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Focus Calibration — 3-Point Fails, Use Lookup Table

CONFIRMED RESOLVED ALL RIGS BOTH

Summary

Standard 3-point focus calibration does not work well with all lenses — particularly cheap or non-cinema lenses, macro lenses, and probe lenses with non-linear focus rings. The solution is to enable the Lookup Table calibration mode, which supports up to 20 evenly-spaced calibration points.

Symptoms

  • Focus Follows Target is consistently soft or off at certain focus distances
  • 3-point calibration gives a curve that doesn't match the actual lens behaviour
  • Lens markings do not match where focus is actually sharp
  • Lenses such as IBE Raptor Macros, DZO Gnosis, Laowa probes, or any Chinese-brand cine lenses

Technical Background

Flair's standard focus calibration uses a 3-point curve (close, mid, far) to map lens unit positions to real-world distances. This works well for high-quality cinema primes and zooms where the focus ring has a predictable, near-linear mapping.

Lenses with non-linear focus rings — including many macro and lower-cost cine lenses — do not fit this 3-point curve well. Flair supports a multi-point Lookup Table mode that stores up to 20 discrete distance/position pairs and interpolates between them, giving a much more accurate map across the full focus range.

Solutions

Solution A — Enable Lookup Table Mode

  1. Open Setups -> Lens Setup for the relevant lens.
  2. On the Calibrate Focus line, look for the Lookup checkbox on the left side.
  3. Check the Lookup box to switch from 3-point to lookup table mode.
  4. Enter up to 20 focus points. 10 evenly-spaced intervals across the full focus range is generally sufficient.
  5. For each point: set the lens physically to a known focus distance, store the axis value, enter the real-world distance.
  6. Middle-click at the top of the column to blank out unused rows (rows default to 0.000 — unused zeros must be cleared or they corrupt the curve).
  1. Same procedure in Setups -> Lens Setup — the Lookup checkbox is on the Calibrate Focus line.
  2. Middle-click at column top to clear unused rows.

How many points?

10 evenly-spaced points across the full focus range gives more than enough accuracy for most lenses. More points are rarely needed.

Solution B — Use Real-World Distances, Not Lens Markings

For lenses where even the Lookup Table proves difficult (e.g., very old or inaccurate lens markings):

  • Measure the actual distance from the sensor plane to the subject using a tape measure.
  • Use these measured distances as your calibration inputs rather than the distance markings on the lens barrel.
  • Łukasz Trojan's method for Laowa Pro2be: browse the robot to position focus while watching sharpness (using the robot's position as the distance reference), rather than reading lens markings. Works reliably where the lens markings cannot be trusted.

Solution C — Avoid FFT, Use Focus Follows Object

When focus accuracy across the full range is difficult to achieve:

  • Switch from Focus Follows Target (FFT) to Focus Follows Object (FFO) — enter measured distances at each key position manually.
  • Or use Focus Independent and manually insert focus keyframes as you browse the move.
  • For macro work past 1:1 magnification: use Focus Independent (FFT and FFO break down past 1:1 as focus is no longer determined by distance).

Focus curve type

FFT and FFO follow an exponential focus curve (matching the focus scale of a real lens). Focus Independent uses a linear curve — so with FI you may need more keyframes to match the actual lens behaviour, especially over wide focus ranges.

Affected Lenses

  • IBE Raptor Macros — confirmed poor 3-point calibration (Robert Eder, 2021)
  • DZO Gnosis Macro — confirmed, lookup table resolves it (Grzegorz Najder, 2023)
  • Laowa 24mm probe — difficult to calibrate (Tom D, 2020)
  • Laowa Pro2be — focus distances measured from front of lens, not sensor (on Pro2be and DZO X-tract); old Laowa still measures from sensor
  • Zeiss CP.2 and other high-quality cine primes — 3-point generally fine
  • Any lens with non-linear or inaccurately-marked focus ring — use Lookup Table

Prevention / Best Practice

  • Always use high-quality cinema glass where possible for FFT work.
  • For new or unfamiliar lenses, test with a focus chart before shooting to verify calibration accuracy across the full range.
  • Keep a spare lens file in Flair using the Lookup Table method as a backup.
  • Lens calibration data is stored in \Flair\FlairClassic\Configs\LENS.DBF — copy this file to transfer all lens calibrations to another Flair PC.

References

Official Documentation

Bolt Quick Start Guide — p.65: Ulti-box Connector Summary — Lens, Focus and Zoom Ports

Flair 7 Manual — Ch.5 Setups: Lens Setup: Focus Calibration — p.40

WhatsApp Excerpts

  • 2021-03-19 07:23 - ~ Jeremy Andrews: I’ll give this piece of advice again - but I feel it should be in the manual! You can make your target tracking focus axis a ‘dummy’ axis (not on the network), but still designated as the focus axis. You can use orbital and also move around an object in TT You then copy all your focus settings to a spare axis, and run the focus as independent. You can happily store any focus keyframes you like on an orbital or TT move, but you can’t use ‘follow target’ or ‘follow object’ Frankly, I usually have...
  • 2021-03-19 18:14 - ~ Robert Eder: Hi There, is there a way to calibrate the focus motor with more than 3 points? I am using IBE Raptor Macros and they do not calibrate well with just 3 points for the motor.
  • 2021-03-19 18:18 - ~ Raphael: You can set a lookup table in the lens setup with more than three points
  • 2021-03-19 18:20 - Timothy Heys Cerchio: Lookup 'check' box on the left of the Calibrate Focus Line 😉
  • 2021-03-19 18:21 - Timothy Heys Cerchio: You can put up to 20 points. But 10 evenly spaced intervals on the lens will be more than enough 😁
YouTube Flair 7 Quick Tips: Focus Calibration Flair 7

▶ 00:49 — Setting up a new lens: entering lens data

▶ 01:26 — Zero focus axis before calibration

▶ 01:46 — Store focus midpoint in calibration table