Farpoint 21.5 Inch 57.3 Series Universal Dovetail Plate (Radian Bar)

Product Overview

The Farpoint FDP573-215 is the long version of the 57.3 Series universal dovetail plate: 21.5″ of light-weighted, black anodized aluminum cut to the D-size (Losmandy) profile. The series began as the Radian lightweight universal D-style bar, which Farpoint machined for OPT; after OPT closed, Farpoint continued the line under the 57.3 Series name on the same tooling and extended it to this length. At 21.5″ it is the longest universal bar Farpoint lists, and Farpoint publishes a 4 lb weight for the item.

Who It's For

This is a good match if you…

• have a long optical tube and want wide ring spacing rather than rings crowded together.
• are balancing a heavy imaging train and want the fore-and-aft travel that a long bar gives.
• are mounting on a D-size Losmandy saddle on a heavy-duty equatorial.
• want to carry a main tube and a guide scope or second instrument along one bar.
• own a 14″ bar already and need more length for a larger tube.

Key Features & Design

• 21.5″ bar length: the longest universal bar in the 57.3 Series, giving the widest ring spacing and the most balance travel.
• D-size (Losmandy) profile: the wider of the two common dovetail standards, matched to heavy-duty saddles.
• Light-weighted construction: material is machined away between mounting points, so length is added without a proportional weight penalty.
• Universal hole pattern: a variety of mounting hole options is machined along the bar for rings, blocks and accessory clamps.
• Black anodized aluminum: a hard, non-reflective finish over CNC-machined aluminum.
• Radian lineage: an extension of the original Radian design, produced in the United States by the company that made the Radian bars.

Mechanical Design

Length is the whole point of this bar, and length is also what tests a dovetail. A bar that is twice as long deflects far more under the same load unless section and stiffness are handled properly, so Farpoint keeps the dovetail flanks and the mounting bosses at full section and removes material only from the web between the faces. The D-size profile helps here too: the wider clamp footprint gives the saddle a longer moment arm to resist droop than a narrower bar of the same span. In practice the 21.5″ length buys two things — ring spacing wide enough to support a long tube near its ends instead of near its middle, and enough travel in the saddle to bring a tube back into balance after a camera, filter wheel and off-axis guider go on the back. The variety of hole positions along the bar is what keeps it universal: rings, radius blocks and accessory clamps with different spacings all find holes.

Recommended Uses

• Carrying a long refractor or astrograph in rings on a Losmandy G-11 or Titan, or a Celestron CGX-L.
• Mounting a large SCT on radius blocks such as the Farpoint FDM12R or FDM14R.
• Running a main tube and a guide scope in line along a single bar.
• Rebalancing a setup whose imaging train has grown past the travel a shorter bar allows.
• Building a permanent observatory setup where the bar stays bolted to the tube.

Compatibility and Accessory Notes

The bar is cut to the D-size Losmandy standard, so it seats in Losmandy G-8, G-11 and Titan saddles, Celestron CGE, CGEM, CGX and CGX-L saddles, and the dual-format saddles on many iOptron, Sky-Watcher and Astro-Physics mounts. A saddle machined only for the narrower Vixen (V-size) profile takes a different bar or an adapter. On the tube side it works with any rings or blocks whose hole spacing lines up with one of the bar's hole positions, including Farpoint's own radius blocks and ring sets. Farpoint publishes the hole layout as a product drawing rather than a spec table, and does not publish the bar's width, thickness or hole spacing in figures. Send us your rings or tube model and their hole spacing and we will check the layout against the drawing for you.

Good to Know Before You Order

• This is the bar alone. Rings, radius blocks and mounting screws are separate items.
• The profile is D-size, not Vixen. A Vixen-only saddle calls for an adapter or a different bar.
• At 21.5″ the bar overhangs most saddles considerably. That overhang is what gives the balance travel, and it also means the bar is longer than the tube on some shorter instruments.
• Hole positions are published as a drawing, not as dimensions. We are glad to look them up against your hardware before you order.
• Farpoint publishes no width or thickness figures. The 21.5″ length is the only published dimension.
• The published weight is 4 lb. Farpoint lists the same 4 lb figure for the shorter 14″ bar, so this is best read as a shipping figure rather than the net weight of the plate.

Frequently Asked Questions

Is it difficult to install?

No. The bar bolts to rings or radius blocks through the holes already machined in it, and then slides into the saddle and is clamped. It is hand-tool work, though the length makes it easier with the tube resting on a bench.

How does it differ from the 14″ bar?

Length. Both are 57.3 Series light-weighted universal D-size bars from the same Radian design; this one is 21.5″ instead of 14″, which widens the available ring spacing and the balance travel.

Will it fit a Vixen saddle?

It is a D-size bar, so it fits saddles cut for the Losmandy profile and dual-format saddles. A Vixen-only clamp is a narrower standard.

What hole spacing does it have?

The bar carries a variety of mounting hole options along its length rather than one fixed spacing. Farpoint publishes the positions on a product drawing, and we can check a specific spacing against it.

Can two instruments share one bar?

Yes, within the saddle's capacity. The 21.5″ length leaves room for a main tube's rings and a guide scope or second clamp along the same bar.

Bottom Line

In short: the 21.5″ member of Farpoint's 57.3 Series, a light-weighted universal D-size Losmandy dovetail plate in black anodized aluminum, CNC-machined in the USA for long tubes and heavy imaging trains.