Shooting with the stars... How?

*Ash* · 05-16-2007, 10:38 PM

I wanted to try out long night-time exposures of the clear sky in the hope I'd get some star trails. Looking into what others had done, I tried 3 hour, 2 hour and 45 minute exposures at fairly small apertures (f/22-32) at ISO 200 - no success.

The 2 and 3 hour exposures came out totally white! The 45 minute exposure came out totally wierd! Scrambled colour noise resembling an untuned TV screen, only in a pink shade!

Please forgive me if this is a novice's mistake, but I can't seem to get the balance right for this type of shot. A 2 or 3 hour exposure would be ideal to try and get decent trails, but at what settings will this work? Anyone got any ideas?

Thanks all.

zaku · 05-17-2007, 01:58 AM

Due to hot pixel problem of DSLR, the only way to play with long exposure is using a film camera... ;p

Try to search "star trail" on net, you may get some hints

blende8 · 05-17-2007, 04:23 AM

1. Do you have noise reduction ON? This is important for such long exposures.
2. Was it really dark enough? Use a smaller aperture and ISO 100.

*Matjazz* · 05-17-2007, 05:34 AM

On my DS noise really builds up with long exposures. And I'm talking about 2-3 minutes. During exposure sensor heats up what manifests as noise. I'm not sure if it's wise to do too long exposures. I know that astro photographers make several 3min exposures when using digital cameras.

Ixtl · 05-17-2007, 06:19 AM

3 hours!? Ye Gods!
Don't do that again, please.
I suppose you wanted to catch star trails on the camera. On film cameras, depending on the location, sky-glow, light pollution, it can be done for a few hours, usually with ISO 100-200 film.
On a digital camera over time you will have noise accumulating on the CCD. The idea is to have the lesser noise possible, but to have the IQ good enough for your purposes. The more you will expose the CCD, the warmer/hoter it will get, and this heat will show up in you picture as noise. Eventually the sensor will saturate and the pic will be a beautiful white rectangle.
The CCD cameras used in astronomy, where usually long exposures are used are cooled using a Peltier element and a fan cooler in order to avoid noise due to heat. Even so, with these cameras (which cost from ~1000USD up to several k USD) that are designed especially for this kind of exposures, one shot doesn't take more than a few tens of minutes. The ulterior image processing is the one that makes these exposures into one beautiful color image like the ones you can see on ESO and Hubble sites.
Now, my advice would be to use ISO 200 or 400 and start in small steps from 1 min., let's say in one minute steps. See at what duration your pic is clear enough - that's up to you - and then start doing several exposures at that duration*. Later you can combine all those pictures into a sort of star trail pic.
You can use noise reduction, but that will usually take longer, as the dark frame needed for this reduction is taken automatically after the shot itself.
You can deactivate noise reduction from the menu and take one dark frame before and one after your shooting session, at the same settings. These dark frames are ideally made with the visor cap and the body lens mount cap on. Later you can combine and average these two dark frames and subtract the result from each of your star trail pictures, before you combine them.
Good luck for now, and please do not take any more 1-2-3 hour pictures with a DSLR.

LE - *you should start from the widest aperture on your lens and close it by a stop until the vignetting disappears or it is within decent limits for correction with photo software.
Bear in mind that astro photography, starting from the film days, requires a lot of post-processing in order to get decent results.

-spam- · 05-17-2007, 06:34 AM

Originally Posted by Matjazz

During exposure sensor heats up what manifests as noise. I'm not sure if it's wise to do too long exposures.

In a lot of cases, it is not the sensor heating up but the components around the CCD. But in exposures longer than 30mins it will be a mix of both.

There are only a few ways around it, like has been suggested use a film slr to do it, stack several shorter exposures or even get your hands on an older canon CMOS dslr (dont shoot me down) and use that if you are really serious about it.

Ixtl · 05-17-2007, 06:40 AM

Canon isn't the panacaea, those too have these issues but they are waay less serious than the Sony CCD DSLR's. Plus better S/N ratio at higher ISO. Or both.
I'm waiting for the day Nikon and Pentax switch to quality CMOS's (not Canon's, God forbid

), as Sony CCD's, as good as they are, don't seem to focus very serious on high S/N ratios. Or maybe I'm missing something :P

taveren · 05-17-2007, 07:11 AM

I have taken some star trail shots with my K100D. I used a number of short exposures with no noise reduction and combined them with startrails.exe. This works quite well for producing long exposures, and the process of adding the shots together removes a great deal of noise, including that of high ISO. You can get startrails here

The image below is the result of such a process. I didn't use a dark frame for this one, but it was very cold this night, so heat wasn't a big issue.

This is 92 30s shots. 24mm, f5.6, ISO 800.

*igowerf* · 05-17-2007, 02:21 PM

I've been actually wondering the same thing.

Thanks for the tips and photo taveren. Did you use a remote shutter release when you took these? Also, did you actually stand there for 92 x 30 secs and repeatedly click?

Also, does anyone have some tips on how to do this in an older film camera? I have a roll of Ilford XP-2 in my ME Super and would like to try some star trails on B&W film.

-spam- · 05-17-2007, 06:07 PM

Originally Posted by igowerf

Also, does anyone have some tips on how to do this in an older film camera? I have a roll of Ilford XP-2 in my ME Super and would like to try some star trails on B&W film.

Get yourself a proper cable release, screw it into the shutter button and start shooting. They arent to expensive either.

taveren · 05-17-2007, 06:40 PM

Originally Posted by igowerf

I've been actually wondering the same thing.

Thanks for the tips and photo taveren. Did you use a remote shutter release when you took these? Also, did you actually stand there for 92 x 30 secs and repeatedly click?

I set my camera to continuous shooting mode, manual setting (M on the dial) for 30 seconds and f5.6, then locked the remote shutter cable switch in place. This will repeatedly fire 30 second exposures until the card is full, or the battery runs out.

mikerigel · 05-17-2007, 06:55 PM

You can do some long exposure photography with the K10D, but I don't know about 2 or 3 hours..... I think that's too long.
Here's a 9 minutes shot at f/4, ISO 200.

My longest exposure on digital was done with the Ds, it's a 24 minutes pose, f/3.5 at ISO400.

-spam- · 05-17-2007, 07:25 PM

Originally Posted by taveren

I set my camera to continuous shooting mode, manual setting (M on the dial) for 30 seconds and f5.6, then locked the remote shutter cable switch in place. This will repeatedly fire 30 second exposures until the card is full, or the battery runs out.

I must say that i never thought of doing it that way. Great idea

*Ash* · 05-17-2007, 11:14 PM

Originally Posted by taveren

I have taken some star trail shots with my K100D. I used a number of short exposures with no noise reduction and combined them with startrails.exe. This works quite well for producing long exposures, and the process of adding the shots together removes a great deal of noise, including that of high ISO. You can get startrails here

The image below is the result of such a process. I didn't use a dark frame for this one, but it was very cold this night, so heat wasn't a big issue.

This is 92 30s shots. 24mm, f5.6, ISO 800.

Much appreciated guys. I hope not too much damage was done with my previous massive exposures. I appreciate your input taveren. I'll give that a try. And great shot indeed! I'll submit my attempt when I've got one in the bag!

Cheers again.

taveren · 05-18-2007, 06:31 AM

Originally Posted by Ash

Much appreciated guys. I hope not too much damage was done with my previous massive exposures. I appreciate your input taveren. I'll give that a try. And great shot indeed! I'll submit my attempt when I've got one in the bag!

Cheers again.

I forget to mention one thing. Make sure it's a clear night. Clouds will ruin the multi-exposure process. A few clouds are great for a single exposure however.