Introduction to Astrophotography

Regular news about alignment of planets, their form in the sky, their closest approach to Earth and related other news that I used to read in the newspapers every year made me think about knowing more about them. They inspired me to see them with my eyes. After building my own house, I had that opportunity to look at the sky unhindered from its terrace. I was pleasantly surprised that I didn’t need a telescope to see the planets Venus, Mars and Jupiter. Even Saturn could be seen, though like a speck. I was very eager to see bands of Jupiter and rings of Saturn. Hence, I bought Meade DS2114-S reflector telescope, sometime around 2005.  Even though it is a 5.5” telescope, I could barely see the bands or rings. I was disappointed. I didn’t use it for many years. Surely, I didn’t know how to observe planets properly with a telescope at that time. The situation didn’t change even now because I’m more interested in deep sky objects than planets. Aren’t planets very close by?!

When I became free from my office activities, I wanted to use the telescope once again. But I found that its GOTO functionality, a feature to point telescope automatically to any space object, stopped working. No way to get it repaired as I don’t think there is any company or anybody to repair like there are street corner repair shops and authorized service centers for two-wheelers and cars. It was bought about fifteen years ago. Can’t ask the shop from which I bought to repair or replace it. By this time, prices of telescopes almost doubled or tripled! To reduce expenditure, I bought only a mount without tripod as I wanted to use tripod of my earlier telescope. Cost of the mount, without telescope and tripod, was more than double the cost of the fully functional advanced Meade telescope that I bought a long ago!

In this blog, I will explain what equipment I bought, stores I bought from, how to take photographs of celestial bodies and how to process them to get beautiful images. However, please note that you don’t need to follow my approach of buying telescope parts one by one if you are new and you don’t have any equipment or you have only a camera; you may purchase tripod, mount and telescope tube as part of one package to reduce time to use it!

Equipment

There are many parts of the equipment used for observing and photographing celestial objects such as planets, nebulas and galaxies. A tripod is necessary. It should be sturdy and should stand the weight of mount, telescope and other related accessories. A mount is the equipment that is used to mount telescope and add related accessories such as finder scope, red dot finder, guide scope, camera and counter-weights. The mount itself is fixed over the tripod using a knob. Unless you buy all parts as a single package, you need to make sure that the mount you buy can handle the weight of telescope and other equipment, tripod is compatible with the mount and it is capable of handling all load. Various vendors sell tripods and mounts with various load capacities.

For photography of celestial objects, you need to buy a telescope with a mount that tracks the objects automatically. Tracking is required to make telescope always point towards the desired object while Earth rotates about its axis. The mounts with tracking capability compensate for the rotation of Earth to make the objects in the viewing field of telescope almost fixed.  There are primarily two kinds of mounts – altazimuth mounts and equatorial mounts. There are some other kinds of mounts but they may not be quite popular. You need to decide which kind of mount of telescope you want. My first telescope was altazimuth mount. The current mount I use is an equatorial mount. I bought equatorial mount because that’s what most photographers seem to use, and it has a few advantages over altazimuth mount.

There are also multiple kinds of telescopes (tubes with lenses and/or mirrors) – refractor and reflector and some hybrids. You have to decide which one you want. Refractors are costlier compared to reflectors but small and lighter. You get a reflector with bigger aperture, an important parameter for getting quality pictures, for the same cost of a refractor. My first telescope tube was of reflector type and so I bought a refractor only because it is very small!  

Mount

I bought iOptron SkyGuider Pro Camera mount with I-Polar. Here is its image:

Though title of the mount says it is for camera, it can be used with small refractor telescopes such as RedCat 51. I bought only the mount because I already have a tripod of unused reflector telescope. I-polar is a camera inside the mount. It is used to do polar alignment of the mount by looking at the pole star displayed in a laptop.

Note:- This mount is definitely not suitable for all kinds of telescopes. You can't use this with heavy telescopes.  So, you need to select a mount based on required payload capacity you need,  Since a mount is usually a onetime investment in your hobby, go for the best mount that can handle required weight of telescope and other accessories such as finder scope, guide scope, main camera and guide camera.

Telescope

I wanted to use RedCat 51 refractor telescope because I saw a photograph of the Andromeda Galaxy taken by somebody with the refractor and the mount! It was one of the less pricy refractor telescopes compared to some costlier ones.  Further, it is like a camera lens, small and not so heavy. It can be used to take photos of birds and landscapes. Later, I found that it is not so light, after all. It weighs about 1.3 kg.

