Star photography

[redstone]

Can anyone advise the settings for star photography?

My attempt with 15s, f2.8 and ISO 400 was not good.

[Francis247]

Originally Posted by redstone Can anyone advise the settings for star photography? My attempt with 15s, f2.8 and ISO 400 was not good.

Hi redstone,

Maybe you can try to post your attempt picture so that others can better advice you.

[redstone]

Originally Posted by Francis247 Hi redstone, Maybe you can try to post your attempt picture so that others can better advice you.

Ok, will post later. Got tons of my photos from Bintan to edit.
What colour does noise appear? Reddish?

[Francis247]

Originally Posted by redstone Ok, will post later. Got tons of my photos from Bintan to edit. What colour does noise appear? Reddish?

Possible. What White Balance did you use?

[redstone]

Originally Posted by Francis247 Possible. What White Balance did you use?

Auto.

Shot by placing camera on beach (no tripod).

[paradigm]

Originally Posted by redstone Auto. Shot by placing camera on beach (no tripod).

no wonder ... 15sec w/o tripod ... tried w/o tripod before but I put it on the table w padding beneath the camera, timer triggered ... even if you are at the beach, should put it on a beach bench or something ... direction wise can always be obtained by raising ur camera using wallets (or worse come worse, small stones) etc ...

[redstone]

Pardon my ignorance, but I noticed over half of the 'stars' in my shot moved in 2 pictures taken around a minute apart???

[weixing]

Hi,

Originally Posted by redstone Pardon my ignorance, but I noticed over half of the 'stars' in my shot moved in 2 pictures taken around a minute apart???

Usually, the stars will drift even it is taken at 1 min apart. What is the focal length of your lens? And which part of the sky you aim at (overhead, north or south)?? The higher you aim above northern or southern horizon, the exposure time you can use become shorter before stars trail start to appear.

Have a nice day.

[redstone]

Originally Posted by weixing Hi, Usually, the stars will drift even it is taken at 1 min apart. What is the focal length of your lens? And which part of the sky you aim at (overhead, north or south)?? The higher you aim above northern or southern horizon, the exposure time you can use become shorter before stars trail start to appear. Have a nice day.

Thanks for the explanation.
Used 36mm on my digital cam. Aiming overhead.

[paradigm]

Originally Posted by redstone Pardon my ignorance, but I noticed over half of the 'stars' in my shot moved in 2 pictures taken around a minute apart???

actually, given abt 30 sec exposure, u would see that the star is no longer a "point" but becomes a small trail ...

so if you want point-stars shots, either u get a german equatorial mount or u push up the ISO so that you expose as short as possible ...

[redstone]

Originally Posted by paradigm actually, given abt 30 sec exposure, u would see that the star is no longer a "point" but becomes a small trail ... so if you want point-stars shots, either u get a german equatorial mount or u push up the ISO so that you expose as short as possible ...

I used 30s exposure. No wonder some stars appeared blurry or as a small trail. Thanks for the explanation.

My cam has high noise at ISO 400. Also max ISO. When I view in full size, there's a lot of noise. Can be confused wih real stars.

[weixing]

Hi,

Originally Posted by redstone I used 30s exposure. No wonder some stars appeared blurry or as a small trail. Thanks for the explanation. My cam has high noise at ISO 400. Also max ISO. When I view in full size, there's a lot of noise. Can be confused wih real stars.

Noise don't have trail... Anyway, try to stop down a few stop... most camera lens will have coma when shooting stars at wide open.

By the way, noise can be reduce by "dark frame subtraction"... meaning that you took another "image" at the same exposure and setting, but cover the lens with your lens hood, so that you'll only capture the noise... this is call Dark Frame. Then use software to subtract the Dark Frame from your image. It'll work best if you took the Dark Frame immediately after you took your image.

Have a nice day.

[redstone]

Pardon me what's a coma?

What will noise in the case of star photography appear as? Faint reddish splotches when viewed in full size?

[weixing]

Hi,

Originally Posted by redstone Pardon me what's a coma? What will noise in the case of star photography appear as? Faint reddish splotches when viewed in full size?

Coma is an off-axis aberration that make stars look like tear drops rather than a round spots... it look like star trail, but it is not. Most camera lens will have them if image star at wide open... even those very expensive Lens.

Anyway, you can go to this link to look at an example (a simple test I done on Canon EF 50mm f/1.8 II lens for wide field astrophotography):
http://www.singastro.org/viewtopic.p...er=asc&start=0

Have a nice day.

[redstone]

Thanks for the explanation

How do you distinguish between noise and real stars?

[chrisyo]

Originally Posted by redstone Thanks for the explanation How do you distinguish between noise and real stars?

Simple. Stars are white. Noise is red or green and everything else.

[weixing]

Hi,

Quote: Thanks for the explanation How do you distinguish between noise and real stars?

Usually, star are not a dot... even you use very sharp lens and got perfect focus. Stars will usually appear as a round spot, but noise will appear as very sharp dot usually make up of one or two pixels and most of the time, noise are smaller than stars.

Also, some digital camera will do some in-camera processing to remove noise by blurring it or if you use a non-RAW format, such as JPEG, noise will become less obvious, but more difficult to remove.

Below is an example crop from one of my astrophoto... no processing had been done and use maximum jpeg quality to make sure noise are not modified due to compression:

See the Stars and the Noise??

Have a nice day.