Coulter DOB Mirror Cell

Greetings...

Well, I got the 13" Coulter Dob. I HATE the mirror cell...Collimation from
HELL. But the mirror appears worth the whole deal....

I want to change the mirror cell but I do not want to make it myself. Will
the University Optics cell work? What's the tolerance for placement of the
mirror from the secondary? An inch? tenths? Less?

Anyone done this to big Coulter?

Regards,

Doink

well I went through this with the 17.5", finally advertised on Astromart,
nothing came back, so did a huge Google search and finally found an
ATM site which lead to an individual who had made a good mount ...
suggest you search likewise and may have to.

Even silicon dots for points on the wood backing, with new gentle mirror
clips, is better than just the flat backing.

Rob





Doink wrote:

Greetings...

Well, I got the 13" Coulter Dob. I HATE the mirror cell...Collimation from
HELL. But the mirror appears worth the whole deal....

I want to change the mirror cell but I do not want to make it myself. Will
the University Optics cell work? What's the tolerance for placement of the
mirror from the secondary? An inch? tenths? Less?

Anyone done this to big Coulter?

Regards,

Doink

Just a thought - the wooden cell might be a real boon for temperature
equalization. Yes it was hard to collimate, but held collimation very well (at
least, mine certainly did!).
Distances from the mirror to the secondary should only matter in eyepiece
position if not too far off from the current distance. Differences could lead
to some light cutoff (not all the cone within the secondary) or more blocking
(more incoming light blocked by the secondary). For very long and very short
FL EP's, there may be a problem with getting into focus.

Clear, Dark, Steady Skies!
(And considerate neighbors!!!)

Thanks. I took it out last night and REALLY enjoyed the views. I don't
have much $$$ in the scope so it's well worth the price of admission. I
think the views could be a bit sharper if I could collimate to a closer
tolerance however. The secondary is in a fixed position and can't be
collimated and the main cell is cumbersome to collimate. I did get it
pretty well lined up and saw some great views...M13 looked like a cluster of
stars rather than cotton candy with a few bright points. That was
impressive. The veil was easy to find---both sides---but it lacked the
detail I've seen with my well tuned 8" reflector. That could be seeing as I
only have one night to compare. The star test was pretty good with a nice
even doughnut but there was a bunch of "activity" in the diffraction
ring---this could be retained heat in the sonotube or poor atmospherics.

Since the UO cell is only $50 and it should allow finer collimation and far
better heat dispersion, it seems like a logical thing to do. I can't find
anyone who would recommend it though! I would think with the huge number of
Coulters out there that this would be a common procedure yet I can't raise
support for it. So, maybe I should just leave it alone!!!!! With limited
experience, it's hard to assess how difficult this would be to do and what
would be gained. I do notice occasional snobery on this board when
questions like this are raised...so I appreciate those who actually take the
time to give real information.

Doink






"Wfoley2" wrote in message
...
Just a thought - the wooden cell might be a real boon for temperature
equalization. Yes it was hard to collimate, but held collimation very
well (at
least, mine certainly did!).
Distances from the mirror to the secondary should only matter in eyepiece
position if not too far off from the current distance. Differences could
lead
to some light cutoff (not all the cone within the secondary) or more
blocking
(more incoming light blocked by the secondary). For very long and very
short
FL EP's, there may be a problem with getting into focus.

Clear, Dark, Steady Skies!
(And considerate neighbors!!!)

On Fri, 12 Nov 2004 09:42:12 -0800, Doink wrote:


The star test was pretty good with a nice
even doughnut but there was a bunch of "activity" in the diffraction
ring---this could be retained heat in the sonotube or poor atmospherics.

Since the UO cell is only $50 and it should allow finer collimation and far
better heat dispersion, it seems like a logical thing to do. I can't find
anyone who would recommend it though!


The UO cell is going to reek havoc with the balance of the OTA.

Install a fan if you can come up with about 20 dollars. Take a look at my
website to see how I did it. It will completely eliminate thermal issues.
If you can't afford the twenty bucks now then at least vent the rear of the
tube at mirror surface level with a few one inch diameter holes. Keep them
at least somewhat more than an inch from each other and don't exceed 5.



--
Martin
"Photographs From the Universe of Amateur Astronomy"
http://home.earthlink.net/~martinhowell

Since the UO cell is only $50 and it should allow finer collimation and far
better heat dispersion, it seems like a logical thing to do. I can't find
anyone who would recommend it though!
I bought the UO cell for my 12.5 inch Discovery. It has an 1.5 inch thick
mirror, some of those Coulter mirrors are pretty thin so a better cell maybe
necessary.

Some things to consider:

1. The UO cell is a 9 point cell but it is not a floating cell like a Novak or
even some of the Asian DOBs, it consists of three thin radial members (spiders)
with 3 pads on each one, not good for a thin mirror IMHO. Over all I would
rate it as pretty chincy...

