[snimcho]

That is amazing shots. How long is the exposure time? How many frames?

Thanks To be honest I don't remember the exact numbers. I think, I followed one rule... to make as many exposures as I can. These are very far objects, the light is weak and a high iso is required. So, for less noise, more than 10 exposures are needed. 20 is a good starting point Also it is good to have some lighter images, some let's say middle images and some dark frames. For these bunches of images we need to reduce the noise and to increase the light. So that's the reason the higher number of exposures will bring better end results. I don't plan making a specific number of exposures. I just do it depending of the conditions and I stay as long as I have fun Exposure time is limited from the Pentax O-GPS1 unit. My experience is near 20 seconds. Again it depends on the current situation. Some tests will show what is possible. Even if the conditions are not optimal for the astrotracer, a good result can be achieved with a higher number of exposures.
Generally I think that the results from O-GPS1 are impressive.
Have fun

I far north in Sweden this week, hoping for some clear weather. Light pollution is minmal up here.

Not sure if the 600 rule has been mentioned yet. But it is a useful guide. motion blur - What is the "Rule of 600" in astrophotography? - Photography Stack Exchange

[skogpingvin]

Not sure if the 600 rule has been mentioned yet. But it is a useful guide. motion blur - What is the "Rule of 600" in astrophotography? - Photography Stack Exchange

Actually I'm not sure that it is useful with an AstroTracer, which (to the extent it can) follows the movement of the stars. The rule of 600 is for cameras that do not move to compensate. If you took a very long exposure of the sky using an AstroTracer, depending on where you pointed it and the focal length of the lens, you could get an hourglass trail pattern. I've seen this demonstrated on a different site - maybe one of the earlier posts linked to it.

Because some amount of trails is always going to happen in a shot using an AstroTracer, there will be a similar kind of rule of thumb, but I've no real idea what the numbers might be. However, a guess of something like half the maximum the camera allows might be a good start.

I'm going to be spending a few days in the Australian desert late next week, fingers crossed I might get some nice shots. I've got a good selection of lenses, a 10-17mm fish eye, a 50mm f/1.4, an 85mm f/1.8 a 150-500mm f (I've forgotten but something pretty horrendous) and a Meade LS6 1540mm f/10.

Ah yes - sorry about that. The initial pictures that were posted looked like typical shots where the shutter was open too long. Perhaps it wasn't working or hadn't been calibrated before use?

How long can these be used for? If they don't actually move the camera, but just the sensor, then there should be a limit to how long it will be effective before trails appear again.

[skogpingvin]

Just returned from the desert having had only one clear night. I took some AstroTracer shots, which would probably not amaze people on this forum, but I have a lot of questions for the assembled experts.

I'm a little puzzled about the colour. This show looks a little too red, but how do people determine what the actual colour is?

I've tried to use some L+RGB post processing on this image. What that means is that I processed the RAW image for some lens distortion, and maybe brighten it a little before saving it as an 8-bit TIF I then opened it in GIMP and copied it as two layers, one of which is a monochome layer which is used to determine overall brightness, and the other is the RGB layer, which I blurred using a despeckle filter. This layer gives overall colour, so doesn't have to be sharp.

What I want to learn to do next is add a graduated subtraction layer to correct for the overall "air-glow" (and in other photos, some light pollution). This is the green glow near the horizon. Any hints as to what I should do?

Bill

[Aaron28]

WB is all I got..and that's prolly not helpful

Nice shot skogpingvin. I think people enhance the colour but try not to overdo too much so that it becomes unnatural. Getting the RGB balance can be tricky. Your shot looks a bit like an faint aurora capture in the bottom right. I think adjusting the colour temperature might help. Our skies tend to be a deep blue that gets lighter with longer exposures. If you look at colour wheels you'll see yellow is opposite blue and green opposite to red so if your shots have a yellow/ green tinge it may want backing off to the blue and red. Then you maybe wouldn't need to enhance the red in the RGB - if that's what you did.
It may be worth shooting Raw+ so you can compare your processed shot to the Jpg. Jpgs tend to have a reasonable balance which shouldn't look too overblown, so the processed Raw shot shouldn't be too removed from it - unless you're after a particular effect.

[mikeSF]

there are many ways to arrive at a reasonable color balance - i may add mine later (between meetings), however for reducing the air-glow effect, since green and aqua are not present in great quantity in the rest of the star field, you could start by lowering the saturation of the individual color channels for green and cyan.
Sometimes the horizon is also overly bright due to light pollution from nearby cities - there is a pixel averaging technique that can help to bring that down a bit as well using a simple digital grad and masking the foreground.

