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CravenMorehead
Post subject: Night sky pics - tips wanted  PostPosted: 27.09.2010 14:39



Joined: 27.09.2010 Posts: 4

Just got a new D-SLR (Nikon D5000) and would like to take some night sky pics. Any suggestions on Aperture/Shutter/ISA settings?
 
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ravnostic
Post subject: RE: Night sky pics - tips wanted  PostPosted: 27.09.2010 15:00



Joined: 14.02.2010 Posts: 2898

1) Make sure to turn 'long exposure noise reduction' on.

2) use mirror lockup if you have a cable or remote-shutter fob (if you don't you might consider getting one.)

3) If you DON'T want star trails, use high ISO's, and short time intervals (viewed at full res, a shot at 28mm for even 30 seconds will cause blur.) You'll have to fiddle with the settings to determine how high you can go with the ISO with reasonable noise (and reducing image size for viewing will often take care of quite a bit of it.)

4) If you DO want star trails, use lower ISO's, and longer exposures.

A decent 300mm lens will give you Jupiter's moons, with a long enough exposure (and I'd have to find the pictures to determine how long you can go without it moving--it's not long--Jupiter will, of course, be overexposed to get the moons). Also, find the absolute darkest skies in the least polluted areas as you can. Light pollution turns the night sky brown. You can use a tungs. setting to minimize this, if need be.

[thinks] what else? If you have that 300mm lens, give Orion's nebula a shot--you should be able to get it. Same with the Andromeda Galaxy, if the skies are dark enough.

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caradoc
Post subject: RE: Night sky pics - tips wanted  PostPosted: 27.09.2010 15:06



Joined: 15.12.2006 Posts: 871

...and a nice, solid tripod.

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CravenMorehead
Post subject: RE: Night sky pics - tips wanted  PostPosted: 27.09.2010 15:08



Joined: 27.09.2010 Posts: 4

I do have a 300mm and a remote shutter fob. Thanks for the suggestions. I live in northern MN and the sky at night is amazing and no light pollution either.
 
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ravnostic
Post subject: Re: RE: Night sky pics - tips wanted  PostPosted: 27.09.2010 15:10



Joined: 14.02.2010 Posts: 2898

      CravenMorehead wrote:
I do have a 300mm and a remote shutter fob. Thanks for the suggestions. I live in northern MN and the sky at night is amazing and no light pollution either.


Ditto on caradoc's tripod comment. You'll do fine under MN skies. I understand October is good for the Aurora (you'd have to ask soosh about that, though.)
 
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orionid
Post subject: RE: Night sky pics - tips wanted  PostPosted: 27.09.2010 15:15
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Joined: 04.09.2008 Posts: 3175

      ravnostic wrote:

If you have that 300mm lens, give Orion's nebula a shot--you should be able to get it.

I ran a couple passes at it two years back. At 1600 ISO, 300mm f/5.6 and five seconds exposure, I got a purple streak with two white lines in the middle. Of course, I was working with sub-urban new york skies, so you may have better luck out in BFE.

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ravnostic
Post subject: Re: RE: Night sky pics - tips wanted  PostPosted: 27.09.2010 15:42



Joined: 14.02.2010 Posts: 2898

      orionid wrote:
      ravnostic wrote:

If you have that 300mm lens, give Orion's nebula a shot--you should be able to get it.

I ran a couple passes at it two years back. At 1600 ISO, 300mm f/5.6 and five seconds exposure, I got a purple streak with two white lines in the middle. Of course, I was working with sub-urban new york skies, so you may have better luck out in BFE.


Camera shake due to mirror movement, I'd bet. Lock the mirror, use a remote shutter release; it should be doable (though 2 seconds at 3200 would be better--wish my cannon had ISO above 1600; but I got a save with piggybacking the camera onto the telescope.
 
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CravenMorehead
Post subject: RE: Re: RE: Night sky pics - tips wanted  PostPosted: 27.09.2010 18:25



Joined: 27.09.2010 Posts: 4

I am in BFE, that's for sure. Should be a nice clear sky tonight so I'll give it a try. Thanks!
 
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chupathingie
Post subject: RE: Re: RE: Night sky pics - tips wanted  PostPosted: 29.09.2010 10:20



Joined: 10.09.2009 Posts: 924

If you're feeling handy, google "barn-door mount"; a cheap home-brew alternative to an equatorial mount.
While you can get decent wide-field shots from a tripod, shooting the night sky with a 300mm will need some kind of tracking mount. You'll get obvious streaks in a very short few seconds with a stationary camera.

