开云体育

I took the advice and did careful measurements. Ordered a 42" pier
from ATS. Tried it out last weekend and it is the perfect height for
me. This is using a C14 plus AP1200. Any higher and I would have
real problems getting the mount on the pier, and the C14 on the mount.

Thanks everyone for your comments.

Editorially, the AP1200 with the C14 is sensational. I spent much of
my time learning how to polar align, and shim the tube for
orthogonality. But in an hour I saw more hard to find DSO's than in
the last few years!

Thanks again, Ken


--- In C14@y..., "rdcrisp" <rdcrisp@e...> wrote:

--- In C14@y..., "be01753" <be01753@y...> wrote:

Ken,
I suggest you draw a scale model, especially if you want to mount
more than one scope - thats what I did and decided to drop the

pier

size for my ap900 to 32inch. This sits on jmi wheelie bars, that

adds

7 inches. I am 5'10". The 1200 mount is about 4(?) inches bigger

than

the 900. My C14 is very nicely positioned for lifting on an off.

Some


I think Brian has some great advice there, Ken. I will be happy to
photograph my setup with me standing it the picture for a size
reference so you can take various measurements etc from the photo.

I

thought I had a 48" pier but now I forgot what I ordered. I'll
measure it too.
rdc

someone was asking me about whether or not I knew where they could
get one of these. Well today there was one on astromart. Note this is
for the smaller mounts.
rdc


#1 ---------------------------------------------------------
View this ad at
For Sale: Astro Physics 48 inch pier for sale
Posted by Mark Keitel

I have a 48 inch Astro Physics pier (6 inch diameter) for sale. This
pier will fit the AP 400 and 600 mount. $300 (buyer pays for
shipping). The pier came with the mount, but I sold my mount


Thank you

Mark

--- In C14@y..., "be01753" <be01753@y...> wrote:

Ken,
I suggest you draw a scale model, especially if you want to mount
more than one scope - thats what I did and decided to drop the pier
size for my ap900 to 32inch. This sits on jmi wheelie bars, that

adds

7 inches. I am 5'10". The 1200 mount is about 4(?) inches bigger

than

the 900. My C14 is very nicely positioned for lifting on an off.

Some


I think Brian has some great advice there, Ken. I will be happy to
photograph my setup with me standing it the picture for a size
reference so you can take various measurements etc from the photo. I
thought I had a 48" pier but now I forgot what I ordered. I'll
measure it too.
rdc

The C-14 is my dream scope. Well, my dreams may be coming true in a
couple of month. I have the chance to buy an orange tube, fork
mounted C-14. The optics are supposed to be good. At one time it
had problems with the motor drive and also holding collimation.
These have been fixed.

The tripod has a broken bolt and can not be extended until it is
fixed. That should be easy enough.

Once I fix the broken bolt and check the optics and motor drive, what
is a fair price?

I am probably obligated to buy at $2500. If I don't buy at that
price the scope will be put up for a closed bid to members of my
astronomy club. This means I would end up paying more. Is it worth
$2500?

Being it's a fork mount, does CI still support this mount. If not,
where can you get spare parts?

Eventually it will go on a permanent peir with a GOTO system but
that will not be for about 6 years (when I retire from the Air Force
and buy my own house and land).

Any advice and tips are appreciated.

Ron

Ron Wodaski suggested a method to clean up my background star field
in my M82 shot, which was taken through my C14. I had a problem with
the background not being flat fielded properly before.



I did the same thing to my Comet Ikeya-Zhang shot too:



M82 was shot at f/11 and Comet IZ was shot at f/7
rdc

Date: Wed, 06 Mar 2002 03:36:30 -0000
From: "garynburk" <garyburk@...>
Subject: Re: Mirror Locks

Hi Wayne,

Do you know what Meade has done for the mirror locks on their new
LX200 GPS series?

No. I have not seen them.

