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Posts Made By: John Biretta

May 22, 2008 11:05 AM Forum: CCD Imaging and Processing/Solar System

Jupiter's 3rd Red Spot

Posted By John Biretta


October 6, 2008 03:37 PM Forum: Refractors

Re: cleaning a flourite doublet

Posted By John Biretta

I do not know how much experience you have taking lens assemblies
apart, nor what tools you have. I would suggest to not
take it apart until you develope some experience working on
cheaper lenses, etc. It is easy to wedge or chip / crack
the glasses without some special methods and care removing
and inserting them.

The front element is normal glass, and you should be OK with
camera lens cleaning methods there. Just be careful that
no fluid, etc. runs into the lens and creeps between the
elements. The rear element is Fluorite,
and I would suggest to leave that one alone until you get
some experience and advice from experts. A simple blower
bulb is fairly safe on the exposed surfaces of both

If you can count the number of dust particles between the
elements, it is probably not worth worrying about.

October 9, 2008 02:41 PM Forum: CCD Imaging and Processing/Deep Sky

Re: Dark blobs on CCD

Posted By John Biretta

These are dust spots on the CCD window or filter inside
the camera. They can be very difficult to remove due
to static electricity -- there is an electrical attraction
between the dust and window. You can easily move them around,
but getting them "off" the window is much more difficult.
Some type of anit-static brush or swab, or cleaning fluid
might be needed. Careful!

November 17, 2008 02:40 PM Forum: CCD Imaging and Processing/Solar System

Re: Jupiter NOVEMBER 15th, and Long-in-the-Tooth!

Posted By John Biretta

The CA might be due to the atmosphere at low elevation, not the
eyepiece. The "RGB Align" feature in Registax can probably reduce
the effect somewhat.

January 27, 2009 01:52 PM Forum: Reflectors

Re: check r.c. of convex surface

Posted By John Biretta

There must be some way to do this with a laser
and a gauge block. Get some lumber scraps and
clamps and arrange them on a table so you have a
long piece that slides precisely against another
long piece in one direction. Use another piece
to make an accurate end stop for the slide.
Putty or wax the mirror to the sliding piece
parallel to the sliding direciotn. Push the sliding
piece against the end stop. Put a laser on
the table a few feet away perpendicular to
the sliding motion.
Aim the laser at the mirror and adjust/shim everything
so the laser hits roughly in the center of the mirror
and exactly goes back to the laser. Now use a
gauge block (or something with a very accurate
thickness) between the sliding wood (carrying the mirror)
and end stop to slide the mirror sideways by a very
accurate amount (like 1.000 inch). Measure how far the
laser beam reflection moved back at the laser.
Do some math and you have the answer.

March 17, 2009 10:53 AM Forum: CCD Imaging and Processing/Solar System

Nice HST video of recent Saturn transits

Posted By John Biretta

August 22, 2009 02:15 PM Forum: Mounts

Re: Found G-11! Software for Gemini?

Posted By John Biretta

No software is needed. There are probably ways to interface it to
a computer, if you really wamted to.

You can download a manual at

August 29, 2009 11:03 AM Forum: CCD Imaging and Processing/Solar System

Jupiter Double Shadow Transit 8/27

Posted By John Biretta

Jupiter + 3 moons + 2 shadows from the other night. Moons from left to right are Io, Ganymede (in transit as dark patch near right hand limb), and Europa.

C14 w/fans + Baader T prism + Baader Fluorite Converter + Astronmik RGB + 4 deg wedge prism + SKYnyx2-0m. Operating around F30. 66 fps. Exposure time R:G:B 40s:40s:70s. Seeing 4/10. Processed in K3ccd, Registax, and Corel Paint Shop Pro Photo.

October 28, 2009 02:28 PM Forum: Meade

12" LightBridge optics upgrade?

Posted By John Biretta

I recently picked up 12" LightBridge to use during a dark skies trip out west. Had it shipped direct to the site, used it for a week, then left it with some astro-friends out there. I'm generally not a big fan of Meade products, but I have to say I was very impressed with the design and mechanics -- highly useable scope. Very solid OTA. Decent 2-speed focuser. I did have to shim the focuser 0.03" on one side to nail the collimation. And some Bob's Knobs and springs were a good upgrade. But considering the price and that it was "in stock" lots of places, I was very impressed.

Optics were pretty good, though I wanted better. Star testing with a 5mm Nagler showed the primary mirror had some astigmatism -- maybe quarter wave -- that rotated around with the mirror. Meade probably only guarantees "diffraction limited" which I feel it was -- Epsilon Lyra showed reasonable Airy disks.

This leads to my question: Has anyone had any luck upgrading the mirrors, or getting them refigured? It seemed to be a slightly odd size -- about 303mm diameter. The mirror cell design only has about 1mm of leeway on the mirror diameter, so a standard 12.5" drop-in replacement seems out of the question.

January 30, 2010 11:49 PM Forum: Telescope Making

Spherical Aberration Plates

Posted By John Biretta

A curious new product has appeared in the latest Edmund
Industrial Optics catalog -- Spherical Aberration Plates.
These must be like miniature Schmidt corrector plates.
Available in 0.25, 0.5, and 1 wave corrections, both
+ and - correction, and diameters up to 2".

These must open up a wide range of new possibilities for
scopes. Perhaps make a Newtonian with a smooth spherical
mirror and introduce spherical correction near the eyepiece.
Probably the useful field would be small, but certainly
sufficient for planetary observing or other high-power

Or fix that big scope with 1/4 wave spherical error
using a filter-like device that would thread-on to
eyepieces or attach inside the focuser.

Or make a device to adjust the spherical correction of
your scope. For example get +0.25 wave and -0.25 wave
plates, and adjust the spacing between them to make a
variable -0.1 to +0.1 wave spherical adjustment.

They state these are on BK7 substrates. I presume they
are using MRF technology to "machine" the curves onto
the glass. Wavefront accuracy stated to be 1/16 wave
a 587nm (in the paper catalog, though online says 1/10 wave).
I suppose one might wonder if the surface is very rough, etc.

What do folks think?