Astrophotography

Image Credits: Joe Haberthier, Dave Morgan, Steve Childers, and Bruce Gavett

Astrophotography is a fascinating area. The night sky is full of great objects to image and bring to life. The downside is that it isn’t one of the easier things to do. It is dark out at night and most objects are very far away. In addition, the Earth rotates, making it difficult to track objects and capture long exposures.

However, fear not! We have some information for you, although this page is very much a work in progress. Go here for more information on the Deep Sky objects visible in the night sky.

On This Page

General Information

Image Processing

Image Processing Software

Astrophotography with your smartphone

One of the long-time members of FAS gave a presentation on how to capture images with your smartphone. Here are several resources from his presentation along with a few more.

Image Credits: Sean Wood.

“Smart” Telescopes for Astrophotography

Astrophotography used to be the domain of the more experienced amateur astronomer. However, there are now several options even a beginner can use.

The ZWO Seestar S50 is becoming popular with several club members. It is around 5 1/2 lb., priced at $500 with a 2 MP (? um pixel size) camera, 50 mm aperture, and 250 mm focal length. ZWO has announced the Seestar S30, a smaller version of the S50. For more information, see the ZWO website.

Seestar S50 Image Credits: Bruce Gavett.

There are several choices out in the marketplace.

TelescopeWeightPriceAperture mmFocal Length mmCamera (MP)Note
Dwarf III3 lb.$50035 (1.4”)1508.3Telephoto & wide angle lenses
Seestar S303.5 lb.$35030 (1.2”)1502.1Telephoto & wide angle lenses
Seestar S505.5 lb.$50050 (2”)2502.1Portrait mode – now with a Mosaic option
Vespera II & Pro11 lb.$1,700 & $3,00050 (2”)2508.3 & 12.5
Unistellar Odyssey Base & Pro8.8 lb.$2,300 & $4,00085 (3.3″)3203.4 & 4.1Auto focusing. Pro has eyepiece
Unistellar eQuinox 2 & eVscope 215.5 lb.$2,500 & $4,900114 (4.5”)4506.2 & 7.7Manual focusing & collimation. eVscope has eyepiece.
Celestron Origin~ 40 lb.$4,000152 (6”)3356.4
Information is as of August 2024 and is accurate as possible. See Supplier’s website for up to date specifications.
  • Seestar S50 (ZWO). See above for more information.
  • Seestar S30 (ZWO). Just introduced (November 2024). At around 3.5 lb., this is a new alternative to the ZWO Seestar S50 and the Dwarf 3.
  • Dwarf III (Dwarf Labs). At just under 3 lb., this is a low priced ($500) alternative to the ZWO Seestar with a 35 mm aperture, 150 mm focal length, and 8.3 MP (2 um pixel size) camera.
  • Vespera (Vaonis). It is around 11 lb. and has a 50 mm aperture and 250 mm focal length.
    • Vespera II. It has a 8.3 MP camera (2.9 um pixel size) and is priced around $1,700.
    • Vespera Pro. It has a 12.5 MP (2 um pixel size) camera and is priced at $3,000.
  • Odyssey (Unistellar). It is 8.8 lb. with a 5 hour battery life, an 85 mm (3 1/3”) aperture, 320 mm focal length, and 3.4 & 4.1 MP (1.45 um pixel size) camera. It has an autofocus and does not require collimation.
    • Odyssey Base model comes without an eyepiece and is priced at $2,300.
    • Odyssey Pro model comes with an eyepiece and is priced at $4,000.
  • Expert Range (Unistellar). It is 15.5 lb. with a 114 mm (4 1/2”) aperture, 450 mm focal length, 2.9 um pixel size camera. It has a manual focus and does require collimation.
    • eQuinox 2 comes without an eyepiece, 6.2 MP camera, 11 hour battery life, and is priced at $2,500.
    • eVscope 2 comes with an eyepiece, 7.7 MP camera, 9 hour battery life, and is priced at $4,900.
  • Origin Intelligent Home Observatory This is Celestron’s high end 6” smart telescope. The total system weighs over 41 lb. It has a 152 mm aperture, 335 mm focal length, 6.4 MP (2.4 um pixel size) camera, and is priced around $4,000.

