Learn to combine images from multiple astrophotography sessions into a calibrated and color corrected image that’s ready for processing in your favorite image editor.
A detailed tutorial on the best methods for removing light pollution on any RGB or narrowband image in Astro Pixel Processor.
Here’s my setup at 5:30 am this morning. Taking good flats is key. I had been using the dawn sky to shoot flats for some time. EKOS has a feature where it will shoot flats of any desired ADU value. I’ve found that a median ADU value of 22,000 is perfect for my setup. I found this value through trial and error, by taking flats ad different ADU values, then calibrating with them to see what the results were. Anything above 24,000 overcorrected, and anything less than 20,000 under corrected, so I’m right in the middle now.
I recently discovered this really awesome and inexpensive light source for flats. It’s worked like a charm.
A3 Light Box by AGPtek - currently $47.99
First off, A3 is large enough to cover the front of most large scopes. It’s 11.69” x 16.53” and it’s a flat evenly lit LED panel with three built in brightness settings. It can be powered by the A/C plug it comes with, or through USB plugged into your laptop.
In the photo above I have it plugged into the laptop, and am taking my flats through EKOS. This makes capturing flats quick and easy.
Within EKOS, I build a camera sequence for all my filters, 50 images each, auto exposure set to ADU value 22,000. Then I run the sequence. Within seconds it measures the light from the frame, and knocks out 50, then switches filters, measures the light again, and bangs out another 50 frames. In about 2-5 minutes I can capture all my flats in one go.
Below are the two sequences I captured for the evening (Double Cluster, and M33). While short at under 2 hours each, you can see that they are clean and well calibrated thanks to the easy flats system I’ve been using.
To get started, you'll need to have taken a full set of light images to process. In addition you will need darks, flats, and bias for calibration of those light images. The calibration process is going to remove any artifacts caused by dead pixels in your camera, and correct for lens dust and uneven illumination caused by your image train. Starizona has a great page detailing why you would do image calibration.
If you don't have Astro Pixel Processor, you can download an unlimited 30-day trial at the website. If you like the process, and find the program easy to use, it's fairly affordable in comparison to some of the other tools out there.
Loading your images into Astro Pixel Processor
When you first open the program, you'll be asked to choose a working directory. I typically make a folder on my desktop called Processing, and put all my images neatly organized into folders within. I label them Light, Darks, Bias, and Flats. Inside each folder there are more folders for each filter. For this particular image, I have HA and OIII images of the Veil Nebula, so there is a folder for each in the light folder, and a folder for each in the Flats folder. Bias and Dark can be shot as a single set (the filter doesn't matter since the frames are dark) and used to calibrate both HA and OIII.
From here, I need to go to the Load tab on the left panel in APP. I'm going to check off a setting here for Multi-channel/filter processing since I'm processing two channels/filters at once. You do both at once here, because you want them to register the alignment of all stars across all images at the same time.
If I had shot the same filters over multiple nights, I could select Multi-Session processing, which allows you to do day 1, 2, 3, 4, etc. of each filter and use a different set of flats for each day of the same filter. This is especially useful if you re-image an object over multiple nights throughout a year, you can keep adding data to improve your image. But in this case, I shot all my images for each filter on a single night.
NOTE: If you have a One Shot Color (OSC) camera, and need to make some modifications to the images as they are processed, you would go to the RAW/FITS tab and you can select debayer options there before you load your lights in.
On the load tab, you will now select the Light button, navigate to your first lights folder and select your first set of images for the first filter. In this case, I'm selecting my HA images. You can select the first image in the list, scroll to the last, hold shift, and select it. This will multi-select all images in the window, and you can then press OPEN to import them.
When you add them, it will ask you which filter these light images are, be sure to select the correct filter. In this case they are Hydrogen Alpha images. I select that, then you'll see that there are a bunch of images now associated with the Light button on the left pane. Press the light button again to add the second filter's images. This time go to your OIII light directory and select all OIII frames. Open them, and choose Oxygen III for the filter.
