New Scope - Darkstar 10" - Restoration Project

[Stub Mandrel]

Thanks to a tip-off in another thread, I've just gone and bought a Dob. Oops!

Quite a story really, the seller's aunty had it made specially, and looking through it at the planets led the seller to do an astrophysics degree. He went on into teaching, became a head of physics, but now he's sold his house and in a few days is off to teach in South Korea. Although the scope is in need of much TLC he put off parting with it but was glad to see it go to an appreciative new home.

It's a Darkstar scope with a 10" mirror of what appears to be about 1800mm focal length. It feels very 'hand made' and certainly needs every single screw adjusting, if not replacing! The mirror is stained, not just dirty, and will need recoating, and probably the secondary will as well. It has very thin vanes and relatively small obstruction. The 1.25" focuser is basic and needs tuning. A hefty 2" straight-through finder looks like its made from half a pair of binoculars with the prism taken out. The eyepiece is an 18mm circle-T marked 'Or.' Presumably this means 'orthoscopic' and would fit with the scope being intended partly as a planet-killer.

The wooden dob base isn't too bad in alt, but the az is very stiff and probably needs new teflon pads.

It's probably a bit big to try and mount on my HEQ5 pro ?

Can anyone tell me a bit about Darkstar scopes? My assumption is that this is a decent scope well worth a bit of investment in time and beer tokens that will reward me with amazing views and the opportunity to do some pretty hefty planetary imaging, if I can get the knack of keeping it on target!

Other than not ruining the mirror trying to clean it, what sort of things should I watch out for on the assumption it needs a full strip down and rebuild?

I may even look at making a new truss-tube OTA in the long run, but first things first.

 

Edited July 31, 2018 by Stub Mandrel

[Whistlin Bob]

Oooh- I saw that one. Very exciting! Nothing like spontaneity! ?

The HEQ5 copes fine with my 8 inch, so you might be lucky- although the tube rings may cost more than the scope...

[Stub Mandrel]

Some pictures.

It's big. Bigger than full-size a labrador:

Every screw in this picture is loose! But apparently this 'volcano top' circle-T eyepiece is not to be sneezed at:

This looks to have been made using binocular objective and eyepiece, joined with a plain tube, but will surely do the job:

Looks like I may need to send this off to be redone! Black staining suggests it may be silvered rather than aluminium?

The maker's details. the mirror appears to be glues to a wooden triangle. Three bolts through this second triangle adjust collimation:

[Stub Mandrel]

1 minute ago, Whistlin Bob said:

Oooh- I saw that one. Very exciting! Nothing like spontaneity! ?

The HEQ5 copes fine with my 8 inch, so you might be lucky- although the tube rings may cost more than the scope...

Amazing to have such a scope virtually given away less than half an hour from where I live. It was meant to be!

[johninderby]

Long gone manufacturer but some info here.

http://darkstartelescopes.blogspot.com/

[NGC 1502]

 

Great scopes from a sadly different era, although many of us prize kit like that ?

Indeed the mirror needs a recoat, but you may be surprised at how well it would work as it is.

Best wishes with your “new” scope, Ed.

Edited July 30, 2018 by NGC 1502
Added info

[Stub Mandrel]

I found a PDF about an almost identical scope that appears to be by the chair of my astro club!

My main worry is that, unlike others, the primary appears to be glued to a plywood triangle instead of held with clips!

I can make a mirror cell, but how to get it off for recoating????

[johninderby]

There’s always the saw method which isn’t as crazy as it sounds. 

Edited July 30, 2018 by johninderby

[John]

Congrats on the Darkstar dob

I've got a 1980's brochure on Darkstar somewhere. I'll see if I can find it and post some info from it.

If the mirror is bonded to the cell with silicone or similar, I've heard of fishing line or even guitar strings being used to cut through the glue "blobs" to release the mirror.

 

[Stub Mandrel]

12 minutes ago, johninderby said:

There’s always the saw method which isn’t as crazy as it sounds. 

 

I did wonder about using a router to thin it down to a couple of MM then prising what's left off with hand tools.

[Stub Mandrel]

Mirror seems to be 'close bonded' to the backing piece.

Next 'issue' - the mirror cell isn't central, a quick check shows the three attachment points aren't evenly spaced around the tube, so the tube is distorted. That, at least, will be an easy fix.

Looks like focal length is about 1.7m

At least one teflon pad is missing from the base, which has a few minor issues. The alt movement is very smooth.

The devilish words 'barn door tracker' are already forming in the back of my mind...

[John]

Many dobs are a "work in progress" even when new. This one sounds worth the trouble

[Stub Mandrel]

5 minutes ago, John said:

Many dobs are a "work in progress" even when new. This one sounds worth the trouble

The heart of it is a 1/8 wave David Hinds mirror set. This appears to be 'a very good thing' ?

 

[nightfisher]

Give it some love and a fettle it will be a nice scope

[mapstar]

Bitten by the dob bug eh Neil. 