Please note that FAS does not recommend or endorse any specific telescope, we only provide information that is generally available.

“Traditional” Astrophotography

In general, astrophotography is all about photographing the night sky. There are generally three different levels to this. You can photograph the night sky itself (landscape astrophotography), the Moon and individual planets (planetary astrophotography), or go after deep sky objects such as nebulae and galaxies (deep sky astrophotography). Most choose the latter.

One approach is to use a DSLR camera along with a star tracker or an equatorial tracking mount.

A more complicated, but possibly more rewarding, approach is to utilize a telescope. At the most basic you will need: An imaging telescope & camera, an auto-guiding telescope & camera, and a telescope mount.

You can add a computerized controller such as ZWO’s ASiair, which makes the entire process much easier and something you can control from your smart phone or tablet.

Please note that FAS does not specifically recommend or endorse any specific telescope or setup, we only provide information that is generally available.

Additional Resources (Introduction to Astrophotography using a DSL camera)

Additional Resources (Introduction to more General Astrophotography)

Additional Resources (Astrophotography Guides)

Additional Resources (Astrophotography Equipment)

Additional Resources (Deep-Sky Objects)

ASiair from ZWO

One option for astrophotography that is getting a lot of attention from FAS members is the ASiair from ZWO. This setup was recently added to the club’s observatory near Pilot Mountain. A few images from the observatory setup are below.

Image Credits: Joe Haberthier and other FAS members.

Please note that FAS does not specifically recommend or endorse any specific equipment or setup, we only provide information that is generally available.

Filters for Astrophotography

Filters can be used to enhance your images.

Dual Band Filters

One of the most popular filter, and one that is included in ZWO’s Seestar, is the dual-band filter for viewing emission nebulae. These filters block out all but the Hα (656nm) and OIII (500nm) wavelengths and greatly reduce the effects of light pollution.

UV/IR Cut Filters

Another that can enhance galaxies and star clusters are UV/IR cut filters (aka Luminance Filters), which block UV and IR light and allow only visible light through.

Please note that FAS does not specifically recommend or endorse these or any other filters, we only provide information that is generally available.

Image Processing

Capturing images is only part of the process for astrophotography. To produce really great images, they must be processed, stacked, and combined.

In this section

Stacking

Stacking allows you to take advantage of multiple images and combine them into one. Systems such as the ASiair and Seestar will stack as you go. Although, you probably want to save individual frames (fit files) for later stacking. This offers the advantage of rejecting frames that have distortions, star trails, or other deformities.

Calibration Frames

Enhancing your images often requires the use of calibration frames. Flats, biases, and dark frames are often taken each time you use your setup. They are “combined” with your images (light frames) during your shooting and then again during your stacking.

  • Flat Frames: Taken against a white background. These smooth out differences in light intensity due to dust and other impurities.
  • Bias Frames: Taken against a dark target. These are used to eliminate camera noise from your images.
  • Dark Frames: Taken against a dark target at the same temperature as your imaging. These are used to eliminate thermal noise (temperature differences) from your images.
  • Light Frames: These are your images (fit files).
Stretching Images

Most image processing software produces “final” jpeg images, which can be viewed by most applications. They also produce fit files, which can only be viewed using other astro-image packages, and tiff files. The latter two are typically RAW images in a 14 bit (or maybe 12 bit) format. For us to see anything, the information needs to be “stretched” into a 16 bit format (or sometimes changed to an 8 bit format). The simplest way to do this is by performing a linear stretch, which multiplies by 4. A 14 bit (0 to 16,383) image is stretched to a 16 bit (0 to 65,535) image.

If the stretch results do not look good, you can manually adjust the black and white levels. (More to come here.)

Gradient Removal

Images are usually taken in less than perfect conditions. Light pollution is all around us. On many nights the Moon interferes with our view of deep-sky objects. As a result, our images come out with uneven backgrounds and possibly a grayish background. There are ways of addressing this. If possible, always utilize calibration frames. Also, many software packages allow for a background extraction to address the problem.

Image (PHOTO) Processing settings

Here is a summary of the many image (photo) processing settings available in most software. The articles below discuss some of the steps you might go through using these settings to enhance your images.

