How to capture more stars?

Question

I finally borrowed a tripod from a friend so that I could take pics of stars from my apartment balcony. However, when I did some test shots yesterday, the pics where far from my expectations.

I took these shots around midnight using a 50mm 1.4G lens on a Nikon D5600. Using the 500 rule (i.e 500 / focal length * crop factor = 6.66), I kept the shutter speed at 6, F 1.4, ISO 100. Before taking the shots I manually focused on one of the brightest stars and with AE-Lock I took the pics.

The first click looked normal but its not what I expected, I could only see only two or three stars in the pic. Then I thought maybe I need to capture more light to get the other stars. But that resulted in just a plain white picture.

Now, I have two questions:

1. How to capture more stars?

2. When the shutter speed was increased, why did the image turn out to be plain white instead of star trails?

Answer 1

1) To capture more stars, go somewhere where there is less light pollution. If you can't see the north star, you aren't going to get much. I can't see the north star from my front yard, so attempting to shoot stars is hopeless.

2) If a longer shutter speed resulted in plain white, then the light pollution overwhelmed the image.

Answer 2

Shoot when there is no moon in the sky. e.g. Near the "New Moon" or "Last Quarter Moon" if shooting after sunset. Get away from urban light pollution.

I've generated a simulated field of view (using Sky Safari Pro) for your Nikon & 50mm lens (the blue box is the field of view) and approximated your section of the sky:

You can see a few faint objects that would show up if you were in a dark sky ... such as the Whirlpool galaxy, etc.

You are shooting the northern area of sky (although this time of year the Big Dipper asterism is very high up near the zenith). For more stars, you might pick a different region. The section of sky near Sagittarius is the direction toward the galactic core of the Milky Way and this has the higher number of stars (and other deep sky objects). It's a good target after dark in July (although you can shoot in now if you're willing to stay up a bit later in the night).

A tracking head helps give the camera time to saturate more stars (the Sky Watcher "Star Adventurer" head and the iOptron "Sky Guider Pro" are the popular tracking heads on the market -- they do need a solid tripod.)

Astrophotographers reduce noise by shooting LOTS of frames (e.g. at least 1-2 hours worth of exposures where each exposure may be a few minutes long) and then combining them using stacking software (free stacking software such as "Deep Sky Stacker" and there are many free video tutorials on using it. There are many commercial options as well). Given enough frames, the software can improve your signal-to-noise ratio which results in a final image with more detail and less noise (although typically a lot of manual love goes into the post processing work -- the image that comes out of DSS wont look as good until it has some manual adjustments.)

Answer 3

A few things will really help:

• Go someplace darker. It's a pain, but it's sooo worth it. It can make the difference between seeing only a few stars and seeing the full Milky Way.
• Use a wider lens. 50mm is very narrow for astrophotography if you're not using a moving mount to follow the stars. Try something in the 10-20mm range if you're shooting with an APS-C camera.
• Shoot for a longer period of time. If you have a 20mm lens, the shooting time becomes 16.66 seconds for the same shot. (But you can go longer if you want to get some star trails!) This is the reason you'll see more stars with a shorter lens - you can take a longer exposure without getting trails. (Or more accurately, the trails will be smaller than a few pixels so they won't be noticeable with a wider lens.)
• Increase the ISO. It will become grainier, but it's pretty much a requirement if you want to get lots of stars. I usually shoot ISO 1200-3200 when doing astrophotography.
• As @coblr mentioned in the comments: "In addition to increasing the ISO and ending up with grainier images, if you take multiple (>10) grainy images of the same subject and "stack" them together (reducing the opacity as you move up the stack: 100%, 50%, 33%, 25% etc), the graininess will become smooth and you'll be able to do more with levels to enhance and improve the overall image."

Answer 4

If your camera has digital noise reduction, turn it off. Point sources like faint stars can be interpreted as noise. If you can't turn off noise reduction, or if you just want to try another technique, you can also intentionally set your lens slightly out of focus, rendering the stars as small blurry circles. This deters noise reduction from trying to "fix" them. Bonus: when you defocus, the colors of some of the brighter stars become apparent. For example, Betelgeuse looks distinctly red/orange when photographed this way.

Answer 5

Take many pictures, align them and average them. This way you can achieve sufficient bit depth to make enhancements to the image. This is an image of Andromeda galaxy I took using simple compact camera without any other equipment under pretty bad light pollution.

This is the original picture I used to build the picture above, you can see the Andromeda in the middle just above the trees.

Answer 6

The wider the aperture (in centimetres, not in f/ ratio), the more stars you can capture. This is because stars are point sources and are always points: the more light you get, independently from the field of view, the more stars you get.

The f/ ratio defines the brightness of diffuse objects, but not (the rest being constant) the number of stars. See Clarkvision, chapter "The Lens Clear Aperture is the Key to System Sensitivity"

The rule in photography is that for a given f/ratio lens, the light per unit area per time should be a constant. This means there should be little difference in the sky background between the 50 mm f/2.8 lens and the 20 mm f/2.8 lens. The reason is that the smaller aperture of the 20 mm lens collects less light, but collects light from a larger area of the sky for each pixel, cancelling the effects of the smaller aperture. Stars, are different because they are diffraction disks and further spread by lens aberrations and their size is not dependent on focal length.

Therefore, contrary to the answers by @user1118321 , using a wide angle lens vs a normal lens will NOT increase the number of stars you get (in a specific region of sky). He/she is right that if the region is wider, you may get more stars, but the image will be less densely populated.

Answer 7

Start at very high ISO. You should be able to read reviews on your camera to find out it's max usable ISO. Modern sensors and image processing pipeline should be able to cope with 3200+ ISO (btw with digital photography it's not really actual ISO anymore which described the chemical qualities of the film used - it's more like ISO 'equivalent'). So you should get a nice colorful mess of stars (keep F stop minimum) then concentrate on setting shutter speed to maximum so that you don't get unwanted star trails (unless that is desired). So then it's a matter of dialling back the ISO to something which isn't too noisy (or as a previous poster suggested you could 'stack' multiple images to reduce noise but that starts to get more work on post processing side). Your lens will also behave better (sharper stars) as you stop it down (i.e. increase F stop to say F/5.6 etc) but at the sacrifice of light again. But to begin with leave it wide open and concentrate on getting ISO right. All other comments on darker sites (and even tracking equitorial mount to enable you to increase shutter without trails) all apply but are next steps.... Good Luck