It has a focal length of 250 mm, aperture 51 mm and focal ratio f/4.9. If you have money to spend, go for a higher focal length and aperture telescope.

Note:- Again this refractor is one of the lowest end of refractor telescopes. You may be able to see or image Andromeda galaxy, but you can't image some small DSOs even though they are in the Milky Way, which means they are quite near compared to Andromeda. So, go for a refractor that has bigger aperture and focal length, say, a refractor with aperture more than 80mm. It couldn't show me the rings of  Saturn.

Regular Camera

You can take pictures of planets, nebulas and galaxies using a DSLR or mirror less cameras too. Or, you case use a dedicated astrophotography cameras attached to telescopes. While studying for camera to buy, I realized how costly they are! A good entry level DSLR for astrophotography runs into lakhs of rupees; at least a lakh. Good cameras used by some well-known amateur photographers don’t seem to be available in India. And the one used by some cost a few lakhs of rupees. So, I thought of buying a regular camera as I am just starting the hobby. Before buying any camera,  me and my son tried to photograph Jupiter in mid-2021 when Jupiter was close to Earth. To my surprise, we could capture picture of Jupiter and its four moons using regular Nikon Coolpix camera that I bought for my son when he was in school. If I remember, I spent about ₹30k for the camera. But it started malfunctioning while selecting settings. In any case, it can’t be attached to telescope. So, I had to buy a new camera. I didn’t want to buy dedicated camera because it can’t be used for regular photographs after spending thousands of rupees for the camera. Then a question came about the brand. Since the Nikon Coolpix camera ran into problems, decided to buy a Canon camera. My study indicates that most photographers use cameras of one of these brands for astrophotography. Another big question was whether to buy a DSLR or mirrorless camera. Mirrorless cameras are supposed to be lighter and they are in-things. But you get variety of accessories for DSLR cameras as I was told by camera shopkeeper. I bought Canon M50 Mark II camera with the intention of using it for both astrophotography as well as regular photography. It's a mirrorless camera. It came with a 15-45 mm lens. It was about ₹60k. Surprisingly it is very light. It's not really designed for astrophotography as such. Here is its picture:

Just having a camera is not sufficient. You need some parts to connect the camera to the telescope. Note that you don’t use normal lens that came with your camera while using the telescope. So, don’t buy additional lenses unless you know what you want to use them for. In fact, you can just buy camera body if you want to use it first with your telescope and buy lenses later as per your requirement.   You can’t directly attach your camera to the telescope. This is because cameras come with a flange to attach lenses to the camera body, whereas the telescope eye piece holder comes with threads or a couple of screws to hold an eye piece inside it. Hence, you need to buy T2-mount adapter/ring to connect camera to the telescope. Here is the camera without lens, exposing its flange:

To connect this to telescope, I needed appropriate T2 mount that can be attached to the camera. Here is my T2-mount adapter:

The bottom part can be directly fixed to the flange of the camera. The top part adapter is meant for 1.25” telescope end. It is not useful for 2” telescope such as RedCat 51. Hence I had to buy a 2” telescope to T2 adapter such as the following:

Unfortunately, I am not able get sharp focus with the T2 mount and the adapter. I need an adapter that is much thinner than the above adapter such as the following M48-M42 adapter ring:

Since I don’t have this thinner adapter, I'm not able to use the Canon camera with RedtCat 51. As of this writing, I'm waiting for the adapter to arrive at my door!

Note:- Don’t buy this camera for astrophotography! One reason is that its battery has to be taken out from the camera and put in a separate charger to charge it. Since you may have to leave the camera attached to the telescope for an hour or a few hours for astrophotography, you will have problem in replacing the battery.  So, buy a camera that can be charged without removing its battery from the camera. 