At first glance, this image seems too red and green overall and does not look natural to me. While the true colors of space may reside more toward the warm side than the cooler blues very often seen online, I remind myself that I am interpreting a scene artistically and not necessarily documenting exact light wavelengths for NASA, so I will occasionally render my star field more blue, green, yellow, etc to complement my foreground if applicable.

I have never introduced colors to my milky way shot, but will spend a good bit of time shifting the relative color bias to find where the best mix of individual colors are revealed, which I find lends to a pleasing result (YMMV).

some samples: https://www.flickr.com/photos/mikeoria/albums/72157649944280914


pm me if you want some hints on doing this - happy to help.

gotta run!

[gifthorse]

I think you've done pretty well. You can adjust the white balance to give the sky a more bluish cast before you shoot and there are a number of videos on Youtube that demonstrate how to post process the Milky Way. Just do a search for that term.

[skogpingvin]

Nice shot skogpingvin. I think people enhance the colour but try not to overdo too much so that it becomes unnatural. Getting the RGB balance can be tricky. Your shot looks a bit like an faint aurora capture in the bottom right. I think adjusting the colour temperature might help. Our skies tend to be a deep blue that gets lighter with longer exposures. If you look at colour wheels you'll see yellow is opposite blue and green opposite to red so if your shots have a yellow/ green tinge it may want backing off to the blue and red. Then you maybe wouldn't need to enhance the red in the RGB - if that's what you did.
It may be worth shooting Raw+ so you can compare your processed shot to the Jpg. Jpgs tend to have a reasonable balance which shouldn't look too overblown, so the processed Raw shot shouldn't be too removed from it - unless you're after a particular effect.

Thanks for that, Oricman. I do shoot in RAW+, so I compared the colour balance in the "thumbnail" JPG (after having increased its brightness and contrast, but without changing the WB). You're right, I'm way too much into the red. In GIMP, I was trying to enhance the colour without changing it, but it looks like I got it wrong at that point. I'll go back and have another go.

As to the aurora, yeah, maybe just faint. I've never seen Aurora Australis myself, so that's a surprise. Where the photo was taken was a long way from any light pollution - there's a village called Rainbow about 36km south, which is about the right direction, so it might have been the faintest glow from that.

On an unrelated point, I think that I've strayed off the original topic for this thread.

some samples: https://www.flickr.com/photos/mikeoria/albums/72157649944280914

Wow ! Great shots.

[gatorguy]

Not sure if the 600 rule has been mentioned yet. But it is a useful guide. motion blur - What is the "Rule of 600" in astrophotography? - Photography Stack Exchange

My local mentor used the "Rule of 500", probably just a smaller number for what you mentioned. In essence divide your lens effective focal length into 500 and that's the max number of seconds before blur creeps in. Note that using the same lens on a full-frame would give you a different number than on a crop-sensor.

FWIW I just ordered the Pentax O-GPS to use with my K-s2. Figure I'll wing it and figure it out on my own when it arrives since the camera manual description is so convoluted it makes little sense to me. I just hope I don't end up with leftover parts like I do when I "wing it" putting furniture together.

EDIT: Just read the instructions two more times. I think I get it now, but we'll see.
EDIT2: Well that didn't work out as planned. the on-line retailer who advertised at a pretty cheap price, less than $160 new, doesn't actually have any in stock to sell. Two to three weeks? No thanks. B&H, here I come.

[skogpingvin]

With the K3-II, when you have the GPS set on, and you're in bulb mode (and having done the 'precise calibration dance'), you'll find that you can adjust the exposure time up to a point where it will stop. That's the AstroTracer saying it won't go any further than that because the stabilisation can't move the sensor any further.

That's your limit.

I don't know if it works the same way with the O-GPS1 external GPS.

[Gimbal]

With the K3-II, when you have the GPS set on, and you're in bulb mode (and having done the 'precise calibration dance'), you'll find that you can adjust the exposure time up to a point where it will stop. That's the AstroTracer saying it won't go any further than that because the stabilisation can't move the sensor any further.

That's your limit.

I don't know if it works the same way with the O-GPS1 external GPS.

It’s the same with O-GPS1. But in my experience that calculation doesn’t work that well. If you max out the exposure time the result is often a point star with a long hook on it, indicating that a mechanical limit was reached much earlier than expected.