Re: ATM Focuser Postion

[Brad Davy <bdavy@bigdog.fred.net>]

At 01:43 AM 2/24/97 GMT, Herm Perez wrote:
>
>No bad!, is there a chance of seeing a picture of your focuser?..BTW
>this is how you adjust focus on a helical focuser, you do the gross
>adjustment with the locking set screw, then you turn the whole
>assembly for the fine focus.

I'll be posting pictures on my web page, along with construction details.  I
don't have pictures yet, since I'm more interested in getting it built.  I'm
also not sure yet if it will actually work.  One serious draw back to using
the PVC fittings - they are "flared" threads.  At the beginning of travel,
they are very loose and tend to wobble a bit.  At the end of travel, they
are extremely tight and hard to turn.  I'm considering scrapping the PVC and
looking into  threaded metal pipes.  I may also consider building a Crayford
style focuser, if I can figure out how to do it with a drill and a Dremel.

>I have a 10mm Sirius, the focal plane is exaclty even with the "step"
>on the 1.25" body...in other words, flush with the top of your
>focuser, the body itself ia about 1" long.
>
>The 40 mm will be very different, the focal plane will be almost at
>the end of the 1.25" body..the 40 is not parfocal with the 10", you
>would ahve been bettr of getting the 32mm instead, that will be
>parfocal.

Now you tell me! :)  I was trying to get a good range of focal lengths.
With the 8" f8, I should be getting about 40x, which I expect to be a good
starting point.  Orion has a 30 day guarantee, so I can return it.  Any
other ATMs want to comment?  Would I be better off with a 40 and a 10 with a
Barlow, or should I send the 40 back and get a parfocal 32?
Brad
bdavy@fred.net               http://www.fred.net/bdavy/home.html
bdavy@nox.cs.du.edu