Now your light frames are loaded. You'll do the same for flats, being careful to assign HA flats to HA filter and OIII flats to the OIII filter. This insures the right frames get calibrated with the right flats. Now add your Darks and Bias frames. For both of these when it asks which filter to choose, pick the top options to apply the Darks and Bias to all filters.
Now, we're going to set one calibration option, and that's to have the program create a bad pixel map. You'll press tab two "Calibration", scroll down and find the check box "Create Bad Pixel Map". This will create a map of all bad pixels on your camera sensor, and correct for them when processing the final image.
This is a very straight forward simple process just to give you an idea of how the program works. We're only going to set a few things in this tab.
We're going to integrate per channel under the Multi-Channel/Filter options setting since we're processing multiple filters of light data. We're also going to stack all 100% of the images, because I've already gone through them and removed any images where clouds or airplanes came into the frame. You could lower the % to integrate if you want the program to automatically remove the worst images based on a percent of overall images. I'm going to also set "weights" to quality. This is going to look at all the images in my set, and integrate lower quality images with a lower weight than higher quality images.
I'm going to set "Outlier rejection" to "Windsor clip" and leave the rest of the settings to the default. This is going to average out satellites and other stray objects that get into the frames.
Finally, we now have all settings ready to go. It's time to start the integration process.
You'll press the integration button, and now APP will run through your entire set of images creating master bias, dark, flats, and bad pixel map. It will then apply them to all your light frames to calibrate them, then it will align all frames using the registration process, and finally integrate them into two light images, one for HA, and one for OIII.
Once complete, you should have a folder that looks something like this:
Processing your calibrated images
From here, we're going to load integrated light frames in order to process them into a final image. If you look at the bottom of your files window in APP, the last two files on there should be your Integrated HA and OIII images.
The first thing we're going to do is remove any light pollution that came from either the moon or any nearby lights (or city glow). Even narrowband images can be affected by light pollution, but it will not be quite as bad as RGB images.
Open the tools tab (Tab 9), and double click the first integration image, this loads the image into the viewer, and you can now press remove light pollution on the tools tab to open it for editing.
With your image loaded into the light pollution removal tool, you'll take your cursor and draw boxes over any area that is sky only. Be careful not to draw boxes over any area that has nebulosity or image data in them. It's OK if you include stars. Once you have a good set of boxes covering most of the area, press the Calculate button. This will remove the light pollution based on the boxes you have currently.
Once you see how this has an effect on your screen, it might reveal some hidden nebulosity that was covered by the light pollution. You should now be able to add a few more boxes to finish refining the light pollution removal. Once complete you can check by pressing calculate again. If you're happy with the results, press OK & Save. Rename your file here to remember which version this file is. Each time you process an image with APP it will have you save that image. You can continue to save over the previous image, but I always find it best to rename it different after each save. I use HA-LPR in this case. Keep the format as FITS.
Now you can process your other channel the same way.
Don't worry about the edges of your frame. Due to the different alignment of each frame (assuming you used dithering curing your image capturing) you will have a few pixels on each side of your frame from the registration process. It's not necessary to try and remove any light pollution from here as you'll just crop it out in the next step.
Cropping your frames is a little tricky. You can load them one at a time using the batch modify tool and manually draw a box around each one. But that's imprecise. You might accidentally crop each frame differently. In order to do both at the same time with the same crop, you'll need to NOT load an image before choosing "batch modify". So press Batch Modify, tell it not to load an image, and it will then ask you which files you want to batch modify. Select your two frames that have light pollution removed. It will load the first frame. Draw a box around it, and press the Crop OK button. This will crop both frames at this location you've indicated.
You'll now see two frames at the bottom of your list that are both cropped.
This is the fun part of the process. We're now going to take your two individual frames and combine them into a single color image.
