Newt for the Web

Title: ??
Notes: ??

Design Modification Status: ?

Local Storage ?

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Design Name:

Current Design Name: ?

This button will 'zero out' everything and you can start with a clean slate.

Load a Sample Newt-Web Design ?

The Yellow Sample Design is the build-it-youself Dob at

Open a .newt File ?

Not compatible with NewtWin .NWT files

Save a File to Your Computer ?

Accomplished by round-triping through our server.

Save file name: .newt

Newtonian Telescope Specifications

Use this form to input and adjust your telescope design values.

Unit of Measure
Project Info
Title These fields allow you to add a title to your
design and add notes or comments
about a specific design
Primary Mirror Diameter Typically 4¼, 6, 8, 10 or 12½ inches
Focal Ratio = Focal Length / Primary Diameter
Diagonal Mirror Minor Axis ? Typically .75, 1.0, 1.3, 1.52, 1.83 inch
Diagonal Sizing Assistance: Involves Conflicting Goals - Please Read Help ?
Find range of error free diagonal sizes
100% Illuminated Diameter: ? Maximize, ½ inch or 12mm typical.
Diagonal Obstruction of Primary Diameter: ?% Minimize, 20% or less is a good goal.
Tube Inside Diameter ? Allow ½ to 1 inch around primary mirror
Tube Wall Thickness Adds to overall Focuser Height
Focuser to Front of Tube Measure from Center of Focuser
Mirror Face to Back of Tube Allow room for Mirror Cell
Fixed Diameter Baffles ? Tapered Baffles if not checked
Focuser Minimum Height ? Outside Tube to Top of Focuser
Spare Focuser In Travel ? Allows for Eyepiece Field Stop Variations.
Additional Height for Camera ? Optional, to focus on Camera Film Plane
Focuser Inside Diameter ? Typically 1.25 or 2.00 inches
Eyepiece Performance with this Telescope Design
Focal Length
Power Exit
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  • Optical Axis (Blue)
  • On-Center Rays (Green)
  • 100% Zone (Red)
  • 75% Zone (Yellow)
  • Baffles

Ray Trace ?   Zoom in on Diagonal & Focuser:
  • 1x
  • 2x
  • 3x
  • 4x
  • 5x

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Read about supported browsers in Application Help.

Performance Information for your Telescope

The theoretical limiting magnitude for a ? objective is ?.

The obstruction of the primary surface area by the diagonal is ?% which results in a reduction of light gathering ability. ?

The theoretical resolution (Dawes limit) for a ? objective is ? arc seconds.

The obstruction of the diameter of the primary by the diagonal is ?%, which affects image quality by increasing diffraction and lowering contrast. ?

Maximum useful power is about ?x (for 50x per inch of aperture).

Minimum useful power is about ?x (for a 7mm exit pupil).

Angular field of view for the 100% illuminated area is ?°. The diameter is ? ?

Angular field of view for the 75% illuminated area is ?°. The diameter is ? ?

If you see "NaN" where you expected a number, the specifications resulted in incalculable results, such a division by zero or some other mathematical problem. "NaN" is an abbreviation for Not a Number.

Dimensions for your Telescope
Unit of Measure?
Primary Mirror Diameter?
Focal Length?
Focal Ratio?
Tube Inside Diameter? ?
Tube Thickness?
Focuser Minimum Height? ?
Focuser Inside Diameter? ?
Focuser Extra Travel? ?
Focuser Camera Travel? ?
Diagonal Minor Axis? ?
Diagonal Offset?
100% Illumination Diameter? ?
75% Illumination Diameter? ?
Front Aperture Diameter? ?
Mirror Face to Focuser Hole?
Focuser to Front End of Tube?
Mirror Face to Back of Tube?
Tube Length?
Dimensions for the Baffles ?

If you see "NaN" where you expected a number, the specifications resulted in incalculable results, such a division by zero or some other mathematical problem. "NaN" is an abbreviation for Not a Number.

Newt for the Web (Newt-Web for short) is a Newtonian Telescope Computer Aided Design program. It ray traces a Newtonian telescope design checking for vignetting, optimizes diagonal size, calculates baffle sizes and positions, and produces performance and dimensional data for construction. It runs in your web browser - there is no need to install a program on your computer.

To get started:

Use the File tab to load an existing design or sample designs.
Use the Specifications tab to enter a design of your choice.
Click ? for help on items it is near, or see the Help tab for a list of topics.
Many items, such as tabs or buttons, provide extra information if you hover over them.
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   Newt-Web Release History  Copyright © 2011-2012 by Kenneth H. Slater.

Thanks to Dave Tabor, Julian Shull, Matt Considine, Michael Patterson, Dave Prowten, Glenn Becker & Dale Keller
for their help, expertise, ideas and advice during development of Newt-Web.
Newt-Web is based upon NewtWin and the Newt25 sources by Dale Keller; See Dale Keller's Newt Software Page

Browser Size: ? x ?

Screen Size: ? x ?

Newt-Web is released under the GNU General Public License Version 2 (Click link to view).

Source code for the current, running version. Right click and use the "Save Link As..." function to download and save each file.

General Help Information

Click the Help Icon ? for help on topics it is near. If you hover your mouse over the icon, the help topic it links to will be displayed in a tiny pop-up window.

Help links in the Newt-Web application panes open in a new window in your browser. Note that many people choose an option in their browser to open new windows as new browser tabs (not Newt-Web application tabs).

Newt-Web Application Help

Application Help includes topics about how to save and restore designs between sessions, features needed to run Newt-Web, which major browsers support Newt-Web, screen sizes, printing, and reporting problems.

Newtonian Telescope Design Help

Newtonian Design Help includes topics about how to size your optics and telescope components to maximize performance, and how to solve problems that Newt-Web reports about your design.

Newt-Web Release History

The release history of Newt-Web is available on this help page. It also explains the version numbering scheme.

GNU General Public License

Newt-Web is release under the GNU General Public License (GPL) Version 2. Newt-Web source files are available on the About tab.