Shooting the night sky / shutter speed

[cchoate]

I've been out several nights shooting stars, planets and the moon with mixed results. I experiment with ISO, aperture and shutter speed but what has me perplexed is the longer I leave my shutter open (more than 3 seconds) the stars turn out blurry. I'm guessing it's due to the earth's rotation but I've heard / read other people leaving their shutters open for extended times and not having this problem. I am using a rock steady tripod and there is no wind. I'm also using a remote to take the pictures. Any suggestions?
Here's my set-up:
Sony A77, Tamron 70mm-300mm lens, Manfrotto 475B tripod w/Manfrotto mvh502 fluid head.

 

[Gavjenks]

1) Make sure you don't have image stabilization turned on on your lens, or it will be really blurry on a tripod.
2) Stars will show up as lines, because the earth is moving, yes. How long you can leave the shutter open before you see this depends on the magnification of the stars. And since your distance is pretty much fixed, that boils down to focal length. at 24mm, you can leave the shutter open for like 20-30 seconds before they get too obviously lines. At 80mm, maybe more like 6-8 seconds, at 200mm, only a couple seconds. Since you're using a 70-300 lens, I'm guessing there's a good chance youre using a very long focal length, and 3 seconds might simply be too long.

 

[cchoate]

I am using image stabilization so that needs to be turned off. And yes, I'm using all the focal length I can (300mm) so looks like I need to back off on shutter speed.
Thanks for the help, I really appreciate it.

 

[AR15th]

So then, how are those crazy time-lapse images with bright stars (not lines) captured?
Is it because the slider the camera is mounted on is following the rotation of the sky?

 

[KmH]

The same way telescopes make exposures that take hours.
The camera/lens is mounted on a device that moves opposite the earth's rotation, an equatorial mount/platform. Equatorial mount - Wikipedia, the free encyclopedia

Many telescope owners just mount their camera/lens piggyback on their telescope.

 

[jsecordphoto]

So then, how are those crazy time-lapse images with bright stars (not lines) captured?
Is it because the slider the camera is mounted on is following the rotation of the sky?

Some friends of mine use tracking mounts for timelapses, but a lot of night timelapses are just lots and lots of 30 second exposures.

 

[TCampbell]

If you do not want elongated stars (star trails forming) then you follow the "rule of 600". The rule says you divide 600 by your focal length and that is the maximum number of seconds you can leave the shutter open before the stars appear to become elongated.

BUT... this assumes you have a 35mm camera or a full-frame DSLR. Most DSLRs have a "crop frame" sensor (usually APS-C with a crop factor). You have to divide the result by the crop factor of your camera (usually 1.5 or 1.6).

This means that a 300mm would work out as follows:

600 ÷ 300 = 2
2 ÷ 1.5 = 1.3

This means that a 1.3 second exposure is the longest you can get away with at 300mm if your camera is not on a tracking mount.

Suppose you had a 10mm ultra-wide angle lens... now you can do 600 ÷ 10 = 60 (60 seconds) but when you divide that by your 1.5 crop factor you still get 40 seconds -- not so bad.

You can take longer exposures IF the camera is "tracking" the stars. This requires some gadgetry... such as a Losmandy StarLapse Losmandy StarLapse System or an AstroTrac Astrophotography Made Easy - Home.

You could also use an equatorial tracking mount and adapt the mount for the camera, or "piggy back" the camera onto a tracking telescope.

 

[AR15th]

wow, mind blown... Had a sneaky suspicion there was some extra gadgetry required. I've been shooting portraits and style shoots for a few years now, and have never tried this type of photography... the more you know!

 

[epeddy1]

I'll add that a fast lens helps. And clear, dark skies with no light pollution. Helps with light gathering.

If you just want stars at 300mm and don't really care which stars, I suggest the North Star, Polaris. It doesn't move, and the nearby stars don't move as much either.

If you don't have a foreground, figure out your max exposure time before trailing and snap multiple images. They can be "stacked" with various free software programs to enhance. You can always mask a foreground after getting the starry image you want.

Also post processing is HUGE. Need to "stretch" them to pull out the faint light. Shoot in RAW of course.

 

[Edsport]

Lots of info here...
http://www.thephotoforum.com/forum/articles-interest/276016-shooting-night-pictures-stars-stuff.html

 

[EIngerson]

If you do not want elongated stars (star trails forming) then you follow the "rule of 600". The rule says you divide 600 by your focal length and that is the maximum number of seconds you can leave the shutter open before the stars appear to become elongated.

