Equivalent Focal Length Calculator
Full-frame equivalent focal length and aperture for any sensor format.
Results
- Crop factor
- 2.00x
- Full-frame equivalent focal length
- 50mm
- Equivalent aperture (depth of field only)
- f/3.6
How much narrower this sensor's field of view is compared to full frame, at the same focal length.
The focal length on a full-frame camera that would give the same angle of view as this lens on this sensor.
The full-frame aperture that would give a similar depth of field and background blur. Your actual f-number above still controls exposure on this sensor.
How it works
Full-frame equivalence exists because photographers spent decades building intuition around 35mm film, and that intuition needs translating when the sensor changes. A 25mm lens on Micro Four Thirds frames like a 50mm on full frame, so it is described as a 50mm equivalent.
Equivalent aperture is the part that causes arguments. Multiplying the f-number by the crop factor tells you what full-frame aperture would produce a similar depth of field and background blur at the same framing. It says nothing about exposure: an f/1.8 lens is f/1.8 for metering on every camera ever made.
So a 25mm f/1.8 on Micro Four Thirds frames like a 50mm and blurs backgrounds like an f/3.6, while still exposing like an f/1.8. All three statements are true at once, which is why the topic generates so much confusion.
The formula
equivalent focal length = f × crop, equivalent aperture = N × crop
The equivalent aperture applies to depth of field and total light gathered across the frame, never to exposure.
Frequently asked questions
- Does my lens become slower on a crop sensor?
- No. Shutter speed and ISO stay exactly where your meter puts them. The lens transmits the same light per unit area regardless of what sits behind it.
- Then why talk about equivalent aperture at all?
- Because it correctly predicts two real things: how much background blur you will get, and how much total light the whole sensor collects, which drives noise. Both are genuinely worse on a smaller sensor at the same f-number and framing.
- Does equivalence apply to ISO too?
- In the same sense. Matching total light means the smaller sensor is working with less of it, so equivalent-noise comparisons scale by the crop factor squared, about two stops between full frame and Micro Four Thirds.
Read more about this
- Crop factor and equivalence, without the argumentsEveryone agrees crop factor multiplies focal length. The argument starts one line later, at aperture, and it is mostly people answering different questions.
- Why cheap lens adapters lose infinity focusOne measurement decides whether a lens adapter can ever work properly, and it is not one that adapter listings tend to mention.