Introduction
The Lens Coverage Calculator checks whether a lens's image circle diameter covers your target sensor format without vignetting. Enter the image circle diameter from the manufacturer's data sheet and the sensor's width and height. The tool returns coverage status (full, partial, or none), the sensor diagonal, the margin between image circle and sensor diagonal, and the maximum sensor format the lens can cover. When coverage is partial, it shows the vignetting radius at the corners.
What This Tool Calculates
Sensor diagonal = sqrt(width squared + height squared). A lens covers the sensor fully when image circle diameter is greater than or equal to the sensor diagonal. Partial coverage occurs when the image circle is smaller than the diagonal but larger than the sensor width. Worked example: a vintage Leica-R 50mm with a 44mm image circle on a Full Frame sensor (36 x 24mm, diagonal 43.27mm). Image circle 44mm exceeds the diagonal 43.27mm, so the lens covers Full Frame with a 0.73mm margin. On an ALEXA 65 (54.12mm wide, diagonal 59.9mm), the same 44mm image circle falls 15.9mm short — no coverage.
The Formula and How It Works
A camera department considering Zeiss Contax RTS glass for a Full Frame ALEXA Mini LF shoot found that 85mm and 135mm primes at 46mm image circles covered cleanly, but the 28mm at 43mm was borderline — the tool flagged it as a partial coverage risk at maximum aperture. A production using Super 35-rated PL cinema lenses (31.4mm image circle) on an ALEXA LF (Full Frame, diagonal 44.8mm) discovered no coverage — saving a first-day disaster by renting Full Frame glass instead. A film student adapting Nikon AI-S 50mm f/1.4 glass (44mm image circle) to a Blackmagic URSA Mini 4.6K (Super 35, diagonal 26.6mm) confirmed full coverage with 17.4mm margin.
Real-World Examples
Sensor Diagonals vs Image Circle Requirements
Super 16mm (diagonal 14.5mm): covered by virtually any lens. Micro Four Thirds (diagonal 21.6mm): covered by most photo and cinema glass. Super 35 24.89mm (diagonal 31.1mm): borderline with some adapted photo glass. APS-C Sony (diagonal 28.2mm): covered by most photo glass. Full Frame 36mm (diagonal 43.27mm): requires Full Frame or medium format glass. ARRI ALEXA 35 (diagonal 33.9mm): needs ALEXA 35-rated cinema glass. ALEXA 65 (diagonal 59.9mm): requires dedicated large-format glass.
Pro Tips and Common Mistakes
| Detail | Value |
|---|---|
| Image circle specifications are typically measured at infinity focus and often shrink at close focus distances. | |
| Always test coverage at your closest planned focus distance. | |
| When shooting at maximum aperture, image circle can reduce due to optical vignetting — stop down to T2.8 for reliable coverage on borderline lenses. | |
| For anamorphic lenses, the image circle must cover the post-desqueezed sensor width: a 2x anamorphic on Super 35 needs coverage for a 49.78mm effective width. | |
| The most common mistake is assuming a 35mm photo lens covers any cinema Super 35 camera — some Super 35 sensors are wider than traditional 35mm film and fall outside the image circle.. |
Pro Tips and Common Mistakes
Pro Tips
- Checking lens coverage before committing to a rental saves you from discovering vignetting on your first shooting day with no replacement available.
- This tool runs in seconds from the manufacturer's published image circle data and gives you a clear pass or fail before the contract is signed..
Common Mistakes
Frequently Asked Questions
What happens if my lens does not cover my sensor?
You will see dark corners called vignetting. Severity ranges from subtle darkening to hard black circles depending on how far the image circle falls short. Vignetting can sometimes be corrected in post but reduces resolution and shadow detail in affected areas.
How do I find the image circle for a lens?
Check the manufacturer's technical data sheet, available on their website or from the rental house. For vintage lenses without published specs, use the format the lens was designed for as a minimum estimate: a 35mm photo lens typically has a 43mm+ image circle.
Can I use Super 35 cinema lenses on a Full Frame camera?
Only in the camera's Super 35 crop mode. In Full Frame mode, a Super 35 lens with a 31mm image circle will produce heavy corner vignetting on a sensor with a 43mm diagonal. Switching to crop mode reduces the sensor area to match the lens coverage.
Does image circle size indicate lens quality?
No. Image circle indicates sensor format compatibility, not optical quality. A small-format lens designed for Micro Four Thirds can be optically superior to a Full Frame lens in center sharpness. Coverage and quality are completely separate characteristics.
Start Calculating
Use the calculator above to run your numbers before your next production.
