Newt-Web Help: Application

for Program Version: ? and File Version: ?


This help page is devoted to topics about running the application. It deals with topics related to computers, web browsers and the internet. See this page for help about Newtonian Telescope Design.

In the application, we use this icon ?  to link to help topics relevant to the item it is near. If you hover over the icon for a short time, the help topic it is linked to will pop up.

Topics in this Document

Required Technologies

Newt-Web is a Computer Aided Design application that has been built to run in a web browser, without having to be installed on your computer or device. It uses technology that was standardized in the late 2000's and started to appear in web browsers in the 2010-2011 timeframe. It uses the following key technologies to make it work:

Hyper Text Markup Language (HTML) is the main 'language' of the web, and is where the content of a web page is defined. It also defines supporting technologies that are used to manipulate and modify this content. HTML version 5 is just being fully implemented in web browsers in 2011, with some parts available everywhere and some parts currently having only partial or no support, with the expectation that over time all features will be supported. Newt-Web uses the <canvas> facility to draw the telescope and light paths in the Ray Trace pane. It uses LocalStorage, part of the DOM Storage facility, to store your design between sessions. It uses File Reading to open designs from files (File Reading may not be important to you, you may be satisfied with just using local storage).

Cascading Style Sheets (CSS) are used to format the content for display. Just like HTML5, CSS3 is being gradually phased in starting in 2009 over an extended period, piece by piece. Having full CSS support will make Newt-Web look visually nice, but if parts are missing it will still function, it will just not look as good. CSS3 features that Newt-Web uses are: corner-radius, box-shadow, text-shadow, and gradient to make selected items have rounded corners, shadows to add depth, and gradients to soften and give a 3-D appearance to some objects. In several cases we currently use some vendor specific experimental versions of these items because they are not available in standardized versions yet (i.e. -moz-... and -webkit-... and filter:... in the CSS files). Unlike many older web applications, the only image used in Newt-Web is the application icon.

JavaScript is the programming language that does the calculations and makes the page interactive - when you click a tab in Newt-Web or change a value, it is JavaScript that makes the actual changes. You must have JavaScript enabled in your web browser (usually the default setting). All major browsers have all the JavaScript support that newt-Web needs.


There are currently four browsers that have more than 5% market share, and these are the ones we choose to test on and report here how they work. There are many other browsers that, if they have the needed support of standardized features, should work also. Since the next most popular browser has about 2% of the market, and others much less, we choose not to spend time testing them.

All listed web browsers are free to download and use, and we encourage you to use the latest version, which may be a higher version number than we list below. Besides likely working better with Newt-Web, the most current versions of browsers are the most secure, and are also faster and have more modern features than their older versions. Please upgrade to the latest version listed that is equal to or greater then the version we list.

We only have Windows 7 machines to test on regularly, however we have done some testing on Unix/Linux machines and Apple products, but it has not been as through as on Windows. (Listed in alphabetical order)

Apple Safari 4 & 5: All needed functional features except file open. Using two -webkit- pre-standard formatting features. Get Safari.

Google Chrome 9: All needed functional features, using two -webkit- pre-standard formatting features. It is also the only browser that currently supports new form input fields that do automatic input validation. Currently the best browser for Newt-Web (it has more of the features that Newt-Web uses than any other browser), although as time goes the other browsers should catch up. Get Chrome.

Microsoft Internet Explorer 9: All needed functional features except support for file open. We are using several filter: pre-standard formatting features. The visual appearance of Newt-Web is not as good as on the other browsers, text-shadowing in IE is visibly poorer than the others, and causes large size shadowed text to look pixilated. Also gradients do not respect bottom corner rounding while other browsers get this right. And in several cases we have had to program in JavaScript in more awkward and slower way because it does not yet support efficient constructs that all the other browsers do. Not recommended, other browsers are more functional. Get Internet Explorer.

Mozilla Firefox 4: All needed functional features, good formatting support, we are only using -moz- pre-standard formatting features for gradient fills. A very good browser for Newt-Web. Get Firefox.

Mobile Devices: Newt-Web has been casually tested on several mobile devices, as we encounter friends that let us do some testing. In general it is not an explicit goal to run on these small devices, but we try to do nothing that would prevent this.

 See comments about Screen Size below.

Screen Size

Newt-Web is written to run on and is tested on a browser of a minimum total size of 800 x 600 (Newt-Web has less then this to use after window borders and browser controls are subtracted), so it should work on small devices such netbooks and large tablets. It is a not goal to run on smaller screens, and if compressed too much the display will start to behave badly. Many smaller devices do scroll and zoom web pages rather than shrink them, so if there is the necessary HTML5 feature support, it will run on smart phones and small tablets.

The Ray Trace window benefits from a larger screen, and will expand to use as much space as it is given. The zoom feature does allow important areas to be examined even on smaller screens.

