Micrometer eyepiece for astrometry

Does any one know where can I buy one of these for pinpoint accuracy
in astrometric measurements? Ideally it will be a standard 1.25" size,
easy fit on my telescope's eyepiece barrel. I am not aware of
availability outside of professional observing circles, but its always
nice to enquire - just in case.

I'd like to use it primarily for separation and P.A. fixing of fast
moving visual binaries and also for precise tracking of proper motions
of selected nearby stars.

cheers
Abdul Ahad

On 30 Apr 2004 07:51:14 -0700, (Abdul Ahad) wrote:

Does any one know where can I buy one of these for pinpoint accuracy
in astrometric measurements? Ideally it will be a standard 1.25" size,
easy fit on my telescope's eyepiece barrel. I am not aware of
availability outside of professional observing circles, but its always
nice to enquire - just in case.

I'd like to use it primarily for separation and P.A. fixing of fast
moving visual binaries and also for precise tracking of proper motions
of selected nearby stars.

Filar micrometers are hopelessly obsolete for astronomical applications, so I
doubt you can even find a new one (astrometry is done from CCD data now, because
it is much easier and much more accurate). So if you want one of these
eyepieces, I have two suggestions: (1) try the astronomy department at your
local university or college, as they may well have one collecting dust on some
shelf, (2) look for one intended for microscopy- although they are quickly
becoming obsolete here, also, in favor of digital measurement, you can still
find new ones, and I would think it wouldn't be too hard to adapt one for
telescopic use.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

"Abdul Ahad" wrote in message
om...
Does any one know where can I buy one of these for pinpoint accuracy
in astrometric measurements? Ideally it will be a standard 1.25" size,
easy fit on my telescope's eyepiece barrel. I am not aware of
availability outside of professional observing circles, but its always
nice to enquire - just in case.

I'd like to use it primarily for separation and P.A. fixing of fast
moving visual binaries and also for precise tracking of proper motions
of selected nearby stars.

cheers
Abdul Ahad

Meade do (or at least used to) Astrometric Illuminated Reticles (12mm)
Regards
Ed

"Abdul Ahad" wrote in message
om...
Does any one know where can I buy one of these for pinpoint accuracy
in astrometric measurements?

sure, www.scopetronix.com sells reticle eyepieces for exactly that purpose. It costs US$129.95
(I just looked it up).

"Chris L Peterson" wrote in message
...
On 30 Apr 2004 07:51:14 -0700, (Abdul Ahad) wrote:

Does any one know where can I buy one of these for pinpoint accuracy
in astrometric measurements? Ideally it will be a standard 1.25" size,
easy fit on my telescope's eyepiece barrel. I am not aware of
availability outside of professional observing circles, but its always
nice to enquire - just in case.

I'd like to use it primarily for separation and P.A. fixing of fast
moving visual binaries and also for precise tracking of proper motions
of selected nearby stars.

Filar micrometers are hopelessly obsolete for astronomical applications, so I
doubt you can even find a new one (astrometry is done from CCD data now, because
it is much easier and much more accurate).

well it may be true that ccd is more accurate, but it is easy to buy a new reticle eyepiece at
www.scopetronix.com.

(Abdul Ahad) wrote in
om:

Does any one know where can I buy one of these for pinpoint accuracy
in astrometric measurements? Ideally it will be a standard 1.25" size,
easy fit on my telescope's eyepiece barrel. I am not aware of
availability outside of professional observing circles, but its always
nice to enquire - just in case.

I'd like to use it primarily for separation and P.A. fixing of fast
moving visual binaries and also for precise tracking of proper motions
of selected nearby stars.

cheers
Abdul Ahad

this might be what you are looking for

http://www.lomoplc.com/Micrometer%20Eyepieces.htm

On Fri, 30 Apr 2004 22:53:26 +0200, "md" not given to avoid spam wrote:

well it may be true that ccd is more accurate, but it is easy to buy a new reticle eyepiece at
www.scopetronix.com.

