Dovetail Mounting Systems

There are many ways of attaching a telescope to a mount. For some lower-end scopes, the scope is directly bolted to the mount head. For others, the scope's rings, if it uses rings, are directly bolted. For many high-end scopes and mounts, the mounting rings may also be directly bolted to the mount head. But for the majority of amateur telescopes in the mid and higher-end range, the mounting is done through a dovetail bar/plate and saddle method.

Over time, there have been several different specifications for these plates and saddles, with various manufacturers creating their own specifications for use with their equipment. However, over time, a few have become de-facto standards. The most popular such standards are known by the names of the companies that developed or at least popularized them: Vixen, Losmandy, and Synta.

Most dovetail bars are manufactured from extruded aluminum, though occasionally steel or other materials may be used. Aluminum typically provides sufficient strength while not adding significant weight. For lighter applications, some dovetails may be manufactured out of plastics, carbon fiber, or even wood, though these are much less common.

Note: The terms bar, plate, and rail are frequently used interchangeably to describe the portion which fits into the saddle, which will clamp down on the bar/plate/rail.

Here is an example of a typical mounting saddle that would sit on top of the mount. This particular version is a dual-format saddle that can handle both Vixen and Losmandy-style dovetails.

Vixen

Using the Vixen-style system, the telescope payload (which may include the telescope itself, rings, cameras, finders, etc... ) are attached to a bar that is 43 mm (approximately 1.7 in) wide and 15 mm (0.6 in) high. The length varies depending on the size of the telescope to be attached. The sides of the bar are beveled at an angle of 15° from vertical, giving the bar a dovetail-shaped profile.

Here are some images of Vixen-style mounting bars:

Here is a mechanical drawing of the Vixen specification:

Vixen Universal

There is an older, alternative version of the Vixen dovetail that was originally designed for use with the Vixen Polaris German Equatorial Mount. The plate has some special notches cut for a more precise fit into the saddle. This plate is not found often, typically only on older telescopes. The notches are designed to fit the screws that clamp the bar onto the saddle. While the common Vixen and Losmandy style plates allow for the shifting of the payload forwards or backwards in the saddle along the length of the dovetail, the Vixen Universal plate does not allow this as the notches must be aligned to the clamping screws. This offers a more secure attachment, but, as previously stated, does not allow for shifting of the payload which is often useful for balancing the payload on the declination axis. In most cases, a modern standard Vixen saddle can accept the Vixen Universal plate, and vice-versa, but not always.

Here are some examples of the Vixen Universal dovetail bar:

Here is a mechanical drawing of the Vixen Universal plate specification:

Losmandy

A Losmandy-style dovetail plate, also referred to as the Losmandy D Series (to distinguish from the Losmandy V series, which are Vixen-style plates) serves the same function as a Vixen-style bar, but is wider and often used for heavier payloads. It also tends to provide more rigidity and stability. Aside from the overall width, one key difference between the Losmandy and Vixen style bars is that the dovetail portion of the Losmandy plate is typically fond underneath a wider portion for mounting the payload. The width of the dovetail, at its widest point, is approximately 3 inches wide, while the total width of the plate is roughly 4 inches wide. While the Vixen-style bar is 0.6 inches tall, the Losmandy is just short of 0.5 inches tall.

Due to the width and the fact that there is typically more surface area in contact with the saddle, they provide more stability and rigidity (as mentioned above). While you may often find telescopes with apertures of 8 inch (200 mm) or less frequently mounted on Vixen-style bars (though some users prefer the Losmandy plate), most larger telescopes will be found mounted on Losmandy-style plates.

These are some examples of the Losmandy D plate:

Here is a mechanical drawing of the Losmandy D specification:

Celestron CGE

Celestron, manufactured by the Synta Technology Corporation of Taiwan, sells most of its telescopes with a choice of mounting options. The first option they refer to as the CG-5 dovetail, named after the once-popular CG-5 mount. This is identical to the Vixen-style dovetail specification.

The other option they offer they refer to as the CGE dovetail, named after their CGE Pro mount, which used to be their premier German Equatorial Mount (GEM). Superficially it looks much like a Losmandy D plate, though it tends to have a curved portion while most Losmandy D plates rely on radius blocks for mounting larger scopes. However, while it looks similar, the specifications are slightly different and are not entirely compatible. A Losmandy-style dovetail saddle can usually handle a Celestron CGE plate, but a Celestron CGE saddle usually cannot handle a Losmandy-style plate.

Here are some images of Celestron CGE mounting plates:

Here is a mechanical drawing of the CGE specification:

And here is a comparison of the Losmandy and Celestron dovetails:

Synta

The Synta dovetail mount, often referred to as the "Synta Shoe," is a smaller dovetail, similar in style to the Vixen, and primarily used for the mounting of accessory equipment, particularly finder scopes. Due to the fact that most items attached using this mounting method tend to be small, light accessories, many are manufactured from plastic, particularly through FDM 3D printing methods using PLA, ABS, or PETG filaments.

The most common application, as mentioned, is for attaching finder scopes, but there are also synta mounts for things like Rigel Quickfinder reflex sites, red-dot finders, counterweights, laser pointers, dew heater controllers, power distribution controllers, and computers like the ZWO ASIAir.

Here are a few examples of Synta-style mounting hardware: