Wide Angle Photography – Perseus

Image

Shooting wide angle long exposures of the sky is always fun, because you never quite know what you will get. On an August night I decided to take a few 20 seconds exposures of the constellation Perseus hoping to catch a few open clusters.  However got surprised by the faint glow of Messier 33 (Triangulum Galaxy) in the photos. This is the furthest object that can be observed to the naked eye, located 2.7 million light years away, and part of the Local Group which includes Andromeda and our Milky Way.

Constellations Perseus and Triangulum (Benoit Guertin)

Constellations Perseus and Triangulum (Benoit Guertin) – CLICK FOR FULL SCREEN

4 x 20 seconds
ISO 6400
17mm F4.0
Canon 80D
August 30, 2019

For the Moon, leave the tripod behind

Most people don’t plan to take photos of the Moon, they just happen. You are outside doing something else and then you spot it over the horizon or high in the sky: “Hey that’s a pretty Moon tonight Maybe I should take a photo!”

I find that normal camera lens, even telephoto don’t do it justice. The setting and focus can be very tricky. The multi-lens setup of telephoto can also cause internal reflections or chromatic aberrations making the resulting photo less appealing.

So just grab the telescope tube and leave the tripod behind.  If you have a small APO refractor you can simply hold the tube, but for anything heavier you’ll need to prop yourself up on something like a railing or a car roof.

The photo below is a single shot at 1/250sec and ISO400 with Canon 80D and William Optics Gran Turismo 71 held on the end of my arms.

2018-08-31

80% Illuminated Moon on August 31, 2018 [Benoit Guertin]

The setup takes only a few minutes and the results are always worth it.

Leaving the city lights behind

Nothing like leaving the city lights behind and heading to a rural camp ground to check up on our galaxy.

Every summer the galaxy presents itself across the sky in the norther hemisphere, an ideal time to enjoy the view and spot a few open cluster along the way.

Aquila-2018-08-08.idents

Canon 80D 17mm F/4 ISO6400
Stack of 10 x 10 seconds
No tracking

Messier 3 and a Fast Moving Star

A few weeks ago after taking some photos of Jupiter, I changed my setup to do some long exposures on an easy target: a globular cluster. Unfortunately I forgot to note down the name of what I had photographed!  So a few weeks later when I found the time to process the images I was at a loss to identify what Messier object it was. However, after an evening of matching up stars surrounding the cluster and I was able to correctly identify it as Messier 3.

Globular Cluster - Messier 3 (Benoit Guertin)

Globular Cluster – Messier 3 (Benoit Guertin)

The above was taken with my Skywatcher 80ED and Canon 80D. It is a stack of 27 x 10sec exposures at ISO3200 on an unguided and roughly aligned mount.

Looking at my archives I found that I had imaged M3 about 10 years ago with the same telescope, so I decided to align both old and new image and see if anything would stand out. And to my surprise, spotted one star that appeared to have shifted. To help identify the star I colorized one of the photos and subtracted from the other (done in GIMP).  All the stars within the field of view lined up except this one; the two colored spots are not aligned!

High PM Star BD+29 34256

High PM Star BD+29 34256

To be sure this wasn’t on an error on my part I did a bit of research and found it to be a know high proper-motion star BD+29 34256.

It’s not everyday someone with amateur backyard astronomy gear can show how a star has moved in 10 years.

It’s a good time for Jupiter

The last time Jupiter was in a favorable position for good photos was 2010, so while I have photographed the planet a few times since, the results weren’t really satisfactory.  So on July 7th, finally took the equipment out and set my mind to image some planets (Venus was also in a good position).

As luck would have it, the Great Red Spot was pointing our way, and landed my best shot of it yet. We may be past the May 2018 sweet spot for opposition, but that doesn’t mean you should not attempt to observer or photograph the Jupiter. Still plenty of good days ahead.

Jupiter with moons Europa (left) and Io (right)

Jupiter with moons Europa (left) and Io (right)

I took about 11 video sequences of the planet, and sure enough the last one yielded the best result. I guess as the evening progressed, the air cooled and provided for better viewing.

Skywatcher 80ED
Televue 3X barlow
Vesta Webcam with IR/UV filter
Processing with Registax and GIMP.

