Re: ATM new to list and atm

["AstroJack" <AstroJack@AVATM.com>]

Frank:

>To find the length of a tube for a newtonian scope you take the
>diameter of the mirror and multiply it by the focal length.
>

So according to this I would get that the tube would be 24 feet long.

>In your case a 6" f/8 would be 6 X 8 or 48".

Oh, You meant Mirror diameter multiplied by the Focal Ratio!!  : )
>Then you.....


Ok from here out I am in aggreement.  Though a 60" tube might be a tad on the long side it would be well protected from dew!  

The next question for Andy is what the tube will be made from, and how big around it will be.  Most would suggest an 8" (ID/OD doesn't matter) tube.  Metal tubes can be made light but are prone to heat problems. PVC is a great material, nearly indestructible but really heavy unless you can find some thin wall PVC used in air duct work. Wood tubes are cool and can be made to your liking from a simple square tube to some pretty exotic stuff.  Fiberglass tubes are getting more popular, and there is the old trusted "Sonotube" style cardboard tube that when sealed and painted up well looks just fine too.  Lots of options!  

Good luck,

Jack Day 


---------- Original Message ----------------------------------
From: "Frank Ward" <thewards@mindspring.com>
Reply-To: "Frank Ward" <thewards@mindspring.com>
Date:  Fri, 8 Feb 2002 10:34:05 -0500

>
>Andy,
>
>> the tube lenght for a 6" f8 would be 8' or am i way off?
>
>
>You need more than us. You need to get some books
>on basic telescope making. They will be a big help.
>
>To find the length of a tube for a newtonian scope you take the
>diameter of the mirror and multiply it by the focal length.
>
>In your case a 6" f/8 would be 6 X 8 or 48". Then you
>add a little at both ends for baffling and support. Your
>tube would be closer to 60" than the 8 footer you proposed.
>
>Best wishes,
>
>Frank Ward
>Atlanta, GA
>
>----- Original Message -----
>From: andy73
>To: atm@shore.net
>Sent: Friday, February 08, 2002 9:06 AM
>Subject: ATM new to list and atm
>
>
>hi just wanted to ask a few simple(?) questions where can i get
>clarification on how to figure tube length for a given mirror. is it a
>function of the focal length if so am i correct to say that the tube lenght
>for a 6" f8 would be 8' or am i way off? I am enjoying the on going
>discussions within the threads.
>Thank you Andy Harvey
>
>
>