[mr tibbs]

I have been reading up on some techniques today and I decided to try a night sky picture. I set up the camera on the tripod and went outside to try my hand at getting some star pictures. This did not turn out well at all. Even at 200 iso I have a ton of noise. So, what am I doing wrong? I'll give you an example:



Camera: K100D
Iso: 200
Lens: Super tak 50mm f2
Settings: 50mm, f2.8, 10 second exposure, auto white balance, manual mode, shake reduction off

I know it's a little overexposed but why all the noise?.

[Jonson PL]

I think you need to go above 15 sec., for the camera to apply Dark Frame Substraction.
Here are some other posts :

https://www.pentaxforums.com/forums/pentax-news-rumors/67569-k7-astrophotography.html

https://www.pentaxforums.com/forums/post-your-photos/67485-k7-astro-night-photo.html

[flyer]

Try to expose between f:8 and f:11. The sky won't be so washed out, and you will still see the stars. And make sure there is no light close by. Any light close by will wash your pictures.

[ytterbium]

First - it seems that there is huge light pollution, where your'e shooting (white overlay). With dark enough sky you should get only increased amount of visible stars, not such even overlay.
Have'nt you boosted the image in post processing (maybe some automatic raw preprocessing)? It looks more like that than light pollution.

Second. More a reply to Jonson PL. Dont compare those two cameras. It is absolutely invalid.
The visible noise level and pattern is fairly normal for k100d but again, haven't you post processed the image, with such white level the noise should be less visible. Dark frame subtraction helps only against hot pixels which cover the frame in 30s exposures even at iso200 for k100d. It wont do much in overall decreasing noise
for k100d. And if enabled it kicks in after some 1 or 2 seconds.

Third, your'e already seeing star trailing (they show up as ovals/lines instead of dots), so it is preferable to use shorter exposure times or tracking at that focal length (or wider lens).

Here is a 14sec shot without DFS, you see that the noise isn't visible:


And another 20s long shot of the scene, if you boost it the noise becomes visible:

[Ex Finn.]

Sure you can get star trails with that exposure time, depends on the focal lenght. That noise looks like what I get if post processing with photo-shop. Specially if I did the shot in RAW.

Here is a jpeg shot of comet Lulin (barely visible at the bottom) at ISO 3200, F4, 10 seconds, 210mm. Taken at a location with high light pollution level.
K100D. SMCA 70-210 F4.

Cheers. Mike.

[ytterbium]

maritimer, i guess you didnt notice that he's using 210mm lens.

[ivoire]

While in the badlands of SD, I tried my first starscape. This was with the K7 and da12-24mm for 98 seconds. Appreciate the comments here as it should lead to some improvement in my technique.

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Last edited by ivoire; 12-02-2009 at 12:50 PM.

[wildlifephotog]

If you look close, you'll see the stars in the center are pretty darn good. But as you move out to the edge the stars appear to trail. Many lenses will do this unless stopped down. My 50/1.4 is worthless unless stopped down to at least f4.
This appears much like a f5 or 6 newtonion reflector's coma.

[mr tibbs]

So, it looks like a combination of light pollution with the wrong settings. Well, in that case I will wait until the next new moon, pack up my gear amd head to the mountains! Good thing I live close and can be away from all city lights in about 15 minutes or so!

Maybe I will try again tonight with the different settings and see if I can get a little closer. I will still be in the city, but if I can get comfortable with shooting like this I should be able to get a good shot by the time the next new moon rolls around.

Thanks for all of the replies!

[ytterbium]

If you look close, you'll see the stars in the center are pretty darn good. But as you move out to the edge the stars appear to trail. Many lenses will do this unless stopped down. My 50/1.4 is worthless unless stopped down to at least f4.
This appears much like a f5 or 6 newtonion reflector's coma.

Same can happen with polar star in image center:

If the exposure is shorter, most stars will be dots, some a little streaked.

I was making a barn door tracker and damn only now i understood that at my location polar star has very high elevation. So the door will be at very steep, tripod stressing angle. Maybe i should redesign and remake it o_0.

[nightfly]

Ex Finn

I'm not sure what to tell you, but there really is no way you should be getting star trails at such a short exposure time, I'm sorry. What may be the cause is something I forgot to post in my above message.

