This mathematics only works using a teleconverter in between the lens and the sensor, the the diameter of the outermost lens remains the same and thus the aperature shrinks, but with the external lens ontop the existing lens, the outermost diameter becomes the teleconverter lens and thats what should be used to calculate the aperature, not the inbuilt lens diameter.
Hence the post is wrong.
The writer should do more research on this.
Quote from: Sammib on Yesterday at 18:48:06This mathematics only works using a teleconverter in between the lens and the sensor, the the diameter of the outermost lens remains the same and thus the aperature shrinks, but with the external lens ontop the existing lens, the outermost diameter becomes the teleconverter lens and thats what should be used to calculate the aperature, not the inbuilt lens diameter.
Hence the post is wrong.
The writer should do more research on this.
No matter what you put in front of a lens, the diameter of the aperture does not magically get larger, hence the original tele lens is the bottleneck. You can't just stack a 24 – 70 mm f/2.8 zoom and a 50 mm f/0.95 lens and turn that zoom into an f/0.95, for example. You can indeed increase the light throughput depending on the optics to achieve a larger T/ stop, but a longer focal length will always lead to a smaller f/ stop when using a tele converter.