Wayne E. Gondella
AFA Engineering Company
Pittsburgh, Pennsylvania

Regards,
Gary

Ken,
I suggest you draw a scale model, especially if you want to mount
more than one scope - thats what I did and decided to drop the pier
size for my ap900 to 32inch. This sits on jmi wheelie bars, that adds
7 inches. I am 5'10". The 1200 mount is about 4(?) inches bigger than
the 900. My C14 is very nicely positioned for lifting on an off. Some
times I have to sit low down to observe, never on the ground though.
Polar alignment with a polar scope doesn't feel uncomfortably low.
I can wheel it into my garage without hitting anything up above
(though not with a dewshield on). The 32 inch pier however does not
take the AP pier trays if you wanted them.
For me and my set-up the 32inch is spot on, glad I made the scale drawing.
Cheers
Brian

--- In C14@y..., "kberna1376" <kberna1376@a...> wrote:

I have an AP1200 on order to use with the C14. What height pier
should I use? The 48" standard seems like it would be too high

when

you add the 21" of the AP1200. I am 5'-8" and might have a problem
getting the C14 into the losmandy dove at that height. Any
experience you can share?

Ken

Ken, you are in luck.

I am 5'9.5" and have a C14/AP1200GTO and do imaging. I find the
48"pier I bought to be too tall for some applications. I bought the
tall one originally because in the backyard in my old house I needed
it that tall to be able to see Polaris over the roof.

There are two problems with the 48" pier. The first is that it has
more "sway" which can cause a longer damp time when imaging. I get
good results nonetheless, but it does take a bit longer for the
movement to damp out.

The second problem is that I have a hard time getting up high enough
to see my piggybacked scope if I am low on the horizon. See the
following link:




Sometimes I have to stand on a chair during setup but mostly it is
OK. Because I also use the pier with my AP155EDF, I do need the
longer pier, but it would be nice to have a second one too, maybe a
24" or a 36" one. The SCTs are much shorter than the refractors and
therefore don't need such a tall pier.


By the way, on a different topic, my comet picture got linked on the
APOD for March 7 (today). See the link "observers are" at:


(sorry to toot my own horn, but I am happy to have the image
published).
rdc

Take a look at the way Roland Christen designed the focuser mechanism
for the 10" Mak Cass. Really really nice and very very stable. That,
and a cooling fan, would be great additions to a C14.
rdc



--- In C14@y..., "garynburk" <garyburk@h...> wrote:

Hi Wayne,
Actually, I did not expect a good mirror lock to be a simple

thing.

However, that doesn't mean it shouldn't be done. Once the cost of
the C14, guider,AP mount, camera, observatory and eypieces are

summed

up the added cost of fabricating a lock may well be the next most
effective improvement.
The three point course focus mechanism you suggest might not be
overly complicated - perhaps three fine thread lead screws geared
together with the mirror floating on their cams and spring loaded
against them with a force just slightly greater then the mirrors'
weight. Such an arrangement would be reasonable for 0.001"

stability

but it seems that getting much better than that would require high
precision (read that as "very expensive" parts). Again however,

once

one jumps into the pool for a high quality mount, this may not
represent a large additional cost increment.

Do you know what Meade has done for the mirror locks on their

new

LX200 GPS series?

Regards,
Gary



--- In C14@y..., "W. Gondella" <gondella@s...> wrote:

You won't like my answer:

First, to state the obvious, the mirror thimble should have an

extremely

close tolerance to the central baffle. Only a thin film of

grease

can fit

between. Those who complain of excessive mirror shift might have

one of

several problems: 1). Excessive play between the parts due to

wear

(inadequate grease) and age, or improper machining from the

factory

requiring a total rebuild; 2). A mechanical problem resulting

from damaged

or improperly tightened cork and/or silicone seals around the

mirror stays.

Some mirror shift (albeit minor in the best at high power) is

inevitable and

unavoidable, otherwise the mirror couldn't move. Even Questars

have this

problem. A tensioning system can be devised, that would load the

mirror

thimble, but this still might not entirely eliminate mirror shift

during

focus, as the focusing design in an SCT is an inherently low-cost

approach

and the tensioning would induce minor torsional stress. However,

it might

work beautifully.

