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longest focal length / biggest aperture = minimum front element size

most 70-200 have 77mm front elements

200mm / f2.8 = 71.4mm

minimum is 71.4mm.. but to adhere to industry standards, they choose 77mm since 71.4 is the minimum size

most 70-200 have 77mm front elements

200mm / f2.8 = 71.4mm

minimum is 71.4mm.. but to adhere to industry standards, they choose 77mm since 71.4 is the minimum size

The focal length / biggest aperture formula only applies for 200mm and above.. (Canon 200mm f2.8 = 72mm diameter, wider lens with large aperture also have large diameter, eg 24mm f1.4 = 77 diameter)

There is another formula when lens with short focal length kicks in, not sure of the formula myself. Maybe someone else can provides ?

Correct me if I am wrong..

The focal length / biggest aperture formula only applies for 200mm and above.. (Canon 200mm f2.8 = 72mm diameter, wider lens with large aperture also have large diameter, eg 24mm f1.4 = 77 diameter)

There is another formula when lens with short focal length kicks in, not sure of the formula myself. Maybe someone else can provides ?

The focal length / biggest aperture formula only applies for 200mm and above.. (Canon 200mm f2.8 = 72mm diameter, wider lens with large aperture also have large diameter, eg 24mm f1.4 = 77 diameter)

There is another formula when lens with short focal length kicks in, not sure of the formula myself. Maybe someone else can provides ?

But in pure theory, a 24mm f1.7 only needs to be a minimum of 17.14mm wide. Doesn't mean the image will be useable.

The focal length / biggest aperture formula only applies for 200mm and above.. (Canon 200mm f2.8 = 72mm diameter, wider lens with large aperture also have large diameter, eg 24mm f1.4 = 77 diameter)

There is another formula when lens with short focal length kicks in, not sure of the formula myself. Maybe someone else can provides ?

For wide angles, because retrofocus (reverse tele) is used, the large front element is to cover the angle and the rear elements are to project the rays to the sensor. Each element has an aperture but it's the element with the longest focal length which dictates the aperture.

The front diameter applies for all tele lenses including medium teles.

For wide angles, because retrofocus (reverse tele) is used, the large front element is to cover the angle and the rear elements are to project the rays to the sensor. Each element has an aperture but it's the element with the longest focal length which dictates the aperture.

For wide angles, because retrofocus (reverse tele) is used, the large front element is to cover the angle and the rear elements are to project the rays to the sensor. Each element has an aperture but it's the element with the longest focal length which dictates the aperture.

My lens is 17-40 f/4, diameter 77mm! So i'm very doubtful the same formula for medium-tele lens applies.

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