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New Scope - Darkstar 10" - Restoration Project


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On 30/07/2018 at 22:20, John said:

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. 

@John that tasty little nugget has proven to be well-founded. I used an Ernie Ball 0.011" B-string, but I'm not sure if Dean Markley or Super Slinkies might have worked better ?

What's good is it sliced the silicone off the mirror and left 99% of the blobs attached to the (!)MDF lens cell.

The secondary mounting block turns out to be a bit of waste pipe!

I can't believe silicone kept all that in place for some 30-odd years.

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Darkstar were the provider of my very first scope, a Bresser refractor in the 80’s.

I always wanted one of the dobs, but I never had enough money to buy one, so read your thread with much interest.

Good luck with the ongoing fettle.

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Just for the record the back of the primary is lightly engraved: DS 63".3

I thought that's odd, it should be DH, and I couldn't find a mirror maker initials D.S. But of course the mirror was for Darkstar - hence DS not DH. - DOH!

My final estimate of focal length was 64", not far off 63.3" considering I used a tape measure ?

In metric the mirror is 260mm x 1608mm so f6.18.

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10 minutes ago, Astrobits said:

Yes, I believe that Dark Star did start making their own mirrors later in the life of the business.

Unless DS was for David Sinden.

Might be an idea to check the figure on the mirror?

Nigel

I found this 2012 post by @LeoLion:

Quote

The Dark Star mirrors were made by Hinds &/or by John Owen of Halifax. The scopes were originally made & sold from near Brum & laterally from a farm in Powys in Wales.My 10" f 6.4 Dark Star has an excellent Owen mirror & was bought new by me in 1997.It's a keeper & should see my time on earth out . First light was on Hale Bopp's head drawing the concentric shells back in 1997. I've a mate with an 8" Dark Star & he's a happy bunny .and if you look at Gary Poyners webpage you will see he has had two http://www.garypoyner.pwp.blueyonder.co.uk/scopes.html . They merited a review/listing in one of Phil Harrington's Star Ware books . Enjoy the scope.

I could get a report on the mirror, but in all honesty what would I gain from it? Universal positive reports suggests that none of these scopes have duff optics, I'd rather judge it by what is see and not suffer the angst of knowing some minor flaw that will make no material difference to my enjoyment of the scope!

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Yes, He used any suitable supplier, mainly David Hinds, but I still believe that he started making his own at some point. Therefore the early telescopes would be purchased mirror sets but the later ones will be a mixture of purchased and Dark Star made mirrors.

Nigel

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Is there a way of dating the scopes?

Mine seems to have a simplified lens cell compared to another "custom 10" dob" (no counterweight, mirror held on by silicone - in contrast to a counterweight and proper mirror clips). To me this suggests a different date, but which is earlier?

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Lovely to see these, my first was an 8.75” from around 1991, sort of rebuilt, but now languishing at my parents house. I thought the mirrors were Hinds, I see you had the nasty little tube cover... which I am sure is designed to rain crud onto the mirror. As long as no one has tried to clean it, it should recoat nicely. I can sympathise with the focusser.. small and rocks a lot... of replace with a dual speed crayford as a bad focusser can hinder collimation as well as observing... also be good to get some new ultrawide 2” eyepieces plugged in.

The time when imagers talked about TP2415 and hypering!

PEterW

Edited by PeterW
Correction
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57 minutes ago, PeterW said:

Lovely to see these, my first was an 8.75” from around 1991, sort of rebuilt, but now languishing at my parents house. I thought the mirrors were Hinds, I see you had the nasty little tube cover... which I am sure is designed to rain crud onto the mirror. As long as no one has tried to clean it, it should recoat nicely. I can sympathise with the focusser.. small and rocks a lot... of replace with a dual speed crayford as a bad focusser can hinder collimation as well as observing... also be good to get some new ultrawide 2” eyepieces plugged in. 

The time when imagers talked about TP2415 and hypering!

PEterW

I have the remains of a chewed dog-bed asking to become a heavy duty cover ?

The only cleaning has been me gently with clean tap water to get the dust off.

Thanks to the forum I've found a carayford, but I think the 2" EPs may have to wait a goodly while ?