  • Exposure: Change the overall light the image captures, increasing or decreasing the brightness of all pixels.
    • Underexposed: Lack dark details.
    • Overexposed: Lack light details.
  • Brightness: Change how light or dark the image is, increasing the dimmer pixels.
  • Brilliance: A more complex (algorithmic?) method of increasing or reducing an image’s brightness.
  • Contrast: The difference between the brightest and darkest parts of your image.
  • Black Point: The darkest part of your image.
  • Noise Reduction: Removes the graininess in your image.
  • Sharpness: The difference between an object and its background.
  • Vignette: Reduces the sharpness at the image’s edges.
  • Color Adjustments.
    • Color Saturation: The intensity of the image colors.
    • Temperature: Adjustment of blues and reds.
      • Warm: More of reddish tone.
      • Cool: More of a bluish tone.
    • Tint: Adjustment of greens and magenta.
Simple ADJUSTMENTS

After stacking your images (with calibration frames), here are a few very simple adjustments that you might try to further improve your image. However, a more formal workflow using some of the standard astrophotography software (such as Siril and PixInsight) will give you better results.

Examples of these simple adjustments are below. This is very much a work in process and actual image settings may vary from those noted.

  • Increase the Brightness [How light or dark the image is] particularly if the image is dim.
  • Increase the Contrast [Difference between the darkest and lightest parts] to +30 (or less if the color is too dark).
  • Increase the Black Point [Darkest part of the image] to +30 (or more if there are still residual light areas).
  • Increase the Color Saturation [Color Intensity] to +10 (maybe).
Workflow

One of the challenges of working with astrophotography is developing a workflow you can constantly follow rather than pushing a bunch of buttons until your image looks good. A few suggested workflows are provided below for various astrophotography packages. However, here is a general overview you can follow. Individual steps might be performed in a different order. This is still a work in progress.

  1. Use long exposures – the longer the better.
    • Seestar: 10 seconds over at least 1/2 hour.
    • EQ tracking; 2-4 minutes over at least 1/2 hour.
  2. Take your calibration frames (darks, biases, and fits).
  3. Save your individual Light frames.
  4. Review your individual Light frames and remove those that are bad (clouds, trees, and streaks)
  5. Preprocessing: Stack your images. Include your calibration frames.
  6. Crop out the “pixellation” and other distortions around the edges.
  7. Remove the excess Green noise.
  8. Remove noise from your image.
  9. (Optional) Split the stars from the underlying object and background
  10. Extract the Background to remove the gradients.
  11. Perform a “Color Calibration” to correct the color of the object.
  12. Stretch your image.
  13. Adjust the shape of the stars using Deconvolution.
  14. Adjust the Color Saturation to enhance the colors.
  15. (Optional) Recombine the stars with the underlying object and background.

Image Processing Software

There is a multitude of image processing software available. We can’t cover them all, but can provide an outline of which ones appear to be the more commonly used. ZWO’s ASIStudio is designed to be used with the output of ZWO’s ASiair. DeepSky Stacker, GraXpert, and StarNet perform very specific functions (stacking, background extraction, and star extraction respectively). Siril, APP, and PixInsight are three full functional astro-processing packages. Gimp is an alternative to Photo Shop.

In this section

ZWO ASIStudio

If you are processing images from an ASiair, you might use ASIStudio from ZWO to stack and stretch your images.

ASIDeepStack is used to stack and stretch images. After some experimentation, processing images with calibration frames yields some good results.

ASIFitsView is used to view fits frames.

ASIDeepStack Workflow

  1. Open the ASIStudio App.
  2. Open ASIDeepStack to stack individual fit images.
  3. Add Calibration Frames (if necessary, but a really good idea to use these)
    • Select BIAS and then click on “Select Bias” to load your Bias frames.
    • Select FLAT and then click on “Select Flat” to load your Flat frames.
    • Select DARK and then click on “Select Dark” to load your Dark frames.
  4. Select LIGHT and then click on “Select Light” to load your Light frames (fit files).
  5. The files will fill the window.
  6. In the Stack window:
    • Click on the folder (ASIDeepStack) to view and remove old processed images.
    • Click on the “arrow” to start processing.
  7. The app will perform the stacking and alignment.
    • Click on the “swirly” icon next to the “arrow” to toggle back and forth between a single image and the stacked image.
    • Make sure the Auto button is highlighted. This tells the software to automatically stretch the image.
    • Zoom in and adjust the dark and white levels if the image is too dark or too light.
  8. Go to the Image Processing window, to further adjust the final image.
  9. Click the save button at the bottom right of the image to save the stacked image. The final image is saved in three formats (light_stack_#.fit, light_stack_#.jpg, and light_stack_#.tif). 
  10. Click on the folder (ASIDeepStack) to find your images and copy them to another folder.
  11. Click the question mark in the upper right to display the pdf help document.
  12. Note that the folder ASIDeepStack is the default location for processed images. Go to settings to change the location of this folder (if necessary)

