35 mm equivalent focal length
In
On any 35 mm film camera, a 28 mm lens is a wide-angle lens, and a 200 mm lens is a long-focus lens. Because digital cameras have mostly replaced film cameras and the image sensor size that also determines the angle of view is not standardized as the film size was, there is no uniform relation between the lens focal length and the angle of view due to possibilities of using various image sensor sizes at the same focal length (i.e., a different image sensor size resulting in a different angle of view at the same lens focal length). The 35 mm equivalent focal length of a particular lens–sensor combination is the focal length that one would need for a 35 mm film camera to obtain the same angle of view. Two lens-sensor combinations with the same 35 mm equivalent focal length are expected to have the same angle of view.
Most commonly, the 35 mm equivalent focal length is based on equal diagonal angle of view.
Calculation
35 mm equivalent focal lengths are calculated by multiplying the actual focal length of the lens by the
According to CIPA guidelines,[2] 35 mm equivalent focal length is to be calculated like this: "Converted focal length into 35 mm camera" = (Diagonal distance of image area in the 35 mm camera (43.27 mm) / Diagonal distance of image area on the image sensor of the
Depth of field equivalent
Quoted 35 mm equivalent focal lengths typically ignore
Equivalent depth of field can be calculated the same way using the crop factor.
Conversions
A standard 35 mm film image is 36 mm wide by 24 mm tall (35 mm refers to the height of the film including the perforations for film transport), and the diagonal is 43.3 mm. This leads to the following conversion formulas for a lens with a true focal length f:
Image size | diagonal-based EFL | width-based EFL |
---|---|---|
4:3 (sensor width w) | f35 = 34.6 f /w mm | f35 = 36.0 f /w mm |
4:3 (sensor diagonal d) | f35 = 43.3 f /d mm | f35 = 45.0 f /d mm |
3:2 (sensor width w) | f35 = 36.0 f /w mm | f35 = 36.0 f /w mm |
3:2 (sensor diagonal d) | f35 = 43.3 f /d mm | f35 = 43.3 f /d mm |
For historical reasons, sensor size specifications such as 1/2.5" do not match the actual sensor size, but are a bit larger (typically about a factor of 1.5) than the actual sensor diagonal.
Apart from the width- and diagonal-based 35 mm equivalent focal length definitions, there is a third definition: EFL = 50 f /d mm.[1] However, it is not clear to what extent this definition is used.[citation needed]
References
- ^ a b What is "35 mm equivalent focal length?" The Panorama Factory, 2004.
- ^ a b "CIPA DCG-001-Translation-2005 Guideline for Noting Digital Camera Specifications in Catalogs" (PDF). Archived from the original (PDF) on 2017-02-02. Retrieved 2015-10-19.
- ^ Atkins, Bob. "Digital Depth of Field". Retrieved 23 May 2012.
- ^ Butler, Richard. "What is equivalence and why should I care?". DPReview. Retrieved 22 August 2019.
- ^ Vincent Bockaert, Sensor sizes. DPreview.com.
External links
- Focal Length Conversion for medium format and large format, at photo.net
- Focal Length at dpreview