In case you missed the Venus-Moon close encounter

Last Saturday evening, if you happened to look outside and had a clear view there is no way you could miss the Venus-Moon close encounter in the dark blue sky. But just in case it was cloudy, or you weren’t paying attention here it is.

Moon and Venus within 8 degrees on June 16, 2018

Moon and Venus within 8 degrees on June 16, 2018

For those curious on the camera setting, the above is cropped from a single frame at 33mm f/4.5 1/30sec and ISO800 with Canon 80D.

Moving up to 85mm gives you the image below, also at 1/30sec and ISO800.  Both images were hand-held from a bedroom window. Could a tripod have helped? Sure, but I figured I could do just fine , especially with image stabilization enabled on the lens.

Moon and Venus within 8 degrees on June 16, 2018

Moon and Venus within 8 degrees on June 16, 2018

To put a bit of perspective on the distance of these two heavenly bodies and their apparent size in the sky I’ve added a bit of information on the above image. While Venus may be nearly 4 times larger in diameter, it looks quite small next to the Moon in the sky.

Moon and Jupiter Through the Clouds

After yesterday’s photo with the smart phone, I decided to go for a more professional shot and grabbed the Canon 80D and capture once again the Moon and Jupiter through the clouds. However this time around took two exposures, and stitched the together.

Moon and Jupiter Through the Cloud - May 27, 2018

Moon and Jupiter Through the Cloud – May 27, 2018

The wide-angle was 24mm F4.0 1/10s ISO-1600. This was to pick up the clouds against a night sky as well as Jupiter. Then a close-up of the Moon, with a shorter exposure and lowered ISO to pick up details of the lunar surface (85mm F5.6 1/250s ISO-200).

Opened them both in GIMP and played with layers, masks and curves to get the desired image.  The close-up Moon photo was scaled down to match the 24mm wide-angle photo to avoid having gigantic moon.

 

Bright Jupiter

Sometimes all it takes is a little cloud layer to hide the background stars to really reveal how bright Jupiter is right now. The photo below was taken with my smartphone on May 26th, with Jupiter clearly visible next to the Moon.

Jupiter and the Moon shining through the cloud - May 26, 2018

Jupiter and the Moon shining through the cloud – May 26, 2018

Jupiter and Earth were at their closest (opposition) on May 8th, but the entire month of May is a good time to spot Jupiter as it’s up high in the sky most of the night. Once Venus sets in the early evening, Jupiter is the brightest “star” in the sky, a good 20 times brighter than the next brightest stars.

Up until May 28th, Jupiter and the Moon will be near each other in the night sky, making for good photo opportunity.

Moon and Venus on May 17th

Came home from my piano lesson (yes you can still learn a new instrument past 40) and the sight of a 2-day old Moon and Venus in the dusk sky was stunning. Unfortunately by the time I got home to grab the camera, the sky had darken quite a bit, so I lost my opportunity for some color in the photo.

Venus 6 degrees from the Moon (May 17, 2018) - Benoit Guertin

Venus 6 degrees from the Moon (May 17, 2018) – Benoit Guertin

While I did take more close-up photos, I find adding the rooftop in the foreground helps establish scale.

Notice the Earthshine, it was easily picked up to naked eye.

Canon 80D
85mm F/8
ISO3200 (1/15sec)

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)

This Weekend – Beehive Cluster

The Beehive cluster, also known as Messier 44 (M44) is one of the nearest open clusters, and therefore one of the largest in the night sky. While open clusters are often too dim to be seen with the naked eye, all you need is a pair of binoculars or a camera with long exposure to see it.

What makes this weekend special is that in the night of the 22nd to 23rd of April, the Moon will pass within 1-1/2 degrees of this cluster.  So finding it will be child’s play.

Messier 44 - Open Cluster

Messier 44 – Open Cluster Benoit Guertin

On April 22nd, simply look for the Moon once the sky is dark, and just above it you will find the Beehive cluster with its 1000+ stars. OK, even with a telescope you won’t be able to see all the stars, but take some time to notice how this group of stars stands out with regards to background stars further away in our galaxy. And while you are at it, consider that nearly 410 years ago, Galileo made the first observation of these stars.

