Why do I need equivalent focal lengths?

When switching between camera systems with different sensor sizes, equivalent focal lengths tell you which lens on the new system gives the same field of view. For example, a 35mm lens on an APS-C body (1.5×) frames like a ~52.5mm lens on full frame (35 × 1.5 = 52.5), because the smaller sensor crops into the image — so to match that framing on full frame you would reach for about a 52mm lens.

How do I convert between any two sensor sizes?

First convert to full frame equivalent (multiply by the source crop factor), then divide by the target crop factor. For APS-C (1.5×) to MFT (2×): multiply by 1.5, then divide by 2. A 50mm APS-C lens is equivalent to 37.5mm on MFT.

Does equivalent focal length affect perspective?

Equivalent focal lengths give the same field of view, but perspective depends only on camera-to-subject distance. If you stand in the same position, you get the same perspective regardless of focal length — cropping simply selects a portion of the scene. Moving closer or further changes perspective.

What full-frame focal lengths are most common?

Key focal lengths on full frame: 14-16mm ultra-wide landscape, 24mm wide reportage, 35mm street, 50mm standard/portraits, 85mm portrait, 135mm tight portrait/events, 200-400mm wildlife/sport. On APS-C, divide by 1.5 for the equivalent lens: 35mm FF ≈ 23mm APS-C.

Equivalent Focal Length Calculator

How We Calculate This

This calculator converts focal lengths between any two sensor sizes:

Conversion Formula

Full-frame equivalent = focal length × source crop factor

Target focal length = full-frame equivalent ÷ target crop factor

This works because crop factor represents the ratio of full-frame diagonal to sensor diagonal. The field of view is determined by the ratio of sensor size to focal length, so matching the field of view requires scaling the focal length by the ratio of crop factors.

Diagonal field of view

The diagonal angle of view on the source body is 2 · arctan(d ÷ (2f)), where d is the source sensor diagonal (full-frame diagonal ÷ source crop factor) and f is the focal length. A shorter focal length or larger sensor widens the angle.

DoF-equivalent aperture

To match depth of field across systems, multiply the source f-number by the conversion ratio (source ÷ target crop factor). For the same framing and depth of field, a larger sensor needs a smaller f-number (wider aperture) — that is why full frame is prized for shallow depth of field.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates based on standard optical and photographic formulas. Results may vary with specific equipment.

Equivalent Focal Length Calculator — Cross-System Comparison