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Bahtinov Mask Generator
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For information about Bahtinov masks and this generator, see the Overview, the FAQ, and the Change History.

Input values appropriate for your telescope, and press the Generate! button.

Basic parameters
Enter these three values, press Generate!, and you're most likely done.
Focal length (mm)
 
The focal length of your scope, in mm.
Aperture (mm)
 
The clear aperture of your scope, in millimeters.
Edge thickness (mm)
 
The extra distance the mask extends beyond the clear aperture. The amount you enter depends on whether you plan to fit the mask inside your tube/dewshield or somehow mount it over the outside. If you decide the mask needs to be 20mm larger than the clear aperture, enter 10mm. You probably don't want this to be less than 4 mm, depending on the material you use.
 
Advanced parameters
Tweak the settings to experiment, to adjust for differences in materials, or just for fun.
Structural bar thickness (mm)
 
The width of the structural bars - the vertical bar and the horizontal bar separating the upper and lower quadrants.
Central obstruction diameter (mm)
 
If non-zero, this shadows the central of your scope. For refractors, this should be 0. For SCTs and other obstructed telescope designs, this should be 0, unless you plan on fitting the mask over your secondary holder or you need it for added stability/rigidity.
  A "doughnut" is cut out of the central obstruction (to fit over your secondary holder) when checked. Has no effect if the central obstruction diameter is 0.
Bahtinov factor
 
Tough one to describe. Read the CN thread for an explanation. Ideally, should be between 150 - 200. You shouldn't need to tweak this unless your slots are too narrow for cutting, in which case, divide the factor by 3.
Calculated slot width (mm) 7.8 The value calculated for the slot width, given the focal length and the Bahtinov factor. You can override this value below.
Slot width override (mm)
 
Override the slot width here.
Horizontal slot count
 
Something of a misnomer, this actually represents of the cutouts in *each quadrant* of the left side, starting with the middle cutout, which is counted twice.  For example, if you enter 10, you'll actually get *at most* 19 cutouts total on the left-hand side of the mask.  Setting this number "too high" will not have any effect, as the "extra" bands that fall outside of the outer bounds of the mask outline will be masked/clipped. You might want to adjust downwards to avoid generating tiny cutouts at the very top and bottom of the left-hand side.
Some people believe that the center of the left-hand side should be a bar (blocked), and not a slot (open). Unless you feel strongly about it, leave this uchecked.
Angle (degrees)
 
The angle from the horizontal of the angled slots.  The "standard" is 20.
Angled slot count
 
This is the count of the slots in the upper- and lower-right sections. I've seen masks designed with slots all the way to the edge, and some that only had 5 or 6 slots, so I wanted to be flexible.  Setting this number "too high" will not have any effect, as any "extra" slots that fall outside the mask outline will be masked/clipped. You might want to adjust downwards to avoid generating tiny cutouts at the very top and bottom of the right-hand quadrants.
Angled slot offset
 
If 0, the angled slots will start at the center of the mask, and move towards the outside (top or bottom). By setting the amount to a positive number, they start farther to the outside. By setting to a negative value, they start "lower," the net effect of which is to fit more cutouts on the mask - experiment! You might want to adjust upwards to avoid generating tiny slots at the center right of the right-hand quadrants.
 
Print Options
Left margin (mm)
 
Additional space on the left and right to aid with printing
Top margin (mm)
 
Additional space on the top and bottom to aid with printing
Center line color Optional.  The color to print a thin crosshair on the central axes of the mask.  Possibly useful for alignment and/or testing purposes.  Good options are red or black.
Fill color
Back color
Some products (Adobe Illustrator, for example) expect SVG files at 72DPI, while the SVG standard is 90DPI. If you plan to open the generated SVG with Illustrator, check this box - if you forget, you can always scale the drawing by 0.8 for the same effect.

If you have questions, comments, issues, suggestions, or if you'd like to be notified when the generator is updated, shoot an e-mail to david at astrojargon dot net.

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