I found it worked OK but I found a Novak cell via Astromart and it is quite a
different beast all together... Over all I would rate it as pretty chincy...

2. When I installed the UO cell the scope lost about 8 pounds, a good thing to
be sure. But it meant rebalancing the scope entirely and since I did want to
save that weight I build new side boards for the base.

3. I do have an extra 4 vane spider and secondary holder assembly designed for
a 14 inch or so OTA. If you are interested maybe we can work something out.

Best wishes

jon

"Jon Isaacs" wrote in message
...
Since the UO cell is only $50 and it should allow finer collimation and
far
better heat dispersion, it seems like a logical thing to do. I can't
find
anyone who would recommend it though!
I bought the UO cell for my 12.5 inch Discovery. It has an 1.5 inch
thick
mirror, some of those Coulter mirrors are pretty thin so a better cell
maybe
necessary.

Some things to consider:

1. The UO cell is a 9 point cell but it is not a floating cell like a
Novak or
even some of the Asian DOBs, it consists of three thin radial members
(spiders)
with 3 pads on each one, not good for a thin mirror IMHO. Over all I
would
rate it as pretty chincy...

I found it worked OK but I found a Novak cell via Astromart and it is
quite a
different beast all together... Over all I would rate it as pretty
chincy...

2. When I installed the UO cell the scope lost about 8 pounds, a good
thing to
be sure. But it meant rebalancing the scope entirely and since I did
want to
save that weight I build new side boards for the base.

3. I do have an extra 4 vane spider and secondary holder assembly
designed for
a 14 inch or so OTA. If you are interested maybe we can work something
out.

Best wishes

jon

Novak realized that the Coulter Odyssey mirrors were very thin, and would
not be supported adequately in a more standard primary cell, so he sold a
different version for those thin mirrors. Dunno' if he still sells it or
not. He's in sorta' semi-retirement, last I heard, and didn't have some
of the cells, and was having trouble getting someone to produce them for
him, at the time...

Another problem with the old blue tube Coulters is that they are tailgate
Dobsonians. That is, the thin mirror is supported on a cell in a sling,
and all that stuff is attached to the inside of the hinged, fold-down back
wall of the scope, BEHIND the tube (actually, the mirror is JUST inside
the back end of the tube when the tailgate is closed... Installing a
conventional 9 or 18 point cell with adequate side support will move the
mirror some distance forward up the tube, which will almost certainly
require relocation of the focuser forward, and the single vane (obviously
made from a Peterbilt bumper) secondary support is already pretty close to
the front of the tube, allowing little room for this. Replacing the whole
secondary system with a more useful mount might run you out of tube,
relocated focuser and all... I did outline to Doink offline, what I did
to make the Coulter secondary more adjustable. The secondary is now
properly aligned and collimated, and it would have to be hit with a HAMMER
to take it out of collimation...

--
Jan Owen

To reach me directly, remove the Z, if one appears in my e-mail address...
Latitude: 33.662
Longitude: -112.3272

Now I understand why so many posted to just leave it alone. It's probably
too complicated for me to deal with and it does work nicely as is....

So, I'll probably just keep it the way it is until I can afford a Tscope 14"
which seems to be the best Dob for the money at present. I looked at
Discovery but their truss Dob seems over priced for the specs...

Doink


"Jan Owen" wrote in message
news:fm8ld.105235$cJ3.18117@fed1read06...
"Jon Isaacs" wrote in message
...
Since the UO cell is only $50 and it should allow finer collimation and
far
better heat dispersion, it seems like a logical thing to do. I can't
find
anyone who would recommend it though!
I bought the UO cell for my 12.5 inch Discovery. It has an 1.5 inch
thick
mirror, some of those Coulter mirrors are pretty thin so a better cell
maybe
necessary.

Some things to consider:

1. The UO cell is a 9 point cell but it is not a floating cell like a
Novak or
even some of the Asian DOBs, it consists of three thin radial members
(spiders)
with 3 pads on each one, not good for a thin mirror IMHO. Over all I
would
rate it as pretty chincy...

I found it worked OK but I found a Novak cell via Astromart and it is
quite a
different beast all together... Over all I would rate it as pretty
chincy...

2. When I installed the UO cell the scope lost about 8 pounds, a good
thing to
be sure. But it meant rebalancing the scope entirely and since I did
want to
save that weight I build new side boards for the base.

3. I do have an extra 4 vane spider and secondary holder assembly
designed for
a 14 inch or so OTA. If you are interested maybe we can work something
out.

Best wishes

jon

Novak realized that the Coulter Odyssey mirrors were very thin, and would
not be supported adequately in a more standard primary cell, so he sold a
different version for those thin mirrors. Dunno' if he still sells it or
not. He's in sorta' semi-retirement, last I heard, and didn't have some
of the cells, and was having trouble getting someone to produce them for
him, at the time...

