[BenwayB]

Hello,

I'm playing with night photography features for the first time, as I am on vacation :-)

I have 2 different questions, I hope someone can help me :-)

Astrotracer:
I set I up to timed exposure (1 minute), ISO 800, f 4, DFA 21 ... and I get some nice results, that look like being almost free from startrrails, showing a nice milky way.

What I am wondering about: is the astrotracer activated, when I use timed exposure? After pressing the green button, the symbol in the lower right corner looks like the astrotracer is turned off??

INT shooting:

I use the additive bright option, I habe custom setting 13 set to 2, and use minimum time between shots.
I use 30 seconds of exposure, I tried 55 shots in total.

I got horrible dotted lines... where is my mistake? It looks like I have huge gaps between two shots?

Many thanks for helping :-)

[bwgv001]

what camera?

[BenwayB]

K1-II, newest Firmware.

---------- Post added 10-25-22 at 02:31 PM ----------

Hello,

and I have to add another question...

In Astrotracer Mode with timed exposure, it always takes twice the time, I have set, to take the image.

I set exposure to 1 Minute... I hear the shutter and a countdown is running on the small LCD screen.
After 60 seconds I hear a shutter sound again, and again 60 seconds start to count down.

After the second 60 seconds live view turns on again...

What does the camera?
Why does it take twice the time?

I did not manage to find an answer on the internet...

Thanks a lot and best regards :-)

[UncleVanya]

K1-II, newest Firmware.

---------- Post added 10-25-22 at 02:31 PM ----------

Hello,

and I have to add another question...

In Astrotracer Mode with timed exposure, it always takes twice the time, I have set, to take the image.

I set exposure to 1 Minute... I hear the shutter and a countdown is running on the small LCD screen.
After 60 seconds I hear a shutter sound again, and again 60 seconds start to count down.

After the second 60 seconds live view turns on again...

What does the camera?
Why does it take twice the time?

I did not manage to find an answer on the internet...

Thanks a lot and best regards :-)

Dark frame subtraction is on by default when the exposure is 30s or more.

[mlines]

To expand on the previous answer.

With exposures over 30seconds the camera takes two exposures, one normal and one "dark" frame which is an exposure of the same length as the normal exposure but without opening the shutter. This frame therefore consists of the sensor noise only and the camera then subtracts this from the normal frame to reduce the noise in the exposure.

Therefore exposures seem to be twice as long as you set.

If you do not intend to do any post-processing with your own dark frames or any other form of noise reduction then you want to leave this switched on so that the camera does the work for you.

If you are taking a long sequence of exposures that you intend to further process or stack then you want to turn it off and do your own sensor noise reduction

[UncleVanya]

I think it’s called long exposure noise reduction in the menus. I’d have to look to find it and I’m not able to right now.

[AstroDave]

I’d have to look to find it and I’m not able to right now.

For (original) K-1, check p. 45 in the manual, or find "noise reduction" in the index.

[BenwayB]

Hello,

thanks for the replies:-)

Is this black frame substraction also the reason for the issues I am facing in INT mode?

Does this lead to a break in between two shots, causing the dotted line instead of the continues startrail?

Does anyone have a answer to my first questions?

Thanks for helping! :-)

BTW: I am really impressed, how easy it is, to take pictures of the milky way with the K1.
I think it has been the 3thrd picture, that I would claim to be a success, already :-)

[MossyRocks]

As others have stated you have dark frame subtraction turned on. For astro shooting the general advise it to turn it off and if you want to do dark fram subtraction shoot your own dark frames (shoot a bunch) at the end of a session at the same ISO and shutter speed. There are tools that will combine the collected dark frames will using averaging to produce a master dark frame that will be subtracted. A master dark frame made from several darks will be a more accurate representation of the systematic error you are trying to remove from each light as the true random noise will be driven down substantally. This also better preservers the actual data in each of the light frames. I can go into a more detailed explanation if desired but won't at this point.

As far as the dotted lines/trails you are seeing in your final image that is because of the interval mode with additive selected. After each shot astrotracer will reset the sensor position and begin tracking the sky again so the framing is slightly different between each shot. Depending on what you are after the best solution is likely to just shoot a pile of light frames (shoot the darks while you pack up) and then combine them in post processing. There are a bunch of tools available here depending on what you are after. If it is just the night sky there are programs like Deep Sky Stacker (DSS), Astro Pixel Processor (APP), Pixel Insight (PI), Sequator, Siril, and probably others that I am unaware of. These will align images based off of star patterns and then either do some fancy match from simple averages to sigma clipped means and others, I also believe that some will also add the aligned frames together like what you are trying to do in camera. If it is a shot of the foreground landscape with the night sky then you really want to use Sequator as it has a feature to freeze the ground and also freeze the sky. Astrotracer can produce some great results even with huge lenses.

