Planetary Imaging with a Webcam

Posted on April 15, 2015 by Benoit Guertin

Planetary imaging is usually where everyone starts. The targets are bright objects in the sky such as the Moon and the planets that don’t require long exposures; Venus, Mars, Jupiter and Saturn. And because there are no long exposures, no need for a mount that tracks. The electronics of a webcam allows between 5 and 60 frames per second (fps), more than enough to get a good image that can be used with any sized telescope, and the result is a AVI movie that can be easily processed.

There are two ways to use the webcam:

Prime focus: the original webcam lens is removed and the telescope becomes the lens; like swapping lens on a SLR camera. Magnification is provided by the focal length of the telescope and the optional use of a barlow lens.
Eyepiece projection: the webcam replaces the eye and the magnification is provided by the ratio of telescope focal length to eyepiece focal length.

In my case I went with a prime focus solution, hence I needed a webcam where the original lens could be removed and replaced with an 1.25″ adapter to fit into the telescope’s focuser.

Philips Vesta Pro 680K webcam modified for use on telescope

The camera sensor, be it CMOS or CCD is sensitive to a wider spectrum than the human eye, therefore most have build-in UV and IR filter, either on the lens or the sensor. As this filter was on the original webcam lens I purchased a BAADER UV-IR Rejection 1.25″ #2459207 filter for use with the adapter. Refractors have a challenge getting all colours focused at the same spot, and even with an APO scope what falls in the UV and IR range will generally appear out of focus. Best to keep those out with a filter.

Today a good planetary imager can be purchased for under $200, but when I started, most astronomy imaging devices ran in the $1000+ camp. The Philips Vesta 680K was rather popular as a wonderful man by the name of Steve Chambers figured out how to easily modify the webcam electronic to get much longer exposures. The Vesta was also equipped with a CCD-based sensor, more sensitive than the CMOS technology used in most webcam. These modified webcam became to be known as Vesta-SC.

I’ve spotted Jupiter, can I take a photo? Actually you should take a video. The reason is that there is a great deal of turbulence in the atmosphere and this causes the image to blur and giggle about. By taking a video you are doing two things:

Capturing a large quantity of images which can be later processed
May happen upon a brief period of atmospheric stability

Here is a 30 second segment of Jupiter with my setup

I recommend taking a few videos with different settings such that you’ll be able to see after which provided the best results. Select an uncompressed format such as AVI as to not get compression artifacts, and AVIs are easily broken into individual image frames.

Software such as IRIS or REGISTAX can be used to process the video. REGISTAX is actually quite good and painless at doing this. Don’t be intimidated by the large number of settings and parameters, you can get great results out-of-the-box with the default settings.

The process breaks down into 5 steps:

Select your target (what you want the software to track on)
Filter on the frames that have good image quality; only keeping those that are sharp and resemble each other
Align (register) the individual images
Stack the individual images
Wavelet analysis and final brightness/colour balance

Because of the high number of images, you can actually improve image resolution by up-sampling or drizzling the image prior to stacking. The end result is often an image that can be scaled up by 2x while maintaining resolution.

Wavelet analysis is a type of sharpening, similar to unsharp-mask, but treating each level of granularity as a different “frequency”. While unsharp-mask is tuned to a specific size of detail, wavelet is able to treat various levels of details as different layers of the image and add the results.

End result:

Jupiter – April 11th, 2015
Benoit Guertin

Creating Diffraction Spikes with GIMP 2.8

Posted on November 3, 2014 by Benoit Guertin

Updated procedure to use a transparent background for the brush pattern. Also broke down certain steps into more details.

Ben Backyard Astronomy

Updated on November 3rd, 2014

Photos of open star clusters always appear to be more pleasant when stars have diffraction spikes. But if your telescope does not have support vanes from a secondary mirror you are out of luck. One solution is to simply tape in a cross pattern some string or fishing line over the dew shield. Or you can turn to digital enhancement. Below is a procedure to enhance your photos by digitally adding diffraction spikes using GIMP 2.8. in 8 easy steps! No special plugin or filter required.

Lets try with my image of M45 – Pleiades taken with a Skywatcher 80ED.

M45 - Pleiades Benoit Guertin M45 – Pleiades
Benoit Guertin

The first step is to create a new “brush” in the shape of diffraction spikes. To do this, start with new canvas with a transparent background. In the screen shot below, a new 1000 x 1000 pixel image with Fill with: Transparency

View original post 624 more words

Creating Diffraction Spikes with GIMP 2.8

Posted on October 24, 2014 by Benoit Guertin

Updated on November 3rd, 2014

Lets try with my image of M45 – Pleiades taken with a Skywatcher 80ED.

