#MK

Hi!

I hope you don’t mind me asking two questions, regarding amateur
telescope making:



1. How... Ineffective or less “good” is a 6 incher from an 8 inch mirror?

[6 Inch with a F/8 ratio, or 8 inch with a F/6 ratio, hence focal length
isn’t significant].

I am aware that there will be an “effective magnification”

drop from 400x to 300x, but I am unsure as to how that may affect
planetary observing? [I know that aperture is more important, but is say,

240x with some knocked off cos of seeing enough?]

I know that brightness and light gathering will be less for DSO and
planets, but how significant is this? [I.e. 6 inch vs. 8 inch, how much
would I lose? Cos I was gonna make a 8'' but the cost seemed too high for

me, so how sufficient is a 6''? ]



I am also aware that light-gathering and brightness would be reduced in
the 6 inch, but for a first telescope making attempt, is a 6 inch, f/8
too small or insignificant for observing of the cosmos? [Would one be
able to see clouds on Jupiter [small, of course, not like Voyager! ] and

Saturn’s ring(s)]? N.B. I am aware that DSO won’t be in colour or like
pics in books etc. cos of the human retina etc., just wondering how a
planet would look like through a 6 incher].



2. Secondly, I have heard folks comment [and the FAQ!] that making one's
own mirror for cost isn't a good reason for small uns.

Well, I did some comparisons, and found a 6 incher mirror would
cost about £150 to buy, whilst to make it would cost:

£~75 [incl. p+p], including £23 for aluminising + p/p,

£23 for a mirror "kit" [pitch, grit etc.], and £33 for blank incl. p+p+,
roughly]



Well, putting aside labour costs, it seems there is a significant saving?

[If I made an 8 inch one, it would be £40 more tho.]

Have I missed something out significant here in the mirror making
stuff? I know that I'm missing the Tool, but would one be able to make
one cheaply at home?


Any advice would be much appreciated.



Thanks in advance.

#MK.

Mark McIntyre

On Thu, 03 Jul 2003 16:20:17 GMT, in uk.sci.astronomy , #MK
<sorry@dontsendmail.nomail> wrote:

>Hi!
>
>I hope you don’t mind me asking two questions, regarding amateur
>telescope making:
>
>
>
>1. How... Ineffective or less “good” is a 6 incher from an 8 inch mirror?

the 8" will gather 64/36 times more light
any flaws in the grinding will be 64/36ths more noticeable.

>[6 Inch with a F/8 ratio, or 8 inch with a F/6 ratio, hence focal length
>isn’t significant].

the shorter focal length will show a little more aberration I believe.


--
Mark McIntyre
CLC FAQ <http://www.eskimo.com/~scs/C-faq/top.html>
CLC readme: <http://www.angelfire.com/ms3/bchambless0/welcome_to_clc.html>


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Kevin Jenner

Where is a good place for looking into purchasing kits / elements for a
home made telescope?

I'm interested in building one myself (ex-student you see)

What is the general cost of building a telescope yourself?

Cheers

Kevin Jenner

In message <MPG.196e6820251d6108989686@news-text.blueyonder.co.uk>, #MK
<sorry@dontsendmail.nomail> writes
>Hi!
>
>I hope you don’t mind me asking two questions, regarding amateur
>telescope making:
>
>
>
>1. How... Ineffective or less “good� is a 6 incher from an 8 inch mirror?
>
>[6 Inch with a F/8 ratio, or 8 inch with a F/6 ratio, hence focal length
>isn’t significant].
>
> I am aware that there will be an “effective magnification�
>
>drop from 400x to 300x, but I am unsure as to how that may affect
>planetary observing? [I know that aperture is more important, but is say,
>
>240x with some knocked off cos of seeing enough?]
>
>I know that brightness and light gathering will be less for DSO and
>planets, but how significant is this? [I.e. 6 inch vs. 8 inch, how much
>would I lose? Cos I was gonna make a 8'' but the cost seemed too high for
>
>me, so how sufficient is a 6''? ]
>
>
>
>I am also aware that light-gathering and brightness would be reduced in
>the 6 inch, but for a first telescope making attempt, is a 6 inch, f/8
>too small or insignificant for observing of the cosmos? [Would one be
>able to see clouds on Jupiter [small, of course, not like Voyager! ] and
>
>Saturn’s ring(s)]? N.B. I am aware that DSO won’t be in colour or like
>pics in books etc. cos of the human retina etc., just wondering how a
>planet would look like through a 6 incher].
>
>
>
>2. Secondly, I have heard folks comment [and the FAQ!] that making one's
>own mirror for cost isn't a good reason for small uns.
>
> Well, I did some comparisons, and found a 6 incher mirror would
>cost about £150 to buy, whilst to make it would cost:
>
> £~75 [incl. p+p], including £23 for aluminising + p/p,
>
>£23 for a mirror "kit" [pitch, grit etc.], and £33 for blank incl. p+p+,
>roughly]
>
>
>
>Well, putting aside labour costs, it seems there is a significant saving?
>
>[If I made an 8 inch one, it would be £40 more tho.]
>
> Have I missed something out significant here in the mirror making
>stuff? I know that I'm missing the Tool, but would one be able to make
>one cheaply at home?
>
>
> Any advice would be much appreciated.
>
>
>
>Thanks in advance.
>
>#MK.
>
>
>
>

