Aurel Alder 72 achromatic refractor, tube with equatorial mount

Specifications

Description

The Alder 72 is an achromatic refractor with 72 mm of clear aperture and 504 mm of focal length, which gives a focal ratio of f/7. At that ratio the telescope produces a wide field with low-power eyepieces, and it still offers enough magnification for lunar craters and the disks of Mars and Jupiter. The objective is a two-element cemented achromat that brings red and green light to a shared focus. Bright objects such as Venus and the lunar limb may show a faint violet fringe, a common trait of achromats at this focal ratio. Keeping a bright planet near the center of the field reduces the fringe and sharpens the view.

The optical tube is made of aluminum and has an internal baffle near the objective, along with a retractable dew shield that limits stray light from nearby streetlights. The 1.25 in rack-and-pinion focuser moves smoothly under a light eyepiece and star diagonal, but it has no dual-speed fine adjustment, so planetary focusing depends on careful hand control. A 6x30 finderscope on a bracket lets you locate targets before you move to the main eyepiece. The tube accepts 1.25 in eyepieces directly, and the dew shield slides back for storage.

At 1.4 kg for the tube, the Alder 72 sits well on a small alt-azimuth mount or a lightweight tripod, and it packs into a soft case for transport. Small refractors reach the outdoor temperature quickly, so you can start observing soon after you set up. Typical targets include the Moon, the phases of Venus, the double star Albireo, and the Pleiades, which fill a wide field with a 32 mm eyepiece. Under suburban skies, the telescope also shows the brighter open clusters and larger diffuse nebulae. Faint galaxies and small planetary nebulae need more light than 72 mm collects, so you will see more structure in them through larger apertures.

About this configuration

This listing covers one specific configuration of the Aurel Alder 72 achromatic refractor, defined by its bundle, finish, accessory kit, and edition year. The equatorial mount follows the sky along one axis once you align its polar axis with the celestial pole. Balancing the tube and the counterweight before each session helps the equatorial mount move smoothly in both axes. Gloss white paint is easy to wipe clean, and the tube stays easy to spot in a dark yard.

This configuration comes without extra accessories, so budget for at least one more eyepiece if you are starting out. The 2023 edition uses the same optical design as later years, with small differences in fittings and labels. The optical figures in the specifications table apply to this configuration and to every other version of the Aurel Alder 72 achromatic refractor.

What's in the box

• Optical tube with retractable dew shield
• Dovetail mounting bar
• 1.25 in star diagonal
• 6x30 finderscope with bracket
• Front and rear dust caps
• Equatorial mount with steel tripod
• Counterweight and counterweight shaft

Compatibility notes

• Accepts 1.25 in eyepieces directly through the focuser.
• The dovetail bar fits common Vixen-style mounts.
• The focuser has a T-thread at the drawtube end for camera adapters once the diagonal is removed.