A mirror locking mechanism can be devised which would prohibit

the

mirror

from shifting position, and it could be integrated with or

without

the

tensioning system rather nicely, however it is unrealistic to

expect that

the mirror can be locked down without causing *some* movement of

the mirror,

as we are talking about extremely small (less than a thousands of

an inch)

movements beeing detectable at the eyepiece.

This would, however, permit smooth focus and with little or no

free

play,

and would allow the mirror to be locked into place with a minimum

(or no)

movement that is possible, that would resist any outside forces

once set and

would be easy to implement. A crayford focuser with micrometer

fine focus

would probably be advised as you apparently intend photographic

application?

I wonder though, what low levels of vibration you are referring

to? In

practice, a target object would be acquired and focused upon and

the mirror

locked. Then the micrometric focus of the crayford focuser would

be used

along with the ccd software to attain the optimum pixel value.

The

crayford

focus would also allow for periodic fine refocus adjustment

between

images

to compensate for thermal changes as the telescope cools without

causing any

image shift or loss of centering.

The ideal solution would be to create a three-point focusing

scheme

which

would focus (move) the mirror on all three internal points of

support. They

could be tied together by a belt-driven DC servo motor. It could

be a

digital, software-driven or analog, manually electrically

operated

motor,

and this would drive the mirror focus with inherent stability

during focus

and would negate the need for an mirror lock. It may be possible

to

simplify the design so that a single focus knob would drive the

entire

mechanism manually.

Wayne E. Gondella
AFA Engineering Company
Pittsburgh, Pennsylvania

Date: Sat, 02 Mar 2002 12:34:45 -0000
From: "garynburk" <garyburk@h...>
Subject: Re: C14 mods (was: focuser grease)

Hi Wayne,
Have you had any experiance with putting mirror locks on C14s?
Needs to permit the primary to focus smoothly and with little

free

play, and then lock it in place without moving it and tightly

enough

to resist its own weight and low levels of vibration. This

would

address what I consider to be the great deficiency in the C14s
functionality.

Regards, Gary

I have an AP1200 on order to use with the C14. What height pier
should I use? The 48" standard seems like it would be too high when
you add the 21" of the AP1200. I am 5'-8" and might have a problem
getting the C14 into the losmandy dove at that height. Any
experience you can share?

Ken

--- In C14@y..., "W. Gondella" <gondella@s...> wrote:

The enlarged view shows a really, REALLY nice image!! Kudos rdc!

I should

ask where you bought the camera, where one can get specs on it and

what you

paid for it?

I bought it second hand. There is one on astromart now for about
$7500 or so. The chip is the TK1024 chip which was made by Tektronix
until they spun the CCD operation out to be a separate company (SITE,
[ ]). The TK1024 has been replaced by the
SI003 which is basically the same except the well depth is upped to
300K electrons rather than the 150K of the TK1024. Finger Lakes
Instruments makes the camera and has a website:

www.fli-cam.com

The Dream Machine is in their IMG line.

You can also see more information on it by looking at the following
link to my website:

Also, I must point out that a CM1400 (in the strict sense) was not

used, but

instead, a C14. Pictures like this are the result of excellent

stability

and tracking accuracy, neither of which are hallmarks of the CI-700

mount

(which makes a C14 into a CM1400), along with a ccd camera which is

a good

match to the telescope.

You are right about the CI700 mount. Have a look at my website and
you can see my experience with it and with the AP1200GTO which
replaced it.

Thanks for sharing those really fine pictures!

You are welcome, I am just happy someone enjoys looking at them
besides me!
Richard (rdc)

Wayne E. Gondella
AFA Engineering Company
Pittsburgh, Pennsylvania

Message: 2
Date: Mon, 04 Mar 2002 12:55:03 -0000
From: "rdcrisp" <rdcrisp@e...>
Subject: First light in a C14: FLI Dream Machine

I recently acquired an FLI Dream Machine camera using the TK1024
array. Over the weekend I tried it out with my CM1400/AP1200GTO
system.

