A couple of days ago I took my 8″ Newtonian out of the closet to get some fresh air and observe our beloved satellite, our moon. No matter how many times I look at the moon I always get mesmerized. All that detail, mountains, shadows, craters, it is just amazing to be able to look at this distant world, which is at the same time amazingly close to us considering the scale of the cosmos.
Luckily enough, my collimation was just fine so I did not need to re-align the telescope optics. The moon was relatively high around 55 degrees which is a good thing because it means that light coming form the moon has to pass less atmosphere (or “air”) which kind of disturb it. When the moon is low in the horizon, below 30 degrees, usually we don’t get as good a view as we would get if it was high in the sky.
I used the QHY 5L-II Color camera, which has a color CMOS sensor of 1280×960 pixels. The focal length of my newtonian is 1200mm which gave a relatively nice magnification for viewing the moon. I have to say here that I absolutely love using a motor focus which gives an ability to move the focus position without touching the telescope. Touching the focuser moves the telescope (even a little bit) and with a relatively large Newtonian trying to focus can be a bit tricky. You can definitively do it without a motor focus but I consider this to be a nice to have accessory which helps finding a good focus position quickly.
I used Firecapture as the main tool to control the camera settings and capture videos. In case you do not know, yes, this is how you normally take images of the moon, you actually take a video (say 500 frames) and later you process that video with specialized stacking software to combine all individual frames to a single “stacked” image.
After observing various features, I took several videos with the aim of making a small mosaic (combining these images to make a larger image). I decided to take 500-frame videos (each video contained 500 images or frames) which generally is a relatively good number, also considering that my laptop is quite old and the camera only produced around 3 frames per seconds when it came to writing to disk so this process took some time.
Later I observed again several features and decided to end the session after having successfully taken 6x videos, 500 frames each which I combined in the following image
How to combine several images
So now I had 6 videos on my laptop with the goal of combining each resulting image and forming a larger lunar mosaic. I will guide you through the process, which I have done many times with small variations, but the basic tools are the same.
- Autostakkert!3 for stacking
- Registax 6 for sharpening (wavelet sharpening)
- Microsoft Image Composite Editor for combining the images
Stacking
I used Autostakkert in “batch mode” in order to let it automatically process all videos. In order to do this, you have to have all videos on a folder, open one and then click the “all” button, so you manually process the first video and then all other videos get processed the same way.
I used Drizzle 1.5x because I knew the focal length was relatively low and I could already see sharp detail when capturing the videos, which in short basically magnifies the image 1.5x times using data form several images.
Following this automatic process, I ended up with 2 folders containing all the stacked images from all videos (this is because my settings above contain an instruction to stack 25% and 50% of the best frames). I ended up using the 50% stacked images (which used the best parts of 250 images each, from the total of 500 images form each video).
Sharpening and cropping
Following the stacking process, we need to sharpen the images. For this we use a special type of sharpening, called wavelet sharpening. This type of sharpening works remarkably well with stacked images. Below you can see snapshots of the same part of the lunar surface in various images (single raw frames of good and bad quality, the raw stacked image and the sharpened stacked image)
The stacked image is larger because of the Drizzle algorithm used, which magnified the image 1.5x times. Without knowing in depth why it works so well, intuitively I think wavelet sharpening works so well, because we have a special type of blurring in the stacked image from atmospheric seeing and moreover the stacked image contains a lot of information (16 bits per color per pixel) resulting from contributions from all individual images. Its amazing how this type of sharpening brings out detail in stacked images.
For wavelet sharpening I used Registax 6, which hasn’t been updated for some time, but is a very good tool for wavelet sharpening.
I use the “linked wavelets” option and usually try not to over sharpen the image, in this case I used slightly only the first layer. I use the zoom function to check how noise appears while sharpening the image. I press “Do All” to see how the entire image looks and then I save the scheme (wavelet sharpen settings) in order to use exactly the same settings in all images. Finally I save each image as “tif” which maintains its color depth (16 bits per color per pixel).
So now we have a set of sharpened images, but why do we need to crop them? The reason is that wavelet sharpening creates some artifacts at the edge of the image.
Cropping is done easily using the native Windows “Photos” tool or with any other tool that can read and save 16 bit per color tif images.
combining the final images
So now we have a set of sharpened cropped images that are ready to be combined to form a larger image. For this final step I use Microsoft ICE (Image Composite Editor) which is a fantastic tool that you just drop a number of images and it automatically combines them.
You can see in the 2 figures above, how the images where combined automatically. Then I export the resulting (large) image as a tif file and do some final touches with any image editor by increasing/decreasing the brightness and save as a “jpeg” file.
I hope you have enjoyed reading this and find it useful in your journeys when observing and capturing the cosmos.