DIMM seeing test, seeking prism source

"Del Johnson" delastro@{right star in Orion's belt}.sdsu.edu wrote in
message ...
Thad,

I just set up a DIMM system here at San Diego State University. The
telescope is a 12-inch Meade LX-200 equipped with a flip mirror and an
ST-5
CCD camera. The telescope has an aperture mask with four small openings
(about 2 inches diameter or so). One opening is a one arc-minute prism
and
the other three are just pass-throughs. The opening opposite the prism is
used for actual DIMM measurements. The other two openings are for
focusing
and are otherwise covered up. Unfortunately, I don't know where the prism
originally came from as we received it from another individual.

The purpose of the prism is to create a second star image while in focus,
thus allowing for a differential positional measurement. The general
idea
is that the change in separation is due to turbulence, and that measuring
the differential is a lot easier and more reliable than trying to measure
a
single star width. The software was written by Armin Rest during the
course
of his studies at the University of Washington. Here is some information:

http://www.astro.washington.edu/rest/dimm/

Del Johnson


Del,
Do you know if there is any way to obtain a copy of the DIMM software for
personal use ? Even if it only works with SBIG ccd cameras it would be a
valuable tool for me at this time .

Thank you,
Matt Tudor

"Del Johnson" delastro@{right star in Orion's belt}.sdsu.edu wrote in message ...
Andrea,

Hi Del,


The "Big Guys" actually use Meade SCTs for DIMM stations. Here is the one
at Cerro Tololo:

http://www.ctio.noao.edu/telescopes/dimm/dimm.html

We have DIMM set up on a 12" Meade here at SDSU and I may move it to a 10"
Meade in a RoboDome. The point is that DIMM does not require a professional
grade telescope.

That's exactly what I wrote.


Why is it that you say that precise positioning and S/N is required? The
whole point of DIMM is a differential measurement so only casual guiding
corrections are required. Also, one typically selects a bright star so S/N
is not an issue.

I haven't said anything about guiding precision. Only errors in
meauring the PSF centroid. Even with a bright star in a small aperture
at high focal ratios with not so sensitive CCD with exposures as short
as possible (10 ms or shorter) S/N and photon noise might be a
problem.

Regards

Andrea T.

"Del Johnson" delastro@{right star in Orion's belt}.sdsu.edu wrote in message ...
Andrea,

Hi Del,


The "Big Guys" actually use Meade SCTs for DIMM stations. Here is the one
at Cerro Tololo:

http://www.ctio.noao.edu/telescopes/dimm/dimm.html

We have DIMM set up on a 12" Meade here at SDSU and I may move it to a 10"
Meade in a RoboDome. The point is that DIMM does not require a professional
grade telescope.

That's exactly what I wrote.


Why is it that you say that precise positioning and S/N is required? The
whole point of DIMM is a differential measurement so only casual guiding
corrections are required. Also, one typically selects a bright star so S/N
is not an issue.

I haven't said anything about guiding precision. Only errors in
meauring the PSF centroid. Even with a bright star in a small aperture
at high focal ratios with not so sensitive CCD with exposures as short
as possible (10 ms or shorter) S/N and photon noise might be a
problem.

Regards

Andrea T.

I cannot speak for the author Armin Rest. It might be free for individuals.
We received it in an equipment trade from another individual. From what I
have seen the software specifically supports the ST-5C and ST-237 cameras.
I run the software on Windows 98 as I have had troubles getting it to run on
Windows 2000. I know that it does but only if set up just right and the
particulars are not documented..

Del Johnson


"matt" wrote in message
...


Del,
Do you know if there is any way to obtain a copy of the DIMM software for
personal use ? Even if it only works with SBIG ccd cameras it would be a
valuable tool for me at this time .

Thank you,
Matt Tudor

I cannot speak for the author Armin Rest. It might be free for individuals.
We received it in an equipment trade from another individual. From what I
have seen the software specifically supports the ST-5C and ST-237 cameras.
I run the software on Windows 98 as I have had troubles getting it to run on
Windows 2000. I know that it does but only if set up just right and the
particulars are not documented..

Del Johnson


"matt" wrote in message
...


Del,
Do you know if there is any way to obtain a copy of the DIMM software for
personal use ? Even if it only works with SBIG ccd cameras it would be a
valuable tool for me at this time .

Thank you,
Matt Tudor

I guess when you said "precise positioning" you were not talking about
telescope pointing...

The setup at Cerra Tololo doesn't seem to have any problem with 5-10ms
integrations. BTW, this is done with custom firmware as such short
integrations are not normally suported by SBIG cameras. The new version of
the software can extrapolate from longer to shorter integration times.

Not sure why you are being so negative. The system has been working just
fine for the last few years and it is easy to do with amateur-grade
equipment (if you can get hold of the software).

Del Johnson


"andrea tasselli" wrote in message
I haven't said anything about guiding precision. Only errors in
meauring the PSF centroid. Even with a bright star in a small aperture
at high focal ratios with not so sensitive CCD with exposures as short
as possible (10 ms or shorter) S/N and photon noise might be a
problem.

Regards

Andrea T.

I guess when you said "precise positioning" you were not talking about
telescope pointing...

The setup at Cerra Tololo doesn't seem to have any problem with 5-10ms
integrations. BTW, this is done with custom firmware as such short
integrations are not normally suported by SBIG cameras. The new version of
the software can extrapolate from longer to shorter integration times.

Not sure why you are being so negative. The system has been working just
fine for the last few years and it is easy to do with amateur-grade
equipment (if you can get hold of the software).

Del Johnson


"andrea tasselli" wrote in message
I haven't said anything about guiding precision. Only errors in
meauring the PSF centroid. Even with a bright star in a small aperture
at high focal ratios with not so sensitive CCD with exposures as short
as possible (10 ms or shorter) S/N and photon noise might be a
problem.

Regards

Andrea T.