Now you'll choose Combine RGB in the tools area of APP (left Tab 9). It will open a new area with nothing in it. From here we're going to add in our images using the Add button. We'll pick the cropped HA image, choose HA channel. Then we'll pick OIII and choose OIII channel. Then, since a full color image actually consists of three channels Reg, Green and Blue, we need to add the OIII frame again. On the left column, you should now have 3 channels listed, each with a few settings underneath them. From here, we can assign which color we want each frame to be colored.
Take the slider under Hydrogen Alpha labeled R (for red), and slide it to 100%. Then make one of the OIII channels B (for blue) 100%, and the last channel of OIII G (for green) 100%. Now press the calculate button at the top of the column. This will process the three channels into an RGB image, and you should see the results in your main window.
Now press the create button, save it as your RGB integration (any name you choose), and keep the format as FITS.
We're now going to use the background calibration tool on our new RGB image. This is going to make sure that the black in the background is a true neutral color. If we had just a little bit too much red, or blue, this will knock it out and make sure the black background is true black.
Load your image using the Background Calibration tool (tab 9). Draw your boxes around only background area that is black sky and stars. Do not get any of your nebulosity in the boxes, because we don't want it to neutralize your pretty colors. Press calculate to see the results. If it looks good press OK & Save. Name your file and pick FITS again for the format.
Because we're making a false color image with two filters, our star colors are going to be exaggerated a bit. I like to use the star calibration to bring them more in line with the typical star color temperature they should be.
The calibrate stars tool is is also in the tools menu (tab 9). Select the image where you calibrated the background. Load it into the calibrate stars tool. And draw your boxes around large sets of stars. Press the calculate button, and this will process the image. You'll notice your bright red stars drop down to a more normal color. The stars are now in a proper temperature color range. But you'll notice that we also lost a little color in the nebulosity. We're going to bring that color back in the next step. Save your image, and again name it and pick FITS for the format.
In this last step, I'm going to process the final color in another app that I'm more familiar with. These steps can be done in APP using the tools always shown to the right of the image. But for me, I can achieve the results faster by using an app I know better. In this case, I'm going to use Photoshop, but the same tools I'll use here are also available in a number of other apps on the Mac. GIMP, which is free has these tools, as well as Acorn, Pixelmator, and others.
First things first. We need to get the last image we did out of APP and into a regular image format for use an a standard image editor. In the upper right hand corner of APP, you'll see a Save button. Load your last star color calibrated frame, and then press the save button.
Keep the stretch option checked, and it will export the image as you see it in the viewer. If you uncheck this, and export, you'll have to stretch your image in your other image app instead. I find the default stretch here to be adequate. When saving, make sure to pick a format you can read in your image application. I picked 8-bit Tiff, but you can also pick JPG if you want a smaller file at the expense of a little bit of quality.
I now load the image into photoshop and apply some Curves to darken the blacks, and brighten the lights.
I also add some saturation here to make the colors more vibrant. With those two things done, I'm ready to save my final image and complete the process.
This tutorial is provided to show the basic steps in processing with APP. It is capable of so much more, and I only touched the surface with this tutorial. To achieve the best results, experiment with all the tools to see what you can achieve.
The final processed Veil Nebula image
This will be a general walkthrough of a typical capture session with my AstroTech AT6RC setup.
This should be a good walkthrough for someone not familiar with the system to enable capturing their own images. However, I'm not covering equipment setup in this post, but might cover it in the future in another post.
A few caveats with my particular setup. I break it down and set it up each night, so I require a new polar alignment before each session. My AVX mount doesn't fully support the park function in EKOS, so after a nights session, I cannot auto park, but others may have a mount that supports this feature.
Connect your equipment
The first step in my process is to set up all my equipment, connect it to the Mac laptop and start with an All Star Polar Alignment (I can't see Polaris, so use this method built into Celestron mounts). After this procedure is complete, I load up Kstars, then press the EKOS button on the top bar to launch the EKOS capture system. I then press the connect button to connect to my equipment which I have pre-setup within EKOS prior to this nights session.
