Lens equivalence calculator
Full equivalence means matching framing, depth of field and total light. That takes changing the focal length, the aperture and the ISO together.
Equivalent focal length
50.00mm
- Equivalent aperture
- 3.600
- Equivalent ISO
- 1600
- Difference in stops of depth of field and light
- 2.000
- Ratio of total light gathered
- 4.000
- Full-frame equivalent focal length
- 50.00
- Full-frame equivalent aperture
- 3.600
Show the working
- Focal length = 25
- Aperture = 1.8
- ISO = 400
- Crop factor of the source format = 2
- Crop factor of the target format = 1
- ratio = 1 > 0 ? 2 / 1 : 0 = 2
- Equivalent focal length = 25 * 2 = 50
- Equivalent aperture = 1.8 * 2 = 3.6
- Equivalent ISO = 400 * 2^2 = 1600
- Difference in stops of depth of field and light = 2 * log2(2) = 2
- Ratio of total light gathered = 2^2 = 4
- Full-frame equivalent focal length = 25 * 2 = 50
- Full-frame equivalent aperture = 1.8 * 2 = 3.6
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
Scenarios & local history
Compare a saved scenario
Recent calculations
The formula
- equivalent focal length = focal length x crop ratio
- equivalent aperture = f-number x crop ratio
- equivalent ISO = ISO x crop ratio squared
Equivalent aperture does not change the exposure. It describes depth of field and the total light on the sensor, which is what sets noise.
A 25 mm f/1.8 on Micro Four Thirds frames and blurs like a 50 mm f/3.6 on full frame.