Fotografering – Astrofotografi

For alle dere fotoentusiaster der ute som har drømt om å ta astrofotografier (bilder av verdensrommet) trygt fra bakkenivå, så kommer her en ganske grei forklaring på hvordan dere kan få til dette med riktig utstyr.

Denne artikkelen er henta fra http://asignobservatoryii.webs.com/astrophotographytips.htm og kan leses i sin helhet der. Artikkelen forklarer mye rundt astrofotografering også, så det er absolutt verdt å ta en kikk der.

For min egen del, så har jeg alltid hatt lyst til å fotografere utover mot stjernene, så denne artikkelen kommer godt med nå som det er vinter og perfekte lysforhold for å fotografere verdensrommet fra jorda; bekmørkt.

Her kommer et par eksempel på fotografier man kan ta med et vanlig speilreflekskamera under riktige forhold


Så, til artikkelen så forklarer hvordan man kan gjøre det:

Widefield Astrophotography

You’ll need a tripod, a camera that has a full-manual control option with the ability to do a 30 second exposure, (A DSLR is best) and a wide-angle lens. I can highly recommend the Canon 16-35mm f2.8L lens. You can also use a 10-22mm, 18-55mm in any brands. The point is, you need to use the wide end of the scale, around 16mm. Full-frame cameras are more expensive, but they get more image in and their chips are inherently less noisy. You can still do it with a crop-frame sensor though. If you have live view, that’s awesome, we’ll use it!

Here’s how. Go for a drive out of the city and away from the light. Pick a night when there is no moon, no clouds, no family or work commitments, no party invites, no responsibilities or obligations. Good luck with that.

Set your uber expensive and solid tripod down on the ground and make sure it is stable. If you went cheap and bought a $20 Aldi tripod because you are not as serious as you think you are, you can hang a heavy camera bag from the hook under the bottom of it to make it more stable. Alternatively knock a tent-peg into the ground and use an elastic strap to pull it down firm. Don’t stretch it too tight or you might find yourself with a dirty tent peg up your nose.

Put your camera on top and point it at a bright star. Yes the sun is a star and no it doesn’t count. If you use the sun you are an air-head and you are also out at the wrong time of day. Use the switch on the side of your lens and turn it to manual focus. (MF). Leave it there and never touch it again.

Looking through the viewfinder and using the lens zoom ring, zoom in on any bright star and centre it using your tripod head adjustments. (For a 16-35mm lens, zoom to 35). Using the manual focus ring on your lens, focus the star as best you can. For most lenses focus will be all the way to infinity and back just a poofteenth to find the sweet-spot. Switch your camera on now and turn on live view. Using the digital zoom buttons, (+-) zoom in as far as it will go, still keeping the star centred. Now very carefully, use the manual focus ring on the lens and fine-tune the focus. Go back and forward a few times to get it right. Once it is focused, do not play with it again! Turn off live view and zoom all the way back out again to 16mm.

Now you can re-frame to an area of sky you want to photograph. I find it easier to frame what I want with the camera switched off, that way the LED screen on the back isn’t playing havoc with my super owl-like night vision. The milkiest part of the Milky Way is a great place to start so try that. It’s the area with the greatest concentration of stars, but remember it’s not always visible as the Earth rotates.

Turn your camera on, switch the top dial to M for manual. Make sure you are shooting in RAW, not JPEG. Set your shutter speed for 30 seconds. Set your ISO for 800 or 1600. Remember the higher the ISO, the more sensitive to light your sensor is. The downside is the image will be grainier, (noisier). You decide on the trade-off. Open your aperture to fully open. (F2.8 for my 16-35mm) Turn on your timer delay. I use ten second delay so the vibrations from me pushing the button (camera shake) have time to settle before it goes off. If you have your flash prepared to go off, self-administer another uppercut because you are a twit and put your flash away in the car.

Press your shutter button and ten seconds later the shutter will open, thirty seconds after that you have taken your first successful wide-field astrophoto.

Run your photo through Photoshop to adjust curves and levels as well as colour balancing, resizing and finally sharpening. If you want to make it even better, take ten identical photos and stack them. Post it up on astrophotography forums, tell them how awesome you are and then get ready for life-shattering humiliation, ridicule, mockery and torment when they tell you how to fix all your mistakes. Let’s face it..you deserve it.

If you want to do long-exposure widefield work, then you will need to take your camera off the tripod and put it on a mount that tracks the motion of the stars, other wise you will get long star trails after 30 seconds. This is where the second mortgage on your house or selling your child for medical experiments comes in handy.

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