I have the optics from a 14" darkstar dob sat in the house which I'm going to build a scope for a friend from. I'm not 100% certain but I think the optics were made by David Hinds?

Just under F7 should be good for the planets and I'm sure you'll get it fettled. Welcome to the dobside 

[Stub Mandrel]

Good news, the mirror is held on by four blobs of silicon. The  holes are in the wrong place, the elderly tube sprang back into round when I had removed two of three screws. Also, most of the mirror is still reasonable, the dark patches are missing silvering (about 10%) and there is  one large patch of blooming about 30mm across and a few small ones. I've washed it off gently under and dried carefully to avoid scratching. Even dirty it cast a clear image of a window onto a wall.

I will a go of it under the stars before I send the mirror to recoating, I can't miss a chance to see exactly what I've got first!

The finder scope is two bits of binoculars fitted to a tube. I'll swap in a 50mm finder I have made already. I have a 0.925" 20mm huygens EP that I have fitted crosshairs to that will do for the finder for now.

The focuser is 'serviceable' and of decent metal construction. It may reward gentle reworking.

The secondary is tiny, probably about 40mm! Mostly in OK condition, but will get a recoat at the same time as main mirror. I don't imagine it's worth upgrading to a 2" focuser unless I get both a bigger secondary and some 2" EPs.

Basic assessment - after cleaning the mirror and fitting a better finder, all I need to do is sort out the pads on the base to get it working well enough to try out.

In the longer term with recoated optics, I think this can be smartened up into a really nice scope. Question is, do I keep the blue hammerite or go for another colour? It has adhered perfectly to the tube so I'm not going to risk stripping it, the texture will have to stay. Perhaps white would be nice? But on the other hand the original Dark Star finish has weathered time OK.

 

Edited July 31, 2018 by Stub Mandrel

[AndyH]

Great stuff !

Like John,  I'll find some pics of my mid 80's Dark Star catalogue. I take it they must have moved at some point as mine says ... "Ashley Heath, Market Drayton". I think my parents bought mine about 1986/7.

I notice the following which will be of interest.... 10.20" / 60" Focal Length ... 2.25" secondary .... all low expansion Pyrex ..... main mirrors 25-30mm thick up to 16"...... double aluminised.... std models have normal optical quality..... custom models(yours) finest optical quality.

I'll upload the pics once I find them on my old hard drive. I'll also take a few pics of my 6" Dark Star Dob's mirror cell

[AndyH]

The 50mm finder objective is perfectly fine. Make it into a right angle version !!!!

[AndyH]

My opinion, but I like the blue hammerite colour. Quite iconic of Dark Star I reckon. My 6" is a deep copper colour. I think I prefer the blue though.

[AndyH]

My mirror cell is similar but has mirror clips. It's off the scope so I'll take some pics.

[AndyH]

[AndyH]

[Stub Mandrel]

45 minutes ago, AndyH said:

I notice the following which will be of interest.... 10.20" / 60" Focal Length ... 2.25" secondary .... all low expansion Pyrex ..... main mirrors 25-30mm thick up to 16"...... double aluminised.... std models have normal optical quality..... custom models(yours) finest optical quality.

Interesting! Thanks for going to the effort of posting all that, it's fascinating.

This one is definitely not less than 64" focal length and probably a bit more 60" would barely get the focal point out of the main tube. Together with the lack of mirror clips and choice of metallic blue hammerite, I wonder if it is an early prototype, or if it's just natural variation in hand-made mirrors.

The 10x50 finder looks like the one in the photo, it appears heavily vignetted by the tube, they must have bought in a big job lot of cheap binoculars to 'repurpose'!

I love the marketing speak which makes just about every aspect of the scope a 'feature' ?

It makes you realise what a massive impact the arrival of mass produced scopes must have made.

[Bruce Leeroy]

I have the 8.75" copper colour version, I would say the mirrors are in a similar condition to yours...maybe not so degraded, I get decent views but with some light scatter, I chopped the original plastic finder down and added a mirror diagonal from a low end telescope. My primary mirror is held in with clips.

I took these 2 unprocessed images some time ago using the Dark Star dob.

The 3rd Image is processed from a 20-30 second video.

Good luck renovating the old girl.

All images captured with an iphone 4s.

 

Edited July 31, 2018 by Bruce Leeroy
+info

[AndyH]

Note the extremely strong springs. Once collimated it stays there. Also, where the name sticker is, that's a piece of steel from a length of round bar, for balance. I can see the tooth marks where it was cut! The board is 19mm(3/4") thick.

I'd guess optic focal lengths were whatever was available from their supplier at the time.

As Jules says, a bit of fettling over time(no need to rush, just bit by bit) and you'll have a lovely scope.

Sorry for all the underlining, my furry cat decided to walk accross the keyboard. No idea how that happened. My furry boy is an A class plonker at times.

 

Edited July 31, 2018 by AndyH