M82 from a 16inch Meade in Kildare

I got a Moonlite focuser recently which connects directly onto the 4" thread on the back of the OTA. The focuser has dual speed, is rotatable and has a t-thread in the drawtube. The t-thread is handy if you want to use a focal reducer although requires a bit of work to remove the focuser to put it on. Ideal for astrphotography though.
www.astroshot.com/Mount/focuser.jpg
From the graph in Chris Lord's paper, every inch added to the rear of the scope adds 3.2inches to the focal length.
However, Chris Lord's paper and calcs assume of course that the primary mirror is exactly f/2 and the secondary is exactly f/5. In reality, I doubt that Meade can match this exactly with every SCT. Any slight deviation from these could significantly change the focal length, and considering how dfficult it must be to shape a 16" mirror to f/2, then it is likely to vary somewhat.
Michael.

Michael --

That Moonlight adapter is quite a bit shorter than the Starlight Instruments one, and the whole setup is quite a bit shorter than my Van Slyke was. I'd guess you're at 4200mm to 4250mm.

As you say, though, the only real way to know is to time a star drift or compare fields to a planetarium program.

Cheers,
-- Jeff.

Here's a sketch I tried this evening of the same object.

www.astroshot.com/Sketches/2008-11-30-M82-V1.jpg


If you want to learn how NOT to do a sketch, this is it but unfortunately is how I went about this sketch:
1.Make sure you know where you left your sketch pad. Searching the house for 20mins is not a good idea.
2.Ditto re graphite pencils
3.Draw circle to represent eyepiece FOV before starting - don't draw it in after sketching the object.
4.Learn how to draw circular stars of various sizes (to represent variation in brightness) - harder than it may seem.

SO all in all, it could be alot better. But fun all the same.

Michael.

I concur with what Michael said about being prepared to sketch.
You also need to look very carefully at the object before you begin, so your eyes can pick out any tiny details that will make the sketch work and become that object on your page.

For deep sky objects I like to get the background as black as possible.
So far I have only found one type of paper to fulfill the kind of black I need.
When I have to use standard black paper which is really dark grey I have to use my blackest pastel to give me a black as the night sky background for the messier or star pattern that I am after.

The best point Michael made is to have fun, and enjoy the exploration of whatever subject you choose.

Nice sketch, more please

Deirdre Kelleghan
PRO IFAS
President IAS

Michael --

You might also try sketching with black pencil on white paper, and then inverting it on the computer. I greatly admire Dee's pastel sketching, but I (at least) find it much harder to master than pencil.

Cheers,
-- Jeff.

Thats a sketch to be really proud of Deirdre. Many congrats.