I had to look up TP2415, but I vaguely associate 'hypering' with extreme push processing?

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Kodak's Technical Pan film no 2415. A fine grain film that responded to "Hypering" or Hypersensitising. There were several ways that were used. Simple baking in an oven ( water tends to desensitise film ), baking in nitrogen or even in Hydrogen ( v. dangerous but was the best result ).

Nigel

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You are correct, sensitising film to help keep the exposure linear. One could similarly ask about reciprocity failure, but I fear it would just get blank stares too.

i have a friend who has dog hair and snail trails on his mirror... still seems to work.best to use a nice plastic cover to stop the dust getting on in the first place. You can get good eyepieces very reasonably now, but first things should be better focusser and a right angle correct image finder... avoid back strain and mental gymnastics. When I ordered mine I  asked for a telrad instead of the finder... with good enough skies you ought to be able to drop the scope on anything you want to find and you don’t even have to be close to it to use it.

Peter

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How many older imagers might have old rolls of film in the freezer at home....?? Keep hold of any film pots (with lids) you have as they are impossible to find now and very useful for science demos and storing things. I always thought I’d paint any scope I built that famous hammerite blue.... I made a solar projection box for the front end of mine (with aperture mask of course).

Peter

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21 minutes ago, PeterW said:

right angle correct image finder..

No way! They damage my brain. Either a fully corrected finder or a straight through one for me. The one I've made can be used as either as I have a 0.965 445-degree prism diagonal and crosshair ep AND a 25mm cross plossl fitted witha 1.25 to 0.965 reducer  ?

36 minutes ago, PeterW said:

old rolls of film in the freezer at home....??

I have some relatively new 120 film for my Yashicamat

36 minutes ago, PeterW said:

I’d paint any scope I built that famous hammerite blue

I bought a tin today to touch up the scope but horrors! It is now proper blue, not the classic greeny blue.

Someone must sell the 'real' colour as you can still get tools painted with it.

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12 hours ago, PeterW said:

Quite a latebone then.... relatively speaking.

Peter

It would seem so! Interesting that the change was from metal clips to silicone and not the other way around, and apparently from plywood to mdf for the construction. 

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14 hours ago, PeterW said:

 Keep hold of any film pots (with lids) you have as they are impossible to find now and very useful for science demos and storing things. 

Peter

 

My local branch of Snappy Snaps ( Southend on Sea ) recently gave me a free bag of 35mm film containers.  As they process film and sell it too, they accumulate empty containers and just put them out to recycle.

Ed.

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  • 3 weeks later...

The mirrors are with Scientific Mirrors, awaiting recoating.

Today I painted the inside of the tube with heat resistant black paint, which has made a huge difference. The tube is so big you can put your whole arm in and spray an aerosol!

I've enlarged the focuser hole for the orion focuser (thanks Chaz!) but I can't fit it yet as I'm waiting for some M4 screws to come to hold the two parts together (third attempt!)

I've also made some tasteful decals to copy the Dark Star logo ?

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  • 2 weeks later...

My mirror has been done. Unfortunately the main mirror wouldn't strip completely with a few bad patches, and the edges of the secondary were similar.  The coaters say this is unlikely to be enough to have any observable effect, but I suppose bit disappointing. Understandable given the state of the mirrors as received I suppose - the primary looked like a map of Mars - without the dust storm.

It must be better than  it was and it gave me impressive views on first try ?

Should be with me in a few days.

Edited by Stub Mandrel
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2 hours ago, mapstar said:

Whats it like now, come on Neil we're all waiting impatiently :icon_bounce:

How do you think I feel?

Apparently it has a few percent of 'dull' spots where the old coating wouldn't come off. He said 'they may bond to the new coating in time and come off when it's next recoated, or they may be poor patches on the glass'.

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7 hours ago, Stub Mandrel said:

How do you think I feel?

I’d probably feel a bit naffed off myself if a freshly coated mirror didn’t look perfect. But your earlier post mentioned that you got good views from the mirror before the recoat, so I think the coaters would be right in saying the less than perfect coating will be ok.

Hope you feel a lot better when you get first light from the refurbished mirror. Have a look at some of the more famous objects to cheer yourself up ?

HTH, Ed.

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