So.. aperture size is proportional to the cross-sectional area divided by focal length, or something like that.
Clearly variable aperture lenses e.g. 70-300 f4-5.6 are cheaper than constant e.g. 70-200 f4 because they don't need to cope with the increased cross-sectional area that would be required to produce f4 aperture at 200/300mm focal lengths, which would mean more glass required.
So.. in making a 70-200 f4, they are making a lens for which the cross-sectional area changes from e.g. 7cm² to 20cm².
Since that amount of glass is already there for the long end, could they not use the same optical formula/price and instead make it a 70-200 f2.8-4?
Just a thought!
Clearly variable aperture lenses e.g. 70-300 f4-5.6 are cheaper than constant e.g. 70-200 f4 because they don't need to cope with the increased cross-sectional area that would be required to produce f4 aperture at 200/300mm focal lengths, which would mean more glass required.
So.. in making a 70-200 f4, they are making a lens for which the cross-sectional area changes from e.g. 7cm² to 20cm².
Since that amount of glass is already there for the long end, could they not use the same optical formula/price and instead make it a 70-200 f2.8-4?
Just a thought!
