[alohadave]

I don't think that is star trailing. You'd never get star trails at 10 secs. You should be able to get pretty close to 40 secs before you see any noticable star trails. Looks like camera shake... was it windy? even a little bit?

That is exactly what it is. Anything longer than about 5 seconds will produce short trails.

As well, a fixed prime is not ideal for star scapes. Fixed primes, of higher focal lenths ( ie, 300-600mm ) are great for Deep Sky Imaging but not star scapes. As you can see, the stars seem to be zooming away from the centre of the frame. This is caused by the diffraction of a smaller, fixed prime lens. Use your kit lens, you'd be quite surprised how well it performs for astrophotography.

Please explain what you are talking about in regards to prime lenses, it is non-sensical.

To be honest, I shot for about a year before I ever even bothered with DFS ( dark frame subtraction ) and still always got nice, dark skies with perfectly round stars. DFS is really only needed if you're combining ( stacking ) shots.

Try this next time you go out. These settings will take a image of the sky as you see it:

Length = 12-35mm
Aperature = F4-F6.7
ISO = try 200 first, then go to 400
Exposure time = 20-25 seconds

The exposure time will give you star trails every single time. There is no reason to increase your ISO as all you are doing is increasing the effect of noise in your shots.

[alohadave]

When done correctly, I have never ever seen star trails at a shutter speed below 20 seconds. This 'ten second star trail phenomenon' is more commonly called mirror slap

Wrong. I shot many star shots with 15 second exposures and the camera I used doesn't have a mirror.

[mr tibbs]

wildlifephotog, no problem at all! I didn't do any post processing because I wanted to show the difference between Picasa and Lightroom. That shot does look better. I did save the link to deep star tracker, but have yet to look at it.

ytterbium, it never occurred to me that the problem might be Picasa. I thought it was a good program up until this shot. It looks like I am going to have to look else where for some post processing software. Man this hobby is expensive!!

Now that I know what the problem is I am going up into the mountains tonight to take some pics of the meteor shower! I think I'll grab some extra batteries and something to write on and keep some notes on the pics I take. This should be an interesting time. I know I am a beginner, but I have some high hopes for this evening. If I can get a shot like that in my back yard with all of the city light pollution around, I think I might be able to get some good shots in the dark mountains!!

Thanks again to everyone for helping me out! I love trying new things with the camera and learning stuff!!

[PentaxPoke]

I just took this picture a few hours ago. It is the Milky Way near the Eagle (Aquila) constellation. For us folks in the northern hemisphere, that is facing south around 10pm central.

Camera: K-7
Lens: Pentax FA 35mm f/2 @ f/2.4
Exposure: ISO 3200, 10 seconds each
No tracking
Time of shot: 10:32 pm
Location: Within city limits, facing south
8 exposure stack using deepskystacker (freeware)



Oh,one more thing: I would listen to nightfly's advice. I think he knows what he is talking about.

---

Last edited by PentaxPoke; 08-12-2009 at 12:03 AM.

[mr tibbs]

Great shot!! I took a few tonight, but my session was cut short by a sick wife. It looks like I am going to have to learn how to use the stacking software. That shot is phenomenal!!

[PentaxPoke]

Great shot!! I took a few tonight, but my session was cut short by a sick wife. It looks like I am going to have to learn how to use the stacking software. That shot is phenomenal!!

Thank you. It is really not too difficult with modern DSLR's. It was much more challenging in the low ISO film days.

First thing, as the people that know what they are talking about in this thread said: you are getting star trails. Even with my 35mm prime you can see it above 10seconds exposure. That is why I use a high ISO if I am on a tripod as opposed to my 8in scope with tracking. 10 seconds, at f/2.8 and ISO 3200 will give you a pretty darn good exposure of the milky way on a dark night without star trails if you are using say a 35mm or less lens (see nightfly's chart.). You may be surprised at the detail in the single exposure. However, you may be bothered by the noise from the high ISO and relatively long exposure. That is where the stacker can help you. As wildlifephotog indicated, stacking significantly increases signal to noise ratio. It won't help though, unless you have enough exposure (signal) to begin with. After you stack, you can then adjust the levels upwards to bring out more detail from the noise.

I'll bet you'll be able to get some beautiful shots from the mountains of Utah that will blow my picture away...

[scorpionbowl]

I have a few questions before I start out with my new K20. Since the noise reduction isn't optional at these speeds, how is it applied in the camera? If I shoot raw+jpg, is the noise reduction frame only eliminated from the jpg? and the raw file includes just the light-frame data? If so, isn't jpg the best for noise, or can you still win with raw and post-processing?