The mount is probably already aimed at your last alignment star from your polar alignment, and this is typically good enough to use for focusing. I select the Focus Module and then press the capture button. This grabs a single screen and displays it in the screen preview window. Since I have a motorized Moonlite focuser, I can select a star with the cursor (it puts a green box around it in the screen), and then press the Auto Focus button. This begins the auto focus routine where it begins automatically focusing in and out and measuring it's effects on FWHM (Full-Width Half-Maximum) which continually measures the width of the star to get it as small as possible after iterating multiple times. Now, we're in focus, and can move on to the next step. (Side note, if you don't have an automated focusing system, you can use the camera module's live preview feature and a Bahtinov mask to focus instead of using this module.)
Mount Control Window
The next part of the process is to open up the Mount Control module, and select "Mount Control" in the upper right of the window. This will open a small control pad with arrows, and a target search to move your mount. I'll press the search icon and type in a target name for a simple, easy to identify target for plate solving. Usually I pick an open star cluster for this process. I selected NGC129, then pressed the GOTO button to slew the mount to that target.
Now that I have slewed to NGC129, I press the Alignment Module tab to go through a plate solving process to improve my GOTO model inside the mount and EKOS module. The reason you want to do this is both so that you have increased slewing accuracy, and so that once you pick your target and slew to it, you have confirmation that this is in fact the target you picked. Additionally, this helps with the meridian flip and ensuring that once the mount has flipped, after passing the meridian line, that your target is picked up in the exact same spot it left off before the flip.
Usually what I do in this first step is select Sync under Solver Action. Then I press Capture and Solve. All I'm doing here is plate solving the current position to tell the mount exactly where it's aimed. I had told it to aim at NGC129, but after this first solve, it shows the mount is way off. Not knowing for sure if this is an adequate target, I pick a new one using the Telescope Control and aim at M39, an open cluster. I once again set it to Sync, and press Capture and Solve. Now I'm fairly close to the target, but not quite in the green area. I press goto one more time now that my mount knows where it is, and then Capture Solve/Sync one more time and see if the last slew was closer to the target. Finally, we're in the green and good to go to our final imaging target for the night. I pick the Wizard Nebula NGC7380, and press goto. Once there, I perform a Capture and Solve/Move to target. This will perform multiple Capture and Solve routines moving the mount each time getting the target lined up perfectly. Once it's good the Capture and Solve process stops. Time to turn on guiding now.
The Guide Module
With our target picked, and GOTO plate solved to the target, we're ready to start guiding. This process is fairly straight forward. Dithering is turned on by default (you can check it by going to the options button in the lower right corner of the window). Now, we press capture, this shows you a single image from your guide cam. Select a star with your mouse, and it highlights with a green box. Press Guide, and the guiding calibration begins. This process is automatic, and you can watch the steps it's performing in the text window at the bottom of the screen. Once it's complete, guiding starts automatically. Now it's time to program our image sequence and start capturing.
The Sequence Module
This is the final step for my process for an evening capture session. For the Wizard Nebula, I had planned on capturing it in bi-color over a two night period. Tonight is the first night, so I only plan to capture 7-8 hours of HA (Hydrogen Alpha filter), basically as long as I can before the sun comes up. Tomorrow night, I'll be capturing OIII (Oxygen III filter) for another 7-8 hours using the same routine. Since I have a cooled camera, the first thing I do here is set it's temperature to -15°C, and press the set button. The temperature quickly begins to lower. I can check that box next to the temperature, and the sequence will not start until the temperature has been reached. Next I plug in my Exposure time, I've set it to 180s, or 3 min images. A count of 240, which is more than enough to cover me to sun up. I make sure the type is set to "Light" for light frames (as opposed to dark, bias, or flat). I set the filter to H-a, then under file settings I name the files with a prefix, in this case NGC7380, and I check off Filter, Duration, and TS (Time Stamp) so that those are appended to the file names that I'm capturing.
