Constellations at the Zenith

We don’t often look “straight up”. Unless you are laying down, it’s not a comfortable viewing position. However there is lots to see and the Big Dipper (Ursa Major) is right overhead this time of year.

Setting up a camera with a 10 second exposure can capture quite a good deal of the sky, and you don’t have to worry too much about star trails. What stands out is the large variations in the colors of stars, from cooler deep reds, to hot bright blues.

Constellation Near Zenith 08May2018

Constellations right above in the May evening.

17mm f/4
Canon 80D (ISO 3200)
12 x 10sec (2 minutes)

My photo in this week’s SkyNews

Today I got an e-mail from Gary that a photo of the Big Dipper that I had submitted a few months ago got selected for this week’s column on SkyNews. Couldn’t be happier. I wish all my weeks could start this way.

My photo featured on SkyNews

Astrophotography is a combination of equipment, experience, location/timing and luck. With this photo I just happen to hit everything right and was lucky.

Using the best equipment helps, but for this photo it was the simplest of setup: my very worn Canon Rebel XTi DSLR with a zoom lens set to 17mm F4 mounted on an old steel camera tripod my father used in the 60s. So nothing special, and within everyone’s reach.

OK, for the next part I had experience on my side. It allowed me to pick the right camera settings, but was also lucky as my photo viewing was limited to that small LCD screen on the camera. I had no laptop to fully explore and review the photos and make the necessary adjustments.  Even the focus was reviewed through the small camera LCD.  That night I only took 4 images with 20 second exposure crossing my fingers that I would have something worthwhile once back home.

And then there is the post-processing on the computer, which is a lot of trial-error. In image processing doing steps A + B will not give you the same results as performing B + A. We all have our “recipes” for what produces good results, but every photo ends up being a unique project. With this one, I knew there was good potential.

Finally there is the location and timing.  I was up in cottage country, away from city lights, and a clear sky. However there was a full moon rising, couldn’t wait too long as the sky would start to brighten. A Big Dipper low in the sky next to the trees framed everything very well.

Thanks Gary and SkyNews for selecting my photo. For all the experimentation that I do with the camera, once in a while I get everything right. I’m just happy someone noticed and said “Hey, that’s a great photo we could use.”

Cassiopeia – the W in the sky

Some constellations are easier to spot than others.  Cassiopeia with its distinctive W is visible year round in the northern hemisphere above the 34th parallel. In the image below it easily stands out from the fainter background stars.

Cassiopeia above the three line - Benoit Guertin

Cassiopeia above the three line – Benoit Guertin

The five stars drawing a W in the sky are all naked eye magnitude 3 and brighter stars, and in the image above I used a layering technique to increase the color and brightness of those stars to really make them stand out.

  1. Duplicate your base image, and set this layer to lighten only
  2. Apply a blur to the top layer(about 8-12 pixels)
  3. Increase the color saturation and brightness.  Play with the curves to brighten the bright stars, but not the background sky.
  4. Use a mask as required to filter out the bright foreground elements, such as light reflecting off a building roof-line in my image above.

Canon Rebel XTi
17mm f/4
4 x 20sec ISO800

 

Ursa Major

Ursa Major, or Big Dipper is one of the most recognizable constellation in the Northern hemisphere. People often use it to locate Polaris, the North Star.  Can you find Polaris? (Hint: upper right)

Ursa Major (Big Dipper) low in the sky in late summer around 11pm

Ursa Major (Big Dipper) low in the sky in late summer around 11pm

Canon Rebel XTi (450D)
17mm f/4
Stacking of 4 x 20 seconds @ ISO800
Post processing with GIMP

Composition with Landscape

I’ve mentioned it before that you don’t need a fancy telescope and tracking equatorial mount to get into astrophotography.  Simply a camera on a tripod with a short focal lens can do wonders, especially with the high ISO settings in new cameras. A single 10 seconds exposition can reveal lots of stars, however to capture more photons a longer exposure is not better as the stars will become streaks.  But one can easily improve the image and get better signal/noise ratio by stacking multiple images.

However, there is one drawback to stacking multiple exposures if you decide to also capture the landscape: Earth rotates, therefore the sky moves while the landscape stays still.  If you align the images using the stars, then the landscape becomes a blur.  Not the end result that we want.  Luckily a quick composition with two layers and a mask solves everything.