Please note that FAS does not specifically recommend or endorse this or any other software, we only provide information that is generally available.

DeepSky Stacker (DSS)

DeepSky Stacker is an alternative software package you might consider to stack your images. It can also be used to review your FIT frames and discard ones with issues. It appears that DSS only runs on in a Windows environment and not on a Mac. (More to come here.)

Please note that FAS does not specifically recommend or endorse this or any other software, we only provide information that is generally available.

GraXpert

GraXpert is a software package designed to help you remove gradients from your images. It has five basic functions/steps.

  1. Loading: Load your image. This could be a stacked fit file from ASIStudio or Siril.
  2. Crop: Crop your image to remove noise and other defects around the edges.
  3. Background Extraction: Extract the background to remove gradients.
    • Method: RBF (same as Siril) or AI (enhanced & automatic)
    • (RBF Only) Points per Line: Adjust this to decrease or increase the number of background squares.
    • (RBF Only) Grid Tolerance: reduce or increase the background coverage. Increase this if light areas are not included in the background. Decrease this if too much of the target object is included in the background.
    • Smoothing: reduce this to remove more gradients. Increase it to remove less gradients.
  4. Denoising: Remove the noise from your image.
    • Denoising Strength: Reduce or Increase this as needed.
  5. Saving: Save the resulting file either as a processed fit (non-stretched) or as a stretched fit file.

As you work with your image, stretch it so you can follow the process. There are a three options to choose from.

  • 10% to 30% Bg, 2 or 3 sigma, which allows you to choose a less to more aggressive stretching. The more aggressive (30% Bg) allows you to clearly see the gradients in the background. Once you remove the background, switch back to a lower percentage for a more reasonable image.
  • Channels linked … (more to come here).
  • The Saturation allows you to reduce or increate the color saturation.

You can view the results of each step by clicking on the options at the top.

  • Original
  • Gradient-Corrected
  • Background
  • Denoised

Please note that FAS does not specifically recommend or endorse this or any other software, we only provide information that is generally available.

StarNet

StarNet is a software package that allows you to split your image into stars and the target nebula. It is integrated with PixInsight and with Siril.

Downloading StarNet++ to a Mac for use in Siril is somewhat problematic. Here is how I was able to get it to work (good luck).

  1. Download the command from here: https://starnetastro.com/wp-content/uploads/2022/03/StarNetv2CLI_MacOS.zip
  2. Open the zip file (StarNetv2CLI_MacOS.zip)
  3. Save the folder (StarNetv2CLI_MacOS) somewhere where you can find it. I saved it with other Applications.
  4. Open terminal on your Mac. You should find terminal in your applications window.
    • run the command: cd /Applications
    • run the command: cd StarNetv2CLI_MacOS
    • run the command: chmod u+x starnet++
  5. Open Siril.
  6. Click on the three line “burger icon” in the top right corner.
    • Choose Preferences.
    • Choose Miscellaneous.
      • Enter StarNet++ as the executable
      • Enter lib as the gnuplot installation directory (I’m not sure about this choice?)
      • Click Apply
  7. Open an image in Siril.
  8. Choose Image Processing -> Star Processing -> Starnet Star Removal.
  9. You will have to grand permissions for your Mac to run three executables. For each.
    • A message will display that says it is dangerous to run this file and your Mac won’t allow it. Click the left button. Then:
      • Open System Settings.
      • Open Privacy & Security.
      • Scroll down to the bottom.
      • Allow your Mac to run the executable.
  10. At this point StarNet++ should function normally.

