Thanks, everyone.
Originally posted by dcshooter First, the astrotraceer does appear to be mis-calibrated, since there a trails even at the center of the image. 300 seconds is a fairly long exposure, even with such a wide angle, so if the calibration is off even slightly, you will get errors. You might get better results boosting the ISO and doing several shorter exposures (<1 min) and stacking to reduce noise.
However, even when calibrated, you will still see trails on the corners of an astrotraced image with a lens this wide since the corrections it provides are only in a flat XY axis along the sensor plane, while the apparent star movement is sidereal i.e. along the curved inner surface of a rotating sphere.
I'll watch some calibration videos and try performing it again. Apparently it can be inconsistent? I'm not even sure what exposure times the astrotracer is supposed to provide for. Anyway, more reading and experimenting required. Thanks for the note on the limitations, too.
Originally posted by Na Horuk I think you could get away with f4 or something; f8 makes even the 300second image rather dark.. You can probably use a higher ISO, as well. Yes, f8 and ISO 100 should give "best quality", but with astrophoto gathering as much light as possible is more important than that. And the lens and camera you are using are both good enough to use lower f number and higher ISO.
Anyway, make sure you are using the latest firmware on your gear.
Okay, I'll definitely try out those kinds of settings next time. There weren't any firmware updates available for the K-3 II last time I checked. (Only the K-3.)
Originally posted by Nass Agree with dcshooter about the sidereal aspect - I think the lens is so wide it captures paths that look like they go in different directions, so can never be 'stopped' as such. Here are some old diagrams I once did for another forum explaining the shape of trails you get and the direction.
Thanks for sharing those diagrams. I've seen some shots showing those paths, like
Elia Locardi's Church of the Good Shepherd shot. However, I think in this case it's not due to that as the paths of the stars in
the non-traced shot aren't like that.
Originally posted by maxfield_photo I think that's quite possible since 15mm is about 7% wider than 16mm, even though it's "only 1mm". That's a real bummer.
Maybe something can be done from the debug menu?
I've done a little searching on Pentax DSLR debug menus and I haven't found any reference to setting focal lenghts, unfortunately.
My wife has the Pentax 12-24mm, so I'll also try some traced shots with that and compare. Thanks again.