--
Kevin Jenner

Stephen Tonkin

Kevin Jenner <kevin@jenrus.demon.co.uk> wrote:
>Where is a good place for looking into purchasing kits / elements for a
>home made telescope?
>
>I'm interested in building one myself (ex-student you see)
>
>What is the general cost of building a telescope yourself?


All the info you may need is linked to from:
http://astunit.com/tonkinsastro/atm/beginner.htm

Best,
Stephen

--
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+ Stephen Tonkin | ATM Resources; Astro-Tutorials; Astro Books +
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+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

Stephen Tonkin

#MK <sorry@dontsendmail.nomail> wrote:
>but would you happen to have a suggestion as to where I could obtain
>primary for under 100 quid?

£89: http://www.scsastro.co.uk/it290004.htm
£109 (with flat):
http://www.galvoptics.fsnet.co.uk/te....htm#parabolic

Also monitor: http://www.ukastroads.co.uk

Best,
Stephen

--
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+ Stephen Tonkin | ATM Resources; Astro-Tutorials; Astro Books +
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Stephen Tonkin

#MK <sorry@dontsendmail.nomail> wrote:
><--- Cheap student, for whom time is not an issue, though cost is!

You want to go cheap? OK. Lots of things can be made very cheap or are
scroungeable.

Mirror-blank: Porthole glass (just make sure it's not hardened glass --
you will *never* get it to figure.

Sub-diameter tool for hogging out: Cat-food tin or similar, with
"rolled" end, full.

Tool for fine-grinding: cast plaster or cement base, with pieces of
bathroom tile epoxied on. Use a plaster base for your pitch lap.

Grits for hogging out and first stage of fine grinding: Sand. You will
need lots of it, but it's free. Grade it yourself.

I'd still advise buying finer powders, CeO and pitch.

Flat: prism from broken binoculars or similar, or bit of first-surface
mirror from photocopier. (CA isn't too bad if the scope is f/8 or above)

Timber for building scope and mount: scrounge from skips or building
sites. Or you can sometimes get offcuts of large-diameter tubing from
agricultural suppliers.

The junk corners of 2nd hand chandlers are a treasure trove of stuff for
broke ATMs (I was devastated when "Yot Grot" in Lymington closed down!).
So is Anchor Surplus in Nottingham (just next to Trent Bridge cricket
ground), although they seem to be getting wise to it and the prices are
going up.

Best,
Stephen

--
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
+ Stephen Tonkin | ATM Resources; Astro-Tutorials; Astro Books +
+ (N51.162 E0.995) | <http://www.astunit.com> +
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A. Edwards

Err - Stephen Tonkin mumbled something like:
> #MK <sorry@dontsendmail.nomail> wrote:
>> <--- Cheap student, for whom time is not an issue, though cost is!
>
> You want to go cheap? OK. Lots of things can be made very cheap or are
> scroungeable.
>
> Mirror-blank: Porthole glass (just make sure it's not hardened glass
> -- you will *never* get it to figure.
>
> Sub-diameter tool for hogging out: Cat-food tin or similar, with
> "rolled" end, full.
>
> Tool for fine-grinding: cast plaster or cement base, with pieces of
> bathroom tile epoxied on. Use a plaster base for your pitch lap.
>
> Grits for hogging out and first stage of fine grinding: Sand. You will
> need lots of it, but it's free. Grade it yourself.
>
> I'd still advise buying finer powders, CeO and pitch.
>
> Flat: prism from broken binoculars or similar, or bit of first-surface
> mirror from photocopier. (CA isn't too bad if the scope is f/8 or
> above)
>
> Timber for building scope and mount: scrounge from skips or building
> sites. Or you can sometimes get offcuts of large-diameter tubing from
> agricultural suppliers.
>
> The junk corners of 2nd hand chandlers are a treasure trove of stuff
> for broke ATMs (I was devastated when "Yot Grot" in Lymington closed
> down!). So is Anchor Surplus in Nottingham (just next to Trent Bridge
> cricket ground), although they seem to be getting wise to it and the
> prices are going up.
>
> Best,
> Stephen

Failing that, mail me a sensible address and there's some stuff around here
you can have *real* cheap...