The first results:

Hi Wayne,
Actually, I did not expect a good mirror lock to be a simple thing.
However, that doesn't mean it shouldn't be done. Once the cost of
the C14, guider,AP mount, camera, observatory and eypieces are summed
up the added cost of fabricating a lock may well be the next most
effective improvement.
The three point course focus mechanism you suggest might not be
overly complicated - perhaps three fine thread lead screws geared
together with the mirror floating on their cams and spring loaded
against them with a force just slightly greater then the mirrors'
weight. Such an arrangement would be reasonable for 0.001" stability
but it seems that getting much better than that would require high
precision (read that as "very expensive" parts). Again however, once
one jumps into the pool for a high quality mount, this may not
represent a large additional cost increment.

Do you know what Meade has done for the mirror locks on their new
LX200 GPS series?

Regards,
Gary



--- In C14@y..., "W. Gondella" <gondella@s...> wrote:

You won't like my answer:

First, to state the obvious, the mirror thimble should have an

extremely

close tolerance to the central baffle. Only a thin film of grease

can fit

between. Those who complain of excessive mirror shift might have

one of

several problems: 1). Excessive play between the parts due to wear
(inadequate grease) and age, or improper machining from the factory
requiring a total rebuild; 2). A mechanical problem resulting

from damaged

or improperly tightened cork and/or silicone seals around the

mirror stays.

Some mirror shift (albeit minor in the best at high power) is

inevitable and

unavoidable, otherwise the mirror couldn't move. Even Questars

have this

problem. A tensioning system can be devised, that would load the

mirror

thimble, but this still might not entirely eliminate mirror shift

during

focus, as the focusing design in an SCT is an inherently low-cost

approach

and the tensioning would induce minor torsional stress. However,

it might

work beautifully.

A mirror locking mechanism can be devised which would prohibit the

mirror

from shifting position, and it could be integrated with or without

the

tensioning system rather nicely, however it is unrealistic to

expect that

the mirror can be locked down without causing *some* movement of

the mirror,

as we are talking about extremely small (less than a thousands of

an inch)

movements beeing detectable at the eyepiece.

This would, however, permit smooth focus and with little or no free

play,

and would allow the mirror to be locked into place with a minimum

(or no)

movement that is possible, that would resist any outside forces

once set and

would be easy to implement. A crayford focuser with micrometer

fine focus

would probably be advised as you apparently intend photographic

application?

I wonder though, what low levels of vibration you are referring

to? In

practice, a target object would be acquired and focused upon and

the mirror

locked. Then the micrometric focus of the crayford focuser would

be used

along with the ccd software to attain the optimum pixel value. The

crayford

focus would also allow for periodic fine refocus adjustment between

images

to compensate for thermal changes as the telescope cools without

causing any

image shift or loss of centering.

The ideal solution would be to create a three-point focusing scheme

which

would focus (move) the mirror on all three internal points of

support. They

could be tied together by a belt-driven DC servo motor. It could

be a

digital, software-driven or analog, manually electrically operated

motor,

and this would drive the mirror focus with inherent stability

during focus

and would negate the need for an mirror lock. It may be possible to
simplify the design so that a single focus knob would drive the

entire

mechanism manually.

Wayne E. Gondella
AFA Engineering Company
Pittsburgh, Pennsylvania

Date: Sat, 02 Mar 2002 12:34:45 -0000
From: "garynburk" <garyburk@h...>
Subject: Re: C14 mods (was: focuser grease)

Hi Wayne,
Have you had any experiance with putting mirror locks on C14s?
Needs to permit the primary to focus smoothly and with little free
play, and then lock it in place without moving it and tightly

enough

to resist its own weight and low levels of vibration. This would
address what I consider to be the great deficiency in the C14s
functionality.

