Halden Farrow 5 mm wide-field eyepiece

Specifications

Description

The Farrow 5 mm is a seven-element wide-field eyepiece with a 70-degree apparent field and a 1.25 in barrel. It is built for high-power observing in telescopes with long focal lengths, where a short focal length is needed to reach magnifications above 200x. Its 5.5 mm field stop gives a true field of about 0.26 degrees in a 1,200 mm telescope. That is enough to hold a small planetary disk or a close double star with room around it, and the wide apparent field keeps the target in view as it drifts across the eyepiece.

A 5 mm eyepiece gives 240x in a 1,200 mm refractor, 200x in a 1,000 mm telescope, and 100x in a 500 mm telescope. At these magnifications, the image is dimmer and small movements of the air are more visible, so the eyepiece is most useful on nights of steady seeing and once the telescope has cooled to the outside temperature. Slower optics, around f/8 and slower, show the sharpest image across the field. Faster telescopes show some softening toward the edge, and the effect is more noticeable at high power. Use a steady mount and a stable tripod to limit vibration at this magnification.

The eyepiece has 9 mm of eye relief, which suits most observers, including many who wear glasses, although the eye must sit close to the lens to see the full field. The lens surfaces are fully multi-coated, and the edges of the barrel are blackened to reduce internal reflections. The barrel accepts standard 1.25 in filters. Its short focal length makes it a useful companion to a 10 mm and a 14 mm eyepiece in a set of planetary eyepieces, covering the middle and high powers in a single telescope.

About this configuration

The Halden Farrow 5 mm wide-field eyepiece is offered in several configurations, and the notes below describe what this particular one adds. This configuration comes without a case, which suits observers who keep their eyepieces in a shared foam box. No case is included, so the eyepiece ships in a simple box with its two dust caps fitted. The fold-down rubber eyecup blocks stray light, and you can fold it back if you observe with glasses.

Silver anodizing has the same wear resistance as the black finish, with a lighter look. This is the 2025 edition, which added a safety groove to the barrel and a firmer eyecup detent. To find the magnification, divide the focal length of your telescope by the eyepiece focal length in the specifications.

What's in the box

• Eyepiece
• Top and bottom dust caps
• Plastic storage case

Compatibility notes

• Fits any 1.25 in focuser, diagonal, or Barlow lens.
• The barrel accepts standard 1.25 in filters (M28.5 x 0.6 thread).
• Sharpest at f/8 and slower; softer at the edge in faster telescopes.