Astro Photo Question (trying this forum)...

John Retsal wrote:

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Camera is Nikon Z6II with the Z 14-30 f/4 lens.

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I'd be shooting at 14mm and maybe 20mm, wide open at f/4 tripod mounted, no tracking and VR off.

I'm pretty sure I need to keep my exposure times (per the NPF rule) to around 11 sec for 14mm and 8 sec for 20mm in order to have no trailing visible.

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I think you are going to find those exposure times to be way too short to gather enough light, especially for an f/4 lens. You might need say, 20 seconds and 6400 ISO with an f/4 lens. Using either my 20mm @f/1.8, or my 14-24 @f/2.8, I might start out at 20 seconds and ISO 1600 and adjust from there, and those are way faster lenses than the 14-30 f/4.

There are a lot of factors to consider as to what setting to use to collect the most light and not get movement in the stars, including what portion of the night sky you are pointed at. The NPF rule might help a little, but it also identifies a multiplier (K value) that might need to be used in front of the ratio. Some rule of thumb guides suggest using a K value of about 2.5 or 3 (so your exposure times may be too low).

I would suggest that the best recommendation is to experiment in the field and adjust your settings as needed to get a reasonable exposure without any visible star movement. Maybe start at 15 seconds and ISO 3200 and adjust accordingly from there.