Regards, Gary

--- In C14@y..., "W. Gondella" <gondella@s...> wrote:

The corrector is a very, very weak lens. It doesn't sound right

that a

small tweek in alignment would noticably alter the color of the

system.

Does color get worse and worse as you go further off axis?

I will check that.

Is the fringe

concentric to the Airy disc, and have you tried different

eyepieces?

No not yet.

What

eyepiece are you using?

Nagler series usually 7,9 or higher depending on seeing.

Further, there is little chance the primary could

be tilted or off-center, as the mirror stay forces the glass into

alignment

with machined metal surfaces. However, the corrector *could* be

off-center,

and can be easily remedied.

I'll take some measurements.
Wayne, Thanks for the reply. Ed

Wayne E. Gondella
AFA Engineering Company
Pittsburgh, Pennsylvania

Date: Sat, 02 Mar 2002 18:29:50 -0000
From: "ejoganic" <astron1@m...>
Subject: alignment of optical surfaces

I am new to this group and find the discussion on component
alignment interesting. My C14 is a little unusual. When I

collimate

I start with touching up the secondary alignment by centering the
secondary shadow. When I bring a star into center field there is

a

slight but noticeable color fringe. Finally I make a very slight
correction to eliminate the fringe. This gives the sharpest image
and smallest stars. It is intereting when I defocus because the
secondary shadow is then very slightly but noticeably eccentric.

It

would seem that one of the elements is tilted. Has anyone

noticed a

slight red to blue fringe at star edges or anything like this?

Check

the next time you are observing. It would be interesting to know
what you find. Any ideas on where the misalignment is? I would

guess

you could shim the corrector to make it parallel to the primary

but

would have to offset the center to keep the optical axis aligned.
Doesn't sound easy. Any ideas? Ed

--- In C14@y..., "W. Gondella" <gondella@s...> wrote:

The enlarged view shows a really, REALLY nice image!! Kudos rdc!

I should

ask where you bought the camera, where one can get specs on it and

what you

paid for it?

The Dream Machine I bought is one of the first ones made. I purchased
it second hand for a fair price (there's one on Astromart right now
that's in the right price range).

FLI (Finger Lakes Instruments) has a web site and that is:

www.fli-cam.com

The "dream machine" is in their IMG family of cameras.

Mine uses the now unavailable Tektronix TK1024 ccd array. Tektronix
spun their CCD operation out a few years back and that particular
chip has been discontinued and replaced with the SI003. The name of
that company is SITE.

The key specs on the imaging chip are basically the same as the new
SITE chip except that the SI003 has a 300K electron well depth rather
than the 150K depth mine has. The SI003 array also has slightly
higher quantum efficency.

Mine is a thinned array that is back illuminated and AR coated.

Also, I must point out that a CM1400 (in the strict sense) was not

used, but

instead, a C14. Pictures like this are the result of excellent

stability

and tracking accuracy, neither of which are hallmarks of the CI-700

mount

(which makes a C14 into a CM1400), along with a ccd camera which is

a good

match to the telescope.

You are right about the difference between my AP1200GTO mount and
the CI700 it replaced. I call your attention to the following URL
which shows my personal experience comparing M57 shot through the
same gear, changing the mount from the CI700 the AP1200GTO.

Thanks for sharing those really fine pictures!

I am just happy that someone is enjoying them.

Richard (rdc)

My recent first light experience using the large format Dream Machine
camera showed serious vignetting with the C14.

I used an Optec TCF-S focuser attached directly to the back of the
scope, followed by a Celestron F6.3 reducer/corrector which screwed
directly onto the shutter housing of the DM.

The vignetting was pretty horrible and really shows up in the Comet
Ikeya-Zhang image:

I tried the setup last night with no focal reducer and still got
pretty bad vignetting, which showed up in my flats. Unfortunately the
clouds covered things up before I was able to really get any images.

I am planning to remove the OPTEC focuser to get the camera closer to
the back of the scope for the next outing.