Local Storage

Local Storage is an HTML5 feature which allows a web page to store data on your computer. To prevent malicious web pages from infecting your computer with malware or viruses, this storage is NOT a computer file that you, or other parts of your computer, have access to - it is stored in a special place, and is never treated like a program so it cannot do bad things to your machine.

While Local Storage is convenient to store your telescope designs, it does not allow your design to be sent to a friend. It is also not shared between different brands of browsers (each brand of browser on your computer has its own local storage). So it is fast and easy to use, and perfect for use when you are refining your design. In order to share your design, you must get it into a File.

Locally stored designs are referred to by a design name, which is similar to a file name. To initially store a design, type a Design Name into the Design Name input box, and click the Save As button. Once the design has been given a design name, you can save again by clicking the Save Design button (the active design name is show above this button).

Your stored designs are listed in the left hand box of the Local Storage area of the File tab. Click the radio button to the left of the design name to select a stored design; you can then open it, rename it or delete it. Renaming requires you to select the design you wish to rename, and then typing a new name for it in the design name box before you click the Rename Selected button.

Design names have no imposed length restrictions, but we suggest you keep them short. There a few characters you cannot use in design names: / ? \ * : | " < >

There is also a New Design button in the Local Storage area. This really has nothing to do with Local Storage, but it was a logical place to put it. When you click this button, a new design is loaded into memory that has all numeric items set to zero and all other items set to a default value. Click this when you want to start a new design from scratch.


Newt-Web save files are saved in the standard JSON text file format, the data fields are specific to Newt-Web. The file contains a version number, so that we can make changes to the format in the future, if warranted, and still be able to read older versions of Newt-Web files in newer versions of this program. Note that some mobile devices do not have a user visible file system, and hence you cannot open and save files.

Opening a File: On the File tab, you can use the Open a .newt File section to browse to a computer file and read it into Newt-Web. Newt-Web can only read Newt-Web save files (.newt file type by convention), not the old Newt-Win files of type .NWT. Some browsers support drag-and-drop of files, you may be able to drag a file into this area to select it instead of using the browse button. If drag-and-drop is active, the background of the Open area will change to light blue when you drag a file over it.

Saving a File: As explained previously in the Local Storage section, web browsers cannot directly write files to your computer - that would be a terrible security problem. Therefore, we have to do extra work to save a file from Newt-Web. When you press the Save File button, we upload your design data to a temporary file on our server, and then immediately push it back to you as a file download. When the download dialog box appears, select a location to save the file in. As soon as the download is complete, or canceled, the temporary file is deleted on our server. See our Privacy Policy.

Loading Samples

On the Files tab, we provide several sample designs to load into Newt-Web. You are welcome to experiment with these, modify them as you wish. You never have to worry about losing the original sample, because you can not overwrite the read-only samples. You can, of course, save your modifications to Local Storage or export as a File.

The sample files included are:

These files are telescopes the authors have owned (first four Dale Keller, last one Ken Slater) and can be used as examples.  They aren't perfect, but they are closer than they were before using this program.  The WHITE and BLACK telescopes are pretty generic, and show a couple of the problems with non-optimized designs. The YELLOW telescope is optimized, and although the focal ratio is a bit smaller, it is very much an improved version of the WHITE sample. Complete, detailed, step-by-step plans for building the YELLOW telescope can be found at; this page also includes some additional discussion about using Newt, how to design a good telescope, and solving problems that Newt reports.

Diagonal Sizing

Diagonal sizing is one the most difficult parts of Newtonian design, because it involves conflicting goals; You would like to maximize the size of your diagonal to get the most illuminated area in your eyepiece and therefore the brightest image; You would also like to minimize the size of your diagonal to improve image contrast and cast as small a shadow as possible on your primary mirror. Newt-Web adds some Diagonal Sizing Assistance to the Specifications tab, right under the place you specify the Diagonal Minor Axis. Here is some quick help to use these tools - but we also suggest your read the excellent advice given in the Newtonian Design Help page, especially the sections on Improper Design and  Illumination Size.

Before you work on selecting the final size of your diagonal, you should fix any problems highlighted in the status box in the header. Some of these fixes may involved adjusting the current diagonal size. A quick way to do this is click the Calc button in the Diagonal Sizing Assistance area (this is an integrative calculation, and may take a few seconds). When done, it will produce two numbers, the minimum and maximum diagonal size that are status-box error free. Pick a size in the middle of this range for starting, and then make sure there are no other errors to be fixed.

Note: If the range returned by the calc button is reversed, that is the large number is first, your telescope is one of those hard-to-make-right designs, such as the Black sample, and you will have to compromise and live with some major design shortcomings.

