The sensor size for the X-mount is 23.5mm x 15.6mm.
So how long is it diagonally? The answer is 28.4mm
You do not need to know trigonometric function to come up with the answer. All you need to remember is the horizontal axis of the MTF chart for the APS-C format goes up to the image height of 14.2mm. It covers the image circle with the radius of 14.2mm or 28.4mm in diameter.
Today, we like to talk about XF27mmF2.8.
It is the smallest and lightest lens for the X-mount.
The lens size was at the top of the priority list upon designing the lens.
So does that mean that we see compromises on the image quality and its optical performance?
The answer is NO.
There is a reason XF27mmF2.8 is named "XF" even if it is missing an aperture ring.
We will not go in depth, but it is easier to design a lens when the diameter of the image circle is closer to the value of the focal length of the lens. The lens can be smaller in size in such case without sacrificing on the image quality.
This also means that as the focal length gets longer or shorter than the the value of diameter of the image circle, then the lens becomes larger in size.
So the size of XF27mm became naturally what it is.
It can even be said that in order to achieve both image quality and compact size, the focal length of 27mm was chosen.
Which prime lens is the best seller for the X-mount?
The XF35mmF1.4 R is the No.1, and the XF27mmF2.8 comes in second place.
This shows the characteristics of many X-mount users who are snap shooters that prioritize on the compact size and flexibility.
With the XF27mm, they know that they do not need to compromise on the image quality.
Continue to read Episode 6
One lens one story - Episode 6: XF27mmF2.8 Part 2
#1 XF14mmF2.8 R
#2 XF23mmF1.4 R
#3 XF60mmF2.4 R Macro
#4 XF35mmF1.4 R
#5 XF27mmF2.8 Part1
#6 XF27mmF2.8 Part2
#7 XF56mmF1.2 R Part1
#8 XF56mmF1.2 R Part2
#9 XF18mmF2 R
#10 XF18-135mmF3.5-5.6 R LM OIS WR
#11 XF1.4 X TC WR Part1
#12 XF1.4 X TC WR Part2