Does anyone here have experience using the large format ccd chips
with a c14? I'd be interested in your experiences regarding the
vignetting.
rdc

The enlarged view shows a really, REALLY nice image!! Kudos rdc! I should
ask where you bought the camera, where one can get specs on it and what you
paid for it?

Also, I must point out that a CM1400 (in the strict sense) was not used, but
instead, a C14. Pictures like this are the result of excellent stability
and tracking accuracy, neither of which are hallmarks of the CI-700 mount
(which makes a C14 into a CM1400), along with a ccd camera which is a good
match to the telescope.

Thanks for sharing those really fine pictures!

Wayne E. Gondella
AFA Engineering Company
Pittsburgh, Pennsylvania

I recently acquired an FLI Dream Machine camera using the TK1024
array. Over the weekend I tried it out with my CM1400/AP1200GTO
system.

The first results:



I also shot a comet that I still need to look up:



I decided to shoot with a Celestron f6.3 reducer despite being
concerned about vignetting. The comet shot shows the vignetting
pretty strongly. Unfortunately I did not manage to take a flat to
help correct the vignetting.
rdc

The corrector is a very, very weak lens. It doesn't sound right that a
small tweek in alignment would noticably alter the color of the system.
Does color get worse and worse as you go further off axis? Is the fringe
concentric to the Airy disc, and have you tried different eyepieces? What
eyepiece are you using? Further, there is little chance the primary could
be tilted or off-center, as the mirror stay forces the glass into alignment
with machined metal surfaces. However, the corrector *could* be off-center,
and can be easily remedied.

Wayne E. Gondella
AFA Engineering Company
Pittsburgh, Pennsylvania

Date: Sat, 02 Mar 2002 18:29:50 -0000
From: "ejoganic" <astron1@...>
Subject: alignment of optical surfaces

I am new to this group and find the discussion on component
alignment interesting. My C14 is a little unusual. When I collimate
I start with touching up the secondary alignment by centering the
secondary shadow. When I bring a star into center field there is a
slight but noticeable color fringe. Finally I make a very slight
correction to eliminate the fringe. This gives the sharpest image
and smallest stars. It is intereting when I defocus because the
secondary shadow is then very slightly but noticeably eccentric. It
would seem that one of the elements is tilted. Has anyone noticed a
slight red to blue fringe at star edges or anything like this? Check
the next time you are observing. It would be interesting to know
what you find. Any ideas on where the misalignment is? I would guess
you could shim the corrector to make it parallel to the primary but
would have to offset the center to keep the optical axis aligned.
Doesn't sound easy. Any ideas? Ed



________________________________________________________________________
________________________________________________________________________

Message: 2
Date: Sat, 2 Mar 2002 14:38:26 -0500
From: "W. Gondella" <gondella@...>
Subject: Re: Mirror Locks

You won't like my answer:

First, to state the obvious, the mirror thimble should have an extremely
close tolerance to the central baffle. Only a thin film of grease can fit
between. Those who complain of excessive mirror shift might have one of
several problems: 1). Excessive play between the parts due to wear
(inadequate grease) and age, or improper machining from the factory
requiring a total rebuild; 2). A mechanical problem resulting from

damaged

or improperly tightened cork and/or silicone seals around the mirror

stays.

Some mirror shift (albeit minor in the best at high power) is inevitable

and

unavoidable, otherwise the mirror couldn't move. Even Questars have this
problem. A tensioning system can be devised, that would load the mirror
thimble, but this still might not entirely eliminate mirror shift during
focus, as the focusing design in an SCT is an inherently low-cost approach
and the tensioning would induce minor torsional stress. However, it might
work beautifully.

A mirror locking mechanism can be devised which would prohibit the mirror
from shifting position, and it could be integrated with or without the
tensioning system rather nicely, however it is unrealistic to expect that
the mirror can be locked down without causing *some* movement of the

mirror,

as we are talking about extremely small (less than a thousands of an inch)
movements beeing detectable at the eyepiece.