Perhaps, but a reticle EP is even more inaccurate for this purpose. The standard
instrument used to be a filar micrometer, an eyepiece with a pair of markers
that could be rotated and spaced to get the position angle and separation of two
stars- very much different (and quite a bit more accurate) than a simple fixed
reticle EP.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

mark wrote in message 1.5...
(Abdul Ahad) wrote in
om:

Does any one know where can I buy one of these for pinpoint accuracy
in astrometric measurements? Ideally it will be a standard 1.25" size,
easy fit on my telescope's eyepiece barrel. I am not aware of
availability outside of professional observing circles, but its always
nice to enquire - just in case.

I'd like to use it primarily for separation and P.A. fixing of fast
moving visual binaries and also for precise tracking of proper motions
of selected nearby stars.

cheers
Abdul Ahad

this might be what you are looking for

http://www.lomoplc.com/Micrometer%20Eyepieces.htm

In principle, yes (esp. the filar one), but note:

"... can be clamped on any eyepiece tube with an outside diameter of
25mm or less. The graduated micrometer knob drives the crossline
across the field of view. The precise mechanism assures smooth
operation and accurate measurement of objects under the microscope.
One full revolution of the micrometer knob corresponds to 1 mm of the
crossline movement."

It ain't gonna clamp on any of your standard 1-1/4" telescope
eyepieces.

On 30 Apr 2004 23:04:35 -0700, (Thad Floryan) wrote:

http://www.lomoplc.com/Micrometer%20Eyepieces.htm

In principle, yes (esp. the filar one), but note:

"... can be clamped on any eyepiece tube with an outside diameter of
25mm or less. The graduated micrometer knob drives the crossline
across the field of view. The precise mechanism assures smooth
operation and accurate measurement of objects under the microscope.
One full revolution of the micrometer knob corresponds to 1 mm of the
crossline movement."

It ain't gonna clamp on any of your standard 1-1/4" telescope
eyepieces.

Because it is made for microscopes. Might be possible to adapt, though- I know
people have used microscope EPs on telescopes. But it looks like this filar
micrometer doesn't have a calibrated rotation system, so it would only be useful
for separation, not angular measurements.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

"Chris L Peterson" wrote in message
...
On 30 Apr 2004 07:51:14 -0700, (Abdul Ahad)
wrote:

Does any one know where can I buy one of these for pinpoint accuracy
in astrometric measurements? Ideally it will be a standard 1.25" size,
easy fit on my telescope's eyepiece barrel. I am not aware of
availability outside of professional observing circles, but its always
nice to enquire - just in case.

I'd like to use it primarily for separation and P.A. fixing of fast
moving visual binaries and also for precise tracking of proper motions
of selected nearby stars.


I'm not sure what Ahad means by "fast moving" visual binaries but there are
very few that move significantly in, say, 2-3 years, that would be
detectable in an amateur telescope. Typical periods of the "fast" ones are
over 50 years. One of the fastest, Delta Equulei, has a period of 5.7 years
but is detectable as double only in large telescopes (over 24-in aperture).

Filar micrometers are hopelessly obsolete for astronomical applications,
so I
doubt you can even find a new one (astrometry is done from CCD data now,
because
it is much easier and much more accurate). So if you want one of these
eyepieces, I have two suggestions: (1) try the astronomy department at
your
local university or college, as they may well have one collecting dust on
some
shelf, (2) look for one intended for microscopy- although they are quickly
becoming obsolete here, also, in favor of digital measurement, you can
still
find new ones, and I would think it wouldn't be too hard to adapt one for
telescopic use.

There is an interesting bias that results from getting separation and
position angle from x,y coordinates on a CCD and then following classical
orbit solution methods. The solution can be done independently from
micrometer RHO and THETA measurements (elements like e and omega have to be
found from both) but transformation to/from x and y differences into RHO and
THETA leads to subtle errors in the weights that lead to mistakes and biases
in the final results.

So care has to be taken to use a measurement in exactly the way it was first
taken.

For visual work (not CCDs) the only proper method is to measure angle and
separation directly. Visual observing has the advantage that seeing
fluctuations are not smeared during the exposure, hence observing to the
diffraction limit is much easier.

I'll agree that buying a filar micrometer can be difficult these days.

--
Mike Dworetsky

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