Now I've set all the perimeters for my sequence. I now add the parameters to the sequence que by going up to the top and pressing the "+" button. This adds it to the right into the que. If I lived in a dark area, and wanted to capture more than HA during the evening, I could change my parameters and add sequences for OIII, SII, or LRGB and just make sure that I only put enough time into each so that the sequence can finish by the end of the night. But since I'm in a light polluted area, I need as much time as I can spend on each filter, so I typically spend one evening per filter and get decent imaging results.
We're done now with setting the sequence, and we're ready to run it for the evening. You'll press the play button at the bottom of the sequence window, and your camera will start capturing images until the sequence is complete. You can now tab over to the main window and watch the images roll in for the evening, or head to bed like I do, ready to wake up by sunrise and take down all the equipment before it gets too hot outside. (I live in the south where it's quite warm during the day).
From here you can monitor the images that are being captured for the sequence you've plugged into the sequence editor.
Below is the final processed image from two nights of imaging. I processed it with Astro Pixel Processor, PixInsight, and Photoshop on my iMac Pro workstation. Full equipment details can be found at Astrobin.
Recommendations for your start in imaging on the Mac
There's a few things that need to be covered here as a starting point. I make some assumptions that you’re familiar with Astronomy, possibly already have a first telescope, and are ready to start taking some images. First you have to make a decision as to whether you want to take photos of the planets and Moon, or if you want to take photos of nebula, star clusters, or galaxies. Basically, the decision between planetary, or deep space objects. These things are not exclusive to each other, and can be done with the same telescope but the results might not be optimal for each choice. Your telescope is probably suited to one or the other.
Planetary imaging on the Mac
Planetary is fairly straight forward. Large aperture scopes like 6" and above are great for this, and you don't need to have an equatorial mount. Any Alt/Az (Altitude Azimuth) mount will work. A high speed web cam or astro camera and Mac laptop are the only additional entry level hardware requirements. Since most planets are relatively small, the larger the scope, the closer/larger they will look, and the more detail you can get out of your images.
Recommended starting software for planetary imaging:
Planetary Imager - for taking pictures or videos: free
SiriL - for stacking planetary images: free
PixInsight - for processing your planetary images to get the most detail out of them: $230 EUR
Unfortunately planetary processing software is a gap right now on the Mac. You need wavelet processing to get the most detail out of your images, and currently PixInsight is the only real option. There are two other apps that might run on older hardware and operating systems (Lynkeos and Keiths Image stacker), but they're not developed any longer, and crash often on modern hardware. They are however, free applications.
For more advanced options, you might switch out Planetary Imager for FireCapture.
Deep sky object imaging on the Mac
DSO imaging requires a little more effort. Because this type of imaging focuses on long exposure shots, where tracking your object across the sky accurately is a requirement, you'll need a German Equatorial Mount (GEM). These deep sky objects can vary greatly in size, with a large number of them being bigger than earth's moon in the night sky. Because of this, a large scope isn't a requirement to get started. In fact, it's preferable to start with a smaller scope, like an 80mm refractor. The reason for this is that the larger your scope, the more accurate your tracking needs to be, the better your mount needs to be to handle the weight and accuracy. The difficulty (and cost) goes up exponentially with larger telescopes. So start small. All of the telescopes I use are relatively small (under 6" in size), and all fit on my entry level GEM mount, the Advanced VX by Celestron.
Additional requirements are going to be a guiding camera and guide scope. This is essentially a small telescope mounted on top of your main scope, with a guide camera. This camera's job is to watch the star movement, and send corrections to your GEM mount when the mount isn't moving accurately. For entry level equipment, this is a necessity, as these mounts are far from accurate for long exposure imaging.