BUT... this assumes you have a 35mm camera or a full-frame DSLR. Most DSLRs have a "crop frame" sensor (usually APS-C with a crop factor). You have to divide the result by the crop factor of your camera (usually 1.5 or 1.6).

This means that a 300mm would work out as follows:

600 ÷ 300 = 2
2 ÷ 1.5 = 1.3

This means that a 1.3 second exposure is the longest you can get away with at 300mm if your camera is not on a tracking mount.

Suppose you had a 10mm ultra-wide angle lens... now you can do 600 ÷ 10 = 60 (60 seconds) but when you divide that by your 1.5 crop factor you still get 40 seconds -- not so bad.

You can take longer exposures IF the camera is "tracking" the stars. This requires some gadgetry... such as a Losmandy StarLapse Losmandy StarLapse System or an AstroTrac Astrophotography Made Easy - Home.

You could also use an equatorial tracking mount and adapt the mount for the camera, or "piggy back" the camera onto a tracking telescope.

Thank you for that.

 

[TheLost]

Lots of info here...
http://www.thephotoforum.com/forum/articles-interest/276016-shooting-night-pictures-stars-stuff.html

Awesome timing on this thread... I tried my first night/sky photos last night and lets just say.. ick! i suck!

I'll try again tonight with some of the ideas posted here. Thanks!

 

[Aloicious]

If you do not want elongated stars (star trails forming) then you follow the "rule of 600". The rule says you divide 600 by your focal length and that is the maximum number of seconds you can leave the shutter open before the stars appear to become elongated.

BUT... this assumes you have a 35mm camera or a full-frame DSLR. Most DSLRs have a "crop frame" sensor (usually APS-C with a crop factor). You have to divide the result by the crop factor of your camera (usually 1.5 or 1.6).

This means that a 300mm would work out as follows:

600 ÷ 300 = 2
2 ÷ 1.5 = 1.3

This means that a 1.3 second exposure is the longest you can get away with at 300mm if your camera is not on a tracking mount.

Suppose you had a 10mm ultra-wide angle lens... now you can do 600 ÷ 10 = 60 (60 seconds) but when you divide that by your 1.5 crop factor you still get 40 seconds -- not so bad.

You can take longer exposures IF the camera is "tracking" the stars. This requires some gadgetry... such as a Losmandy StarLapse Losmandy StarLapse System or an AstroTrac Astrophotography Made Easy - Home.

You could also use an equatorial tracking mount and adapt the mount for the camera, or "piggy back" the camera onto a tracking telescope.

+1, you have to counteract the earth's rotation to do anything longer than the rule of 600 without star trailing...I just picked up a good used astrotrac for a good price and I'm looking forward to using it, I've used a monster Atlas EQ-G mount before, but weighing in at 100-120 lbs for all of it and the stuff needed to run it, kindof puts a damper on traveling with it and it's usability for casual astrophotos where a telescope isn't wanted.

dark skies and clear nights (for non-lunar objects like DSOs, during a new moon is ideal so the moon isn't creating light pollution either) will help immensely with astrophotos. here's a little tool I use to help me find local places that are darker than others, depending on where you live, you may not be able to easily avoid light pollution, but you should be able to find someplace that is at least better than others, this even has some popular astronomy spots marked on it which can help you see where other people like to go:
Dark Sky Finder

 

[Gavjenks]

24mm f/2.8 lenses are pretty popular amongst casual folks who don't want to invest thousands of dollars in this stuff, since they're pretty fast glass, wide angle means lots of seconds of exposure without trails and without tracking, and they're great for including the surrounding landscape in the shot.

 

[cchoate]

Ok, I was out shooting tonight and looks like my problem with star trails is solved. The next issue: I can't tell if the stars & planets are in focus using the lcd screen on my camera. I used manual focus on infinity and backed off just a tiny bit which looked sharp on the lcd. After viewing my pictures on the computer most were slightly and some badly out of focus. When I switch to auto focus the camera tries but can't focus on what it's looking at. I know the camera and lens will focus because I do have some nice clear shots of Jupiter and it's four moons from a week ago. How do you tell if you're in focus of a night sky on a three inch screen?