In-camera noise reduction is fine unless you're planning on taking many long exposures. So if you do make a barn-door, turn the in-camera noise reduction off. Instead, run off a dozen shots in the middle of your shoot at the same settings as your exposures with the lens cap on. Average these together and subtract from each of your exposures before you do any other processing. This will really knock a lot of noise out.

If there's a moon, or nearby light source lighting up the sky, take a shot at full in-focus. Process like the others for noise, then subtract this blurred image from your shot to remove (or reduce) the gradient from the offending light source. I used this trick a lot when I was shooting from within the DFW metroplex area to knock out the horrible light pollution. You can also blur the image you want to process and use that to subtract, just make sure it's *really* blurred or you'll kill any nebulae and the milky way in the final.

Shoot wide-open and look for any blue halos around your stars and also for any non-round stars on the edge of the field. If you see either, close down by a stop and try again. There's a trade-off between image quality and brightness.

Things you can capture with a 300mm: In addition to the Andromeda Galaxy (which fills nearly the entire field of view at 300mm) and the Orion nebula mentioned above, I've taken images of M16, the Trifid nebula, the Hercules Cluster... I even managed one image of the Ring nebula. Most of the Messier Catalog objects can be managed with a DSLR if you can track.

I need to work a lot more OT to get that Losmandy G11.... *sigh*

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CravenMorehead
Post subject: RE: Re: RE: Night sky pics - tips wanted  PostPosted: 29.09.2010 13:13



Joined: 27.09.2010 Posts: 4

Thanks for all the help. I tried several pics over the last two nights. The problem I have in virtually every shot is the little halos around every point of light. The only pic that didn't have them was taken with my 70-300mm and that was at the 70mm setting. The exposures seem to be perfect otherwise. What am I doing wrong?
 
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orionid
Post subject: RE: Re: RE: Night sky pics - tips wanted  PostPosted: 29.09.2010 13:43
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Joined: 04.09.2008 Posts: 3175

I've considered the barn-door mount before and just haven't gotten around to it yet.

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chupathingie
Post subject: RE: Re: RE: Night sky pics - tips wanted  PostPosted: 29.09.2010 14:02



Joined: 10.09.2009 Posts: 924

Craven, if the halos are blue, that's Chromatic Aberration (CA). The only things I know that can be done about that is shoot at a higher f-stop, use better glass ($$$), or correct via software in post. With regards to the first 2, even L-Series lenses don't like astrophotography much wide open, although the fixed-focal length telephoto lenses seem to have much better CA characteristics.

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ravnostic
Post subject:   PostPosted: 29.09.2010 14:20



Joined: 14.02.2010 Posts: 2898

Telephoto is great for reducing CA (if the subject is well centered), though movement makes things difficult to capture. Lens characteristics and a few physical laws prohibit the elimination of CA entirely. If light passes through glass, there will be diffraction--it's why the best telescopes use front-surface mirrors.

Even the earth's atmosphere creates CA. Here's Venus about a week ago. Note the prominent CA (well, it's more prominent if you zoom in). And excepting the aforementioned mirror, there was nothing between the sensor and the planet. It's just it was near to the horizon, maximizing the effect.

 
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ravnostic
Post subject:   PostPosted: 30.09.2010 06:41



Joined: 14.02.2010 Posts: 2898

Here's a shot of Orion's nebula, 2.4 seconds, 300mm focal length. Noise in an xTi is bad. No processing, just the raw shot.



It's at lease discernible. I could do better--but we drinks the day after my birthday, ya know.

Stacking would greatly improve the image. Since this isn't piggy backed, I'm kinda stuck with the shot as is.
 
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SilverStag
Post subject:   PostPosted: 30.09.2010 06:50
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Joined: 25.05.2006 Posts: 769

      ravnostic wrote:
Here's a shot of Orion's nebula, 2.4 seconds, 300mm focal length. Noise in an xTi is bad. No processing, just the raw shot.

[picture]

It's at lease discernible. I could do better--but we drinks the day after my birthday, ya know.

Stacking would greatly improve the image. Since this isn't piggy backed, I'm kinda stuck with the shot as is.


What is stacking? I've seen it mentioned a couple of times now....
 
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