8" Homebrew Dobson Focuser - Low Profile?

Hi,

My brother built a fantastic 8" Dobsonian which is fantastic.
Unfortunately, the plans he used called for a low profile focuser
which was really just a 1 1/4" ring that would provide friction to
keep the eyepiece in place. Well that leaves a lot to be desired.

The problem is that many focusers are too long and he'll have to move
parts of the scope to get the right focal position. Excuse my
terminology as I'm new to this.

So the options seem to be:

A. Buy a suitable low profile focuser, but where and how do you know
what to buy?
B. Drill a new focuser hole (butcher option 1)
C. Move the primary (butcher option 2 but seemingly less invasive).
D. Other options?

What would you recommend? We've already gotten some wonderful deep
space views with a makeshift lens from binoculars. Any tips would be
great!

Thanks,
Matt

What would you recommend? We've already gotten some wonderful deep
space views with a makeshift lens from binoculars. Any tips would be
great!

Try JMI's web site. They have travel specs on there for their focusers.
Affordable focuser kits, with the focus travel listed, which you can assemble
yourself. If you tell them the size of your tube, they can match the base plate
to it. Very nice folks to deal with. Nice focusers.

http://www.jimsmobile.com


john

What would you recommend? We've already gotten some wonderful deep
space views with a makeshift lens from binoculars. Any tips would be
great!

Try JMI's web site. They have travel specs on there for their focusers.
Affordable focuser kits, with the focus travel listed, which you can assemble
yourself. If you tell them the size of your tube, they can match the base plate
to it. Very nice folks to deal with. Nice focusers.

http://www.jimsmobile.com


john

On 26 Dec 2003 11:35:48 -0800, (MW) wrote:

Hi,

My brother built a fantastic 8" Dobsonian which is fantastic.
Unfortunately, the plans he used called for a low profile focuser
which was really just a 1 1/4" ring that would provide friction to
keep the eyepiece in place. Well that leaves a lot to be desired.

The problem is that many focusers are too long and he'll have to move
parts of the scope to get the right focal position. Excuse my
terminology as I'm new to this.

I don't think that anyone has ever built a Newtonian who didn't move
the focusser or the mirror at some time. I've heard that Newton's
first scope has two holes for the focusser.

So the options seem to be:

A. Buy a suitable low profile focuser, but where and how do you know
what to buy?

Whatever you do, get the focusser and measure it before you cut
anything.

B. Drill a new focuser hole (butcher option 1)
You also need to move the secondary, The advantage is that the balance
of the scope isn't affected much.

C. Move the primary (butcher option 2 but seemingly less invasive).
The balance is affected so it depends on how easy it is to move the
Altitude bearing.

D. Other options?

Look up the helical crawford focusser on the www. It looks like a good
and easy design. You may be able to make one that is the same height.

I started with a helical focusser made of American plumbing parts,
worked well but only had a small focus range


What would you recommend? We've already gotten some wonderful deep
space views with a makeshift lens from binoculars. Any tips would be
great!

Well done!

It is possible to make a barlow lens using a 2x teleconverter. these
are available quite cheaply in second hand camera shops, This will
give you more magnification.

For less magnification use both field lenses from binocuars. Fit them
with the most curved surface almost touching


HTH

Chris

On 26 Dec 2003 11:35:48 -0800, (MW) wrote:

Hi,

My brother built a fantastic 8" Dobsonian which is fantastic.
Unfortunately, the plans he used called for a low profile focuser
which was really just a 1 1/4" ring that would provide friction to
keep the eyepiece in place. Well that leaves a lot to be desired.

The problem is that many focusers are too long and he'll have to move
parts of the scope to get the right focal position. Excuse my
terminology as I'm new to this.

I don't think that anyone has ever built a Newtonian who didn't move
the focusser or the mirror at some time. I've heard that Newton's
first scope has two holes for the focusser.

So the options seem to be:

A. Buy a suitable low profile focuser, but where and how do you know
what to buy?

Whatever you do, get the focusser and measure it before you cut
anything.

B. Drill a new focuser hole (butcher option 1)
You also need to move the secondary, The advantage is that the balance
of the scope isn't affected much.

C. Move the primary (butcher option 2 but seemingly less invasive).
The balance is affected so it depends on how easy it is to move the
Altitude bearing.

D. Other options?

Look up the helical crawford focusser on the www. It looks like a good
and easy design. You may be able to make one that is the same height.

