Tessaro Ironwood 250 f/5 Dobsonian, with Dobsonian base

Specifications

Description

The Ironwood 250 f/5 Dobsonian is a Newtonian reflector with a 250 mm parabolic primary mirror and a focal length of 1250 mm, which gives a focal ratio of f/5. The fast optics produce a wide true field at low power, so you can frame large nebulae and star clouds in the Milky Way with a 2 in eyepiece. The open-truss tube and rocker-box base keep the instrument manageable for its aperture.

The primary mirror sits in a cell with three collimation screws, and the secondary mirror is held by a four-vane spider. Check collimation before each session, because the optics shift slightly as the tube cools and is moved. The 2 in dual-speed rack-and-pinion focuser takes heavy eyepieces without slipping, and its fine-focus knob gives a reduction suitable for high-power focusing. The 22.0 kg tube is detached from the base for transport, so plan for a second person or a cart when you move it from a car to the observing site.

The rocker box rests on low-friction bearing pads and turns the tube smoothly in altitude and azimuth, which lets you follow objects by hand as they drift across the field. Set the base on a level, firm surface. Allow the tube about 45 minutes to reach outdoor temperature before observing planets at high power, since a large mirror holds heat longer than a small refractor and produces shimmering images while it cools.

Typical targets include the Andromeda Galaxy, the Orion Nebula, and the globular cluster M13 in Hercules, which resolves into individual stars along its edges at this aperture. Under dark skies the tube shows faint spiral structure in M51 and dust lanes in the Milky Way near Cygnus. Planetary views at high power are sensitive to seeing and thermal settling, so Jupiter and Saturn are best observed after the tube has settled.

About this configuration

This listing covers one specific configuration of the Tessaro Ironwood 250 f/5 Dobsonian, defined by its bundle, finish, accessory kit, and edition year. The Dobsonian rocker base keeps the telescope low and stable, and you aim it by pushing the tube gently by hand. A Dobsonian base needs no alignment, so you can set it on level ground and start observing within a few minutes. The carbon fiber tube expands less as the temperature drops, so the focus point drifts less as the night cools.

The planetary kit adds a short focal length eyepiece and a set of color filters for the Moon and the bright planets. This is the 2023 edition of the Ironwood line, the earliest version that is still listed in the catalog. The optical figures in the specifications table apply to this configuration and to every other version of the Tessaro Ironwood 250 f/5 Dobsonian.

What's in the box

• Optical tube assembly with primary mirror cell
• Rocker box base with altitude bearing pads
• 2 in dual-speed rack-and-pinion focuser
• 9x50 right-angle finder
• Eyepiece holder and dust caps
• Dobsonian rocker base with altitude bearings
• 6 mm planetary eyepiece (1.25 in)
• Four color filters (1.25 in)

Compatibility notes

• Accepts 2 in eyepieces directly and 1.25 in eyepieces through a 1.25 in adapter.
• Eyepieces with field stops up to 46.5 mm are supported by the 2 in focuser.
• The rocker box accepts a standard accessory tray mounted on its side panel.