Photography Calculators

Sensor & focal length

Equivalent Aperture Calculator

f/1.8 on 1.5× APS-C frames like f/2.7 on full frame for depth of field and field of view. It is still f/1.8 for exposure — the meter, ISO and shutter do not change — but the smaller sensor collects less total light, so noise at the same print size is also closer to full frame at f/2.7. Use this when someone says ‘just get the 50 /1.8’ and you are not on the same format.

Inputs

Units
f/

f-number on the lens you will mount.

×

1 full frame, ~1.5 APS-C, ~1.6 Canon APS-C, 2 Micro Four Thirds.

Results

Full-frame equivalent aperture
2.70f/

f-number × crop: the full-frame f-number with the same DoF at matched framing. Exposure stays at the real f-number.

DoF stop delta vs full frame
1.17stops

How many stops more DoF you get versus the same f-number on full frame.

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Calculation method

Multiply the taking f-number by crop factor to get the full-frame f-number that would match field of view and depth of field. The DoF stop delta counts the aperture stops between f/N and that equivalent f-number, which is 2·log2 of the crop: 1.5× is about 1.17 stops more depth, 2× is two stops — the usual ‘Micro Four Thirds gives two stops more DoF than full frame’ claim. Light per unit area on the sensor is still set by the real f-number; ISO and shutter do not get a crop bonus.

Exact formula

N_eq = N × crop. dofStopDelta = 2·log2(crop), the aperture stops between f/N and f/N_eq. Limits: Exposure on the sensor is still N; T-stops, speed boosters and pixel-size noise are omitted.

Why portraits look different

The same 50 mm f/1.8 on APS-C is a tighter crop; step back to match the framing and you also get more DoF than on full frame. To match a full-frame 50/1.8 look you want about a 33 mm f/1.2 on 1.5× — which is why those lenses exist.

Video T-stops

T-stop is transmission. Equivalent aperture here is still f-number geometry. A T1.5 cine lens on S35 is not ‘the same’ as T1.5 on full frame for DoF.

Frequently asked questions

Do I set f/2.7 on the lens?

No. You set f/1.8. f/2.7 is how you would describe the DoF to a full-frame shooter. The camera meters f/1.8.

What about noise?

At the same f-number, shutter and ISO the exposure is identical, so you do not need more ISO. The smaller sensor simply collects less total light, so the picture is noisier at the same print size. That is the same crop² factor: f/1.8 on 1.5× gathers about the light of f/2.7 on full frame, which is why the equivalent also predicts noise.

Speed booster again?

A 0.71× adapter turns a 50 mm f/1.8 into a 35.5 mm f/1.28 on the sensor. Enter that new f-number with the sensor’s own crop (f/1.28 × 1.5 ≈ f/1.9), or keep f/1.8 with the combined crop 1.5 × 0.71 ≈ 1.07. Applying 0.71 to both the f-number and the crop counts the adapter twice.

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