Lens Equivalence Comparator

{{ summaryHeading }}{{ summaryPrimary }}{{ summaryLine }}Scale{{ formatNumber(values.crop_ratio, 2) }}xSource{{ formatNumber(values.source_crop_factor, 2) }}xTarget{{ formatNumber(values.target_crop_factor, 2) }}x

Setup preset:

Start from a common stills, cinema, or compact-camera comparison.

Source format:

Use the camera or recording format you are matching from.

Source active sensor:

Camera active areas and lens markings are conventionally specified in millimetres.

× mm

Target format:

The exact target focal length and depth-of-field-look f-number follow this format.

Target active sensor:

Use the active recorded area, not the nominal sensor package size.

× mm

Source focal length: {{ formatNumber(source_focal_mm, 1) }} mm

Lens focal-length markings use millimetres across camera formats.

Source aperture: f/{{ formatNumber(source_aperture, 1) }}

Enter the f-number used on the source lens.

Source extra crop:

Keep 1.00× for an uncropped stills or open-gate source.

Target extra crop:

Keep 1.00× when the target uses the full selected active area.

Target lens set:

The exact equivalence stays the same; only the nearest stocked lens changes.

Close-match tolerance: {{ match_tolerance_percent }}%

Use a smaller percentage for stricter kit planning.

Measure	Source	Target	Use	Copy
{{ row.measure }}	{{ row.source }}	{{ row.target }}	{{ row.use }}

Nearest practical lens

Exact match

Use {{ formatNumber(values.target_focal_mm, 1) }} mm on {{ targetFormatLabel }} for matched framing from the same camera position.

From the selected set

{{ values.nearest_lens_status }} {{ formatNumber(values.nearest_lens_mm, values.nearest_lens_mm < 20 ? 1 : 0) }} mm differs by {{ formatNumber(Math.abs(values.nearest_lens_delta_percent), 1) }}% from the exact match, giving {{ values.nearest_lens_direction }} framing.

Aperture and exposure

About f/{{ formatNumber(values.dof_equivalent_aperture, 1) }} matches depth-of-field appearance. Meter that target lens at its actual f-number; crop equivalence does not make exposure automatic.

Moving a composition from one camera format to another changes the focal length needed for the same framing. The physical focal length printed on a lens does not change, but a smaller active image area records a narrower portion of the lens's image circle and therefore behaves like a crop of a larger format.

Lens equivalence is most useful when camera position and subject distance stay fixed. Under that condition, matching the angle of view gives a target focal length, while scaling the f-number by the same format ratio gives a rough match for depth-of-field appearance. Exposure is a separate question: the target camera must still be metered at the actual f-number fitted to it.

Active image area: The width and height actually recorded in the selected stills or video mode.
Crop factor: The 36 × 24 mm full-frame diagonal divided by the active-area diagonal.
Equivalent focal length: A comparison value for similar framing, not a different marking on the physical lens.
Equivalent aperture: An f-number comparison for depth-of-field look after framing is matched, not automatic exposure equivalence.

Nominal format names are only starting points. Video crops, digital stabilization, open-gate modes, and manufacturer-specific active areas can change the recorded diagonal. Lens breathing, distortion, focus distance, aspect-ratio differences, and the final crop can also keep two nominally equivalent setups from producing identical images.

How to Use This Tool:

Describe the source setup first, then choose the active target format you need to match.

Choose a Setup preset or select the Source format and Target format directly. For a custom format, enter the recorded width and height in millimetres.
Enter the physical Source focal length and the actual Source aperture. Do not enter a full-frame-equivalent lens marking.
Set Source extra crop or Target extra crop above 1.00× only when a recording mode, stabilization mode, or later extraction reduces the selected active area.
Select the Target lens set. Open Advanced to tighten or loosen the 2% to 20% Close-match tolerance used for the practical lens label.
Read the exact target focal length and depth-of-field-look f-number before checking Lens choice for the nearest stocked focal length.

Interpreting Results:

Use the exact target focal length for the geometric match. The suggested real lens is only the closest value in the selected lens set, and its percentage shows how much tighter or wider its framing will be.

Close match means the nearest lens is within the selected tolerance, including the boundary.
Practical substitute means the miss is above that tolerance but no more than 2.5 times it.
Different framing means the miss is larger; moving the camera or cropping would change perspective or recorded detail.
The equivalent f-number describes depth-of-field appearance at matched framing. Meter exposure with the actual lens, shutter speed, sensitivity, filters, and lighting.

Technical Details:

The model uses sensor diagonals so width and height both affect the result. An extra crop divides both active dimensions before the diagonal is calculated. This keeps a 16:9 or stabilized recording mode distinct from the nominal sensor package.

Formula Core

For active width w and height h, the diagonal is the straight-line distance across the recorded rectangle. The full-frame reference diagonal is based on 36 × 24 mm.

\begin{array}{rcl} d & = & \sqrt{w^{2} + h^{2}} \\ c & = & \frac{\sqrt{36^{2} + 24^{2}}}{d} \end{array}

The source-to-target scale is the source crop factor divided by the target crop factor. That same scale produces the exact focal-length match and the depth-of-field-look f-number.

\begin{array}{rcl} q & = & \frac{c_{source}}{c_{target}} \\ f_{target} & = & f_{source} \times q \\ N_{look} & = & N_{source} \times q \end{array}

The displayed exposure-stop delta is twice the base-2 logarithm of the scale ratio. It quantifies the f-number scaling but does not set exposure. Full-frame reference focal length and aperture are the physical source values multiplied by the source crop factor.

Rule Core

The nearest-lens result compares the exact focal length with a fixed list of common photo primes, cinema primes, or zoom-ring marks. Its signed difference is the nearest lens divided by the exact match, minus one, expressed as a percentage.

Nearest lens classification rules
Status	Absolute focal-length difference	Meaning
Close match	Less than or equal to the selected tolerance	Start with the suggested lens and compare the live composition.
Practical substitute	Above the tolerance and less than or equal to 2.5 × tolerance	Expect a visible difference that may require movement or cropping.
Different framing	Above 2.5 × tolerance	Treat it as another composition or choose a different lens set.

Custom active dimensions must each be from 1 to 80 mm. Source focal length accepts 1 to 1,200 mm, source aperture accepts f/0.7 to f/64, and each extra crop accepts 1.00× to 4.00×.

Worked Examples:

APS-C portrait to full frame

A 35 mm lens at f/1.8 on a 23.5 × 15.6 mm APS-C active area has a crop factor of about 1.534×. With an uncropped 36 × 24 mm target, the exact match is 53.7 mm with an f/2.8 depth-of-field look. In the photo-prime set, 56 mm is 4.3% tighter, so an 8% tolerance labels it a Close match. Exposure still uses the actual aperture selected on the 56 mm lens.

References:

CIPA DCG-X002-Translation-2015 digital camera specification guideline, Camera & Imaging Products Association, 2015.
The DX and FX Formats, Nikon Imaging USA.
Aperture, f-numbers and depth of field, Sony.