Can Digital Camera Take Long Timed Exposures

[larrys]

I will be backpacking in the mountains in a couple of weeks and wanted to try a two hour exposure to show how stars track thru the sky. Am I able to do that with a Nikon D-70? In calling a local photo shop they said the longest exposure I could do was 30 minutes. Any ideas as to how to capture this type of shot with my camera?

[engstrom]

The best way to do it is to take 60 seperate 2 minute exposures (or 120 seperate 1 minute exposures) and use photoshop to combine the images. If you use a sturdy tripod combining the exposure is easy, just create a new layer for each exposure and change the blend mode to "lighten". "lighten" blend mode tells photoshop to use the pixel on the layer only if it is lighter than the equivalent pixel of the stack below it. This mode will let the light star trail from each image in the layer show through.

[AlexMorse]

I'm not sure on the nikon specifics, but generally speaking your limiting factor will be the battery. The sensors do get hot when constantly on, which generates more noise, so taking several shorter exposures helps reduce that. A couple, or even several seconds of cooldown will help tremendously, and not be noticeable for star trails

[n5kzw]

The battery can be a problem. The sensor glow/noise can be corrected by taking a dark frame (with the lens cap on and in Manual Focus) right at the end of the shoot. The length of the exposure should be the same as the exposure time that was used for the photos.

For the D70, it will be best to set the shutter speed to "bulb" and enable the IR remote. The first click on the remote will open the shutter, and the second one will close it.

The battery problem can be solved with an external power supply (Nikon EH-5) powered by an inverter/battery.

[venchka]

Originally Posted by engstrom

The best way to do it is to take 60 seperate 2 minute exposures (or 120 seperate 1 minute exposures) and use photoshop to combine the images. If you use a sturdy tripod combining the exposure is easy, just create a new layer for each exposure and change the blend mode to "lighten". "lighten" blend mode tells photoshop to use the pixel on the layer only if it is lighter than the equivalent pixel of the stack below it. This mode will let the light star trail from each image in the layer show through.

Shaking his head in amazement

Locking cable release. So primative. So effective. So easy. So cheap.

Did anyone mention ISO 100 or slower?

Originally Posted by pvdhaar

It of course depends on your motivation to do star trails, but if you want to make out the constellations, there's a trick..

Expose the star trail normally for any time, then just before the end, cover the lens. Wait for 1000/focal length seconds, and remove the lens cover again. Expose for another 1000/focal length seconds and terminate the exposure.

The constellations will now be separately visible from their trails.

Looks aesthetically pleasing too..

I suppose you could use the above technique as the first and last of the 120 exposures.

[DEMDeepEllumMusic]

Originally Posted by larrys

I will be backpacking in the mountains in a couple of weeks and wanted to try a two hour exposure to show how stars track thru the sky. Am I able to do that with a Nikon D-70? In calling a local photo shop they said the longest exposure I could do was 30 minutes. Any ideas as to how to capture this type of shot with my camera?

As already stated you will be better off taking many shots of around 1 minute each vs a few of 15-20 minute duration because of NOISE that will be associated with the sensor becoming heated. Not so extreme of a problem if it is in the 20's out on that mountaintop.

I would try right now doing say a dozen shots at 2 minutes each with a 5 second break between shots and then doing 2 dozen shots at 1 minute each with a 5 second break and one of 25 minutes. Then go and compare the last exposure's noise level of each shot and the one long shot. I bet the LONG shot will be full of noise and I don't know if that you could even shut down a lens far enough F22 or higher and the ISO set at 100 and not blow out the exposure even at night with a 25 minute exposure unless it was really really dark outside-i.e. no moon, much less a 2 hour exposure!

[venchka]

Star Trails Big Bend NP

Look at the exposure information: f:5.6 @ 4 hours on ISO 100 film.

I bet Larry is too close to Houston for meaningful testing.

[johnastovall]

Originally Posted by larrys

I will be backpacking in the mountains in a couple of weeks and wanted to try a two hour exposure to show how stars track thru the sky. Am I able to do that with a Nikon D-70? In calling a local photo shop they said the longest exposure I could do was 30 minutes. Any ideas as to how to capture this type of shot with my camera?

Here's a discussion of that very subject.

http://www.phototakers.com/forum/ftopic28868.html

and others:

http://www.google.com/search?hl=en&l...ls&btnG=Search

[n5kzw]

Sorry, Wayne, but a locking shutter release won't work on a D70, it doesn't have a threaded shutter button. There are a couple of ways of attaching a threaded shutter release cable to the D70 but they either require metal fabrication or blocking the command dials.

Regards,
Ed

[venchka]

I know. I was very displeased when I opened my EOS Elan 2E and saw the solid plastic shutter button. GRRRRRRRRRRRRR!!!!!!!!!!!

The good news is that I still have several bodies with proper threaded shutter releases and a couple nice cable releases. Of course they use the other kind of sensors.

This does seem like a classic example of an application where film is better.

In fact, I am inspired! The next time I'm at the house with a new moon I think I'll give star trails a try.

[Patti Edens]

Stacking 200 photos in photoshop is a pain, although there might be a way to automate it with Bridge???

Or, you can use this program...
http://www.startrails.de/html/software.html

The person that developed it said that he thought it was pretty tedious to do the stacking in photoshop, so he wrote this program (Startrails.exe) to do it.

It will also automatically correct if you shoot a few totally blank shots (with lens cap on) throughout the exposures.

Some interesting info on Canon's astrophotography site: http://www.canon.co.jp/Imaging/astro/pages_e/05_e.html



p

[engstrom]

Originally Posted by venchka

Shaking his head in amazement

Locking cable release. So primative. So effective. So easy. So cheap.

Did anyone mention ISO 100 or slower?

Originally Posted by venchka

Look at the exposure information: f:5.6 @ 4 hours on ISO 100 film.

Yeah, you can do multiple hour exposures on film. Try it with a digital sensor and you'll get lots and lots of noise.

[venchka]

Originally Posted by engstrom

Yeah, you can do multiple hour exposures on film. Try it with a digital sensor and you'll get lots and lots of noise.

That's the point I've been trying to make all day. You don't need super image quailty either. A sub-$100 used (heck $25) P&S with some way to keep the shutter open (DUCT TAPE!) will do nicely.

[AndrewCCM]

Why not take a single pic and use Photoshop to draw white lines across the image? LOL

I am kidding. :)

[thelegend1472]

its been my experience (which is very little) that anything over the 15min mark or so with a d70 is going to look terrible.

a question for the combining images theory...as say 2 min exposures, are you going to have enough light to enough produce a pic with that? even stars at that length aren't going to show up all that great.