M44_Moon_22Apr2018

From there you can also hop over a to the west and observe the color difference in bright stars Castor and Pollux in the Constellation Gemini. And if you instead decide to go east, the smaller Messier 67 open cluster is also accessible with binoculars.

Astrophotography in the City – Part 1

Most people don’t try astrophotography, shooting the stars and constellations, because they think it requires specialized equipment and dark skies.  While nothing beats getting away from the city and light pollution, anyone with a camera with a MANUAL setting and capability to save RAW files can create nice photos of starry skies even if you live in the city. Below is a quick run-down of a fool-proof recipe: Part 1 – taking pictures.

Astrophotography is heavily dependent on post-processing the images as we are trying to get a desired signal from noise. That noise can be electronics (the camera and sensor) and it can be the light pollution. Like the old saying: garbage in = garbage out. If you can find the right camera settings to reduce noise on your photos, you’ll get fantastic results with much less processing and effort.

original-processed2

 

Setting up the Camera

DSLR are the best camera to use, but any camera that can set to manual will work. First thing is to set the file to be saved in RAW. Astrophotography is a heavy user of post-processing, so you want to work with as much unaltered data as possible. We want the image as the sensor captured it, and leave the processing to powerful algorithms on a computer.raw-format

Next is to set the camera to full MANUAL mode such that you can control lens aperture, exposure and ISO setting. If you are going to use a remote device to take the pictures, you may need to set it to B or BULB, but for my Canon 80D connected via WiFi to the smart phone, below 30 second exposure time M will work.

manual-modet

Next you want to set the lens opening as big as possible.  For most variable focal zoom lens, that is F4.0, but you may have opted for a fixed lens which can open up to F1.2.  Note however that large openings with consumer photo lens tends to cause either chromatic aberration (colors will “leak” around bright stars) or distorted stars the further towards the edge of the frame.  If you notice this, simply stomp-down to a slower opening by 2 or 3 settings.  Yes that means you get less light, but it’s a trade-off. You can also simply crop the final image at the very end.

Next set the ISO to about 6400.  Can’t go that high? No problem, as long as you can reach ISO 400, you are good. I know, high ISO is very noisy, but the next step is simply to get the right focus, so we don’t care about the noise and with the camera live view, the exposure is not very long and we want to see the stars.

Mount your camera on a tripod as the exposure length will be between 2 and 10 seconds. Hand-holding is OK for the Moon, but not to get nice round stars at those long exposures.  If you don’t have a tripod, setting the camera on a bag of beans or rice, even a bunched-up towel will work. Find a spot where you don’t have glaring lights entering the lens, and aim you camera at the desired spot in the sky.  This is also the time when you set you focus to manual and crank it to infinity.  If there is no marking on the lens for focus at infinity and you don’t know which way to turn, simply pick a distant object like a far away house or light post and manual focus on it. The Moon will also do the trick.

If you have live view mode on the camera, enable it and manually adjust your focus to get nice sharp stars. Some cameras will even allow you to zoom on the preview screen, if so zoom as much as possible and fine-tune the focus. If you don’t see stars: 1) increase the ISO setting, 2) increase the exposure duration, 3) verify that you are at F5 or lower.

If you don’t have live view, simply take a picture and then review it (don’t forget to zoom in on a star). Make a small focus adjustment one way and take another picture.  If the stars are smaller and brighter, you are adjusting the focus in the right direction and keep going until you passed the best setting.  Then simply back-it a small amount.

Getting the Right Exposure

Once the focus is right, the next step is to balance the ISO and exposure length.  The longer the exposure the more the stars will become trails instead of pin-points.  However longer exposures gather more light to capture more stars and faint objects. If you are shooting with a 15mm focal length, you can probably go as high as 20 seconds before it becomes too much of a blur. However at higher focal length the stars will “move” faster, so choose wisely.  Aim for about 5 to 10 seconds of exposure.

