Shooting star trails.

[Grandpa Ron]

I am talking about aiming the camera at the North Star (Polaris) after sunset, and leaving the shutter open until just before sunrise. Hence, photographing the stars as they rotate through the night.

I have two questions,
1. Has anyone tried this with a Canon digital camera, with the shutter set on the "Bulb" setting? I would be afraid of damaging the sensor or running the battery down.

2. With 200 ISO film, does anyone know what aperture would be needed?

 

[nokk]

i tried this years ago with a canon 40d. you need a locking cable release. instead of one extremely long photo try taking (shorter) long exposures of one or two minutes or so and just let it run until you get enough shots. stack the images in photoshop or another star stacking program and you'll get some star trails. your aperture should be as wide open as possible to use a lower iso and reduce noise.

 

[Space Face]

As above, I believe multiple shots is the best way to go. Been a long time since I did this but that's how I did it. Was very experimental for me tho.

 

[LWW]

I am talking about aiming the camera at the North Star (Polaris) after sunset, and leaving the shutter open until just before sunrise. Hence, photographing the stars as they rotate through the night.

I have two questions,
1. Has anyone tried this with a Canon digital camera, with the shutter set on the "Bulb" setting? I would be afraid of damaging the sensor or running the battery down.

2. With 200 ISO film, does anyone know what aperture would be needed?

With film it is a piece of cake.

Digital, I would follow the advice already given.

 

[wfooshee]

Yep. Stack a series of images that are the maximum shutter time your camera allows it to stay open. That time is limited for noise, and heat buildup. You are not going to get a digital to stay open for hours, not would you want to with the noise buildup over time.

My camera has an intervalometer in the menu. I set it to some high number of 30-second exposures 32 seconds apart. (Sometimes at 31 seconds apart, the shutter didn't fire, but the intervalometer kept counting, so I had an exposure missing from the sequence.) Basically then, set up the tripod, point north, start it. Retrieve the camera some hours later, stack the images in Photoshop. Select all the layers and set the blend mode to "lighten." Also, if your camera has a long-exposure noise-reduction setting, disable that. (What it does is after every long exposure, it shoots another of the same time with the shutter closed, and subtracts whatever it captures in the shutter-closed frame from the shutter-open one. Theoretically useful, but loses half of your exposure time.)

I don't recall how long this was, 3 or 4 hours, I think. It appears my tripod head settled at the beginning, shown as a little hook at the start end of the trails. These frames were 15 seconds at f:2.8, ISO 100, Sigma 30-1.4 on a crop-frame camera, and the result was cropped to remove my house from the bottom right of the picture.

In this shorter sequence from another night, I had a couple of airplanes shoot through my view. While it's possible to simply paint out the lights with the healing brush, that seems a bit tedious. I just went through the layers and blanked the ones with airplane lights. Dim-looking areas of the trails are the result of clouds, as it wasn't a perfectly clear night. This set was shot with 30-second frames at f:3.5, still ISO 100, and 18mm, with my 18-55 kit lens, again the final image cropped to remove yuckie stuff at the edges. The longer exposure seems to have given smoother trails.

Note to self: Looking at these, I need to try again. Hurricane Michael removed that tree on the left, so my view field is considerably wider now...

 

[Grandpa Ron]

Thanks for the info, though my post processing skills are a bit limited.

 

[wfooshee]

Doesn't need a lot of skill to do, really; just time to let the computer chew on your images.

1. File, Scripts, Load Files into Stack. Select the images from your run. Wait however long it takes to get your files loaded. It could be a while.
2. Select all of the resulting layers and change the pulldown above the layers lit from "Normal" to "Lighten." Again, find something to do while the computer churns. If memory serves, this doesn't take as long as loading.
3. Go to the Layer menu, Flatten Image.
4. Profit.