A calculator for comparing lenses across different camera formats.

Live app: https://lens-calc.codebycarson.com/

Photographers often wonder: "If I shoot 50mm f/1.4 on full frame, what's the equivalent on my APS-C camera?" or "What medium format lens gives me the same look as my 35mm f/2?"

This calculator answers those questions by computing:

• Equivalent focal length — same field of view across formats
• Equivalent aperture — same depth of field or background blur
• Depth of field — near/far limits of acceptable sharpness
• Blur disc size — how blurry the background will be

Crop factor calculators exist, but most only convert focal length. The relationship between sensor size, aperture, and background blur is often misunderstood. This tool makes it concrete: enter your setup, see exactly what you'd need on another format to get the same image.

I built this with Claude Code — 5 hours of upfront research and documentation, then about 2.5 hours of implementation. I've been getting questions about how I approach AI-assisted coding so it's production-robust rather than typical vibe coded junk, so I documented this project as an example.

See how-i-built-this.md for the full process with chat logs and artifacts.

See design_docs/ for requirements, architecture, and technical decisions.

See research/ for the underlying math and sources.