Posts Made By: Roland Christen

To all,
We have notified everyone on our list and are now inviting anyone who wishes to purchase a 900GTO to place their order. Current delivery for new orders will begin in November. This is a perfect mount for mid-sized scopes and is still quite portable.

Here is the link to detailed information. We have updated this information including a better description of the many, varied ways to control your mount:
http://www.astro-physics.com/products/mounts/900gto/900gto.htm

Check it out!

Clear Skies!

Marj Christen
Vice President
Astro-Physics, Inc
11250 Forest Hills Road
Machesney Park, IL 61115
Phone: 815-282-1513
Fax: 815-282-9847
www.astro-physics.com
Please include this e-mail with your response.

To all,
We have notified everyone on our list and are now inviting anyone who wishes to purchase a 900GTO to place their order. Current delivery for new orders will begin in November. This is a perfect mount for mid-sized scopes and is still quite portable.

Here is the link to detailed information. We have updated this information including a better description of the many, varied ways to control your mount:
http://www.astro-physics.com/products/mounts/900gto/900gto.htm

Check it out!

Clear Skies!

Marj Christen
Vice President
Astro-Physics, Inc
11250 Forest Hills Road
Machesney Park, IL 61115
Phone: 815-282-1513
Fax: 815-282-9847
www.astro-physics.com
Please include this e-mail with your response.

Just a quick 2 night effort at this object with 305mm F3.8 R-H astrograph and SBIG STL11K camera, Baader 7nm H-a filter.

Rolando

So many choices, result is that sometimes confusion reigns. So what are these different types?

The attached image shows a diagram that places all the available glasses from the major manufacturers according to their dispersions. It is well known (and has been known since Newton's time) that the longitudinal chromatic aberration (or secondary color) of any two or more glasses depends on their partial dispersions.

If two glasses have the same partial dispersion, then the resultant color error will be zero. However, to make a practical lens that has some realistic focal ratio, the dispersion Vd of the two glasses must be far apart, ideally 2:1 or more.

A quick look at the diagram shows that almost all glasses with few exceptions, lie close to each other on the Abbe Normal line. Therefore most of these glasses will produce the same color error of 1 part in 1800, give or take. The standard for achromats is the venerable BK7 - F4 (or F2) combination which produces almost exactly that. So, for a lens of 1000mm FL, the blue and red will be approximately 1/2 mm longer than the green. The violet will be even further out, and that can be calculated using the partial dispersion from red to violet, versus this chart which shows partials from red to blue.

I did a quick combine of some favorite glasses that can produce a semi-apo, ED doublet apo, Fluorite doublet and highly corrected triplet lens, along with their respective color error. Certainly others exist with slightly different corrections, but these are the glasses that you can actually get in reasonable quality levels.

Note one interesting glass that was touted some years ago as a "semi-ED" glass, which is FK5. "FK" is the Schott designation for Flour-crown, and this type of glass has some fluorite in it, but in this case not much at all. In any case, as you can see, there really are no mates far enough separated in dispersion (Vd) that would produce any sort of meaningful color correction, any better that the plain vanilla BK7-F4 variety.

So, there you are. There is no free lunch.

Rolando

I was recently at an imaging conference in Chile. Got to see two of the large observatories in the Andes mountains. Also was able to do some imaging thanks to Daniel Verschatse and his observatory at his mountain retreat near Cerro Tololo. He let me use his 155EDF refractor and STL11K astrocamera.

This is a quick LRGB, 3 x 5 minute exposure. This Jpeg cannot show the real detail since it's highly compressed to fit the 500k limit. It's also heavily cropped.

Rolando

Using the same 155EDF refractor, I was able to get three exposures of 10 minutes each. The sky down there in the Andes was ultra-clear, compared to what I am normally used to. Lots of deep sky objects were naked eye that require at least binoculars up here where I usually image.

Of course, this image has some noise, it was only 3 exposures of 10 minutes, but it does show what kind of detail can be achieved with modest apertures under pristine skies.

Rolando

On my recent trip to Chile I captured these two observatories high up in the Andes as we were flying by LaSerena, Chile.

Rolando

Hi All,

For those of you interested in how the other side of the world does things, here are a few images of the imaging conference, etc.

First pix shows myself and Ignatio, our Argentinian customer and frequent poster on our AP user group, in the facility of ESO headquarters where the conference was held.

Rolando

.... and leaves him wanting. The R8 Audi supercar with 420hp high revving V8 hung on from 65 to --- but Roush Mustango stayed 1 car length ahead.

I have to say, the Audi engine revving to 8500 RPM was sweet music, reminded me of a Ferrari or Lambo.

Hi All,

I recently received some photos from Gilles Cohen. He is presently at Dome C in Antarctica to do some work on the Ovision scopes that are set up for the French research team from the University of Nice. By the way,
all mounts are working well, having operated through a winter of temperatures approaching -100C.

http://groups.yahoo.com/group/ap-ug/photos/album/355730958/pic/list

Here is what he said in his e-mail:

Hello,

here is a picture I took this afternoon using a tripod.
I needed three days to get the good framing and light angle...sorry, I
could not remove my hood, I did not want to get frostbite within a few
seconds. Touching a screw without gloves burns instantly your finger.

I have several others, that I'll send on a DVD.
You can post this one if you want, no problemo, it is free use for
Astro-Physics :-))))) It is downsized to fit the internet bandpass of
the base.

By the way it is quite hot today, except the wind...

Current conditions
Temperature : -34.7 °C
Dew point : -38.6 °C
Wind-chill : -48
Relative humidity : 67.5 %
Pressure : 635.1 hPa
Wind origin : 193.5 °, south-south-west
Wind speed : 4.9 m/s

Gilles