You'll also need a main imaging camera, and your options vary widely here. You have the option of using a DSLR (maybe you have one already in your possession), or a dedicated astrophotography camera that can do color or mono. Mono is a black and white camera, that when combined with color filters, can achieve a higher fidelity color image than a regular color camera can but with more effort and expense.
Recommended starting software for deep sky imaging:
Cloudmakers Astro Imager - for taking pictures with an astronomy camera: $21.99
Cloudmakers AstroDSLR - for taking pictures with a DSLR camera: $21.99
PHD2 - Guiding software for your guide scope and camera: Free
Astro Pixel Processor - Processing software for your images. $50/year, or $125 to purchase outright.
EKOS is the capture suite that comes as part of the KStars Observatory software package. It's a free, fully automated suite for capturing on Mac, Linux, and PC. It's not to dissimilar to Sequence Guider Pro on the PC. While the capture suite comes with KStars, you're not limited to using KStars. EKOS will also allow you to send commands to your mount from SkySafari on the Mac as well.
I'll break down it's use and capabilities screen by screen.
In the main window shown above, you see tabs that represent each part of the application which include the Scheduler, Mount Control, Capture Module, Alignment Module, Focus Module, and Guide Module. From the main window you will see the currently taken image, the seconds remaining in the next image, as well as which image number you are on during the sequence, and the percent complete of the entire sequence with hours, minutes, and second remaining in your sequence. Additionally to the right of your image, you see your target and tracking status, focus status, and guiding status.
From the Scheduler, you can pick your targets, and assign them capture sequences (which are set up in the imaging module). Additionally there are some overall parameters you can set here for starting a session and ending a session. If you have a permanent observatory, you do things here like open and close your observatory with startup and shut down sequences, or set parameters for when to run your schedule based on the twilight hour, weather, or phase of the moon. The scheduler lets you set up multiple imaging sessions, mosaics, and more. And as the twilight hour approaches, it will start up and pickup imaging based off of priorities you set, or object priorities based on their visibility in the night sky. Imaging sessions can be set for a single night, or can be taken over multiple nights if it wasn't able to complete them in a single night.
Mount control is fairly straight forward. This window shows the current aperture and focal length of your selected equipment. You can save multiple equipment configurations from this window for various telescope and guide scope combinations that you might have. Current tracking information is also shown in this window. If you select Mount Control in the upper right of the screen, it pops up a floating window with arrow buttons, speed and goto functions for manually controlling the mount. You can search for a target, and manually go to an object in the sky to start an imaging session without setting one up in the scheduler.
From here you control all aspects of your imaging camera including setting up imaging sequences. For instance, I might have 7 hours of night time to image before the sun rises. I can divide that time up between each filter, and save the sequence of 120 captures, at 60s each at -20°C for each individual filter, and save that as a sequence which I can later load and reuse anytime I want to run that session during a 7 hour window. Or I could say I want 20 hours total on an object, and set all parameters for each filter to accommodate a 20 hour session, and save it. Or maybe I want one session for LRGB, and one for narrowband imaging. You can also set flat, dark and bias sequences. Flats have an awesome automatic mode, where you can set a pre-determined ADU value, and it will expose each filter automatically to the same ADU and capture all your flats in a single automatic session. It also supports hardware like the FlipFlat so that flat sessions can be run immediately following a nights imaging session. Additionally you can set guiding and focus limits for imaging sessions, and control when your meridian flip occurs.
Here you can control all focus functions if you have a computer controlled focuser. I highly recommend getting one of these. Focusing can be set up to run automatically. It will capture a single image, and auto select a star, then run a sequence where it continues to capture, while moving the focuser in and out. Each time it is graphing the HFR on a curve plot trying to find the best point of focus. Depending on seeing conditions, it can get focusing down in 3-4 iterations, or sometimes 20. All parameters including threshold and tolerance settings for focusing are controlled in this window.
