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mwedel
Works with Sauropods

Reged: 12/16/07

Loc: Claremont, CA

Replica of Newton's reflector? new

new

#5265124 - 06/10/12 06:10 PM

One thing I have always wanted is a functional replica of Newton's reflector, on the ball mount with the screw at the back pushing the tube sections to focus and everything. I've only ever seen three commercial versions (there may be more):
- a little plastic kit from Gakken Mook;
- a Franklin Mint replica;
- the Vixen replica, which from the perspective of my budget might as well be fashioned from sheets of industrial diamond and polished with platypus fur.

So I'm thinking the best way to get a working replica of Newton's scope would be to build my own. I have the optics from the old 80mm Celestron Firstscope (not the mini-dob, the old ball scope that couldn't be aimed at anything more specific than "the sky"), which seem about the right size for a semi-impressive but not overwhelming desktop model.

Now, the hitch is that my engineering and woodworking skills hover at about the Neolithic level (actually that's not true, there was some very beautiful, detailed work done in the Neolithic, waaay beyond what I could achieve). My "shop" is the garage when I park the car outside, I have almost no power tools, do my sawing by hand, etc. As much as I would love to have a Newton telescope replica CNC milled out of some exotic hardwood, I suspect that whatever I produce will have cardboard instead of wood and wood instead of metal.

So, two questions. First, does anyone know of other attempts to make DIY Newton replica scopes? If so, please feel free to post or PM links for me to chase. Second, any ideas on low-cost components for the build--mailing tubes for the OTA, a decorative wooden ball from the hobby store for the mount, etc? Thanks in advance for any ideas.

Finally, I love lurking in this forum, the stuff you folks come up with blows me away. May your inspiration fuel my perspiration.

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kfrederick
Carpal Tunnel

Reged: 02/01/08

Re: Replica of Newton's reflector? new

new

[Re: mwedel]
#5265188 - 06/10/12 06:44 PM

What about Herschels telescopes the 48inch unobstructed .

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John Carruthers
Skiprat

Reged: 02/02/07

Loc: Kent, UK

Re: Replica of Newton's reflector? new

new

[Re: mwedel]
#5265908 - 06/11/12 09:02 AM

Tiny mirror, 1.3" diameter.
http://en.wikipedia.org/wiki/Newton%27s_reflector

"...The diameter of the sphere to which the Metal was ground concave was about 24 English Inches, and by consequence the length of the Instrument about six Inches and a quarter. The Eye-glass was Plano-convex, and the diameter of the Sphere to which the convex side was ground was about 1/5 of an Inch, or a little less, and by consequence it magnified between 30 and 40 times. By another way of measuring I found it magnified 35 times. The concave Metal bore an Aperture of an Inch and a third part, but the Aperture was limited not by an Opake Circle, covering the limb of the Metal round about, but be an opake Circle, placed between the Eyeglass and the Eye, and perforated in the middle with a little round hole for the Rays to pass through to the Eye. For this Circle being placed here, stopp'd much of the erroneous Light, which other wise would have disturbed the Vision. By comparing it with a pretty good Perspective of four Feet in length, made with a concave Eye-glass, I could read at a greater distance with my own Instrument than with the Glass. Yet Objects appeared much darker in it than in the Glass, and that partly because more Light was lost by Reflexion in the Metal, than by Refraction in the Glass, and partly because my Instrument was overcharged. Had it magnified but 30 or 25 times, it would have made the Object appear more brisk and pleasant..."

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careysub
Pooh-Bah

Reged: 02/18/11

Loc: Rancho Cucamonga, CA

Re: Replica of Newton's reflector? new

new

[Re: John Carruthers]
#5266001 - 06/11/12 10:02 AM

Quote:

Tiny mirror, 1.3" diameter.
http://en.wikipedia.org/wiki/Newton%27s_reflector...

Seems like a Newton Replicascope would be an interesting project in small scale mirror making, getting the experience of Newton himself in fabricating it (although you would be working with the much easier glass instead of speculum metal). Maybe you could piggyback coating on to someone else's recoating order.

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benula
member

Reged: 04/27/11

Loc: Stillwater, MN

Re: Replica of Newton's reflector? new

new

[Re: careysub]
#5266053 - 06/11/12 10:34 AM

I can't seem to find any sources for speculum...anyone know of any?

