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Shaving mirror


Tweedledee

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With all these recent posts showing nice big scopes like Grahams monster and Johns beautiful binocular scope, I thought I'd have a look at my mirror. I took some accurate measurements and weighed it so I can plan how to mount it on the bathroom wall. :)

 

20inch.jpg

 

20inchb.jpg

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Ooooh that looks rather nice. 20 inch ???

 

If you send it down to me I can cut some holes through it for your fixing screws. One large one in the center and half a dozen round the edge should do it. :rofl:

Edited by Graham
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Great idea Graham, but with the weight of it I think it will need more holes than you suggest, or it will just pull the plasterboard off. :lol:

 

Yes, 20" F4.

Edited by Tweedledee
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Oooooooo! Looks nice - where did that come from Pete? Any more stats on it like PV/Strehl etc?

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Santa's come early to Mansfield!

Very nice mirror Pete.

You will probably find decent nails would knock through just fine, I wouldn't worry about holes. Araldite would do if all else fails. :lol:

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2 minutes ago, BAZ said:

Santa's come early to Mansfield!

Very nice mirror Pete.

You will probably find decent nails would knock through just fine, I wouldn't worry about holes. Araldite would do if all else fails. :lol:

Thanks, Martyn. Braces as well as a belt. I'll use both. :D

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38 minutes ago, Brantuk said:

Oooooooo! Looks nice - where did that come from Pete? Any more stats on it like PV/Strehl etc?

The mirror is secondhand and was made by Oldham Optical, Scarborough, from low expansion Suprax to 1/10PV. It was used in a domed observatory by an astronomer who has now retired and moved abroad. He claimed it was superb on both DSO's and planets. Both mirrors and coatings look to be in excellent condition and have been well protected in storage for about a year.

 

I haven't made much progress so far, but I do have a 4" flat and spider with built in dew heater, and a 3" low profile dual speed focuser. I have loads of scrapped design drawings, and will probably ditch the spider as I have other ideas for holding the secondary. So there's a little bit of work to do yet. :lol:

 

That eyepiece makes the rest of it look tiny, but that is no ordinary 9mm. :)

 

20inchc.jpg

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Quote

And of course if you do knock some holes in it and then want to put it back into service some polyfilla and Halfords silver car paint should work a treat!

 

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I'm still amazed you got hold of that mirror at that price Pete.

What a bargain !!

 

I will follow the progress of what i'm sure will be an amazing scope. I'm sure most of us dream about owning a 20" :D

 

Regarding the build, have you thought about a solid tube, BUT IN A SPLIT TUBE DESIGN ?

Discovery telescopes , USA do them.

I'm surprised this design it not more popular.

Ticks a lot of boxes for me.

 

27232406573_1f37f907e4_o.jpg

Edited by Bino-viewer
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Just looked at Oldham's prices - they compare favourably against Nichol mirrors of lesser spec - hmmmm....... :)

Edited by Brantuk
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1 hour ago, Bino-viewer said:

I'm still amazed you got hold of that mirror at that price Pete.

What a bargain !!

 

I will follow the progress of what i'm sure will be an amazing scope. I'm sure most of us dream about owning a 20" :D

 

Regarding the build, have you thought about a solid tube, BUT IN A SPLIT TUBE DESIGN ?

Discovery telescopes , USA do them.

I'm surprised this design it not more popular.

Ticks a lot of boxes for me.

 

27232406573_1f37f907e4_o.jpg

 

Thanks Rob. I could build a split tube like that, great idea. I hadn't thought of that method, but will consider it. :thumbsup:

 

I have been drawing up plans for a more radical idea utilising carbon fibre to combine rigidity with minimal weight, easy setup and transport.

 

The split tube would be easier to implement, but heavier than I would like it to be.

Edited by Tweedledee
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I believe Discovery scopes use 'Sonotubes' which are basically heavy duty rolled cardboard.

and are popular for ATM in the US. Cheap to source too.

 

 

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You could mount it on the landing and still use it for shaving in the bathroom! :lol:

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1 minute ago, Smithysteve said:

You could mount it on the landing and still use it for shaving in the bathroom! :lol:

Only if I correctly positioned the flat mirror to see round the corner. :D

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I think there's three of us thinking of building upwards of 20" dobs at the moment - all at the same time. There may be scope for getting together, planning/agreeing a common design, and maybe splitting the work between us.

