Exposure and Star Trails

[ElizaMM]

I'm still not sure how things work here, so I will not be offended if someone tells me that I should be asking for a critique/suggestions in another location.

This image meant to be a thing of beauty - it is exclusively a light test. What am I doing wrong? This was taken near Ottawa, Canada. I don't think it's the camera, as daytime shots have good colour. The sky was near black, not grey/brown. More light and the star trails pale. Less light and they fade. I took a second one from a different angle and exposure time, with the same result.
Shot RAW, then converted to jpeg with PhotoStudio. Once I figure out colour and exposure, I want to leave the aperture open for several hours.

Camera: 7D
Lens: Canon 24-105 AF at 24
Focus: Manual - Infinity
Mode: Bulb
ISO: 100
Aperture: 5.6
Exposure: 1 hour

Album: Profile Pictures

 

[Designer]

Check this thread; you'll learn a lot:

Manaheim's Ultimate Guide to Night Photography | Photography Forum

 

[KmH]

While the sky looked dark to your eyes, your eyes don't accumulate light over time.
The camera accumulated light for the 1 hour exposure and recorded air glow from light pollution your eyes can't detect.

The way to avoid that is to take a long series of much shorter exposures and then 'stack' the series post process using photo stacking software like the free software DeepSkyStacker. Here is the User's Manual.

That will get you a nice dark sky and long star trails.
If your camera has an interval timer you can use that to make the series of photos. If your camera doesn't have an interval timer, interval timers can be bought as a plug in accessory.

For more information use an internet search engine and use the phrase - How To Photograph Star Trails.

 

[ElizaMM]

Thank you, Keith, for both the explanation and the software suggestion. If it is clear tomorrow night, I will try again. I will post my results, after familiarizing myself with DeepSkyStacker.

 

[KmH]

While not about making star trail photos, this video I found yesterday does show how to use DSS.

 

[TCampbell]

The sky was near black, not grey/brown. More light and the star trails pale. Less light and they fade. I took a second one from a different angle and exposure time, with the same result.

<snip>

Once I figure out colour and exposure, I want to leave the aperture open for several hours.

The sky was muddy gray-brown. That's normal and it's the effects of light pollution. You have to travel exceptionally far from an urban or suburban area to reach true "dark sky" area (you can drive for hours trying to get away from it.) My images normally have that background (and I don't need a very long exposure time to see it.) Imagers do some extensive processing to get that out.

Normally, an image of a deep space object or of the sky may, in fact, be many images that have been 'stacked' to reduce noise. After images are aligned and integrated into one image (which looks a lot better than any individual image) there will still be a muddy background, but now you can 'stretch' the image data. This means the muddy background has it's light lowered down to a near-black color, but data which is just a little brighter is enhanced to bring out details. By the time the imager is done working on the image, they've managed to bring out a significant amount of detail previously hidden in the image. The dramatic star-scape, night-scape, and astro-photography images that you see and like are all heavily processed. They are "real" images in that everything you see in the image really was there... but they didn't come out of the camera looking that way.

If you want star trails, don't do a single "hours long" exposure. Instead, set the camera to a 30 second exposure time, but set the camera to "continuous" shooting. Make SURE you disable "Long Exposure Noise Reduction" in the camera (this is ON by default and you need to turn it off.) You'll need a wired remote shutter release. The shutter button on a wired remote has a locking switch. Press the shutter button and lock the switch so the camera will take 30 second exposure after 30 second exposure and will just keep going. Set a timer for a few hours and go have coffee.

There are utilities which then integrate all those 30 second exposures. One popular tool is called "Star Stax" (specifically designed for star-trail images.)

If you tried to do this as a single "hours long" exposure you'd just end up with an over-exposed frame in the end.

BTW, the "Long Exposure Noise Reduction" causes the camera to capture a "dark frame" after any image with a long exposure "light frame" (typically any exposure time longer than 1 minute will trigger this). So the camera really takes TWO shots and subtracts the dark frame from the light frame. The "dark frame" is just an exposure at identical settings -- except the camera leaves the shutter closed while the sensor records the image. This image will only have "noise" in it. The camera is trying to sample the noise generated based on your current temperature and exposure conditions so it can subtract that from your "light" image and get a less noisy light image. BUT... when you do this in star-trail photography you'll get 30 seconds of 'light' exposure followed by 30 seconds of 'dark' exposure and your star trails will have gaps in them (probably not what you want.)

