Originally posted by Kunzite No, Astrotracer cannot work (as you can't get the camera's direction).
I thought about this for a while, and that's not necessarily true.
Astrotracer needs three different kinds of information to calculate the direction of the earth's rotation axis relative to the camera:
- Camera's orientation relative to magnetic North. This is obtained by an electronic compass attached to the camera, and that's why O-GPS1 has electronic compass.
- Camera's altitude angle relative to the local horizontal plane. This should be obtained from accelerometers/tilt meters attached to the camera. Not sure if in-body sensors for SR are used for this too or if Pentax use separate sensors.
- Camera's position on the earth regardless of camera's orientation. This is the only information GPS can provide. GPS antenna doesn't have to move with the camera.
Therefore as far as the camera still retains electronic compass and tilt meter in body, astrotracer should work with cellphone GPS. Not sure if Pentax thought about it (and not sure if it's a sensible thing to do either), but technically it should be possible.
For an enclosure to even partly shield magnetic field (REALLY difficult job) or to throw off electronic compass, you need ferromagnetic elements like iron and nickel. Magnesium alloys, though we cannot know the exact recipe for Pentax bodies, don't have ferromagnetic elements except as impurities (see e.g.
https://www.asminternational.org/documents/10192/22833166/05920G_SampleChapt...5-c9c690c1931e). As an example,
volume magnetic susceptibility of the main component of magnesium alloy (i.e. magnesium) is about 1 per hundred thousand, which is to say that magnetic "amplification" factor, so to speak, inside pure magnesium metal is about 1.00001, i.e. almost nothing.