[Klaus]

https://opticallimits.com/sonyalphaff/1183-viltrox20f28

Cheap and (quite) cheerful.

[Rover]

Yay! An adorable looking little lens I must say.
... but the distortion chart doesn't show at least for me no matter how many times I try to reload (the file name is wrong, when I open it in a separate tab and edit `16` to `20`, I can see it).

[Mistral75]

Indeed, the link is wrong https://opticallimits.com/images/8Review...ortion.png ('16mm_raw_distortion.png')

The right one seems to be https://opticallimits.com/images/8Review...ortion.png ('20mm_raw_distortion.png')

[Klaus]

Ah, sorry, fixed.

[toni-a]

For field curvature I understand you measured center and border resolutions at different focus settings !!!

[Klaus]

The focus field is rarely 100% flat. You won't even notice this with most lenses, so it doesn't make sense to add a note about it or create a dedicated flat-field MTF chart.
Usually, I only do this if I notice something unusual when using the lens out there or if it's crystal clear during the formal testing.

[Rover]

Still it looks like it destroys the Tamron 20/2.8... which has 7+ percent barrel distortion. Mindblowing.