Most Frequently Used Focusers: Crayford Focusers Detail My Preference
Article: A Comprehensive Look at Crayford Focusers
Crayford focusers, a popular choice amongst telescope enthusiasts, are named after the Crayford Manor House Astronomical Society in England, where they were invented. Unlike rack-and-pinion designs, Crayford focusers operate with a smooth friction system, making them known for their precision and smoothness.
The unique mechanism of a Crayford focuser involves a roller bearing gliding against a flat surface on the drawtube body. This surface may be a separate metal plate or machined into the drawtube's body. As the focus knob is turned, the roller, connected to the knob via a rod or shaft, exerts pressure on the drawtube, causing it to slide in or out smoothly along the focuser's body. This system allows for tension and pressure adjustments to accommodate different weights of eyepieces or cameras.
Due to the absence of gears and teeth, Crayford focusers offer high precision and smooth movement. This eliminates backlash, the slight play or jerkiness often found in rack-and-pinion systems. Over time, however, wear on the draw tube and occasional balance tension issues have been noted.
In terms of pros and cons, Crayford focusers are economical, durable, easy to maintain, and often motorizable. Despite their advantages, they may experience wear over time, require careful balancing, and struggle with extremely heavy loads.
One highly praised Crayford focuser is the GSO 2'' model, which is used on Apertura AD Dobsonians and other GSO reflectors/Cassegrains without linear bearing focusers. The dual-speed version provides more precise focusing, while the single-speed version, although less precise, is suitable for telescopes with a slow f/ratio. these focusers are also available for refractors with various flange options.
Another recommended option is the JMI EV1 and EV3 focusers. Despite the problems encountered with linear bearing focusers, such as accumulated dirt causing bumpy movement, they are valued for their ultra-precise fine focusing capabilities.
Linear bearing Crayford focusers, like the Starlight 2'' Feather Touch, handle heavier loads and provide ultra-smooth and precise focusing, making them ideal for astrophotography. However, they are more expensive and complex than standard Crayford focusers, and require regular cleaning and maintenance.
In conclusion, Crayford focusers offer advantages in precision, smoothness, and durability, but may need more frequent maintenance and balance adjustments. Linear bearing Crayford focusers, such as the Starlight 2'' Feather Touch, provide superior precision and load handling but come at a higher cost and complexity. Standard Crayford focusers are cost-effective and simpler, although they may lack the precision and load capacity of linear bearing models.
- Crayford focusers, originally developed by the Crayford Manor House Astronomical Society, are popular in astronomy, especially for their precision and smoothness.
- The unique friction system in a Crayford focuser, with a roller bearing gliding against a flat surface, allows for tension and pressure adjustments, accommodating different weights of eyepieces or cameras in telescopes.
- In astronomy and astrophotography, linear bearing Crayford focusers, like the Starlight 2'' Feather Touch, offer ultra-smooth and precise focusing, handling heavier loads compared to standard Crayford focusers.4.choice of foc user, such as the GSO 2'' model, is prized for its precision and durability, suitable for use on various types of telescopes, including refractors and reflectors.
- In a broader sense, the use of Crayford focusers in telescopes represents a blend of lifestyle, science, and technology, impacting the ease and efficiency of observation and astrophotography.
