Camera sharpness charts and CircleSFR software.

A printed 83-ring target and a pip-installable Python package for focus calibration and image quality measurement: sagittal and tangential MTF across the full field, from one capture.

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400, 800, 1200 mm print widthsNative 4:3 chart artwork83 circle SFR rings per chartDual-contrast edges built inpip install circlesfrSupport: rex@circlesfr.com
CircleSFR test workflow
ISO 12233:2024 informed

Order the printed target, capture it in the lab, then read SFR/MTF curves from the Python package.

CircleSFR chart source image showing the circular target array used on the landing page
Chart source image · circle array preview
circlesfr 0.1.0
CircleSFR annotated capture showing lens distortion with sagittal and tangential sector overlays
83 rings detected
0MTF50Nyquist
MTF50 0.2609 cy/pxNyquist 0.50Clip 0.2%
0.13field -1.00.38field -0.50.60center0.38field +0.50.13field +1.0
Tangential MTF at Nyquist/4 across the camera field, 0.60 at center to 0.13 at the edge. Measured with circlesfr from a single phone-camera capture.

Test workflow

Set up the chart, capture the image, measure SFR.

CircleSFR is a chart-and-software workflow: choose the print size, capture the target, then review SFR/MTF output from the same image.

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  1. 01

    Choose the chart

    Pick the 400, 800, or 1200 mm print from your sensor resolution and lens field of view.

    Use the size picker ->
  2. 02

    Capture in the lab

    Position the print, fill the frame, control lighting, and capture the target image.

    Read capture guidance ->
  3. 03

    Run CircleSFR

    pip install circlesfr, register all 83 rings automatically, and compute SFR/MTF per sector.

    See the software ->
  4. 04

    Read the results

    SFR50/SFR10 summaries, full curves, clipping stats, and annotated renders as Python objects.

    See the output reference ->

Printed chart

Buy the printed chart in the size your camera needs.

Original 4:3 artwork on archival matte inkjet, serialized, with a QC certificate in every tube. High- and low-contrast slanted edges ship on one chart — no separate contrast variants to choose between.

Order printed chartSee pricing
Chart sizes — native 4:3

Named by printed width. Suitability is the single-capture full-field rating on matte inkjet: MP ≈ (width in inches ÷ 8.8)².

CircleSFR 400$290
400 × 300 mm · 15.7 × 11.8 in
up to 3 MP
CircleSFR 800$690
800 × 600 mm · 31.5 × 23.6 in
up to 12 MP
CircleSFR 1200$1290
1200 × 900 mm · 47.2 × 35.4 in
up to 28 MP
Introductory pricing. Every price is confirmed on your order confirmation before payment; volume and academic pricing by email.

CircleSFR software

Measure SFR/MTF from the captured chart image.

A Python package built for lab scripts and notebooks: import a capture, and every ring becomes four measured edge sectors across the field.

  • Register all 83 ring markers automatically.
  • Split sagittal and tangential MTF per ring sector.
  • Summarize SFR50/SFR10 with sampling efficiency.
  • Catch clipped exposures before they skew results.
circlesfr.analyze("capture_042.tif")
CircleSFR annotated capture showing lens distortion with sagittal and tangential sector overlays
Rings83 detected
SFR500.2609 cy/px
Sectors332 measured
0MTF50Nyquist
MTF50
0.2609 cy/px
Nyquist
0.50 cy/px
Rings
83
Clipping
0.2% high

Get the software

One pip install, one license file.

CircleSFR ships as a Python package with offline license keys — no activation server, no phone-home, air-gapped labs supported. Evaluation is free for 30 days with watermarked outputs; commercial use starts at $490 per seat per year.

Get the softwareSee license tiers
circlesfr 0.1.0 · PyPI release in preparation
$ pip install circlesfr
$ export CIRCLESFR_LICENSE=~/.circlesfr/license.key

>>> import circlesfr
>>> circlesfr.analyze("capture_042.tif").summary
Python 3.10+ · NumPy, SciPy, Pillow · macOS, Windows, LinuxOffline license keys — no activation server

Built around current ISO 12233 SFR workflows.

ISO lists ISO 12233:2024 as the current edition for resolution and spatial frequency response measurement. CircleSFR uses original chart artwork that combines circle SFR targets with license-free sharpness features, and describes its pipeline as ISO 12233-informed rather than claiming compliance.

View ISO pageRead the standards note

Start with the chart, the software, or both.

Charts are printed to order and ship worldwide. Software licenses are issued by email while online checkout is in preparation.

Buy printed chartGet the software

Questions: rex@circlesfr.com