M45 – Pleiades
Benoit Guertin

Create new image with transparent background

Then draw a grey straight horizontal line. I’ve used the Pencil Tool to create a thin solid line, 4 pixel width end about 300 pixels length. To ensure a straight line, click once to mark your starting point and holding the SHIFT+CTRL keys click again for the end point. Note that my line isn’t centered, that is because the blur performed in the next step will shift the line to the left.

Draw a gray horizontal line

Next use Motion Blur to create the gradient (Filter > Blur > Motion Blur…) The blur angle must be 0 deg such that it’s in the same direction as the line. In this example I’ve used a blur quantity of 150.

Add motion blur to create the gradient.

Duplicate the layer, rotate by 90deg and align both lines to form a cross. A simple step by step is the following:

Select > All
Edit > Copy
Edit > Paste as > New Layer
Layer > Transform > Rotate 90deg clockwise
Tools > Transform Tools > Move (now align the vertical line to form a cross)

Duplicate, rotate and align both lines

Once both layers align, you can merge them into a single layer.

Merge down to flatten into a single layer

Finally, using the Ellipse Selection Tool, select the cross and Copy to clipboard. This will automatically assign it to the Clipboard Brush (red arrow and box below). Note that I have kept the screenshot of my previous version with the black background in the snapshot below to make it easier to see.

$GIMP - Diffraction Spike Creation - STEP 4$

GIMP – Diffraction Spike Creation – STEP 4

We now have a new brush type that can be used to create diffraction spikes with nothing more than a single click. Yay! The Paintbrush will show up as a cross but with dotted line (see red arrow in screenshot below). Size and angle can be adjusted via the Tool Option Box; see below sections with red boxes. I use the Paintbrush tool to create the spikes.

$Now have a new brush to create the diffraction spikes$

Now have a new brush to create the diffraction spikes

Now it’s time to get down to business and add those diffraction spikes to the stars. Start by opening your astrophoto and duplicating into another layer. This duplicate layer will be blurred and used to transfer the colour information on the spikes.

In the duplicated layer (with the original layer turned off), use a heavy Gaussian Blur (Filter > Blur > Gaussian Blur…) to blend out the colours. In this example, I used a blur value of 60px. As the blurring makes the image darker, use the Curves Tool to bring the brightness back up.

Increase brightness after burring

Result of the blurred layer

Now create a Layer Mask for this blurred layer. Select to initialize the Layer Mask to Layer’s alpha channel.

$GiMP - Diffraction Spike Creation - STEP 7$

GiMP – Diffraction Spike Creation – STEP 7

With both the original and blurred layer visible. The blurred layer is selected and the blend Mode is set to Screen. Select to edit the mask of the blurred layer (right mouse-click on the blurred layer), and click on the stars to draw the cross pattern. A diffraction spike should instantly appear! As your Brush is the cross pattern, you will see in dotted lines the size and angle. If you don’t see your cursor, simple adjust the size (ex: 500).

$GIMP - Diffraction Spikes Creation - STEP 8$

GIMP – Diffraction Spikes Creation – STEP 8

Resulting image after clicking on a few bright stars:

$M45 with diffraction spikes added$

M45 with diffraction spikes added

Try different settings (a larger pen width for the initial cross pattern) or playing with the quantity of blurring and curve adjustment of the blurred layer.

If you have other improvements or suggestions, please share using the comment field below.

Creating GIF Animation with Lunar Eclipse Photos

Posted on October 8, 2014 by Benoit Guertin

Eclipses happen in a relatively short time span and the change can be dramatic, therefore they are great candidate for GIF animations. Below is a sequence of 24 individual photos taken with a Skywatcher 80ED telescope and Canon XTi camera from the February 2008 Lunar Eclipse.

Feb 2008 Lunar Eclipse – Benoit Guertin

To create the GIF animation I used two software packages:

Registax – astro-imaging processing software used to align the individual images in order to ensure the Moon remains centered.
GIMP – image processing software used to create the GIF animation

In GIMP, GIF animation is done by assigning individual images to a layer. The animation is therefore build frame-by-frame as it cycles through the layers. A simple animation tutorial is available to step you through the process.

On the other hand, if you prefer to make a movie, Picasa is capable of creating a video from a series of photos.