f-stop vs focal length observations on xf 18-55

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TOMMMMMM Regular Member • Posts: 117
f-stop vs focal length observations on xf 18-55

It appears there are some discrete steps the focal length gets recorded.

I ran some numbers on my XF 18-55 and it was very consistent in that the steps were approximately 4% of whatever focal length you are using. So if you are at 100mm, the next step would be somewhere around 104mm. Starting at a smaller focal length of 25mm, the next step would be around 26mm, etc.

If this is true, I have a few questions about the inner workings of how the exposure is calculated and EXIF recorded:

1. When the lens is wide open, there shouldn't be any discrete steps in f-stop since the diaphragm isn't closing down to compensate for a change in focal length. I would expect the f-stop to match a similar curve as the orange data points since the f-stop is the focal length divided by the wide open aperture diameter that doesn't change as you adjust focal length. The blue data points is probably FUji's algorithm to place an f-stop to it's nearest 3rd stop. Is this correct?

2. When stopping the lens down, I would expect the f-stops at varying focal lengths to behave as shown by the blue points since the aperture diameter can only change at 3rd stops and thus gives that flashing effect when changing focal length on variable zooms when stopped down and recording video. I've heard other camera manufacturers have gotten around this issue, how do they do it?

 TOMMMMMM's gear list:TOMMMMMM's gear list
Fujifilm X-T2 Fujifilm X-A3 Fujifilm XF 18-55mm F2.8-4 R LM OIS Fujifilm XF 56mm F1.2 R Samyang 12mm F2.0 NCS CS +7 more
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