secondary mirror...supposed to be this way or not

Hope everyone had a happy Christmas. I got an 8" Synta-made dob, but
the secondary mirror is attached to its holder off-centre. This isn't
a collimation isssue, it's the way it was made. Here's a pic:

http://geocities.com/beerauth/dob.html

Its actually more off-centre than it looks in the picture. Looking at
it directly head-on, you can clearly see it's about 1/4 inch in one
direction. Is it supposed to be this way? (I'm assuming not). Should I
try to remove it and re adhere it (if so, what type of adhesive do I
use), or should I return the scope?

"Patrick" wrote in message
om...
Hope everyone had a happy Christmas. I got an 8" Synta-made dob, but
the secondary mirror is attached to its holder off-centre. This isn't
a collimation isssue, it's the way it was made. Here's a pic:

http://geocities.com/beerauth/dob.html

Its actually more off-centre than it looks in the picture. Looking at
it directly head-on, you can clearly see it's about 1/4 inch in one
direction. Is it supposed to be this way? (I'm assuming not). Should I
try to remove it and re adhere it (if so, what type of adhesive do I
use), or should I return the scope?

Patrick,

The photo shows a diagonal in what is probably an acceptable
position. In a well collimated Newtonian (Dobsonian) optical
tube assembly, the diagonal will be a few tenths of an inch
further away from the focuser, and toward the primary, than
a simple geometric centering would indicate. This is because it
must catch a light *cone*, not a cylindrical beam.

In any event, you were wise to ask before taking any drastic
measures. By all reports, Synta makes very good telescopes
(for the money). They are into mass production, and can't afford
to let haphazard assembly techniques ruin an otherwise splendid
reputation. More than likely they have special assembly jigs just
for properly mounting the diagonal for your model scope. Such
processes leave little room for human caused error.

If you want to check out the rest of your collimation, do a web
search on "telescope collimation" or visit any of the popular
websites. Mine is at: http://www.vvm.com/~piscescs/collimat/NoTools2.html

The graphics may prove useful.

Cheers,
Larry G.

"Patrick" wrote in message
om...
Hope everyone had a happy Christmas. I got an 8" Synta-made dob, but
the secondary mirror is attached to its holder off-centre. This isn't
a collimation isssue, it's the way it was made. Here's a pic:

http://geocities.com/beerauth/dob.html

Its actually more off-centre than it looks in the picture. Looking at
it directly head-on, you can clearly see it's about 1/4 inch in one
direction. Is it supposed to be this way? (I'm assuming not). Should I
try to remove it and re adhere it (if so, what type of adhesive do I
use), or should I return the scope?

Patrick,

The photo shows a diagonal in what is probably an acceptable
position. In a well collimated Newtonian (Dobsonian) optical
tube assembly, the diagonal will be a few tenths of an inch
further away from the focuser, and toward the primary, than
a simple geometric centering would indicate. This is because it
must catch a light *cone*, not a cylindrical beam.

In any event, you were wise to ask before taking any drastic
measures. By all reports, Synta makes very good telescopes
(for the money). They are into mass production, and can't afford
to let haphazard assembly techniques ruin an otherwise splendid
reputation. More than likely they have special assembly jigs just
for properly mounting the diagonal for your model scope. Such
processes leave little room for human caused error.

If you want to check out the rest of your collimation, do a web
search on "telescope collimation" or visit any of the popular
websites. Mine is at: http://www.vvm.com/~piscescs/collimat/NoTools2.html

The graphics may prove useful.

Cheers,
Larry G.

On 24 Dec 2003 21:05:14 -0800, (Patrick) wrote:

Hope everyone had a happy Christmas. I got an 8" Synta-made dob, but
the secondary mirror is attached to its holder off-centre. This isn't
a collimation isssue, it's the way it was made. Here's a pic:

http://geocities.com/beerauth/dob.html

Its actually more off-centre than it looks in the picture. Looking at
it directly head-on, you can clearly see it's about 1/4 inch in one
direction. Is it supposed to be this way? (I'm assuming not). Should I
try to remove it and re adhere it (if so, what type of adhesive do I
use), or should I return the scope?

Everything looks fairly normal other than the secondary is quite large
(or appears that way). Just collimate it, and enjoy. Check Saturn,
it's almost near opposition, few more days and were there.

On 24 Dec 2003 21:05:14 -0800, (Patrick) wrote:

Hope everyone had a happy Christmas. I got an 8" Synta-made dob, but
the secondary mirror is attached to its holder off-centre. This isn't
a collimation isssue, it's the way it was made. Here's a pic:

http://geocities.com/beerauth/dob.html

Its actually more off-centre than it looks in the picture. Looking at
it directly head-on, you can clearly see it's about 1/4 inch in one
direction. Is it supposed to be this way? (I'm assuming not). Should I
try to remove it and re adhere it (if so, what type of adhesive do I
use), or should I return the scope?