Temperature:

In the spring and summer months the earth heats up during the day and that heat dissipates at night. Unfortunately, this takes up to 4 hrs after sunset during the hottest summer days. As this heat dissipates, it causes big time movement in the atmosphere. You won't see it with your naked eye, but it's the direct cause for star twinkling.

Go to a dark site during the summer @ around 10pm. Go to that same spot @ the same time in the winter : the stars seems brighter and less twinkly.

You have to remember that ANY movement is amplified thru a camera / telescope lens but you will not see this with your naked eye. We are looking at the stars through Earth's atmosphere, and as the Earth cools at night, that dissipated heat distorts and moves the air, thus causing movement in your lens.

Go out at 10pm in the middle of summer and try to look @ Venus or Jupiter thru a telescope; no matter what you do, you will not get a clearly focused image. You have to wait for Earth's heat blow off to completely dissipate.

Not trying to start an arguement or saying "I'm right and you're not". I have almost 10 yrs of astrophotography under my belt before I even moved to digital, and the above things I mentioned in both posts are all fact in getting good star scapes. I will go thru my archives and find some good star scape shots : none of them shot before midnight, none shot with a fixed short prime, no blurriness or star trails and ALL shot between 20-30 seconds.

I've never pulled my camera out during the summer nights before midnight.

P.S. If you're going to use a zoom lens over 100mm, you have to have a motorized tripod in order to not 'move' the stars. You will never get a clear image over 100mm from a fixed tripod BEFORE midnight in the summer, the air is still just moving way too much. Even your shutter opening and closing will capture movement in the stars to your sensor at that focal length.... It's not as easy as people think.

Leave your lens cap on ( or, use a black piece of construction paper ) open your shutter, remove lens cover, exposure for time desired, re cover the lens, close the shutter. This is how you avoid the above problems. Check out those sites I posted... all the facts from pro star shooters are there.

Stars will trail in 10 seconds, even with a 50mm lens if enlarged enough to see. Wide angle lenses allow longer exposure times, telephoto lenses less......

The Earth turns faster than you think.

See attachment:

[Ex Finn.]

Stars will trail in 10 seconds, even with a 50mm lens if enlarged enough to see. Wide angle lenses allow longer exposure times, telephoto lenses less......

The Earth turns faster than you think.

See attachment:

Exactly, right on.

3 second exposure at ISO 3200 of Orion, taken with 880mm refractor telescope.
For stuff like this to turn out with no trails, you must have a GOOD tracking mount.

And I make no claims of knowing a darn thing about star photography, all I have learned so far is that it is easy to spend a lot of money in gear.

Cheers. Mike.

[ChipB]

Mr Tibbs, some things I haven't seen mentioned:

- Use the 2 sec delay setting (I *think* the K100D has it) - this will immediately raise the mirror and 2 sec later the shutter will fire. This will help quite a bit - and will help even more when used in conjunction with another tip that was posted - use a blackout curtain in front of the lens both before you shoot and just prior to releasing the shutter.

- Use some sort of remote shutter release so you don't "vibrate" the camera with your finger. The Pentax remote F will lock the shutter open until you release it. I, personally, use a remote setup, but the end result is the same - no vibration from your finger.

- Use a lens hood - will help cut down unwanted light.

Above all, try a bunch of different settings - play with shutter speeds, ISO settings and f-stops until you get the results YOU want!! Have fun!!

[Ex Finn.]

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 - might wanna Google that and find out just how much of a problem it is for astrophotographers.

So, what you're saying is that every article, post, essay on all those sites I provided is wrong information. Good to know I've been doing it wrong for years :S

DSLR Cameras for Astrophotography

Mirror slap, hell..... You are absolutely correct about, " when done correctly", it is not a problem. That 3 second with a telescope is real, so is the one with my 70-210, tripod, mirror up, 2 second delay.

Time to go outside and do some BBQ.

Cheers. Mike.

[nightfly]

Add 25 years to my experience..... Sorry gentleman, I can bear no longer. Looks like the Earth does not move.

Ex Finn. You have it right. Good luck in your quest to demonstrate the obvious. To take part in the argument is an exercise in futility. Not what I'm here for. I have astrophotos to take.