The Milky Way is made up of nebulosity, dust and stars. Physical lens area governs the speed that the sensor records stars, f stop governs the speed that the sensor records nebulosity and dust.
The 16mm will record nebulae, dust and extended objects twice as fast as the 10mm and stars six times faster than the 10mm. So the only other question is do you need the wider field of view of the 10mm?
Joe
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