Are Star Trails possible with a Canon S5?

[descorpio]

Hi, I was reading and edition of National geographic recently and saw some really nice star trails which got me thinking. Is it possible to capture star trails on a Canon S5 IS? I am guessing you would need a really low shutter speed for it right? Any ideas??

[dmartin]

By 'star trails' do you mean the tracks left by long exposures? The stock S5 does not have a long exposure time, but if you install CHDK, you can get a longer exposure.

[ChicagoAstronomer]

If you zoom in on a star grouping, you can get nice star trails even with the 15 second limit on the standard exposure.

But, I must look into that CHDK.

(Side note: On my S3, I have noticed that I cannot get the camera to focus down to pinpoints on stars. It just misses by a millimeter or so. I wonder if any others have experiences the same.)

[NrthwoodsS5]

Last time I checked with CHDK you are able to get an exposure time as long as 64 seconds or so, and like ChicagoAstronomer said, if you zoom in more you will get longer trails, and that also depends on where in the sky you are shooting, if you were to shoot the north star you wouldnt get much movement as the sky "spins" around it during the night. Unfortunately for us 64 seconds isnt a long time compared to the bulb settings on the nicer dslrs. But none the less it still makes for awesome pictures!

[JakeDonahue]

I just did my first star trail photo last night. I downloaded CHDK and on the S5 you can do up to a 34-MINUTE exposure!!! Here is an example of a 17-minute exposure:



I plan on doing it for 34 minutes tonight! The only downside is that if you shoot a photo like this at 17 minutes, you have to wait 17 minutes to view the photo. I guess however long your shutter speed is, the camera requires the same amount of time to process. I've heard lots of cameras do this.

[NrthwoodsS5]

Oh wow there must be an updated chdk version then. The current one I use maxes out at 64 seconds. I'm going to have to definitely do some updating!

[brett_93_ex]

Wow I gotta try this.

[SteveB]

Nice result Jake.

I did one with my S3 last month. I used the fast intervalometer script & CHDK to get multiple shots which I stacked together in pp.


This is a single frame from the sequence. It's looking South with the Southern Cross at the top and the two pointers (alpha & beta Centauri) to the left. I had trees in the frame for scale but the site was so dark you can't see them (the dark area in the top left).


Steve.

[NrthwoodsS5]

Awesome photos Steve! Very cool star trails, im excited for the clouds to leave so I can try one for myself. What are the stats of your shots?

[JakeDonahue]

Those are awesome, dude... How long was the exposure? Any Exif data you have would be much appreciated! also, where did you shoot them?

[SteveB]

Thanks.
There were 70 shots of 15 seconds each (19 minutes) f/2.7, ISO400. The trails were made using this Startrails application. I shot in JPEG only as the stacking reduces noise and you can get more shots on a card. I also turned off in camera noise reduction (that's your extra 17 minutes Jake) and used separate dark frames.
The location was about 70 miles north of Auckland, New Zealand. Well out in the sticks.
I might have to update my CHDK (which is limited to 54 sec) and have a crack at a real long exposure shot (if the clouds ever clear again).

[NrthwoodsS5]

So is there a way to make it so it doesn't take 17 minutes to process a 17-minute exposure shot? I took a 30 minute exposure shot tonight but my batteries ended up dying while it was processing so my image was lost! Next time I guess...

[SteveB]

Yes. In RAW Parameters, turn Noise Reduction off.
This will stop the camera from taking a dark frame (the same exposure with the shutter closed) which it then subtracts off your image.
You will still want to do a dark frame subtraction, but you can do it later and then subtract it off yourself in pp. I usually have the camera taking dark frames on the seat while I'm driving home. As long as the settings are the same, you can use one dark frame for multiple images. I've built up a library of dark frames for each camera I own, ISO and exposure and just use the appropriate one.
Ideally, you want to do the subtraction with RAW data, rather than the gamma adjusted stuff in photoshop, so there is some merit in having the camera do it.

Steve.

[NrthwoodsS5]

Awesome thanks Steve! Now do you think you could possible explain that process in some detail so I could do it? I would greatly appreciate it!

[SteveB]

The reason you (or the camera) take dark frames is that with long exposures, some of the image is formed from the light coming in the lens and some is generated by internal heat. If you take a picture with no light, then the resulting image must be due to just the heat. So if you subtract that off your picture you are left with just the real image data.

Taking dark frames is the easy part. You take exposures using the same settings you used for the picture but with the lens cap on. I try to put the camera in a darkish place just to be sure that no light gets in. Ideally you want the conditions to be as close as possible to the image exposure. If you live in the Arctic or Sahara you'll need to do it outside, but for more temperate places, any time will be OK.

In Photoshop you load the two images and use the difference or subtraction blend modes. I don't use that method so I can't tell you much about it. Here's a site that does. They also mention BlackFrame NR. That's nice and simple to use but I can't remember if it will work with CHDK RAW files.

Steve.

[NrthwoodsS5]

Awesome thanks a bunch Steve, hopefully one of these days i will be able to try it out!