A photo shot with an 1:1.8 lens contains the following exif data:
ApertureValue: 1695994/1000000 MaxApertureValue: 16/10
How is this possible? Both values are <1.8
I have seen that exact value (16/10) on a Nikon before. It may just be an incorrect value as Matt says. It could also be a calculated value adjusted for:
For example if you had ISO set on Nikon to L.03 the EXIF data might report ISO 200 and the aperture open a stop wider than it can actually go.
If you can share more information about which camera and lens, and other EXIF data we might be able to make a better guess, but the main point is you can't completely trust EXIF data.
You can also get different results using different EXIF readers. What reader are you using, and what value is reported by your processing software (Lightroom or Aperture or whatever)?