Tom wrote:

Sorry for the fuss here tonight. I have settled on the Dobs, rather than
the
adventure into Apochromats. It's the money.

You'll be a happier camper with the dob, if it's your first scope. 10"
is a very good starting aperture. You'll likely never run out of things
to see.

Nobody has said why the Orion XT10 is worth 50 bucks more, and the
Hardin comes with Messier list and a moon filter if I remember correctly.
I'll go with the Hardin I guess.

I think I recall someone or some reviewer somewhere stating that the
Hardin has a plastic secondary holder/spider that is not adjustable--is
this correct--I may be mistaken, but it's worth looking into. The Orion
has a steel spider.

There is a barlow lense offered for 50
bucks
as an accessory. I assume this scope can handle a 300x magnification, but
the
barlow is achromatic. Would an achromatic barlow cause chromatic aberation
in a newtonian scope?

Also, there is the laser collimator. I read some literature here on star
testing, so
does this make the laser obsolete?

You can't do a good star test if the seeing is poor, but poor seeing
doesn't affect laser collimators, at least not in amateur-sized
telescopes. ;-)

And one more thing, bear with me
here....
is correcting the optics just a harmless excersise in trial and
error...lighly tweaking
the screws? I have read how to tell if something is wrong, and even what is
wrong, but not much on which screws to tweak.

What screws to tweak depends on what is wrong.
Basically, it's:
1.) Square the focuser to the tube/optical axis. (shim/adjust screws
holding the focuser to the tube).
2.) Center the secondary in the focuser. (Adjust spider vane length and
secondary holder rod length)
2a.) add offset if desired
3.) Point the secondary at the center of the primary. (three or four
screws on the secondary holder)
4.) Point the primary back at the center of the focuser. (collimation
screws under the mirror cell).
5.) do a star test and start all over again ;-) --just kidding!

The above assumes the primary is centered in the optical tube.


Is this what you were wondering about, or have I misunderstood your
question?


Regards,
Uncle Bob

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