Follow these steps at your own risk.
Please make sure you understand what you are doing when loading this software on your Mac.
FAS makes no guarantee that the installation process outlined here will work correctly.

Please note that FAS does not specifically recommend or endorse this or any other software, we only provide information that is generally available.

Siril

As you get more comfortable with processing your images, you might take a look a Siril, which is a free open sources astro image processing package. A workflow using Siril is as follows (this is very preliminary – more to come here). Note that some of the documentation refers to Siril 1.4, which has not been released (as of December 1, 2024).

Siril Workflow

FINDING SCRIPTS: If necessary, locate the “Without” and Seestar scripts. They are not visible by default.

To locate your scripts, click on the “burger” (three lines) icon in the top right. Choose Preferences and then choose Scripts to see your scripts and their location.

  1. Find the location for your scripts. It should be /user/“your name”/Siril/Scripts.
    • Click on the burger (three lines) in the top right.
    • Click on Preferences.
    • Click on Scripts.
  2. Go here.
  3. Click on the script.
  4. Download it to /user/”your name”/Siril/scripts.
  • The OSC_Preprocess script performs the following steps.
    • convert bias -out=../process -> stack bias rej 3 3 -nonorm
    • convert dark -out=../process -> stack dark rej 3 3 -nonorm
    • convert flat -out=../process -> calibrate flat -bias=bias_stacked -> stack pp_flat rej 3 3 -norm=mul
    • convert light -out=../process
    • calibrate light -bias=bias_stacked -dark=dark_stacked -flat=pp_flat_stacked -cfa -equalize_cfa -debayer
    • register pp_light
    • stack r_pp_light rej 3 3 -norm=addscale -output_norm -out=../result
  • The Seestar_Preprocessing script performs the following steps.
    • link light -out=../process
    • calibrate light -debayer
    • register pp_light -2pass
    • seqapplyreg pp_light -filter-round=2.5k
    • stack r_pp_light rej 3 3 -norm=addscale -output_norm -rgb_equal -out=result
    • mirrorx_single result

SCRIPT PRE-PROCESSING: If you are starting with individual light frames and want Siril to stack them follow the steps below.

  1. Create a folder for Siril with four subfolders (Biases, Darks, Flats, Lights). Just create a lights subfolder if you don’t have calibration frames (and when you have Seestar images).
  2. Load your image frames into the appropriate folders.
  3. If you already have master calibration files (such as those from an ASiair), place them in the appropriate folder (Biases, Darks, and Flats). Duplicate them so there is more than one of each.
  4. Click the Home button and point to the folder where Siril will find the images (the subfolders) and place the results.
  5. Run the appropriate script.
    • OSC_Preprocess if you have a set of all three types of calibration frames.
    • OSC_Preprocess_WithoutDark if you don’t have individual dark calibration frames.
    • OSC_Preprocess_WithoutDBF if you don’t have individual calibration frames.
    • Seestar_Preprocessing if you have lights (and no calibration frames) from a Seestar.
  6. Open the result.fit file (in the process folder) or the file with information about the stacked image (e.g., M##_300x10sec_T10degC_yyyy_mm_dd.fit) and process it (below).

MANUAL PRE-PROCESSING: As an alternative, you can manually pre-process your light frames.

  1. Create a folder for Siril to place the results (e.g., process).
  2. Click the Home button and point to the folder you created in step 1.
  3. Conversion: Click + and then go to your folder containing your light frames, highlight them and click Add. Specify a Sequence Name (e.g. results). Check Debayer. Click Convert.
  4. Calibration: Specify the location of your calibration frames (fits, biases, and darks). Skip this step for Seestar images (lights only).
  5. Registration: Choose Global Star Alignment (deep-sky) or Two-pass Global Star Alignment (deep-sky). Click Go Register. The registration stars will appear in the image to the left.
  6. Plot: Switch to “AutoStretch”. Click on the “Frames” icon in the lower right. Review the frames – click on the space bar or uncheck the line to remove any “bad” ones.
  7. Stacking:
    • Choose the Stacking Method: Sum stacking or Average stacking with rejection.
    • Choose Image rejection: all (include all frames) or selected (include only frames selected in the previous step).
    • Click Start Stacking.
  8. Continue on and process the stacked file (below).

