How to use this chart:

If you are using digital FX or 35mm film format (both a 24 x 36mm frame), and wish to determine what a digital DX format (16 x 24mm) lens equivalent would be, look at the FX focal length and then find the equivalent in DX.

If you are using, for example, a 4”x5” camera with a 150mm lens and wish to know which FX format lens would be its equivalent on a FX camera, the FX equivalent would be 50mm. 

If you want to know which 4x5” camera lens would be equivalent to a 80mm FX lens, the chart shows that it would be a 240mm lens.  The lens equivalent for a 80mm 6x6cm format lens on a 4x5” camera would be a 150mm  lens.

THIS CHART IS MATHEMATICAL EQUIVALENTS.  Sometimes there is a slight difference due to lens performance characteristics.

Another example: You are using a 24mm x 36mm format (a.k.a. 135 film) with an 85mm lens.  You want to use a large format 5x7” camera and with the equivalent to that 85mm lens.

Look at the 24mmx36mm format column and locate the 85mm len.  Now look across that row until you reach the 5x7” format row.  Where they intersect is the 372mm lens designed for the 5x7” format.  Ergo, a 5x7”  camera with a 372mm lens would render a similar image to a 35mm camera using an 85mm lens.  The actual lens in 5x7” would be 360mm as a 372mm does not exist.

Compared to a FX (24x36mm) format lens, an equivalent lens for 6x4.5 cm is 1.5 times longer.

Compared to a FX (24x36mm) format lens, an equivalent lens for 6x6 cm is 1.6 times longer.

Compared to a FX (24x36mm) format lens, an equivalent lens for 4x5” is 3 times longer.

Compared to a FX (24x36mm) format lens, an equivalent lens for 5x7” is 4.37 times longer.

Compared to a FX (24x36mm) format lens, an equivalent lens for 8x10” is 6.5 times longer.

Lenses designed for smaller formats are not designed for cameras with larger image formats.  The light coming through the lens will not cover the larger the format.  For example, a lens designed for DX format will only produce a circle on a larger format.  Therefore a 150mm lens designed for a FX camera will create a circular image on a 4x5” camera; a 150mm lens designed for a 4x5” camera will easily cover the FX format, but will need to be adapted to fit or work with the camera and because it is a longer focal length for FX would act as a telephoto.

Theoretical standard or ‘normal’ lens is determined by the diagonal  of the format’s frame.