First Impressions Astro Tracer

The Pentax K-1 comes with an inbuilt astro tracer function which makes it possible to extend the exposure time during night shots considerably. In other words, we can reduce the iso and get cleaner shots with less noise. Pentax’ floating sensor technology makes this possible – the sensor follows the movement of the stars. I have only been out testing the feature once, and I merely shot wide angle, that is, 15 mm.

The astro tracer did its job perfectly after I had followed the guidelines and calibrated the inbuilt GPS. However, it cannot counter wide-angle distortions. In other words, the center of the frame is pin sharp whereas the extreme corners show trailing. 60 seconds seemed to give the best result using such a wide angle lens as I did.

Rising Up

The finished image from that evening.

I am not a physicist but have read that since the sensor is linear whereas the wide angle lens yields a curvature these effects of trailing are bound to occur. If we narrow the focal length to for instance 24mm or even 50mm the star trailing in corners will more or less be cancelled out even when increasing the exposure time. To put it like this: the narrower the focal length the longer the exposure times without having trailing in the corners.

If we prefer to shoot wide angle a fix can be as follows: Shot 60 seconds or longer for the center and shoot one regular exposure at 25/30 secs for the extreme corners and blend the two in Photoshop. With the milky way in the center of the frame we can have a pin sharp and very clean MW whereas the corners will be a bit more soft since they will require more noise reduction due to a higher iso.

Samle images (Pentax K-1 and Pentax 15-30):

15mm iso 1600 90 secs f2.8 center:

15 mm 90 secs center iso 1600

15mm iso 1600 90 secs f2.8 right corner (I was shooting north west) – star trailing is well controlled:

15 mm 90 secs right corner iso 1600

15mm iso 1600 90 secs f2.8 left corner (not sure why there is more trailing in the left than the right corner – see last samle image for a possible explanation):

15 mm 90 secs left corner iso 1600

15mm iso 1600 60 secs f2.8 center:

15 mm 60 secs center iso 1600

15mm iso 1600 60 secs f2.8 right corner (less star trailing than 90 secs):

15 mm 60 secs right corner iso 1600

15mm iso 1600 60 secs f2.8 left corner (again more trailing in the left corner – Worth mentioning that this was in the middle of January just north of Oslo, Norway. An unverified theory I have is that the earth’s velocity relative to the stars is bigger towards the south than towards the north that time of the year this far north, and this may explain the difference between the corners – remember I was shooting north-west. The lens is, btw, not the guilty part in this – it is not askew in any way):

15 mm 60 secs left corner iso 1600

Further tests will be carried out as soon as I get a chance and then I will direct the camera towards the south.

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