Here is where we adjust the ISO.  High ISO setting will generate a noisy image.  In astrophotography we “stack” multiple images to improve the Signal to Noise Ratio (SNR). Hence a noisy high ISO image isn’t so bad, but you still need to keep the noise to a minimum. When we focused with the live view, the ISO was cranked quite high, but this will result in an image with the background sky way too bright. In the image below, the “hump” in the histogram is entirely past the half-way mark in the over-exposure region, this is not good for astronomy post-processing, where we want to have as much dynamic range as possible. As a general rule in astrophotography, you are better off under exposing.

overexposedIn the photo above, I was at ISO 6400 with a 5 second exposure. You can barely make out the constellation Orion in the sky. After reducing both the ISO and the exposure to ISO 3200 and 2 seconds the sky darkens, and pin-point stars start to appear.

iso3200_2sec

Once you’ve got the right settings, take a series of pictures.  If you can trigger the shutter from your smart phone, tablet, remote or laptop then it’s best as you avoid nudging the camera and smearing the stars. If not, well… go gently. Take about 20 images. These will be your “LIGHT” frames as they are the images you captured light photons.

Once this is done, you need to two other sets of images that will be used in post-processing.

Dark and Offset Frames

With all cameras, the longer the exposure, the more noise and “hot pixels” appear. This noise needs to be removed from the image. Some camera have settings to automatically do this for night shots, but it will do so with every image, doubling the time it takes every image, and the result is not optimal.  Software on your computer is much more powerful than the camera to process and remove the hot pixels, so you are best to take a series of DARK frames yourself.

Hot pixels are essentially pixels “firing off” during a long exposure causing it to create a bright pixel in your image.  Two factors increases the number of hot pixels in an image: 1) exposure length; 2) temperature. Most of your photos with your camera are daytime, short exposures, hence hot-pixels are either non-existent, or not visible. However with a dark sky and exposure in the 5 to 10 seconds range, they will be present.  Temperature will also play a factor, it’s why specialized astro-cameras are Peltier cooled to 40deg C below ambient. Yes, you will get more hot pixels in a summer night shot, then in winter.

Furthermore, all digital cameras uses an electronic circuit with an amplifier to read the sensor.  This amplifier generates heat, which often shows up on the sensor by making one corner brighter than the rest of the image. The longer the exposure, the greater the effect.

DARK frames are REALLY easy to take.  After you are done taking your LIGHT frames, simply put on the lens cap and take another 10 photos with the lens cap on. You are essentially capturing the noise of the sensor when no photons enter the camera. The reason to take a high number like 10 is to generate a MASTER DARK, which will be an average of those 10 dark images, this gets rid of any random elements to the noise.

Last you will also need to take OFFSET frames. These are like the DARK frames explained above, but this time with a short exposure setting like 1/250s.  Here we want to capture the electronic read noise of the sensor.  With such a short exposure, there are no hot pixels or amplifier glow. Yes, still with the lens cap on, so it’s a nearly black image, but there is a bit of signal, a bit of noise registered within it, and this is what we want to isolate. So like the DARK, take another 10 images.

IMPORTANT: Every-time you will do astrophotography, you will need to take DARK frames to match the camera settings and temperature.  However for OFFSET frames, you only need one set per ISO setting. So OFFSETs can be kept for use another day if you took photos with the same ISO setting.

To conclude if you followed the above steps you now have:
– 20 light frames of the night sky
– 10 dark frames
– 10 offset frames

I’ve purposely kept FLAT frames out of this process as they are a pain to take, and if done incorrectly cause more trouble than good, FLAT frames are images of a uniformly lit white surface with no texture or details. The purpose is to capture the shadows on the sensor caused by dust as well as to correct to brightness uniformity and optical imperfections. Lets just keep that out for the time being…

Now head back indoors, it’s time to process these images