Why is 50mm a normal lens?

Its 46-degree FOV on full frame matches natural human perception.

What focal length for a specific field of view?

FL = sensor width / (2 x tan(FOV/2)). This calculator lets you experiment.

Photography

Focal Length Calculator

Calculate equivalent focal length across sensor sizes using crop factor. See field of view and coverage at any distance.

Quick Answer

Equivalent focal length = actual focal length × crop factor. A 50mm lens on APS-C (1.5x crop) gives a 75mm equivalent field of view. The crop factor is 36mm divided by your sensor width.

Lens & Sensor

Focal Length (mm)

Your Sensor

Subject Distance (m)

Results

50mm

FF Equivalent

1.00x

Crop Factor

39.6°

Horizontal FOV

7.2m

Width at Distance

Equivalent Focal Lengths Across Formats

Sensor Format	Equivalent FL	Crop Factor
Full Frame (36mm)	50mm	1.00x
APS-C Canon (22.3mm)	31mm	1.61x
APS-C Nikon/Sony (23.5mm)	33mm	1.53x
Micro Four Thirds (17.3mm)	24mm	2.08x
1" Sensor (13.2mm)	18mm	2.73x
1/2.3" (6.17mm)	9mm	5.83x

About This Tool

The Focal Length Calculator helps photographers understand how their lenses behave on different camera sensors. A 50mm lens on an APS-C camera doesn't give the same field of view as a 50mm on full frame. This calculator shows the equivalent focal length, horizontal field of view, and scene coverage at any distance.

What Is Crop Factor?

Crop factor is the ratio of a 35mm full-frame sensor diagonal to your camera sensor diagonal. Since most lens focal lengths are specified for 35mm film, the crop factor tells you what focal length on full frame would give the same field of view. An APS-C sensor with a 1.5x crop factor makes a 50mm lens frame like a 75mm on full frame.

Field of View

The field of view is the angle of the scene your camera captures. Wide-angle lenses (14-35mm on FF) have a broad field of view of 63 to 114 degrees. Normal lenses (40-60mm) see about 40-57 degrees, similar to human perception. Telephoto lenses (70mm+) have a narrow field of view, magnifying distant subjects. The sensor size and focal length together determine the FOV.

Practical Impact

Understanding crop factor matters when buying lenses, especially for different systems. If you switch from full frame to APS-C, your 24-70mm zoom effectively becomes a 36-105mm. You lose wide-angle coverage but gain telephoto reach. Conversely, switching from APS-C to full frame makes all your lenses wider, which is great for landscape but means your 200mm telephoto becomes less of a reach advantage.

Coverage at Distance

Knowing how wide your frame is at a given distance helps with planning shots. A 200mm lens on full frame covers about 1.8 meters wide at 10 meters. This is useful for sports and wildlife photographers who need to know if they can fill the frame with a subject at a known distance. Event photographers use this to plan their position relative to the stage.

Frequently Asked Questions

What is the crop factor for my camera?

Full frame: 1.0x. APS-C Canon: 1.6x. APS-C Nikon/Sony/Fuji: 1.5x. Micro Four Thirds (Olympus/Panasonic): 2.0x. 1-inch sensor: 2.7x. Phone cameras vary but are typically 5-7x. Check your camera specs for the exact sensor size.

Does crop factor change the actual focal length?

No. A 50mm lens is always a 50mm lens regardless of the sensor behind it. Crop factor only changes the field of view by cropping the image circle. The perspective, compression, and optical characteristics of the lens stay the same. Only the framing changes.

Why is 50mm considered a 'normal' lens?

On full frame, a 50mm lens has a field of view (about 46 degrees diagonal) similar to what the human eye perceives as natural. On APS-C, the equivalent is about 33mm. On Micro Four Thirds, it's 25mm. The 'normal' focal length is roughly equal to the sensor diagonal.

Does crop factor affect depth of field?

Indirectly, yes. To get the same field of view on a crop sensor, you use a shorter focal length or stand further away. Both increase depth of field. A 50mm f/1.8 on APS-C gives the DoF of roughly a 75mm f/2.7 on full frame at the same framing.

What focal length do I need for a specific field of view?

Use the formula: focal length = sensor width / (2 x tan(FOV/2)). For a 90-degree horizontal FOV on full frame (36mm sensor width), you need about 18mm. On APS-C, you'd need about 12mm. This calculator lets you experiment with different values to find the right lens.

Was this tool helpful?