Originally posted by beholder3 That is very normal behaviour and the very reason why for ages there has been the concept of dark frame subtraction and that is the case for special astro cameras as well.
http://starcircleacademy.com/2012/10/darkframes/ https://www.dpreview.com/forums/thread/3617190
If you want to do it properly you not only have your light frames in raw, but also bias, flat and darkframes - the latter are required per focal length, per ISO, per sensor temperature.
The lazy noob approach is to just switch on the in-camera dark frame subtraction called "long exposure noise reduction". This is automatically at the right focal lnegth, ISO and temperature.
No issue at all, other than lack of user knowledge.
Go to a astro forum and let them teach you, how to approach this.
I have to say, that I find this post disappointing, as you personally don't know me, or how much time I have spent working on this type of photography. I have put in the time and for star trail photography, this is an issue that your mention of a manual dark frame subtraction won't fix. But needless to say, your points merit a response as I disagree with them.
This issue has been found before years prior and I would have hoped that Pentax would have taken similar steps to address it, which it appears they did not. Depending on your workflow and end result it can become problematic.
Don't really consider myself a noob, but will take it as you will. And for sure it's not "lack of user knowledge" sorry you feel necessary to take that approach. You can go to all the astro forums you want, and this particular issue will not be fixed as it's an issue that is different than traditional noise. I would also ask if you have tired this yourself? I have thousands of exposures and hours of time in stacking with various cameras. Only wanted to point out that this same problem existed in a different brand which uses the same sensor, the other company fixed it.
If you want to go through all the process of taking a dark frame and trying to manually subtract it that is fine. Net, there are plenty of cameras out there, basically all from Canon, Nikon, etc that can take such a exposure without creation of a white dot, which by the way is not that easy to remove even with a true dark frame ( I have tried it) and the white dots don't clean up as well as traditional dark noise, which tend to show up in red, red, or blue dots, which a dark frame subtraction can remove.
I had hoped that the K1 would at least equal the long exposure quality from other cameras I have used, none of which require taking a dark frame and manually removing the noise. again this is mostly for traditional stuck pixels, which are both larger and brighter than the dots. With any modern digital DSLR, you should be able to take a up to a 2 hour long series of stacks, anywhere from 30 seconds to 2 minutes to 3 minutes each and not have the dots, yes you will have noise, but most of that can be removed during the stacking process later on, as the dots will stay in the same place throughout the entire stacking process. The problem comes in when you combine the images.
Working with a intervalometer, you will always have a faint gap between the exposures, and I only know of one tool that will remove these in post, and that is "star tracer". By design it will move the stacked image in a series of controlled blurs, which will combine the gaps into complete trails, and help to give faint trails a brighter look, however this process of movement also moves the dots into dotted trails throughout the image that with a 36MP image will show up. Net, the dots have to be out prior to this final step, and manual dark frame in my experience will not remove them.
The in camera noise reduction, which you seem to feel is also noob feature, works well and in fact more than likely works better than any manual dark frame process, but it defeats the stacking process due to the gaping it creates.
As I already pointed out, Capture One can remove most of this in a raw file, but if you capture in jpg, then it will work on the dots.
Paul C