 

[ElizaMM]

I just realized that I am trying to do two things at once - night sky snapshots and star trails (which is really what I want to master, first) . I read Manaheim's Ultimate Guide to Night Photography and kitted myself with tripod, flashlight, remote shutter release and set the camera to RAW. Forrest Tanaka's video was very interesting - at some point I will look into getting a longer lens, but I have decided to think about advanced photography and more expensive equipment, after getting a grip on technique. It has been cloudy here, the last few nights, but yesterday evening was better - the sky was fairly clear of cloud and the almost-full moon was behind the camera. I had better results with much shorter exposures, and the composite picture, created with DeepSkyStacker gave me a better quality still pic. When I installed SkyStax to try to produce better star trails, last night's shots, I got something that looks much better, but stilted - a series of dots, rather than the smoother paths I see in on-line photos. Other than creating longer lines, does setting a timer "for a few hours" make a difference in quality? Can I improve this by changing camera settings, or is this always done in post processing? I managed to make things a little smoother, using PhotoStudio, but only by using a Gausian blur and increasing the contrast. I have uploaded the image created by StarStax "as is" (pre-blur).

70 photos
10 dark frames
24 mm
f/4
ISO 350
Exposure 30 seconds
Interval set to 0

 

[ElizaMM]

I just realized that the photo I reduced in size for upload does not clearly show the disjointed star trails, so I uploaded a small section of the larger photo.

 

[TCampbell]

The gap indicates that some time elapse between the shutter closing at the end of one 30-second shot, and re-opening for the next 30-second shot.

I've noticed that some intervalometer (because mine does this) can't actually take the next shot immediately and has a bit of a delay. So to get around that problem, switch your camera to "continuous" shooting mode (e.g. as if you want to do rapid fire shooting for sports/action) but still dial the shutter speed to 30 seconds. Now all you need to do is use the lock switch on the remote shutter release to keep the shutter button held down and the camera will immediately start recording that next frame right after the first frame with minimal possible delay. This eliminates the gaps.

 

[ElizaMM]

I have now tried the intervalometer suggestion, three times over the last three weeks, which does produce smoother star trails (using Startrails to process). One small problem -- the battery goes dead after about an hour and a half in, usually around 190 shots. The professional, as well as the beautiful amateur pictures I look at on line have very obviously longer total exposure time. How does one remove the camera from the tripod, change the battery, reattach keeping the tripod perfectly still, then make sure that the camera is in precisely the same position?

 

[astroNikon]

I have now tried the intervalometer suggestion, three times over the last three weeks, which does produce smoother star trails (using Startrails to process). One small problem -- the battery goes dead after about an hour and a half in, usually around 190 shots. The professional, as well as the beautiful amateur pictures I look at on line have very obviously longer total exposure time. How does one remove the camera from the tripod, change the battery, reattach keeping the tripod perfectly still, then make sure that the camera is in precisely the same position?

Some cameras allow multiple batteries, such as using a vertical grip.
Others you can purchase a direct, wall plug type in connector.
I don't know Canon, but I'm surprised you aren't getting more life out of the battery.

 

[TCampbell]

One small problem -- the battery goes dead after about an hour and a half in, usually around 190 shots. The professional, as well as the beautiful amateur pictures I look at on line have very obviously longer total exposure time. How does one remove the camera from the tripod, change the battery, reattach keeping the tripod perfectly still, then make sure that the camera is in precisely the same position?

Do you have an original Canon battery and, if so, how old is it? I just did 2 hours of continuous data collection last night (astro-imaging of deep-space) and used about 1/2 the battery. I'm wondering if your battery isn't holding much of a charge (1.5 hours is enough to take a good chunk of battery power, but I don't think it should totally kill your battery to the point that you need to swap batteries.)

I usually use AC power when available (I use a Canon AC adapter -- basically a "dummy battery" that has a wire coming out of it (there's a flap in your battery compartment for the wire) and that goes into a power brick that transforms AC into DC for the camera.)

Normally my camera is attached to a telescope and swapping the battery is no problem.

If you use a battery grip, the battery tray can be removed without removing the camera from the tripod.

 

[ElizaMM]

Thanks for the suggestion about a battery grip and AC - it sounds like it would make life easier. However, I was not clear - what I meant was the CR2032 in the intervalometer. How many hours should it last? My Canon battery seems to be holding up well. No deep space for me, at the moment with only a 100mm and a 24-105, I will be sticking to star trails.

 

[astroNikon]

what kind of intervalometer do you have ?

fyi, I don't use an external one. My Nikon has it built in so I can't really compare. Though my wireless trigger battery has lasted a couple years so far.

 

[beagle100]

what kind of intervalometer do you have ?

fyi, I don't use an external one. My Nikon has it built in so I can't really compare. Though my wireless trigger battery has lasted a couple years so far.

Generally for most models you have to use Magic Lantern for a built in Canon intervalometer
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