Focus Calibration — 3-Point vs Lookup Table¶

BOTH

Flair offers two methods for calibrating a lens: Three-Point calibration and Table (lookup) calibration. Choosing the correct method depends on the quality of the lens, how well it is collimated (or back-focused), and whether its focus markings are accurate. Using the wrong method will produce poor or unusable focus tracking regardless of how carefully you calibrate.

Three-Point calibration — when it works¶

Three-Point calibration uses three measured focus distances to define an exponential curve that models the physics of the lens. This works correctly when:

The lens is a high-quality prime (Cooke, Zeiss, Arri, or similar)
The lens behaves close to "perfect" lens physics — an infinitely thin, exponentially curved focus response
The lens is correctly collimated (the focus chip plane is at the correct distance behind the lens mount)
The infinity mark is accurate and clearly defined on the lens barrel

For high-quality primes that meet these conditions, three-point calibration is the preferred method and should give excellent results.

Table (lookup) calibration — when it is required¶

You must use Table calibration instead of Three-Point when:

The lens is poor quality — it does not follow a predictable exponential focus curve
The lens has marks in the wrong positions on the focus ring — some lens sets (including certain Summilux and Summicron lenses) have incorrectly positioned markings despite looking correct on camera
The lens is a macro lens — the focus response at very close distances departs significantly from the standard exponential model
The collimation is wrong — the lens mount is not correctly shimmed, or the back focus is misadjusted

Macro lens note: For macro lenses using Table calibration, you must include points for the longer distances between the furthest calibration mark and infinity. If there is a large gap at the far end of your table, Flair will not know what to do in that region.

Collimation and back focus — why they matter¶

Collimation (historically called "optical bench collimation") means the lens is mounted so that the focal plane is at exactly the correct distance behind the lens mount flange. In older systems this was set in the lab. Modern camera bodies implement this via back focus adjustment.

If the collimation is wrong, neither Three-Point nor Table calibration will work reliably. The lens will appear to focus correctly at the calibration points but will drift between them.

Changeable lens ports and shims: If your camera has changeable lens mount ports (e.g. switching from PL to Canon EF), a shim is provided to adjust collimation for each mount. If you have the wrong number of shims installed, collimation will be off and no calibration method will compensate for it.

Testing collimation before calibration:

Set up a screen or target at a known distance.
If the lens markings are correct and collimation is right, the focus ring should read exactly what the chart says. If 5 feet does not read 5 feet on the lens barrel, the collimation or lens markings are suspect.

Broadcast (news gathering) lenses — special note¶

Broadcast (news gathering / ENG) lenses measure focus distance from the green ring on the front of the lens, not from the camera chip plane. This is fundamentally different from cinema lenses, which measure from the film/sensor plane. This must be accounted for in the Measure Offset and Measure Optical Offset settings in the Flair lens setup.

For broadcast lenses with internal motors, see Broadcast Lens Calibration for the specific calibration procedure.

Zoom lens calibration note¶

If you need to use Table calibration on a zoom lens, set the zoom somewhere in the middle of its travel at a known focal length mark, and use that focal length value in subsequent calculations. The internal scale used by broadcast zoom lenses is not necessarily the same as the physical focal length in mm.

Flair measure offset and measure optical offset¶

These two Flair lens setup fields can cause confusion. There are references to these in the Flair manual and in tutorial videos that explain the correct usage for different lens types. Consult those references if unsure which offsets apply to your lens.

Tutorial Videos¶

Tutorial	Link
Lens Calibration — Part 1 (Three-Point calibration procedure)	Watch
Lens Calibration — Part 2 (Table/lookup calibration)	Watch

Source: Three Point versus Table Lens calibration — talk.mrmoco.com