nut by about one turn.

then follow step one again.

tonight if possible try and focus. it's possible the collimation has moved the primary up or down the tube just enough to take it out of the available range of focus in the focuser.

assuming this works then we can help with collimation later to get it right.

if it does not work then try an eyepiece in the focuser and pull it out until it focuses (I suspect you won't need to do this).

report back when you have tried these things and we can then get you further on. I can guarantee that we'll have you up and running in no time.

[Moonshane]

at least John and I agreed!

[ChrisR36]

Ok I didn't have much luck with FLO. I tried to call twice this morning, but there was a recorded message asking me to try emailing them instead. I sent an email, but so far, I'm still waiting for a reply, maybe they're not open today.

Daz, I've had a go at finding the focus point using the method you suggested. First of all, there didn't appear to be any image at all on the piece of paper when I held it in front of the focuser, so I tried to measure the distance by eye. I pointed the scope at some distant rooftops, and I could see the image in the primary mirror as I looked down the focuser tube. The only thing is, as I moved my head further away from the tube, the image was going in and out of focus. Whether that has anything to do with the mirror itself, or just my eyesight ... the closest I could get to the focuser while seeing a crisp image was about 15 inches. Does that sound about right? Or too much? I have no idea what it's supposed to be.

Jahmanson and Moonshane, I'll come back to your suggestions later. Right now I have to pop out for a while. Thanks

[daz]

Yeah, I thought they might be busy....

OK, I have cleared Saturday morning with the wife! So, can pop over and take a look.

Just realised that your focuser is 1.25" and my tools are 2" ones!! Not a huge problem, I have my laser with me, and my friend Steve has a cheshire I can bring.

Pretty sure we can get it sorted!

PM your address Chris

[FLO]

Ok I didn't have much luck with FLO. I tried to call twice this morning, but there was a recorded message asking me to try emailing them instead. I sent an email, but so far, I'm still waiting for a reply, maybe they're not open today.

We recieved your email yesterday, Martin responded this morning. You are welcome to call in any week-day next week but you will probably need to leave the telescope with us. A home-built scope with an f4ish focal ratio, R&P focuser, single secondary support and what looks like a home-made mirror-cell might be a pig to collimate. James may need to mutter a few obscenities so might not want an audience

Daz' offer to call in is very generous and he certainly knows his stuff when it comes to collimation. If I were you I'd accept his offer.

HTH,

Steve

[ChrisR36]

PM sent daz, thanks very much!

And thanks Steve, I received your email