Photo – Sun April 21st 2018

After a weeks of clouds, rain and even snow, I finally get a sunny weekend without a cloud in the sky.  With the warmer temperatures, time to take the telescope out. Unfortunately no significant sunspot happening on April 21. Just a small region (AR2706) on the western part of the sun.

Canon 80D (ISO 100, 1/400s)
Skywatcher 80ED (80mm F/7.5)

Sun with sunspot AR2706 (21-apr-2018). Benoit Guertin

Sun with sunspot AR2706 (21-apr-2018). Benoit Guertin

Astrophotography in the City – Part 3

In Part 2, I explained the steps involved in improving the signal to noise ratio (SNR) by stacking multiple images and removing camera sensor noise (DARK and OFFSET frames). In this third article I will deal with sky gradient removal and white balance.

IRIS is a powerful astrophotography tool, and learning how to use the numerous commands can lead to fantastic photos. You can find good documentation and procedures on the IRIS website, so I won’t go in too much detail here.

While IRIS can process images in 32-bit, it cannot open the 32-bit FIT files generated with DSS. With my image still opened in DSS from the previous step (or by opening the Autosave.fit created by DSS), I select to save the image as a 16-bit FIT such that it can be opened in IRIS.

Below is the result in IRIS, and two things become apparent: 1) the sky has a gradient due to the light pollution from city lights; 2) the sky has a pink hue. These two elements will be corrected in this article.

iris sky gradient

Note, when I opened the image in IRIS, it was inverted, I had to flip it horizontally (menu bar – Geometry/Flip/Horizontal).

The sky gradient removal tool works best when two elements are addressed: 1) nice clean image edge, 2) the background sky is black

Trim the Edge

The image needs to have a nice edge around the border (i.e. be smooth all the way to the edge). Hence any dark bands, fuzzy or slopping edges needs to be trimmed. Zooming in on the left part of the image, I will trim at the yellow line, keeping the right-hand part.
photo edge trimming

Typing win at the command prompt within IRIS will give you a cursor to select the two corners to crop your image.

A Black Background

The background needs to be black and have an RGB value near 0. To do that, select a small area in a dark portion of your image, with no stars, and use the black command. This will offset the RGB values to be 0 based on the average within the square you selected. Essentially what you are telling the program is that the darkest portion of your image should be black.

White Balance

The sky gradient removal tool can also correct the background sky color, but before doing so, we need to adjust the white balance such that white stars appear white. To do this correctly you will need a star map (Cartes du ciel, C2A, Stellarium) and locate a star in your image that is as close to our own star color: G2V. This is not exactly for beginners, if you don’t know how, skip and do the white balance later in a photo editor. Once the star located, simply selected it with a small box and use the white command in IRIS.

We perceive a white piece of paper in sunlight to be white, hence light coming from a star of the same spectrum as our Sun should also look white in photos. It’s essentially a white balance exercise, but selecting a star in your image to calibrate instead of most programs which uses the average of the whole image.

Sky Gradient Removal

With that done, you can now select from the menu Processing / Remove gradient (polynomial fit) to get the following pop-up

remove gradient

If you have just stars in the image, a Low background detection and Low Fit precision will work.  However if you have intricate details from the Milky Way with dust lanes and all, then a High setting will better preserve the subtle changes. Try various combination to see what works best for your image. You can also do one pass with Low, and then follow it with a 2nd pass at High.

The result of all this is presented below: the sky gradient is gone, and the sky background is now a nicer black instead of a pink hue. And if you did the white balance, then the stars are also of the right color.

iris-completed

I should mention that the two most important dialog boxes in IRIS are the Command prompt and Threshold. When viewing and performing the various operations, the threshold values (essentially the min/max for brightness and darkness) often needs to be adjusted to get a good image and see the required detail.

iris-command-threshold

The next step will be importing the file in a photo editor for final adjustments. Color saturation, levels and intensity can be adjusted in IRIS, but I find a photo editor to offer better control. And because I will continue my editing in a photo editor do not set the Threshold values too narrow. I prefer a grey sky and then do a non-linear adjustment in a photo editor to get a darker sky.

More to come in another article