Everything looks fairly normal other than the secondary is quite large
(or appears that way). Just collimate it, and enjoy. Check Saturn,
it's almost near opposition, few more days and were there.

Looks as if Synta knows what they're doing: offsetting the secondary, for
optimal colimation. In a former iteration of the secondary mount of my 20
inch f/5 Dob I used the same offsetting method. When I, placed the secondary
hub on the mirror without glue to see how it looked, I thought I had made
wrong calculations, because it looked as if the offset was to large. But
after calculating and measuring again, everything turned out te be correct.
--
Jan
http://home.wanadoo.nl/jhm.vangastel/Astronomy/


"Patrick" schreef in bericht
om...
Hope everyone had a happy Christmas. I got an 8" Synta-made dob, but
the secondary mirror is attached to its holder off-centre. This isn't
a collimation isssue, it's the way it was made. Here's a pic:

http://geocities.com/beerauth/dob.html

Its actually more off-centre than it looks in the picture. Looking at
it directly head-on, you can clearly see it's about 1/4 inch in one
direction. Is it supposed to be this way? (I'm assuming not). Should I
try to remove it and re adhere it (if so, what type of adhesive do I
use), or should I return the scope?

Looks as if Synta knows what they're doing: offsetting the secondary, for
optimal colimation. In a former iteration of the secondary mount of my 20
inch f/5 Dob I used the same offsetting method. When I, placed the secondary
hub on the mirror without glue to see how it looked, I thought I had made
wrong calculations, because it looked as if the offset was to large. But
after calculating and measuring again, everything turned out te be correct.
--
Jan
http://home.wanadoo.nl/jhm.vangastel/Astronomy/


"Patrick" schreef in bericht
om...
Hope everyone had a happy Christmas. I got an 8" Synta-made dob, but
the secondary mirror is attached to its holder off-centre. This isn't
a collimation isssue, it's the way it was made. Here's a pic:

http://geocities.com/beerauth/dob.html

Its actually more off-centre than it looks in the picture. Looking at
it directly head-on, you can clearly see it's about 1/4 inch in one
direction. Is it supposed to be this way? (I'm assuming not). Should I
try to remove it and re adhere it (if so, what type of adhesive do I
use), or should I return the scope?

"Patrick" wrote in message
om...
Hope everyone had a happy Christmas. I got an 8" Synta-made dob, but
the secondary mirror is attached to its holder off-centre. This isn't
a collimation isssue, it's the way it was made. Here's a pic:

http://geocities.com/beerauth/dob.html

Its actually more off-centre than it looks in the picture. Looking at
it directly head-on, you can clearly see it's about 1/4 inch in one
direction. Is it supposed to be this way? (I'm assuming not). Should I
try to remove it and re adhere it (if so, what type of adhesive do I
use), or should I return the scope?

The secondary on my Orion SVP 8EQ (f/5 Synta) looks pretty much like that.
No worries.

"Patrick" wrote in message
om...
Hope everyone had a happy Christmas. I got an 8" Synta-made dob, but
the secondary mirror is attached to its holder off-centre. This isn't
a collimation isssue, it's the way it was made. Here's a pic:

http://geocities.com/beerauth/dob.html

Its actually more off-centre than it looks in the picture. Looking at
it directly head-on, you can clearly see it's about 1/4 inch in one
direction. Is it supposed to be this way? (I'm assuming not). Should I
try to remove it and re adhere it (if so, what type of adhesive do I
use), or should I return the scope?

The secondary on my Orion SVP 8EQ (f/5 Synta) looks pretty much like that.
No worries.

"Patrick" wrote in message
om...
Hope everyone had a happy Christmas. I got an 8" Synta-made dob, but
the secondary mirror is attached to its holder off-centre. This isn't
a collimation isssue, it's the way it was made. Here's a pic:

http://geocities.com/beerauth/dob.html

Its actually more off-centre than it looks in the picture. Looking at
it directly head-on, you can clearly see it's about 1/4 inch in one
direction. Is it supposed to be this way? (I'm assuming not). Should I
try to remove it and re adhere it (if so, what type of adhesive do I
use), or should I return the scope?

It's not a problem. I have an Orion 8-inch Dob -- mine looks just like
yours.

Before you do anything, haul it out and do some observing for a few nights.
The collimation from the factory is probably good enough but you should
check and adjust, as necessary, the collimation after a few days.

Here is a link to how I collimate mine -- I'm no expert so you may want to
follow the links on my page and read what the experts have to say.
http://www.schlatter.org/Dad/Astronomy/collimate.htm

Your scope should have come with a collimating cap -- a little plastic piece
with a peephole in the center and the inside coated with a reflective
coating -- it mounts just like an eyepiece, which it is. You can spend a
lot of money on collimating tools but the little cap will do as fine a job
as anything else. You will need a #2 Phillips screwdriver and at least one
2mm hex wrench -- get a long one. The Phillips screwdriver moves the
secondary toward/away from the primary. The hex wrench(es) adjust the tilt
of the secondary.
-----
JAS