START WITH A PRE-PROCESSED IMAGE: If you have a previously stacked tiff or fit file produced by Seestar, ASIStudio, or another package follow these pre-processing steps.

  1. Create a folder for Siril to place the results.
  2. Click the Home button and point to the folder you created in step 1.
  3. Open the previously stacked file and process it (below).

INTIAL PROCESSING (within Siril): Begin processing your previously stacked file or your results file in Siril.

  1. Switch your view from Linear to Autostretch, which will stretch the file so you can see what it looks like. It might have a lot of green (RGGB format) – if so, run remove Green Noise.
  2. Right mouse click and choose Rotate&Crop to crop the image and remove the stuff on the edges.
  3. Perform Background Extraction. This is always done against the original image – so you can experiment with multiple passes.
    • Click Generate.
    • If necessary make adjustments to better cover the background. Then click Generate.
      • Smoothing: reduce this to remove more gradients. Increase it to remove less gradients.
      • Grid Tolerance: reduce or increase the background coverage. Increase this if light areas are not included in the background. Decrease this if too much of the target object is included in the background.
      • Samples per Line: Adjust this to decrease or increase the number of background squares.
    • Manually adjust the background area.
      • Right mouse click to remove background squares over your object.
      • Left mouse click add background squares in the background.
    • Click Compute Background.
    • Click Apply.

INITIAL PROCESSING (within GraXpert): Begin processing your previously stacked file or your results file in GraXpert. Most people recommend using GraXpert.

  1. Loading: Load your previously stacked file or results file to GraXpert
  2. Crop: Crop the image and remove the stuff on the edges.
  3. Perform Background Extraction.
    • Choose the Background Extraction AI-Model (advanced options over on the right).
    • Choose the Background Extraction Interpolation Method.
      • RBF is the same (somewhat manual process) as Siril.
      • AI uses the (automatic) AI-Model.
    • (RBF Only) Adjust the settings.
      • Points per Line: Adjust this to decrease or increase the number of background squares.
      • Grid Tolerance: reduce or increase the background coverage. Increase this if light areas are not included in the background. Decrease this if too much of the target object is included in the background.
    • (RBF Only) Click Create Grid.
    • (RBF Only) Manually adjust the background area.
      • Right mouse click to remove background squares over your object.
      • Left mouse click add background squares in the background.
    • Adjust Smoothing: reduce this to remove more gradients. Increase it to remove less gradients.
    • Click Calculate Background.
  4. Denoising:
    • Choose the Denoising AI-Model (advanced option over on the right).
    • Denoising Strength: Reduce it for less of an adjustment and increase it for more of an adjustment.
    • Click Denoise Image to reduce the noise in your image.
  5. Saving: Save your results.
    • Choose the file type (32 bit Fits).
    • Save either the
      • Processed (pre-stretched) file or
      • Stretched & Processed file (if you don’t want to stretch it again in Siril).
  • Stretch your image using 10 Bg, sigma 3 to view the results as you are going through this work flow. Use 30 Bg, sigma 2 to really bring out the gradients.
  • You can choose to view the results for each of these steps by selecting the appropriate image at the top of the screen.

FINAL PROCESSING (within Siril): Continue processing your image in Siril.

