Astrophotography blurry stars! :(

[putrescent82]

Hello all I am a beginner learning astrophotography and was hoping I could get some advice on what I am doing wrong. Below are my shots I made tonight as well as my settings I was using. Also how would I set my 18-55 and 55-300 to infinity mode I cant figure that out. I shoot f3.5 ISO 800-3200 10-30 second shots.

Gear:
Nikon D3100
18-55
55-300
tripod

 

[weepete]

Infininty focus is not a mode, its the focal point where really far away stuff is in focus. In lenses with a distance scale its marked as infinity and is the maximum focal distance of your lens. I recently found out that some lenses can focus past infinity, so the easiest way to get this is use live view and zoom in (in the view not on the lens) to magnify on a bright star and turn the focus ring until its as sharp as you can get it.

Other than that eliminate camera shake by enabling mirror lock up, use a tripod, use a shutter release or timer And make sure you are away from sources of vibration for long exposures. If you have done all of that then the star trails that you see is because of the earths rotation, and you need to use a faster shutter speed

 

[j-digg]

Yep, weepete makes some good points.

The stars are beginning to trail in your second photo, you will need to use a shorter shutter speed at that focal length if you want them to be pinpoint stars.

 

[Judobreaker]

In the second shot there's definitely some star trailing.

A rule of thumb to make sure you don't get star trails: max shutter speed = 600/focal length
At 300mm you'll start seeing star trails with exposures longer than 2 seconds.
At 50mm that's 12 seconds and at 18mm that's 33 seconds.

 

[astroNikon]

to add a few things to the above advice,
For taking pictures of the stars there are several things you have to be attuned to:

1 - air pollution. To check before I start taking pictures of planets is to focus on the moon and see if you can see craters in very good detail. If not, then there could be too much air pollution issues, or even a thin layer of clouds that you don't see that obscure details. And the further away you want to focus on, the more obscure they will become.

If the moon isn't available then pick something really far away such as a mountain, building, airplane lights to see if it is clear or not, or at least the outline of it being you are in the dark..

Any pollution, thin cloud cover, etc will make the picture blurry.

2 - also remember that the earth is rotating in space. So if you keep a longer shutter speed you will get the objects moving. Just set your tripod and camera up on the moon and watch it for a minute through the view finder or live view. It will move out of the frame.

To correct this you get into systems that slew the telescope/camera to keep it in time with the object. This can get very, very expensive as the cheaper solutions usually are just an introduction to astrophotography. A good intro setup is for slewing is a used Meade ETX-90 telescope. No smaller as the gears for the 90 slewing unit is capable of slewing with a smaller camera.

3 - tripod. You also need to keep your camera as steady as possible - use a remote switch to initiate it if you can. This is the hard part. Even on concrete/cement driveways walking on it can cause the setup to shake. So don't jump away, walk lightly away from the camera. The tripod also can get shaken in any wind too. I use a Silk Professional tripod (extremely sturdy and expensive) for photo shoots of the moon or quick ones of planets (using a 2000mm lens on a D7000). I normally use a Telescope capable of slewing (keeping the planetary object in the frame). For the moon I may use that or a Nikon 500mm lens. I've also used my 75-300 on the long end for handheld Moon shoots.

But your setup should be good for star/moon pictures. The more "careful" and attentive you can be of everything the better the shots will get. And play around with the ISO/shutter/aperture.

I nearly forgot
4 - turn off your porch light and any other light from your house. Use a lens hood or make one from black construction paper too.

FYI, in astrophotography you will hear that is it best to do it in the winter as air pollution is minimalized. I prefer the summer myself for air temperature

 

[Gavjenks]

5 - Turn off any vibration reduction or image stabilization your lens might have when doing long exposures (>1/20th of a second or so) on a tripod. The floating element can get confused and spin around unnecessarily, blurring your image if you don't, even if you had correct focus and everything else good.

 

[Patrice]

FYI, in astrophotography you will hear that is it best to do it in the winter as air pollution is minimalized. I prefer the summer myself for air temperature

The cold temperatures of winter help a lot with keeping your sensor cooled. A cold camera sensor makes for a happy astrophotographer.

 

[Gavjenks]

FYI, in astrophotography you will hear that is it best to do it in the winter as air pollution is minimalized. I prefer the summer myself for air temperature

The cold temperatures of winter help a lot with keeping your sensor cooled. A cold camera sensor makes for a happy astrophotographer.

Real photographers install filtered air conditioners in their camera bodies to reduce noise

Or even more hardcore, direct contact coolant fluid, with gasketed sensors to prevent seepage and custom designed lenses to account for the different refractive index of coolant versus air between the lens and the sensor. The reflex mirror would encounter a lot more resistance though, so you might have to suffer a lower FPS and more shutter lag I'm afraid. And you'd have to change lenses upright and bleed off any trapped air each time with a valve.

 

[putrescent82]

Thank you all for your replies unfortunately due to the full moon and light pollution here in florida I havent had a chance to try out your methods. I will soon though and post updated pics