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RE: Sanity Check Needed On Newt Design.

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Posted by Keith Venables on October 20, 2000 19:27:36 UTC

Sorry. I fat fingered the keyboard and posted prematurely.

I`m in the process of building my first scope which will be my first scope. I`ve decided on a 8" f/8 and am running the numbers through the Newt software. A lot of terms and concepts are a bit new to me so if someone wouldn`t mind providing some anaylsis on the results I would be very grateful.

Units are in inches.
Primary dia. 8
Focal ratio 8(I have the mirror and verified this)
Diagonal axis 1.52

Tube ID 10
Tube thick. 0.25
Focuser to front 7
Mirror face to bk 4.5

Focuser height 3.25 (fully racked-in)
Spare focuser 1 (has 2" of travel)
Camera 0
Focuser ID 1.25

The status window reads:
Diag. too small for 100% light: NO
Vignetting of 75% ray at front: None
Vignetting at focuser of 100% ray: None
Vignetting at focuser of 75% ray: None

The performance window reads:
4% obstruction of primary surface area.
19% obstruction by diamater.
Angular field for 100% illum. is 0.3514 deg. = 0.3905 inch.
Angular field for 75% illum. is 0.9182 deg. = 1.02 inch.

The eyepieces at this point are 26, 17, and 10mm with apparent field of 50 deg. I plan to add a barlow as my next purchase.

The resulting 66in. tube length is fine for me since I have a truck to transport it and I thought it would allow room to move the primary and/or spider holders outwards if I needed to later (I hope not). I expect most use of this scope in my backyard and have some light pollution to contend with. Sun, Moon, and planets will be likely targets followed by deep space objects.

At this point I am constructing the base and Dob rings and primary cell. It is not too late to modify primary size, spider, and focuser hole if needed. My goal is too have everything completed by Thanksgiving.

Thanks for your advice and help of a newbie.

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