Another problem with the old blue tube Coulters is that they are tailgate
Dobsonians. That is, the thin mirror is supported on a cell in a sling,
and all that stuff is attached to the inside of the hinged, fold-down back
wall of the scope, BEHIND the tube (actually, the mirror is JUST inside
the back end of the tube when the tailgate is closed... Installing a
conventional 9 or 18 point cell with adequate side support will move the
mirror some distance forward up the tube, which will almost certainly
require relocation of the focuser forward, and the single vane (obviously
made from a Peterbilt bumper) secondary support is already pretty close to
the front of the tube, allowing little room for this. Replacing the whole
secondary system with a more useful mount might run you out of tube,
relocated focuser and all... I did outline to Doink offline, what I did
to make the Coulter secondary more adjustable. The secondary is now
properly aligned and collimated, and it would have to be hit with a HAMMER
to take it out of collimation...

--
Jan Owen

To reach me directly, remove the Z, if one appears in my e-mail address...
Latitude: 33.662
Longitude: -112.3272

Yes. My back is quite attracted to their Far Star scope line (and
aesthetically, it is quite nice, too).

When I told you off-line that I was soon going to replace the Coulter, it
was the Far Star that I was talking about, but didn't specify...

--
Jan Owen

To reach me directly, remove the Z, if one appears in my e-mail address...
Latitude: 33.662
Longitude: -112.3272
"Doink" wrote in message
...
Now I understand why so many posted to just leave it alone. It's
probably
too complicated for me to deal with and it does work nicely as is....

So, I'll probably just keep it the way it is until I can afford a Tscope
14"
which seems to be the best Dob for the money at present. I looked at
Discovery but their truss Dob seems over priced for the specs...

Doink


"Jan Owen" wrote in message
news:fm8ld.105235$cJ3.18117@fed1read06...
"Jon Isaacs" wrote in message
...
Since the UO cell is only $50 and it should allow finer collimation
and
far
better heat dispersion, it seems like a logical thing to do. I
can't
find
anyone who would recommend it though!
I bought the UO cell for my 12.5 inch Discovery. It has an 1.5 inch
thick
mirror, some of those Coulter mirrors are pretty thin so a better
cell
maybe
necessary.

Some things to consider:

1. The UO cell is a 9 point cell but it is not a floating cell like
a
Novak or
even some of the Asian DOBs, it consists of three thin radial members
(spiders)
with 3 pads on each one, not good for a thin mirror IMHO. Over all I
would
rate it as pretty chincy...

I found it worked OK but I found a Novak cell via Astromart and it is
quite a
different beast all together... Over all I would rate it as pretty
chincy...

2. When I installed the UO cell the scope lost about 8 pounds, a
good
thing to
be sure. But it meant rebalancing the scope entirely and since I did
want to
save that weight I build new side boards for the base.

3. I do have an extra 4 vane spider and secondary holder assembly
designed for
a 14 inch or so OTA. If you are interested maybe we can work
something
out.

Best wishes

jon

Novak realized that the Coulter Odyssey mirrors were very thin, and
would
not be supported adequately in a more standard primary cell, so he
sold a
different version for those thin mirrors. Dunno' if he still sells it
or
not. He's in sorta' semi-retirement, last I heard, and didn't have
some
of the cells, and was having trouble getting someone to produce them
for
him, at the time...

Another problem with the old blue tube Coulters is that they are
tailgate
Dobsonians. That is, the thin mirror is supported on a cell in a
sling,
and all that stuff is attached to the inside of the hinged, fold-down
back
wall of the scope, BEHIND the tube (actually, the mirror is JUST
inside
the back end of the tube when the tailgate is closed... Installing a
conventional 9 or 18 point cell with adequate side support will move
the
mirror some distance forward up the tube, which will almost certainly
require relocation of the focuser forward, and the single vane
(obviously
made from a Peterbilt bumper) secondary support is already pretty
close to
the front of the tube, allowing little room for this. Replacing the
whole
secondary system with a more useful mount might run you out of tube,
relocated focuser and all... I did outline to Doink offline, what I
did
to make the Coulter secondary more adjustable. The secondary is now
properly aligned and collimated, and it would have to be hit with a
HAMMER
to take it out of collimation...

--
Jan Owen

To reach me directly, remove the Z, if one appears in my e-mail
address...
Latitude: 33.662
Longitude: -112.3272

On Fri, 12 Nov 2004 11:53:13 -0800, Doink wrote:


So, I'll probably just keep it the way it is until I can afford a Tscope 14"
which seems to be the best Dob for the money at present. I looked at
Discovery but their truss Dob seems over priced for the specs...


Be wary of the bigger aperture ladder. . .there is no final rung on it.
For me, 13.1" would be just the right height.



Martin