When I chase Deep Sky Objects (DSOs) I will use astrotracer with an intervolometer (functions like an interval mode shooting but likely with more options) but you are collecting individual light frames so not in camera averaging, addition, etc. After a few shots (depending on location and linear speed) I will reframe on the object and let the intervolometer take some more shots for me. I also shoot untracked with wides and ultra wides (photography wide and ultrawide astronomy used very different definitions) and use the rule of 200 for each shot (200/focal length= exposure time in seconds). There I will put the camera into the high speed continous drive mode and use a remote release cable with the button pressed (I made my own with a toggle switch) and just let the camera roll. Then I combine all the images in post processing.

A Deep Sky Object shot with my 400mm lens, K-3, and O-GPS1 for astrotracer with almost 9 hours worth of shots:


A night landscape shot taken untracked with my 12mm lens, K-3ii, Vivitar 285HV speed light at 1/16 power and diffuser with about 10 minutes of shots:

[BenwayB]

Hello,

Just perfect, many thanks for the explanation, this helps a lot and is more than enough to start with :-)

If I manage to get something acceptable, I will share it here :-)

Thanks again and best regards:-)

[BenwayB]

Hello

Ok, this has been a challenge - next time I will be prepared with more coffee, warmer clothes, and so on ;-)

The following pictures have been taken with a K1 MK2, a DFA 21 and a cheap Rollei carbon tripod.
It has been cold and about 4 bft of wind - I used the tripod at its lowest position, but the camera was still shaking in the wind I think.

I was playing around with my phone, I did not recalibrate the astrotracer more than 1 time... there is a lot of room for improvement ;-)

Please don't judge on the pictures, this is my first try, it's really all about the technical aspects.

First of all, messed up star trails using INT, minimum time between shots, 25 seconds per shot.

Then a picture with an without astrotracer (pretty impressive I think) and some more other results :-)

[BenwayB]

Some more :-)

Suggestions are welcome ;-)

[BenwayB]

Hello,

does anyone have an idea, why my startrrails look like they do?

Why the line is dotted at the beginning, then solid?

Best regards :-)

[MossyRocks]

First of all, messed up star trails using INT, minimum time between shots, 25 seconds per shot.

Don't bother with interval shooting for star trails. My advise is use a 30s shutter speed and then set you f-stop and ISO to get what you want. Basically take a test shot and decide if you have too many stars or not enough. Then put it into continuous high speed drive mode and let it run until the battery dies, you get sick of being out, or you think they have moved enough. The high speed continuous drive mode won't allow enough movement of the stars from one shot to another to allow a gap to appear. If deliberately going for star trails 30s minimizes the number of shots but if you are in a spot where people might result in a bad frame because of a brief opps (excess light because lots of people are really bad at managing their light) going with a shorter shot length but still doing continuous high speed shooting should result in being able to drop the odd sing bad frame here or there without losing the nice continuous trails. For figuring that out you want to use a shutter speed half of what the rule of 200 would give you, so a shutter speed in seconds of 100/focal length.

does anyone have an idea, why my startrrails look like they do?

My best guess is that the focus shifted slightly and that papered over the jaggedness of the interval shooting that was showing up in the early shots.

In looking at the shot you took with the FA 50/1.4 there is a lot of bloating of stars and what appears to be some pretty bad coma. I wonder if you missed the focus slightly as that will make these things worse. My experience, and others, is that the Pentax 50mm lenses basically peak for astro at f/2.8 and clean up pretty good at that point with only some minor coma in the corners. This seems to hold for my M42 SMC 50/1.4 Takumar , A 50/1.2, and M 50/1.7 and I believe others have used the FA 50/1.4 and even the new D FA* 50/1.4 with similar results. Nailing the focus really is key and I would suggest getting a bahtinov mask with very find spacing. I have one that is fine enough to work down to a lens with a 28mm focal length.

I did not recalibrate the astrotracer more than 1 time...

If you didn't move the camera then recalibrating shouldn't be needed. By move the camera I don't mean move it around on the tripod but actually move the location of the tripod it is sitting on. Checking and adjusting the focus is usually needed as time progresses because the focus will shift slightly as things cool down and as the night get cooler. The longer the lens the more this is needed. I try to have my lenses out coming to the ambient temp while I get everything else setup and is really critical for my 400mm as that thing takes a long time to come to temp.

[UncleVanya]

The FA 50 wide open is a dreamy lens at best. Very weak corners indeed.