Sumerian Canopus 16" update

[Scooot]

I've had my scope a few months now, and anyone reading some of my posts will know that I'm still very pleased with it. I have however had a couple of issues I've been trying to get to grips with, which I hope I've now fixed.

1.Inexplicably, I'd noticed the finding accuracy of my nexus unit seemed to deteriorate near the zenith and horizon. I knew it was something to do with the scope, as its accuracy is superb with my OO Dob.

2. I've noticed a few times my collimation seems to go out when I move the scope to the zenith or horizon. I'd put this incorrectly down to mirror shift.

I hold the secondary mirror cage to rotate the scope, and I'd noticed when the scope is low, a small gap appeared between the Teflon pads on the front of the altitude bearings. Therefore, when turning the scope, I was creating a bit of lateral play in azimuth. I've removed this by inserting a couple of washers on either side to tighten it up. This seems to have mostly fixed the finding inaccuracy I was experiencing.

I put the scope together today in daylight, and did a bit of experimenting with the collimation and my Howie Glatter laser, (which is very accurate). Collimation was moving whilst raising and lowering the scope, which I finally fixed by the very simple method of tightening the knobs that hold the truss tubes in their shoes. Once tightened, this improved the way it held collimation in all positions. It was only at the horizon it had noticeably moved by a small amount.

This was the view of the laser through the bottom of the focuser after I'd setup the collimation pointing at about 50°. The small white light is the laser exiting the Focuser and the fat white light is it returning from the primary mirror.

This was the view again at the horizon, it had moved slightly.

This was the view at the zenith, still fairly spot on.

I'm gradually learning more about the scope!

[alan potts]

Pleased you got sorted Richard, your scope is a little different to mine and I have not put a Navis system or anything like on it yet. I am most impressed the way mine holds collimation, in fact I don't really believe it. I put some little black dots on things so I can take apart and replace in the excat same place, only so the truss is always the same way. Last night was the first run and it bearly needed collimation after, and I don't believe that either.

I am most impressed with mine but if I am honest I am not very good at finding things yet, that's what goto's do for you.

Alan

[Scooot]

Thanks Alan, I've always had to tweak the collimation when I put it back together and I'd have been surprised if it hadn't moved a little bit. I haven't labeled the poles to put them back on in the same order, that does seem like a good idea so I might do that.

[damnut]

What a great scope, nice tips for others. Colleague has a 14" Orion and has modded it to bits. But has labelled and marked everything whilst doing so, so if things don't work out he can retrace it.

[niallk]

Hi Richard, very interesting post! I too have been doing very similar experimentation re collimation shift with my barlowed laser - for what its worth, my Obsession 15 exhibits a small shift near horizon, but pretty good otherwise. I think I could tighten up things a little - slightly cautious about over tightening. I should take some pics to illustrate the shift that I see. I haven't labeled my poles but I'm quite impressed at alignment when reassembled - of course needs some tweaking each time I set up.

Its outside cooling as I type here getting the kids asleep

Best of luck, Niall.

[Scooot]

I'd be interested to see the pics to compare with your obsession Niall as they're reknowned for being market leaders in the dob world. Mines outside as well

[alan potts]

Richard,

Market leaders or not I think your mirror and my slightly lesser PV mirror would take some beating and I feel our scopes are perfectly good enough.

I saw a French site, can't remember the Company name but the scope only was a massive outlay with rosewood and all sorts of exotic stuff. I imagine it is only taking things to a different level but I feel it is all a bit un-necessary, only my opinion of course, it's the mirror that really makes the scope though of course the structure needs to be sound.

Alan

[Scooot]

Yes Alan, I think the scopes are great but I'm still interested in comparing their rigidity if it was at all possible. A positive comparison, If nothing else, would help establish they do the job as well as other heavier more robust scopes. Regardless, as you say its plenty good enough for me.

I didn't spend much time talking about my mirror because on a custom scope you can put a good mirror in anything. I am of course delighted with it.

I think the French Company is Dobson Factory, I had a look at those as well. I think the waiting time was about 18 months.

Incidentally, anyone from the UK wanting to buy a Sumerian now would get a much better deal with the current exchange rate. I worked out mine would be about £400 cheaper

[alan potts]

Richard,

Yes that was the name of the company, I think they grow the trees for the job, beautifully crafted and I guess if you have a money tree or two in the garden it's great.

Mine worked out OK money wise because I had mirror money in the Uk and the Bulgarian Leva to Euro is fixed, but a very good point you make there, are you thinking about a 20 inch then .

alan