For night shots, I usually use my 28mm f1.7, some have indicated I may get better results [away from the center of the view] up near f4. Any thoughts if shorter times at f1.7 versus longer exposures at f4 would give better results?

Here's an old pic...
K100, Sigma 28mm, f1.7
iso 3200, 30 sec
one frame
no tracking

[mr tibbs]

Here is my best shot from last night. This is a single frame shot using my kit lens f4.5, iso 400, and a 30 second exposure. I wanted to try higher iso shots with less time, but the wife was feeling sick. I know there is a new moon coming up so I plan to try this again in a week or so.

[Marc Sabatella]

ytterbium, it never occurred to me that the problem might be Picasa. I thought it was a good program up until this shot. It looks like I am going to have to look else where for some post processing software. Man this hobby is expensive!!

Doesn't have to be too bad. Lightroom is only $100 if you qualify for the educational discount, and there are other very good choices in that same price range (Photoshop Elements, ACDSee Pro, Lightzone). And if you want free, the Pentax software (PPL) that comes with the camera works fine, although it's very cumbersome to use on large numbers of images compared to modern software designs like any of the others mentioned.

Picasa actually works just fine for lots of pictures, though - ones with "typical" exposure and color as opposed to oddball ones like this where its auto corrections might really screw things up. So the idea of using Picasa "most" of the time, but PPL when you need it, isn't completely unreasonable. Although I'd still rather be using any of the others.

[PentaxPoke]

Here is my best shot from last night. This is a single frame shot using my kit lens f4.5, iso 400, and a 30 second exposure. I wanted to try higher iso shots with less time, but the wife was feeling sick. I know there is a new moon coming up so I plan to try this again in a week or so.

There clearly is some potential in that shot. Since you are limited to f/4.5, you are going to have to crank up the ISO. Also, 30 seconds is too long for the focal length you used. You can clearly see the star trails which degrades the quality of your image.

Scorpion: The noise reduction is applied for the RAW image as well. Learn to embrace it. In the shot I posted, I turned the long exposure NR on. It helps to not need as many dark frames in the stacking. Heck, it is actually doing part of what the dark frame stacking does, so it can be helpful for this application. Also, opening up your aperture is a good thing. Stars are discrete points of light. There is no other "detail" per se, so you will not notice significant softness when you open the aperture. Star trails due to long exposure are much more of a problem than lens softness. Even a small bit of star trail will "blur" your image. My shot was almost completely wide open. It would have been wide open had I not been in a rush and noticed 2.4 instead of 2.0.

[scorpionbowl]

Here are my results with the K20. Essentially the same conditions as my post above, 30 seconds may be a little too long. This time I was lucky to catch a meteor. Now I need to play with stacking...

[mr tibbs]

That is a nice shot! I love the meteor streaking across the sky! If the weather holds tonight I am going out to try to get some shots to stack. I'm thinking of using my 50mm prime wide open with high iso in short (10 second) bursts to get some good shots to stack. As long as I am there I might throw on the zoom and try the same thing to see the results. Even if I don't get anything to show off at least I can get some practice!!

[mr tibbs]

Well, I did get out last night and try this some more. I'm not sure that I am doing the stacking correctly though. It seems that I am reducing the noise in the shot by stacking, bu the detail that I was expecting is just not there. Here are the results from last nights shots.

This first one is 10 frames shot in 10 second intervals, all of the shots I took last night were with my 50mm prime wide open at f2 using iso 1600. Here is the first shot:


The noise is down, but I thought there would be more detail. Maybe I'm just not shooting the right part of the sky??

This next couple of shots were 5 frames stacked together. I shot a little bit of horizon just for fun in these and played around with them in Lightroom. I'm finding that it is hard for me to get the right detail and not induce noise using Lightroom. I'm sure this is just a practice issue as I am unfamiliar with the program.





I don't think the stacking works quite as well with some horizon in the frame. Obviously the horizon is moving with me and not the sky so the stacking program has a hard time tracking with both of them in the frame. Also, even with only a 10 second exposure I can see that I am getting some star tracking. I guess next time I will have to try the wide angle of the kit lens and see if that minimizes the star tracking.

Well, even though these are nowhere near what some of you guys are showing I think I am showing some improvement. I'm hoping that practice makes perfect here and I can keep getting better. Any comments will be appreciated!

[mr tibbs]

Another question, why are my brighter stars cone shaped??

[newarts]

Another question, why are my brighter stars cone shaped??

I don't know for sure but the distortion of the stars is radially symmetric and increases with distance from the center of the frame. I added some arrows indicating the approximate axes of the distortion for illustration.


It is a result of the software or lens. I suspect it is due to the wide open lens & out-of-focus coma. Try stopping down a bit next time.

Dave