It would be good to get together initially and compare ideas. :) 

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5 hours ago, Brantuk said:

I think there's three of us thinking of building upwards of 20" dobs at the moment - all at the same time. There may be scope for getting together, planning/agreeing a common design, and maybe splitting the work between us.

It would be good to get together initially and compare ideas. :) 

Good idea Kim. :thumbsup:

Discussing and comparing ideas sounds very useful, but as for splitting the work between us, I'm happy to balls up my own build (I always do at various stages :lol:), but not sure I'd want to trust or embarrass myself doing it with someone else's. Having said that, I'm sure we could learn a lot by throwing ideas into the pot, so any form of collaboration could be a great benefit.

 

I bet a good deal could be struck if 2 or more people were to purchase their mirror sets as one order, unless you get lucky with a pocket change secondhand bargain like I did:).

 

Regarding a common design, I suspect my ideas might not be in sync with others anyway. I'm leaning towards a highly unconventional design which I believe has only been used by several people around the world. Though I could possibly be persuaded otherwise and Robs suggestion above, of a split tube design seems very uncomplicated and worthy of further consideration.

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Great stuff Pete - we'll see what Mick says when he comes along - loving the idea of a bulk purchase of two mirrors for a discount lol. :)

 

At the moment I'm favouring a 20" f4 along the lines of the mapstar build myself - dunno what Doc has in mind yet. But yes - getting heads together on design issues, ideas for a whole scope, or various parts, and bulk buying (eg trusses, bearing materials, wood, etc) would be smashing. It would all make a great presentation for a club night or two too.

 

 

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It is a great idea but i'm pretty far behind you guys. I've still got my workshop to kit out, that isn't cheap.

 

20" F4 is a good call but haven't got the dosh at the moment.

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You can still participate Mick - just for the ideas - I'm still behind finishing off the Lightbridge rocker box so it's all projection into the future for me as well. And I can half inch a few ideas off you guys too hehehe! ;)

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1 hour ago, Doc said:

It is a great idea but i'm pretty far behind you guys. I've still got my workshop to kit out, that isn't cheap.

 

20" F4 is a good call but haven't got the dosh at the moment.

Not far behind at all Mick, you have a big advantage with your engineering skills and a workshop to die for. :thumbsup:

 

I've got a black and decker workbench a couple of hand tools and a shaving mirror. :lol:

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Well, here's my current favourite idea to keep the shaving mirror off the bathroom wall...

 

Mapstars wonderful build really is the ultimate, but I'm lazy and looking for less work and less set up time. His aluminium 18 point slimline mirror cell with a third whiffletree, is the bit I want, and after that the similarity ends.

 

As I said before, my idea is quite unconventional.

 

I'm planning a minimalist single arm scope using a super rigid (and rather expensive) 80mm diameter carbon fibre tube as the backbone, and a hybrid “dob-fork” three point altitude bearing. It will have a built in light shroud that draws up or down like a circular concertina style curtain. This 3 point dob mount design was, I think, originally conceived by EMS's very own Francis Milsom (FWM891) about 20 years ago, and was featured in Sky and Telescope magazine July 2001. It was then taken up in the US by Ross Sackett who won Stellafane ATM awards in 2007 for his 18" scope, that weighed in at just 34kg in total! With a good back, and correct lifting techniques, it could be manhandled in one lump! If you didn't have a long enough vehicle, it could be stripped down for transport by removing just a couple of bolts. I'd still fit wheels though, not risking my back.

 

Here's Ross Sacketts 18" Moonsilver IV, that was featured in Sky and Telescope December 2008. His open design may be OK at a really dark (and low humidity) site, but mine will have a (hopefully very neat looking) concertina style full light shroud to cut stray light and provide more dew protection.

http://stardazed.com/MoonsilverIV.html

 

I'll be very interested in your thoughts on this idea.

Edited by Tweedledee
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Interesting design but having a totally unprotected 20 inch mirror is just asking for a disaster to happen. 

How many times have you dropped some thing in the dead of winter when your hands are cold and numb.

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17 minutes ago, Graham said:

Interesting design but having a totally unprotected 20 inch mirror is just asking for a disaster to happen. 

How many times have you dropped some thing in the dead of winter when your hands are cold and numb.

If you read it again Graham, you'll find that the mirror will be completely protected and enclosed the full length of the optical train. :)

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2 hours ago, Tweedledee said:

If you read it again Graham, you'll find that the mirror will be completely protected and enclosed the full length of the optical train. :)

Agh yours will I was commenting on the one in the link. :)

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