Unlike a simple Hartman or Bahtinov mask, the Astrozap focusing cap is a multi-purpose tool which allows for quick 'shutter-like' operation. Just turn the wheel to the open position for focusing, and then turn it again to the closed position to keep the dust out, or to image dark frames with your ccd or dslr camera.

The focusing wheel can be easily removed and replaced with an off-axis wheel for off-axis viewing, or an off-axis solar filter wheel for solar viewing on larger telescopes.

Simply turn the thumbscrew to the open position, and turn to close.
No plastic plugs required, and no tools needed.
Optional wheels for off-axis viewing and off-axis solar viewing
available for larger telescopes.
Astrozap focusing caps are made from lightweight aluminum
and powder-coated texture black