I started with a helical focusser made of American plumbing parts,
worked well but only had a small focus range


What would you recommend? We've already gotten some wonderful deep
space views with a makeshift lens from binoculars. Any tips would be
great!

Well done!

It is possible to make a barlow lens using a 2x teleconverter. these
are available quite cheaply in second hand camera shops, This will
give you more magnification.

For less magnification use both field lenses from binocuars. Fit them
with the most curved surface almost touching


HTH

Chris

Take a look at this:

http://www3.bc.sympatico.ca/gwolanski/FOCUSERS.HTM

chin kiak

(MW) wrote in message . com...
Hi,

My brother built a fantastic 8" Dobsonian which is fantastic.
Unfortunately, the plans he used called for a low profile focuser
which was really just a 1 1/4" ring that would provide friction to
keep the eyepiece in place. Well that leaves a lot to be desired.

The problem is that many focusers are too long and he'll have to move
parts of the scope to get the right focal position. Excuse my
terminology as I'm new to this.

So the options seem to be:

A. Buy a suitable low profile focuser, but where and how do you know
what to buy?
B. Drill a new focuser hole (butcher option 1)
C. Move the primary (butcher option 2 but seemingly less invasive).
D. Other options?

What would you recommend? We've already gotten some wonderful deep
space views with a makeshift lens from binoculars. Any tips would be
great!

Thanks,
Matt

Take a look at this:

http://www3.bc.sympatico.ca/gwolanski/FOCUSERS.HTM

chin kiak

(MW) wrote in message . com...
Hi,

My brother built a fantastic 8" Dobsonian which is fantastic.
Unfortunately, the plans he used called for a low profile focuser
which was really just a 1 1/4" ring that would provide friction to
keep the eyepiece in place. Well that leaves a lot to be desired.

The problem is that many focusers are too long and he'll have to move
parts of the scope to get the right focal position. Excuse my
terminology as I'm new to this.

So the options seem to be:

A. Buy a suitable low profile focuser, but where and how do you know
what to buy?
B. Drill a new focuser hole (butcher option 1)
C. Move the primary (butcher option 2 but seemingly less invasive).
D. Other options?

What would you recommend? We've already gotten some wonderful deep
space views with a makeshift lens from binoculars. Any tips would be
great!

Thanks,
Matt

I had the same thing when I built my first scope, a12 inch Dob. I moved the
primary up a bit. Cost me 15 minutes.

--
Jan
http://home.wanadoo.nl/jhm.vangastel/Astronomy/


"MW" schreef in bericht
om...
Hi,

My brother built a fantastic 8" Dobsonian which is fantastic.
Unfortunately, the plans he used called for a low profile focuser
which was really just a 1 1/4" ring that would provide friction to
keep the eyepiece in place. Well that leaves a lot to be desired.

The problem is that many focusers are too long and he'll have to move
parts of the scope to get the right focal position. Excuse my
terminology as I'm new to this.

So the options seem to be:

A. Buy a suitable low profile focuser, but where and how do you know
what to buy?
B. Drill a new focuser hole (butcher option 1)
C. Move the primary (butcher option 2 but seemingly less invasive).
D. Other options?

What would you recommend? We've already gotten some wonderful deep
space views with a makeshift lens from binoculars. Any tips would be
great!

Thanks,
Matt

I had the same thing when I built my first scope, a12 inch Dob. I moved the
primary up a bit. Cost me 15 minutes.

--
Jan
http://home.wanadoo.nl/jhm.vangastel/Astronomy/


"MW" schreef in bericht
om...
Hi,

My brother built a fantastic 8" Dobsonian which is fantastic.
Unfortunately, the plans he used called for a low profile focuser
which was really just a 1 1/4" ring that would provide friction to
keep the eyepiece in place. Well that leaves a lot to be desired.

The problem is that many focusers are too long and he'll have to move
parts of the scope to get the right focal position. Excuse my
terminology as I'm new to this.

So the options seem to be:

A. Buy a suitable low profile focuser, but where and how do you know
what to buy?
B. Drill a new focuser hole (butcher option 1)
C. Move the primary (butcher option 2 but seemingly less invasive).
D. Other options?

What would you recommend? We've already gotten some wonderful deep
space views with a makeshift lens from binoculars. Any tips would be
great!

Thanks,
Matt