Noob astrophotography question

Got a beginners' question? No matter how elementary, our friendly forum community and magazine writers will answer it.

Noob astrophotography question

Postby bluesdragon » Fri Sep 03, 2010 12:03 pm

I have just started to take an interest in astrophotography and have bought a T-ring and T-adapter to link my Canon D1000 to my Skywatcher telescope. I have started to have a play around with the kit having read up a bit on the subject but what I find confusing is when people talk about setting the aperture on the camera - obviously the lower F-stop meaning more light comes into the camera. As soon as I take the camera lens off and replace it with the T-ring and T-adapter there no way of changing my aperture setting. It defaults to F00 on the back of the camera. How can I overcome this?

bluesdragon
 
Posts: 10
Joined: Mon Feb 13, 2012 6:52 pm

RE: Noob astrophotography question

Postby Chanctonbury » Fri Sep 03, 2010 1:43 pm

The short answer is that you cannot change the aperture setting (also known as 'F' Stop) because this is a function of the lens itself, not the camera that it is attached to.

Using the 'T' ring, you will be taking images at what is known as 'prime focus' so the telescope in effect becomes the camera's lens and telescopes do not have any aperture control - the aperture is set for you physically by the dimensions of the telescope. If you have an 'F5' telescope then that is your aperture and you have no control over it.

What you do have control over though is MANUAL focus of the telescope using the 'scope's focusing mechanism and the exposure length which you set using the camera - for deep sky images, this would be long exposures, using the camera's 'bulb' setting and for Lunar imaging, short exposures in the region of perhaps 1/500th of a second.
Chanctonbury
 
Posts: 4457
Joined: Thu Feb 03, 2011 5:57 pm

RE: Noob astrophotography question

Postby bluesdragon » Fri Sep 03, 2010 4:13 pm

Thanks Skywatcher. I thought that was the case but thought I would double check. I think stuff I have read about changing aperture must refer to a camera just piggybacked on the telescope, and not actually looking through the telescope lens.
bluesdragon
 
Posts: 10
Joined: Mon Feb 13, 2012 6:52 pm

RE: Noob astrophotography question

Postby worcspaul » Fri Sep 03, 2010 5:03 pm

Hi bluesdragon. You'll find you can get quite acceptable results with the 1000D mounted on a tripod. I presume you have an 18-55mm "kit" lens (doesn't matter whether it's IS or not)? First thing to do is set your lens to 18mm and use the AF to focus on a distant object, either in daylight or, perhaps a streetlight at dusk. This should mean you're focused at, or very near to infinity (What I've done is use a highlighter pen to put a small mark on the lens tube/focus ring to mark this point to make it easier to manually focus if/when I move the camera about).

With the camera focused to infinity, switch the AF [b]off[/b] and try to avoid touching the focus. Set the camera to [b]M[/b] and set the camera to maximum aperture. Aim the camera in the direction of Cassiopeia and set exposure time to 15s. Experiment with different aperture/exposure time settings to see how the results are affected. Note that the further away from the pole you move, the greater the likelihood of star trailling, so you'll need a shorter exposure to combat this.

For something different, you might want to try imaging the ISS. Register on [url=http://www.heavens-above.com]Heavens Above[/url] and enter your Latitude/Longitude or nearest city. You'll be able to obtain details of ISS passes that will be visible to you (skies permitting, of course) along with sky maps showing the path of the ISS. Some passes are short, whereas some can be visible for several minutes.

Set your camera up on a tripod and aim it in the general direction of the path. Set exposure to 30s and wait. When you see the ISS press the shutter release. As soon image has been taken, press the release again. Keep doing so until the ISS is no longer visible.

Hope that helps you get started!
worcspaul
 
Posts: 328
Joined: Sat Jun 18, 2011 8:42 am

RE: Noob astrophotography question

Postby bluesdragon » Fri Sep 03, 2010 5:53 pm

Nice one Paul. I'll give that a try.

Its funny because I have had decent cameras for years but never thought of photographing the night skies until I got into astronomy more recently, and as you pointed out with your info you don't even need a telescope.
bluesdragon
 
Posts: 10
Joined: Mon Feb 13, 2012 6:52 pm

RE: Noob astrophotography question

Postby ronin » Fri Sep 03, 2010 6:26 pm

Confused: The ISS goes across the sky usually Westish to South-Eastish at a fair rate, as in 4-6 minutes if you are lucky to go right across.

Wouldn't a 30s exposure simply just give a series of streaks?
Is there are settable rate for a mount to track it?
ronin
 
Posts: 85
Joined: Mon Feb 13, 2012 6:58 pm

RE: Noob astrophotography question

Postby worcspaul » Fri Sep 03, 2010 10:03 pm

Depends on how dark it is and how bad light pollution is. 30s gives me a decent track without too much washout by pollution. First shot would probably be 10s to check ISS in frame then set to continuous mode at 15-30s
worcspaul
 
Posts: 328
Joined: Sat Jun 18, 2011 8:42 am


Return to Ask a silly (astronomy) question

Who is online

Users browsing this forum: No registered users and 0 guests