Is the yongnuo yn42 5mm f 1 7m ii sharp wide open?

Here is what the site says about that.

From Yongnuo YN42.5mm f/1.7M II: Yongnuo YN42.5mm f/1.7M II: A prime lens by Yongnuo for Micro Four Thirds cameras, 42mm f/1.7. A cheap autofocus portrait prime for Micro Four Thirds. Specs - Maker: Yongnuo - Focal length: 42mm (prime) - Maximum aperture: f/1.7 - Made for: Micro Four Thirds sensors - Mounts: Micro Four Thirds - Stabilised: no - Autofocus: yes What it frames like - On Micro Four Thirds (Micro Four Thirds): like 85mm on full frame; f/1.7 ...

From Lenses: Aperture: The f-number says how wide the lens opens. Smaller numbers let in more light: f/1.8 lets in about ten times as much light as f/5.6, more than three stops. A wide aperture means faster shutter speeds in dim light and more background blur. Zooms with a constant aperture, like a 24-70mm f/2.8, keep the same exposure throughout the zoom range; cheaper zooms get darker as you zoom in.

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