Observatory · Optical bench

Focal Plane / Back-Focus Builder

Build

TypeBrandModel

Type → Brand → Model. Not listed? Choose Custom…

Target & tolerance

Reference pointMeasure from the rear shoulder of the reducer/corrector. The target is that reducer's required back focus (often 55 mm, but combination-specific); the reducer body itself is the origin and is not counted as consumed spacing.ToleranceManual target (mm, optional)

Saved trains

Saved on this device — sign in to sync to your account.

No saved trains yet. Build a train and save it to reuse it later.

Your optical bench is ready

Add your first part from the build rail — pick a Type, Brand and Model, create a custom part, or open a saved train. The bench draws and measures itself as your rig grows.

Train

Select a part to adjust it — or open the full table below.

Advanced — full equipment table, threads & per-segment breakdown

Order

Selected equipment

Reorder from telescope (top) toward the sensor (bottom); remove any row, or confirm/edit a contributing dimension.

No components yet

Add equipment from the build rail, or load a saved train.

Component	Category	Contribution	Threads	Confidence	Source

Tonight

Loading cockpit

Preparing source and confidence states.

Imaging train — telescope left to sensor right, on one measurement axis

Selected equipment

Loading cockpit

Imaging train — telescope left to sensor right, on one measurement axis

Selected equipment