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. We have information elsewhere about the various Deep Sky objects visible in the night sky. 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.

Astrophotography used to be rather complicated and expensive. We’ve provided some general information below. However, today, there are some ways to simplify the whole process. ZWO’s ASiair devices make operating a complex setup much easier. There are also several “smart” telescopes that take some great images, including those from ZWO (Seestar S30 & S50) and Dwarf Labs (Dwarf 3) that are relatively inexpensive. Just like regular visible astronomy, filters can be used.

However, you will find that taking the images is just a start. There is a great deal to understanding about how to process your images. Fear not! We have some information for you.

  • The section on Image Processing will introduce you to the various terms and techniques. Calibration frames can help remove some of the distortions that might come from your equipment. In almost all cases, it is best to take a series of images (frames) and then stack them to yield a combined final image. Then there are various techniques that can be applied to further process and improve your images. If this is too much, there is a simplified workflow at the end.
  • Most folks that process their images utilize various software packages that are available. One of the most common is Adobe’s Photoshop. This is a generic photo application, and as such, we won’t provide much information about it here. Today, it seems that most people use one of three packages: Siril (which is free), Astro Pixel Processor, or PixInsight – with PixInsight becoming more and more the choice. DeepSky Stacker is used by many to stack their frames. GraXpert and StarNet++ are used to enhance Siril and possibly other packages.

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.

Astrophotography in General

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 (Astrophotography YouTube Channels)

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.

The Optolong L-Quad Enhanced filter can replace the UV/IR Cut Filter, but is more generic and can be used for nebula as well.

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

Dithering

Dithering is a process where the frame of your telescope (or camera) is moved slightly to adjust the area of the sky being captured. This shifts the stars to a slightly different place to avoid the over sampling of ”Hot Pixels” and noise. It can be thought of as randomizing errors so they don’t build on each other.

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

This section is very much a work in progress – much more to come.

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. These Fit files are typically 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. The simplest way to do this is by performing a stretch, which multiplies by 4 to stretch a 14 bit (0 to 16,383) image into a 16 bit (0 to 65,535) image.

However, you can do more than simply multiply by a number. Generally, when you are stretching an image, you start with a linear view. This is the way the camera records the information, but not the way our eyes see it. With the initial linear view, most of the useful information in the image is over on the left hand side. When you stretch the image, you are adjusting the pixels so that most of the information is shifted to the midtones, and as such, becomes more visible.

An important tool used when stretching your images is the histogram.

Your image is composed of pixels, which have a value that defines the brightness of each. The allowable values depend on the bit size. Each pixel is assigned a number corresponding to its brightness (or three numbers, RGB, if in color). The larger the number, the brighter the pixel.

  • 8 bit images have values from 0 to 256
  • 14 bit images have values from 0 to 16,383
  • 16 bit images have values from 0 to 65,536

The histogram is displayed on a graph with two axes (horizontal and vertical).

  • The allowable brightness range of the pixels contained within your image is displayed across the horizontal axis from darkest to lightest. Its range depends on the bit size of the image.
  • The vertical axis (and the histogram) shows the number of pixels with each level of brightness.

Initially, with a linear view, there are many dark pixels – so the distribution is skewed to the left and the image is mostly dark. When you preform a stretch, the resulting histogram shows the distribution of brighter pixels (now more in the middle) and is shaped like a standard bell curve.

  • The pixels for the sky are toward the left (darker) and the stars (brighter) to the right.
  • Your nebula or galaxy is represented by the midtones and the peak of the histogram somewhere in the middle.
  • The wider the histogram (the larger the standard deviation), the greater the contrast in your image – and the greater the noise in your images.
  • If your histogram has a flat area to the left, this means that none of the pixels have the darkest values. It could be because the sky is never completely black and there is some degree of light pollution. Typically, you can remove this area and shift the histogram all the way over to the left to darken the sky. Don’t go too far and “clip” some of the useful information.
  • If your histogram is too far to the left, your image will be dark and underexposed.
  • If your histogram is too far to the right, your image will be washed out and overexposed.

A Few References

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.

Deconvolution

Deconvolution is a method of removing “blur” from your images. It is applied in two steps using a linear (non-stretched) images.

  • First, determine the point-spread function (PSF), which is a measure of the amount of blur. This is usually done by looking at a star, which should be a point source of light – but usually is not.
  • Second, the PSF value is used to “correct” the image. Typically, an algorithm is applied. the Richardson-Lucy deconvolution algorithm is the usual choice. It is applied through a series of iterations, which you specify. If done well, the stars will look better. If done poorly (typically too many iterations), you will see dark areas around the stars – this means you went too far.
Drizzle

Drizzle is a method used to increase the sharpness of your images. It is a processes initially created for the Hubble Telescope. The main idea is to take (under-sampled) images, reduce the pixel size, and fill in the image with more pixels.

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).
Generic 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 flats).
  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. Extract the Background to remove the gradients.
  8. Remove noise from your image.
  9. Perform a “Color Calibration” to correct the color of the object.
  10. Remove the excess Green noise.
  11. Perform Deconvolution to reduce the blur in your stars.
  12. (Optional) Remove the stars from the underlying object and background
  13. Stretch your image.
  14. Adjust the Color Saturation to enhance the colors.
  15. Adjust the shape of the stars using Deconvolution.
  16. (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 fully functional astro-processing packages. Gimp is a free 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.

Go here for an ASIDeepSack workflow =>

ASIDeepStack Work FlowDownload

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.

Go here for help in downloading StarNet++ for a Mac =>

Downloading StarNetDownload

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

Astrosharp

Astrosharp is a free software package that will sharpen your astro-images. It runs only on Windows – sorry nothing for Macs at the moment.

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 found below (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

In general, a workflow for Siril involves the following steps: Stack your images (Preprocessing usually with a script) -> Crop your image -> Remove Gradients by Extracting the Background -> Remove Noise -> Color Calibration -> Remove the Stars -> Stretch the Starless Image -> Recombine the Stars. Two additional steps include: Remove Green Noise & Adjust the Color Saturation – often done on the starless image.

Go here for a detailed Siril workflow =>

Siril WorkflowDownload

Siril References

References: A Few More Details

References: Working with Seestar images in Siril

References: Siril Workflows

References: 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 and in the world of astrophotography. (Much more to come here.)

A Few References

PixInsight Workflow

PixInsight Documentation

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.