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Crayfordjon
Vendor - Zerochromat

Reged: 06/17/09

Loc: UK

Re: Replica of Newton's reflector? new

new

[Re: careysub]
#5266060 - 06/11/12 10:38 AM

I have seen Newtons original scope, the tube looks as though it is made from thick cardboard, metal fittings are brass and the ball is wood. Herschel made his eyepieces in coco wood which looked and felt like lignum vitae, when I was at the Old Royal Observatory at Greenwich, I cleaned quite a number of Herschels eyepieces.

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RossSackett
Pooh-Bah

Reged: 08/17/07

Loc: Memphis, TN

Re: Replica of Newton's reflector? new

new

[Re: Crayfordjon]
#5266085 - 06/11/12 10:58 AM

I know of at least three designs for Newton's scope--his early hand sketch, the engraving in the Philosophical Transactions, and the surviving Royal Society presentation scope. Each is slightly different. There have been a number of replicas of the presentation scope (on the big ball mount), but I haven't seen an attempt at the other designs.

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cheapersleeper
Carpal Tunnel

Reged: 01/22/10

Loc: Sachse TX

Re: Replica of Newton's reflector? new

new

[Re: John Carruthers]
#5266249 - 06/11/12 12:37 PM

Quote:

Tiny mirror, 1.3" diameter.
http://en.wikipedia.org/wiki/Newton%27s_reflector

"...The diameter of the sphere to which the Metal was ground concave was about 24 English Inches, and by consequence the length of the Instrument about six Inches and a quarter. The Eye-glass was Plano-convex, and the diameter of the Sphere to which the convex side was ground was about 1/5 of an Inch, or a little less, and by consequence it magnified between 30 and 40 times. By another way of measuring I found it magnified 35 times. The concave Metal bore an Aperture of an Inch and a third part, but the Aperture was limited not by an Opake Circle, covering the limb of the Metal round about, but be an opake Circle, placed between the Eyeglass and the Eye, and perforated in the middle with a little round hole for the Rays to pass through to the Eye. For this Circle being placed here, stopp'd much of the erroneous Light, which other wise would have disturbed the Vision. By comparing it with a pretty good Perspective of four Feet in length, made with a concave Eye-glass, I could read at a greater distance with my own Instrument than with the Glass. Yet Objects appeared much darker in it than in the Glass, and that partly because more Light was lost by Reflexion in the Metal, than by Refraction in the Glass, and partly because my Instrument was overcharged. Had it magnified but 30 or 25 times, it would have made the Object appear more brisk and pleasant..."

Newton's assistant disputed much of that account. He posted in the Refractor forum that "the thing put up mushy images while the refractor he was comparing it to showed pinpoint stars..."

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Dave O
super member

Reged: 12/21/11

Loc: Sri Lanka

Re: Replica of Newton's reflector? new

new

[Re: cheapersleeper]
#5266624 - 06/11/12 03:55 PM

^^^

I also like the use of the term 'overcharged' in the original account ...

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EJN
Pooh-Bah

Reged: 11/01/05

Loc: Highway 61

Re: Replica of Newton's reflector? new

new

[Re: cheapersleeper]
#5266635 - 06/11/12 03:58 PM

Quote:

Newton's assistant disputed much of that account. He posted in the Refractor forum that "the thing put up mushy images while the refractor he was comparing it to showed pinpoint stars..."

That comparison was made when Newton was still using a Ramsden eyepiece,
after he bought an Ethos & Paracorr, the images were tack sharp.

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careysub
Pooh-Bah

Reged: 02/18/11

Loc: Rancho Cucamonga, CA

Re: Replica of Newton's reflector? new

new

[Re: benula]
#5266643 - 06/11/12 04:00 PM

You aren't going to find this specific alloy (2/3 copper, 1/3 tin, plus maybe a little lead, zinc or arsenic) I think, not much call for it. Probably you will have to mix some up yourself from tin-bronze (~85% Cu, ~15% Sn) and tin.

