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Focal Length Equivalent Calculator

Work out focal length equivalent instantly with clear inputs, formula shown and shareable results.

About Focal Length Equivalent Calculator

Equivalent focal length is the actual focal length times the crop factor, and equivalent aperture multiplies the f-number by the same factor when comparing depth of field. Crop factor changes framing and depth of field but not exposure, which is why a 35 mm f/1.8 on APS-C frames like 52 mm and blurs like f/2.7 while still metering as f/1.8.

Formulas

Equivalent focal length

equivalent = actual focal length x crop factor

Equivalent aperture

equivalent f-number = actual f-number x crop factor

Worked example

With the default values below, Focal Length Equivalent Calculator returns Full frame equivalent focal length of 52.50. Change any input above and every figure here is recalculated in your browser.

Inputs used

Actual focal lengthminimum 1 mm
35 mm
Crop factorminimum 0.1
1.5
Apertureminimum 0.5 f
1.8 f

Results

Full frame equivalent focal length
52.50 mm
Equivalent aperture for depth of field
2.700 f
Stops of depth of field difference
1.170
Change in apparent reach
50.00%

Step by step

  1. 1Values used
  2. 2Equivalent focal length
  3. 3Equivalent aperture
  4. 4Full frame equivalent focal length= 52.50 mm
  5. 5Equivalent aperture for depth of field= 2.700 f
  6. 6Stops of depth of field difference= 1.170
  7. 7Change in apparent reach= 50.00

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Focal Length Equivalent figure worked out?

equivalent = actual focal length x crop factor. Equivalent focal length is the actual focal length times the crop factor, and equivalent aperture multiplies the f-number by the same factor when comparing depth of field.

Why does this matter?

Crop factor changes framing and depth of field but not exposure, which is why a 35 mm f/1.8 on APS-C frames like 52 mm and blurs like f/2.7 while still metering as f/1.8.

What do I need to enter?

Enter actual focal length, crop factor, aperture. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.

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