From this window you can polar align (assuming you can see Polaris), and also plate solve to locate an object center window or improve GOTO accuracy. Since I can't see Polaris from my location, I have to use my mounts built in All Star Polar Alignment process, then I can come to this window to capture & solve a target to improve it's GOTO accuracy. There are several nice features accessible here. You can load a fits file from a previous imaging session, it will plate solve the image, then move your telescope to that precise point to continue an imaging session. Or you can select targets from the floating mount control window, then capture and solve, or capture and slew to bring the mount as close to center of the target as possible. EKOS automatically uses this function during an imaging session to initially align to a target, and then realign once the meridian flip occurs.
The guide module handles all guiding through your guide scope and camera. Press capture in the upper left, and hit guide, a star will be automatically selected, calibration starts, and once calibrated guiding begins. Additionally options can be set for dithering, and guide rate. For people who prefer PHD2, EKOS integrates seamlessly with it, and even shows PHD2's guiding graphs within the app and on your overview tab. I've not personally had any issues using the EKOS guiding, and it has an additional benefit of being able to reacquire a guide star after clouds interrupt your imaging session, and can continue the imaging session when it's clear again.
As someone who images regularly, and doesn't have a permanent setup (like an observatory), I like how much of the application can automate my nights imaging sessions. There is little else available on the Mac that is this full featured. The Cloudmakers suite comes in a close second for me, but is initially easier to set up and use. Additionally TheSkyX is also a full featured suite, however I've not used it. The setup process with EKOS isn't too difficult once you get an understanding of how the modules interact with each other and what all the options do. I hope this brief overview gives you enough of an idea that you can setup and use the software on your own. EKOS has a healthy number of contributors on the project, and regularly sees updates on a monthly basis, and has good support through it's user forums.
This simple guide helps you polar align your Celestron equatorial mount when you have no view of the north star.
Some things that will be helpful for this tutorial:
Steps to align:
- The first thing you’ll need to do is set up your mount on level ground facing roughly north. Make sure you use a bubble level to ensure your mount is on a flat plane so that when it’s rotating around it’s azimuth the mount is not moving up and down slightly.
- It’s important you’re facing north within a few degrees, you can achieve this by using your phone’s compass feature (or Astro Locator) and laying it across the main telescope tube on a flat surface. You’ll want the phones settings set to face true north. This is already established in Astro Locator.
- Turn on your mount, and plug in your home site settings or let your GPS system update your time and location in the mount’s hand controller. I currently use a GPS, but prior to that I would watch the clock in Astro Locator, and set the time setting down to the second for accuracy.
- Use your mount’s hand controller to select 2-star alignment. It’s going to show you the name of a suggested star in the western hemisphere that it thinks is visible in your location. Since your mount is pointed roughly north, west is going to be anything directly to the left of your mount, and east will be anything directly right of your mount. The star it suggests might not be visible to you depending on your location and any objects that might be in the way (like houses or trees). This is where Sky Safari comes in handy. I open it up on the iPhone, zoom out so that I can see a fairly large portion of the sky, and press compass (one of the buttons on the bottom of the app). This allows you to pan your phone around the sky, and look for stars that you can actually see. Typically, the named stars in Sky Safari, are only the brightest stars, and you should now be able to visually identify stars in your night sky. Look for a bright star to the left of your mount, and correlate it to a named star in Sky Safari. Once you have a star picked out, use the up and down arrows on your telescope’s hand control to scroll alphabetically through the list of named stars until you find the one you’re looking at. Press enter on the hand set and the mount will now move to the first star.