Tin-bronze (used to just be "bronze" before modern aluminum-bronze, silicon-bronze, etc. copper alloys mostly replaced it) melts at 975 C, which can be reached by an inexpensive flower pot furnace: http://www.backyardmetalcasting.com/book_fp.html.

You would melt a bronze specimen, take it out of the furnace, then add the necessary amount of tin (the melting point drops 230 C with the addition of the tin, so it may not be necessary to remelt).

You probably realized you would have to cast your metal into the desired mold anyway, so having to mix up the metal is not really adding any work.

Although I have found several sites quoting prices on pure tin, I have found none doing so for tin-bronze. There are plenty of places offering it for sale mind you, lots of artists cast bronze, but they always want you to request a quote.

Sounds like a fun thing to do!

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dave brock
sage

Reged: 06/06/08

Loc: Hamilton, New Zealand

Re: Replica of Newton's reflector? new

new

[Re: EJN]
#5267491 - 06/12/12 03:15 AM

Quote:

Quote:

Newton's assistant disputed much of that account. He posted in the Refractor forum that "the thing put up mushy images while the refractor he was comparing it to showed pinpoint stars..."

That comparison was made when Newton was still using a Ramsden eyepiece,
after he bought an Ethos & Paracorr, the images were tack sharp.

He did have some balance issues though.

Dave

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Dave O
super member

Reged: 12/21/11

Loc: Sri Lanka

Re: Replica of Newton's reflector? new

new

[Re: dave brock]
#5267556 - 06/12/12 06:11 AM

Perhaps aluminum would be a suitable substitute for speculum ...

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mwtse
member

Reged: 06/03/11

Re: Replica of Newton's reflector? new

new

[Re: Dave O]
#5267710 - 06/12/12 09:19 AM

How about this one:

http://www.pulsar-optical.co.uk/prod/Newton's%20first%20telescope/hand-made-replica.html

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careysub
Pooh-Bah

Reged: 02/18/11

Loc: Rancho Cucamonga, CA

Re: Replica of Newton's reflector? new

new

[Re: mwtse]
#5267939 - 06/12/12 11:44 AM

Interesting - it uses a "soft metal mirror" which I suspect is aluminum (speculum metal is rather hard), which would I imagine a modern optician would find much easier to work. Arguably if you aren't going to use speculum metal, a substitute metal would more representative of Newton's scope than one made of glass.

Speculum metal seems to be finicky about the proportions to get a good white color, as opposed to yellowish or bluish:
http://chestofbooks.com/reference/Henley-s-20th-Century-Formulas-Recipes-Processes-Vol1/Speculum-Metal.html

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Howie Glatter
Vendor

Reged: 07/04/06

Re: Replica of Newton's reflector? new

new

[Re: mwedel]
#5268391 - 06/12/12 04:48 PM

By 1717 when Newton published the last edition of his Optics, his ideas on primary construction had evolved. He describes a meniscus mirror of glass, "quick-silvered over on the back" (as I remember), and he cautions against wedge in the glass, lest you get color fringeing. I guess it was then known how to make second-surface mirrors with mercury, but first-surface metal films had not yet been developed.

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Darenwh
Carpal Tunnel

Reged: 05/11/06

Loc: Covington, GA

Re: Replica of Newton's reflector? new

new

[Re: Howie Glatter]
#5268407 - 06/12/12 05:05 PM

For the ball consider a bocce ball. They are 100mm diameter and some are made of wood. You may have to sand a bit to get rid of some engraved markings but that should be easier then making one from scratch. Another option is to contact a wood turner and have him/her turn a ball for you.

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mwedel
Works with Sauropods

Reged: 12/16/07

Loc: Claremont, CA

Re: Replica of Newton's reflector? [Re: Darenwh]
#5268861 - 06/12/12 11:40 PM

Thanks, all, for the ideas. I know Newton's telescopes were tiny, and it would be a cool challenge to build something that small, but I was thinking of something around 3", partly because those are the optics I already have. So maybe "replica" isn't the right word for what I have in mind. Homage, maybe? (Up)scale model?

...maybe I could get a 1.5" or 2" mirror from Edmunds or Surplus Shed and have it refigured by Zambuto. I mean, if I'm going to put up with 1.5" of aperture, they should at least be 1.5 premium inches, right?

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