  1. If necessary, switch your view from Linear to Autostretch, which will stretch the file so you can see what it looks like
  2. Perform Color Calibration -> Photometric Color Calibration.
    • Click Get Metadata from Image to populate information about the image including the focal length and pixel size.
    • If metadata from you image is not available, search for your object from the Sinbad catalog.
    • Click Force Plate Solving?
    • Click Apply and Siril will match the color of your object to the Sinbad catalog.
  3. (Optional) Run Star Processing -> StarNet Star Removal. This will create two files: a starless file and starmask file. You will continue to work with the starless file.
    • You view should be Autostretch
    • Check Pre-stretch linear Image
    • Check Generate star mask.
    • Click Apply.
  4. Stretch the image. Switch your view back to Linear from Autostrech. If using a Starless image, make sure to Save when finished.
    • Option 1: Auto Stretch Your Image using the Histogram Transformation.
      • Run the Histogram Transformation. Click on Clip % to apply the autostretch algorithm. Click Apply. This gives you a staring point. However, there are a couple issues with this: Galaxies tend to look too bright, and backgrounds tend to look too light.
      • (Optional) Manually make some more adjustments as needed.
        • Click on the + to zoom into your histogram.
        • Move the middle slider (midtones) a short way to the left or right. Click Apply. Repeat until the object looks good. Don’t go too far to the right otherwise the object (particularly a galaxy) will be too bright.
        • Move the left slider (shadows) to the right toward the histogram. Repeat until the histogram is over on the left and the flat area is gone. This darkens the background.
    • Option 2: Manually Stretch Your Image using the Histogram Transformation.
      • (Optional) Run the Asinh Transformation. Move the Stretch factor to the right until you see a faint image of your object. Click Apply.
      • Run the Histogram Transformation. Use the middle (midtones) and left (shadows) sliders to manually stretch the image.
        • (Optional) Hit the + button once or twice to zoom in a little.
        • Move the middle slider (midtones) a short way to the left. Click Apply. Repeat until the object first comes into view and then looks good. Don’t go too far otherwise the object (particularly a galaxy) will be too bright.
        • Move the left slider (shadows) to the right toward the histogram. Repeat until the histogram is over on the left and the flat area is gone. This darkens the background.
        • Repeat the above two steps by moving the left slider to the right and the middle slider back and forth. This spreads the histogram out and results in a better balance.
    • Option 3: Manually Stretch Your Image using the Generalized Hyperbolic Stretch Transformations.
      • More to come here.
  5. (Optional & If Stars were previously split out into a separate file) Stretch the Starmask file. (more to come here)
  6. (If Stars were previously split out into a separate file) Run Star Processing -> Star Recomposition to combine the Starless and Starmask files.
    • Specify your Starless file (which you have been working with) on the left. (Optional) Adjust the Stretch factor a little.
    • Specify your Starmask file on the right. If not done in the previous step, adjust the Stretch factor (ln(D+1)) for the Starmask file.
      • Choose Advance and then Generalize Hyperbolic Transform. This gives the stars a more rounded look.
      • Move the slider to the right to include the original stars (maybe .7?).
      • Keep the slider a little to the left to diminish the stars (maybe .5?).
    • Click Apply.
  7. Additional Optional Steps (If necessary)
    • Remove Green Noise. You might do this earlier in the process?
    • Perform Noise Reduction, although this doesn’t always work well.
    • Adjust the shape of the stars using Deconvolution.
    • Adjust the Color Saturation to enhance the colors. This can be used to artificially enhance the shape of a nebula.
      • Set Amount to around .4 (maybe).
      • Set Background Factor to around 1.25 (maybe). This removes the saturation from the background.
    • Stretch your image using the Asinh Transformation. This can be used to darken the background.
      • Choose (maybe) 10 to 150 for the Stretch Factor. However, this often gives a very white washed out image.
      • Choose (maybe) .01 to .04 for Black Point. This might be useful to get a darker background.
      • Click Apply.
      • (maybe) Repeat Stretching your image using the Histogram Transformation in the previous step.
  8. Save the final image as a 16-bit or 32-bit fit, png, jpg, or tif file.
    • Right mouse click and … , or
    • Use the “down” button to the right of the SAVE button on the top right. The image will be saved in the home folder.

Siril References

A Few Details

Siril & Seestar Images

Siril Workflow

Siril Release 1.4

Siril Documentation & Tutorials

Please note that FAS does not specifically recommend or endorse this or any other software, we only provide information that is generally available.

Astro Pixel Processor (APP)

Astro Pixel Processor (APP) is a software package you might consider as an alternative to Siril. (More to come here.)

Please note that FAS does not specifically recommend or endorse this or any other software, we only provide information that is generally available.

Pixinsight

PixInsight is a software package that seems to be gaining use among our members. (More to come here.)

A Few References

PixInsight Documentation

PixInsight Workflow

Add-Ons

Please note that FAS does not specifically recommend or endorse this or any other software, we only provide information that is generally available.

Gimp

Gimp is an open source (and free) alternative to Photoshop.

Please note that FAS does not specifically recommend or endorse this or any other software, we only provide information that is generally available.

Other Software Packages

There are several other software packages that can be used to process your astro-photos.

Please note that FAS does not specifically recommend or endorse any software, we only provide information that is generally available.