The Dutch Open Telescope (DOT) is an optical solar telescope located on Roque de los Muchachos Observatory, La Palma (near the Swedish 1-m Solar Telescope). With a main mirror of 45 centimeters, it can reach an 0.2 arcsec resolution for sustained periods. For further optimization of the images, the DOT uses the image despeckle mechanism. It was used to record movies of the 2004 Venus transit.

The open design was a departure from vacuum-style solar telescopes, and helped pave the way for bigger solar telescopes.

thumb|right|Main mirror of the DOT

Cameras

The DOT has 6 cameras, each with a different filter. These filters can be used at the same time, and allows images to be taken at different wavelengths to be compared. Furthermore, some filters are tunable, allowing observers to take images at several points in the spectral lines.

Open structure

thumb|right|[[William Herschel Telescope and the DOT]]

The DOT is an open telescope, which means that the structure is physically open, and the wind can blow through. Because the wind blows along the mirror the air has a more or less constant temperature, and this prevents seeing. Conventional telescope designs have the problem that hot air from the ground (which is hotter due to solar heating) is blown up along the tower, and this causes air with different temperatures to blow along the telescope, which degrades the image.

A drawback of this open structure is that the skeleton has to be very rigid (do not confuse with strong), to prevent the structure from moving in the wind. Normally a solid tower takes care of this (as is done with the Swedish 1-m Solar Telescope (SST), for example), or the telescope is placed inside a dome. The DOT does not have this and thus has to be very rigid. The optical part of the telescope is mounted 2 meters in front of the main mirror, and to prevent blurred images, the cameras are mounted very rigidly and can move with a precision of micrometres.

The telescope mirror can be upgraded in size to 3/4 of a meter with small modification, and even larger with additional adaptions.