- If you’ve set the time, location, and position of your mount properly, you should now see the star within the mount’s field of view either through your finder scope, eyepiece, or camera video. (TIP: Here’s a shortcut to improve the initial setup. Once you’ve aimed at your first star, but before aligning it in the crosshairs with the hand controller, use your mounts manual azimuth and altitude adjustments (the physical knobs) to move the star inside the crosshairs. Once done, you can then use the hand control to align the star, and you will not need to use the arrow keys to move the mount around in this step. All this does is improve the GOTO of the alignment stars during this alignment process. Using the mount’s hand control, follow the directions on screen to center the star in your crosshairs. Accuracy is important here. You want to get the star as centered as possible. Press ‘align’, and then a suggestion for star two should show up.
- Repeat the process for a second star in the western hemisphere. Find a second visible star using Sky Safari, then select the name in the mount’s hand controller to move to that star and align it centered in your crosshairs.
- You will now be prompted to add up to 4 additional calibration stars from the mount’s hand controller. These will all be in the eastern hemisphere, and you’ll want to continue repeating the process for all four of these stars.
- Your telescope now has a an accurate GOTO pointing model stored in it’s system for your specific night sky. The 2+4 alignment process you just finished is not the polar alignment, but the pointing model for the GOTO system. For visual observers you’re set now, and can stop following the tutorial here. If you intend to do imaging, the next steps will cover the polar alignment process to dial in that last bit of precision for long exposure imaging.
- Press ‘Align’ on the hand controller, and use the arrow keys to select ‘Polar Align’.
- Use the scroll arrow keys to move to and select ‘display align’. This will show you (with a reasonable degree of accuracy) how close you are aligned to polar north. An error less than 00 10’ 00’’ is fairly good, but you want to get as close to 00 00’ 00” as possible, especially if your telescope is a long focal length or you expect to use really long exposures. Now use the back button, and select Align under Polar Align.
- You’ll be asked to align your mount to the last star you were pointing at. If this star does not match the criteria required for Polar Alignment, you’ll get an error message saying this star isn’t appropriate, and to pick another star. If you get that error, you need to back out of the Polar Align menu to the home screen where it says ‘ready’, select ‘Stars’ on the hand control, and scroll to ‘Named Stars’. Using Sky Safari, you need to locate a bright star near the horizon, as close to north as you can find, then select it in the hand controller and move the mount to that star.
- Now, press ‘back’ on the hand controller to get you back to the controller home screen, select ‘align’, ‘polar align’ and this will now start the polar alignment process. The scope will now goto the star you’re already pointing at, and it will ask you to center it in your crosshairs. Once you’ve pressed align, it’s going to move once more to that same star, but this time you’ll see it’s not centered again, the scope is now pointing to where it thinks the star should be if your mount is perfectly aligned. The hand controller is going to ask you to now use your manual altitude and azimuth physical mount knobs to re-center the star. Once complete, you’ll press ‘Align’ again. Select ‘Display Align’ to check how close to 00 00’ 00” you are now. Assuming you are at 0 or even a few arc seconds of error, you are close enough to 0 to move on to setting up your guiding software and pick your first target of the evening. If you want to try getting to 0 error, you can repeat the polar alignment part of this process.
I imaged IC410 over a single night using my Explore Scientific 102mm FCD-100 telescope, ASI1600MM-Cool camera, and the ZWO narrowband filters. I took 75 images that were exposed for 5 minutes each. 25 HA, 25 OIII, and 25 SII images in total.
I used AstroPixel Processor to combine and integrate the images into a single master HA, OIII, and SII frame. From there I imported all three into PixInsight and followed this Light Vortex Astronomy tutorial for processing the individual frames. Note that their tutorial covers a two frame process, and I had three. I just applied the same processing techniques to each of my three frames.
Where I had to diverge from the above tutorial was when combining the images into a single color RGB image. I researched and found the following PixelMath formula for PixInsight to combine the 3 frames:
R: 0.5*SII + 0.5*HA
G: 0.15*HA + 0.85*OIII
Once done, I wrapped up the tutorial and concluded with the finished image seen above.
I also went back to this same image and reprocessed it in the Hubble telescope pallet.