Below is a single 10 seconds exposure at ISO 800 with a 17mm F4 lens; you have the landscape with city lights and the stars above.  Yes that is Orion…

Single 10sec exposure (ISO 800)

Single 10sec exposure (ISO 800)

In order to improve my signal, I worked with IRIS to align and stack 5 frames, this reveals many more stars, but also amplified the light pollution.

Aligning and stacking 5 images. More stars appear.

Aligning and stacking 5 images. More stars appear.

Luckily within IRIS there is a function to remove sky gradient.  The algorithm takes a series of sample points and attempts to make the sky uniform.  Not bad, the images are not a hopeless case.

Removing the sky gradient with IRIS

Removing the sky gradient with IRIS

As mentioned above, the alignment was performed with the stars, hence the background is now blurring.  Below is a close-up.

But when aligning on stars, the landscape blurs.

But when aligning on stars, the landscape blurs.

That is just 5 images, stack a much larger quantity or with more time between frames and it will only get worse.  It becomes pointless to shoot with the landscape if the end result is blurry.  Luckily working with layers in a photo editor can easily solve the issue.  We want to keep the stars from the stacked image, but the landscape from a single frame.  Follow these easy steps:

  1. Load into your base layer one of you single frames.  This is what will be used for the landscape.
  2. Load into a new layer your stacked image.  As your stacked image contains more and brighter stars select to Lighten Only instead of normally adding both layers.  You can play with the brightness of the stacked layer, and/or darken the base layer to get the desired blending.
  3. Create a mask to the stacked layer such that the blurred landscape is not permitted to show through.  See image below, I simply grabbed the airbrush and blackened the landscape area in the mask such that it will not show through the layer.  Note that the I only edited the mask, not the image itself.
Creating a mask for my layer: white is transparent, black will block

Creating a mask for my layer: white is transparent, black will block

The end result, is improved image of the sky, and a landscape that is still sharp.

Both layers added with the mask

Both layers added with the mask

Below is a comparison the composition with stack and layer (left) and a single shot (right).  We are able to achieve both of our goals of getting more stars (more signal) while keeping the landscape from becoming a blur.

Comparing the composition with layers (left) and single shot (right)

Comparing the composition with layers (left) and single shot (right)

And why not take some time to identify some key features in the image.

Constellations Orion and Taurus above the landscape.

Constellations Orion and Taurus above the landscape. (Click to open)

Tripod and a Camera? Make a TimeLapse

Video

You don’t need a telescope to enjoy astro-photography.  All it takes is a camera, a tripod and a timer remote controller to take interval images without you having to be there.  I know that most of the image taking is done with the camera connected to a computer.  But this remote controller allows for control of the shutter in the BULB setting without a laptop.  See it as a “grab-n-go”, travel-light type of accessory to the camera.

Canon_tc_80n3_remote_control

Set it up to take a large sequence of shots and you got the makings of a timelapse video.  Because there is no tracking with the tripod, keep the exposures under 10 seconds.  Then use video editing software like Microsoft Movie Maker to covert all those images into a video (see my article here).

It’s always interesting to analyse your frames to determine what you’ve capture, to identify key or important elements.

Wide field of the sky, mountains and horizon from a Montreal south sore suburb. March 4th, 2016. Benoit Guertin

Wide field of the sky, mountains and horizon from a Montreal south sore suburb.
March 4th, 2016. Benoit Guertin

Unfortunately, my camera battery wasn’t fully charged, and the cold drained it quickly, therefore only got about 100 frames in.

August 13th – Celestial Pole Over the House

Image

The Perseids peak had already passed, but the sky was better so I decided to set up the trusty Canon XTi and see if I could catch some meteors.  This time instead of pointing the camera straight up, I decided to frame the top of the house to provide some reference.

Out of the over 120 shots taken, a sequence of 30 frames were without clouds obscuring the stars.  This was a perfect opportunity to mark the celestial pole by adding the images without alignment.

Celestial Pole on August 13, 2015 30 x 30sec

Celestial Pole on August 13, 2015
30 x 30sec

Canon XTi
17mm F4.0 ISO800
30 x 30sec