This would, however, permit smooth focus and with little or no free play,
and would allow the mirror to be locked into place with a minimum (or no)
movement that is possible, that would resist any outside forces once set

and

would be easy to implement. A crayford focuser with micrometer fine focus
would probably be advised as you apparently intend photographic

application?

I wonder though, what low levels of vibration you are referring to? In
practice, a target object would be acquired and focused upon and the

mirror

locked. Then the micrometric focus of the crayford focuser would be used
along with the ccd software to attain the optimum pixel value. The

crayford

focus would also allow for periodic fine refocus adjustment between images
to compensate for thermal changes as the telescope cools without causing

any

image shift or loss of centering.

The ideal solution would be to create a three-point focusing scheme which
would focus (move) the mirror on all three internal points of support.

They

could be tied together by a belt-driven DC servo motor. It could be a
digital, software-driven or analog, manually electrically operated motor,
and this would drive the mirror focus with inherent stability during focus
and would negate the need for an mirror lock. It may be possible to
simplify the design so that a single focus knob would drive the entire
mechanism manually.

Wayne E. Gondella
AFA Engineering Company
Pittsburgh, Pennsylvania

Date: Sat, 02 Mar 2002 12:34:45 -0000
From: "garynburk" <garyburk@...>
Subject: Re: C14 mods (was: focuser grease)

Hi Wayne,
Have you had any experiance with putting mirror locks on C14s?
Needs to permit the primary to focus smoothly and with little free
play, and then lock it in place without moving it and tightly enough
to resist its own weight and low levels of vibration. This would
address what I consider to be the great deficiency in the C14s
functionality.

Regards, Gary

________________________________________________________________________
________________________________________________________________________



Your use of Yahoo! Groups is subject to

You won't like my answer:

First, to state the obvious, the mirror thimble should have an extremely
close tolerance to the central baffle. Only a thin film of grease can fit
between. Those who complain of excessive mirror shift might have one of
several problems: 1). Excessive play between the parts due to wear
(inadequate grease) and age, or improper machining from the factory
requiring a total rebuild; 2). A mechanical problem resulting from damaged
or improperly tightened cork and/or silicone seals around the mirror stays.

Some mirror shift (albeit minor in the best at high power) is inevitable and
unavoidable, otherwise the mirror couldn't move. Even Questars have this
problem. A tensioning system can be devised, that would load the mirror
thimble, but this still might not entirely eliminate mirror shift during
focus, as the focusing design in an SCT is an inherently low-cost approach
and the tensioning would induce minor torsional stress. However, it might
work beautifully.

A mirror locking mechanism can be devised which would prohibit the mirror
from shifting position, and it could be integrated with or without the
tensioning system rather nicely, however it is unrealistic to expect that
the mirror can be locked down without causing *some* movement of the mirror,
as we are talking about extremely small (less than a thousands of an inch)
movements beeing detectable at the eyepiece.

This would, however, permit smooth focus and with little or no free play,
and would allow the mirror to be locked into place with a minimum (or no)
movement that is possible, that would resist any outside forces once set and
would be easy to implement. A crayford focuser with micrometer fine focus
would probably be advised as you apparently intend photographic application?
I wonder though, what low levels of vibration you are referring to? In
practice, a target object would be acquired and focused upon and the mirror
locked. Then the micrometric focus of the crayford focuser would be used
along with the ccd software to attain the optimum pixel value. The crayford
focus would also allow for periodic fine refocus adjustment between images
to compensate for thermal changes as the telescope cools without causing any
image shift or loss of centering.

The ideal solution would be to create a three-point focusing scheme which
would focus (move) the mirror on all three internal points of support. They
could be tied together by a belt-driven DC servo motor. It could be a
digital, software-driven or analog, manually electrically operated motor,
and this would drive the mirror focus with inherent stability during focus
and would negate the need for an mirror lock. It may be possible to
simplify the design so that a single focus knob would drive the entire
mechanism manually.

Wayne E. Gondella
AFA Engineering Company
Pittsburgh, Pennsylvania