In picking an illumination size, you need to think about how you will use the scope and what it is designed for; high magnification planetary scopes can get away with a smaller illuminated area than wide-field deep-sky scopes can. A high focal ratio scope is easiest to maximize 100% illuminated area size with a 'small' diagonal; low focal ratio scopes need larger diagonals to achieve the same results (because the light cone is wider when it reaches the diagonal). In any event, general advice for every situation is hard to give, but if you are a novice and struggling with "how much is enough" consider aiming for approximately a ½ inch or 12mm 100% illuminated diameter for the typical 6 to 8 inch (150 to 200mm) f/6 to f/8 scope. Do not minimize your diagonal such that you end up with a zero or tiny 100% illuminated diameter at the focal plane.

Selecting the smallest size diagonal that provides the needed 100% Illumination Diameter is good - diagonals that are too large block more light from reaching your primary mirror, and there larger diffraction effects scatter more light into the image reducing contrast. A very general rule of thumb is to keep the diagonal minor axis at less than 20% of the diameter of the primary mirror. This is general guideline, the Yellow sample scope has a 22% obstruction and it performs beautifully. But smaller is better in this area, without comprising to an unusable illumination area at the focal plane.

The Ray Trace Tab

Newt-Web does a simple geometric ray trace of the telescope design to check for design problems. The results of this ray trace are presented in the Ray Trace tab, in a properly scaled cut-away diagram of a telescope, allowing you to visualize many of the parameters presented in the Performance and Dimensions tabs as well as see why warnings are issued in the Status Box.

Unlike the rest of Newt-Web, which is limited by design to be less than 800 pixels wide, the drawing area of the Ray Trace tab will grow as wide as possible so you can see your design at the largest possible scale. The height of the drawing area is automatically adjusted by the program to show the entire telescope with minimal white space above and below.

The telescope drawing can get cluttered with rays, axis and baffles, so checkboxes are provided to turn each of these on and off individually. When the telescope tube is too small to allow baffles to be drawn, the baffle drawing is disabled and a warning message is displayed above the top of the tube. Unchecking the Baffles check box will also turn off the warning.

When the diagonal is too small to reflect a ray, the ray stops were it misses the diagonal (in reality, it would continue on out the front of the tube). When the 100% illuminated area is zero, the on center and 100% rays are truncated. When the 75% illuminated area is zero, the 75% ray is truncated. Again, a warning is printed above the telescope tube when any of these conditions occur (if you are zoomed in, you may not see the warning).

When you zoom in, the drawing is shifted to the right so that the diagonal and focuser area is always visible, since that is the area where you want to be able to examine the rays, reflections and vignetting in detail. The line above the focuser is the focal plane, with gray representing the 75% illuminated area and gold representing the 100% illuminated area.

Non-Round Tubes

Newt-Web assumes you are building your telescope into a round tube, but there are certainly many fine telescopes built into square, hexagonal, octagonal or other shapes made from multiple flat sides. You can still use Newt-Web for your telescope design, you just need to make sure to adjust a couple of specifications as necessary.

A key specification is Tube Inside Diameter. For a non-round tube, calculate the diameter of an inscribed circle for your non-round tube and use that. This parameter is used in checking and calculating the Front Aperture Diameter and with other specifications discussed below to calculate the base height of the focuser.

In order to check vignetting at the focuser, the base height of the focuser is calculated (from the optical axis) by adding (Tube Inside Diameter / 2) to Tube Thickness. You must adjust the Tube Thickness so that this calculation works out properly. Note that it is possible to have a negative value in this parameter, as might occur if the focuser is mounted on an inset. Also note that if the focuser is centered on a flat side, it should be used normally, as the inscribed circle should be tangent to the flat side at the center of the focuser hole.

Baffle calculations may not work properly for non-round tubes.


There is no specific support for printing in Newt-Web - use the built in browser printing facilities. The relatively narrow format of our presentation prints well in portrait format, although on some browsers you may want to select "Shrink to fit page width" to insure your printing won't overflow to the right.


With the exception of Save File, all data is kept on your computer or device and no data or information is uploaded.

Due to necessary security rules that prevent web browsers from writing files to your computer, the Save File feature uploads your design data to our server so that it can be immediately downloaded and saved by you. While briefly on our server, your design data resides in a special type of file, a temporary file, that is deleted as soon as it is closed. It is not our policy to retain our use design data from this feature. However, system failures or bugs could possibly leave your data on our server; we will immediately delete any such data that we find. Your design data is also transmitted unencrypted while going to and from our server making it more susceptible to interception. However, since there should no data of value to a third party in this file, we do not believe this presents any risk to you.

Problem Reports

We always appreciate receiving problem reports, so we can investigate them, fix them if necessary and generally improve Newt-Web. You can submit problem reports to the e-mail address on the About tab. If this problem is related to a specific design please, please Save your design to a File in the file tab, and attach the file to your e-mail. Thank you (in advance) for helping to make Newt-Web better for everyone!