Arthur

--
--
52:30:25N, 1:17:51E
http://www.ambermile.co.uk


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#MK

In article <uyQB0CEhfcB$Ewqa@astunit.com>, nospam@astunit.com says...
> #MK <sorry@dontsendmail.nomail> wrote:
> >but would you happen to have a suggestion as to where I could obtain
> >primary for under 100 quid?
>
> £89: http://www.scsastro.co.uk/it290004.htm
> £109 (with flat):
> http://www.galvoptics.fsnet.co.uk/te....htm#parabolic
>
> Also monitor: http://www.ukastroads.co.uk
>
> Best,
> Stephen
>
>

Gosh, much thanks indeed! Quite a nice find, I will probably just buy
one of 'em and make the mount, tube etc. by hand

Thanks for all the advice, everyone!


P.S. It seems that the cost savings pop up at the 8 incher and above
side, as I originally calculated that an 8'' f/6 could be made for about
£130... give or take a few £10/20, which is quite a saving over the £190
for the 8 incher... but a £99 quid 6'' mirror, compared with it costing
about £86 or so quid to make one incl. P+P.... quite nice deal!

#MK

In article <941cd3a9.0307050102.2a5f6a14@posting.google.com >,
chris.b@mail.dk says...
> #MK <sorry@dontsendmail.nomail> wrote in message news:<MPG.1970336a9fce559c98968a@news-text.blueyonder.co.uk>...
> >
> > P.S. It seems that the cost savings pop up at the 8 incher and above
> > side, as I originally calculated that an 8'' f/6 could be made for about
> > £130... give or take a few £10/20, which is quite a saving over the £190
> > for the 8 incher... but a £99 quid 6'' mirror, compared with it costing
> > about £86 or so quid to make one incl. P+P.... quite nice deal!
>
> Cost savings? How do you value your own time? <g>
>
I don't I have summer hols, for the most part of which I'm wondering
what should I do, and is spent staring at my computer screen wandering
aimlessly through the web. Too much time

I had factored in all the cost of aluminising and P+P, and it turns out a
pre-built mirror costs only a tenner or so above it, which is a nice deal
for a 6'' [An 8'' is cheaper to build than buy, by far however!]. Given
the fact that I will probably get errors, or make mistakes, and could
avoid the hassle by buying one, I will prolly buy a 6'' f/8 [Planets
better in this than in the 6'' f/6.7, though the FoV is smaller, right?]

John Carruthers

http://www.dhinds.co.uk/frames.html

6" mirror £40
in "for sale- used products"

Colin Smith

Somerset
Telephone: 01458 440366
E-Mail: colin@street440.fsnet.co.uk
Mobile No: 07860 825942

Price: £ 40





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#MK

In article <S1ENa.1648$fH3.74711@newsfep2-gui.server.ntli.net>,
are@tesco.net.useless.bit says...
> Err - #MK mumbled something like:
> > In article <be6rhd$m6r$1@newsg4.svr.pol.co.uk>,
> > joncarruthers@hotmail.com says...
> >> Subject: Re: Questions regarding ATM
> >> From: "John Carruthers" <joncarruthers@hotmail.com>
> >> Newsgroups: uk.sci.astronomy
> >>

>
> Dunno about your maths - f/13 would be good for planets. bBt of a bugger to
> point, mind you.

Hehe, and uncomfortable to use at the Zenith!
Would the FoV be significantly smaller than f/8, which could make it
harder to lock on to a planet or whatever?

>

>
> PS - where are you? (geographically speaking, of course...)
>
Birmingham, UK, so I am considering that transport with such a scope may
be difficult to get out of town...

Stephen Tonkin

#MK <sorry@dontsendmail.nomail> wrote:
>f the F = 1900mm,

I wonder if he meant fl 900 (which would make it f/6)?

>and a 6 inch mirror is 150mm, then is the F-Ratio: f/13 [roughly]?
>Hence, it wouldn't be quite curved,

Could be left spherical, which makes it easier to make, but f/13 is a
bugger under the Foucault test. The shadows are very indistinct.


>and whilst magnification would be high, would this be any good for
>planetary observation

In theory it could be very good, as you could have a minute secondary.
Play with NEWT (ATM software on my web site) to see what I mean.


Best,
Stephen

--
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+ Stephen Tonkin | ATM Resources; Astro-Tutorials; Astro Books +
+ (N51.162 E0.995) | <http://www.astunit.com> +
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +