Instructions
Attach a camera to the telescope, centre a fairly bright star and achieve rough focus. Then place the mask over the front aperture of your telescope by “hanging” it on the plastic screws from the front dew shield. Take a short exposure. The image of the star will show diffraction spikes. The “centre” set will most likely be shifted to one side or the other. This is showing the defocus.
Adjust the focus of the telescope and re-expose the star, once again showing the diffraction spike pattern. Iterate the process until the central diffraction spike is centred against the star and the other spikes. When a symmetrical pattern is achieved, the best possible focus is then reached. Simply remove the mask, centre the target object and take amazing, sharp images!
Farpoint manufactures this essential astrophotography tool out of virtually indestructible ABS plastic.
How it works
The slits in the mask are the focus assist, when the star is in focus it will appear on your screen display as an “X” with a line through the centre.
These masks will work equally as well on the end of a scope or on the end of a dew shield on top of that. The mask itself does not need to be perfectly centred on the scope this is due to the angle of the slits themselves.
Select a bright star, this will be your guiding object. Place the Bahtinov focusing mask on your telescope’s lens and secure it into place using the provided rubber tabs.
The slits in the mask design create a set of diffraction spikes on the star that will assist in the accuracy of our focus. It will appear on your DSLR display screen or computer as an “X” with a line through the centre (when in focus).
The diffraction spike pattern from a bright star using a Bahtinov mask.
As you adjust the focuser of your telescope, the central spike will move in and out of the X-pattern. If you are using capture software be sure to compensate for the lag time between exposures on the screen, typically 4-5 seconds.
The same process applies using Live view display on your DSLR camera. The difference is, the image will be much dimmer, as you are essentially looking at a live video feed rather than a short image exposure.
Carries full one year UK warranty.