Dedicated Camera

Getting any part such as an adapter to connect camera to the telescope takes time for two reasons. The first one is the time taken to identify the right component that fits your telescope or camera and the second is time it takes to reach you once you order. There are a few vendors in India who sell the telescope and camera related components. All most all are made in China! Now I understand why the country has become a manufacturer of the world!! Sometimes, specifications of parts on e-commerce sites are very vague. Despite this, you may want to try your luck by purchasing it as you can’t wait for another few weeks to try your telescope! If you buy entire telescope package with tripod, mount and the telescope tube, you may face less problems in attaching your camera to the telescope. Since I was not able to focus anything, including even the Moon, I could not use the regular camera with Red Cat 51 (But I used it with reflector telescope to take pictures of the Moon). Hence, I wanted to try a cheap dedicated camera.  Most of the amateur astronomers mentioned using dedicated camera from ZWO. So, I went for ZWO ASI224MC color camera. Purchased it from GoScientifics.com in Madurai for ₹19k! It looks like this:

You need to unscrew the black lens and attach to the camera with a T adapter that fits your telescope. In my case, I needed a T adapter having  one end with M48 internal threading for attaching to RedCat 51 and the other end with  M42 external threading to attach to the camera. There is a link at the end of the article on what is M48 or M42 threading.

As the resolution of ASI224MC is very low, I bought another camera ASI071MC that is a 16MP dedicated camera having a big sensor compared to that of ASI224MC. 

With this camera, the positioning of telescope towards the DSOs became easier as it could capture large part of the sky. Now I use the earlier camera for auto guiding. Again, there are much better cameras than ASI071MC for higher price and also there are less pricey ones that are more or less as good as this camera.

Finder scope or Red dot finder

When there is no camera attached to the telescope, you look through an eyepiece of the telescope to locate interesting objects in the sky.  Different kinds of finder scopes/red dot finders are as following:

If you want to take photographs, camera has to be attached to the eyepiece holder of the telescope. Once that is done, you can see objects either on LCD screen of DSLR or mirrorless camera or a laptop screen if you are using a dedicated camera. Once a camera is attached, it may become difficult to point the telescope towards an object as you lose the means of seeing through telescope! Hence, one can use either a finder scope or a red-dot finder. Finder scope is a small telescope with wide field so that you can see a large area of sky and find your object of your interest and center it in the finder scope field of view. Any minor adjustments can be done by looking at the object in the camera or laptop screen. The finder scope may have a cross-hair to pinpoint it towards the object. Another option is red-dot finder which shows a red dot, cross hair,  red dot with circle, etc.,  in the sky. You have to attach the finder scope or red-dot finder to the telescope parallel to its tube. Once it is powered on (uses button battery power), you see a red dot or cross hair through a lens in the sky. You have to move your telescope such that the red dot or cross hair points to the object of interest in the sky. Once this is done, you can see the object either through telescope if camera is not attached, or camera LCD screen or laptop screen and do any finer adjustments to keep the object in view. You can attach a red-dot finder in addition to or in place of finder scope. When objects are at zenith, the telescope tube will be almost perpendicular to the ground. In such situations, finding an object using finder scope or red-dot finder may pain your neck. Hence, you may want to use a right-angle finder scope, instead. But then pointing to the object will become a little tricky!

Night Head Torch

Since we are going to photograph objects in the sky during night, dark time, you need some light to set-up telescope equipment that has now become costlier! You don’t want to drop your telescope, camera, adapter or injure your feet with any counter-weight by mistake in the dark nights! You can use head torch you might have already used for trekking. It’s available in Decathelon shops. A photograph of the one I use is as following:

This can be worn around your head so that your hands are free to set up the telescope equipment. The head torch shown in the figure can throw light in red as well as white and with required luminance.

It’s good to have this but definitely not essential if you can manage with some other light source.

Laptop

You definitely need a laptop if you use a dedicated camera for capturing images of celestial objects. You may not need if you use DSLR or mirrorless camera. Make sure it is fully charged or a power source is close by. You may need a power source for your camera. You may also need power source for dedicated camera. High-end dedicated cameras need power to cool its sensor, even in the night, to reduce noise to get better pictures. In case of laptop, make sure you already installed appropriate camera image capture software such as ASI Studio from ZWO for its cameras.

Set-up

Attach mount on the tripod. Attach telescope to the mount. In my case I attach the telescope to the declination bracket of the mount with a counter-weight to balance the telescope. Make sure the telescope and/or camera won’t hit the tripod legs and break. After all, they are quite expensive!

 

The declination bracket came with my iOptron SkyGuider Pro mount. Since the telescope is at one end of the declination bracket, you need appropriate weight(s) at its other end attached to a counter-weight rod. Both the counter-weight and rod came with the mount. But I had to buy another 1.3 kg counter-weight to offset added weight of auto guide-scope, its camera and red dot finder (not shown in the picture). When powered on, the declination bracket moves in the clock-wise direction to offset movement of Earth to keep objects of sky in the viewing field of the telescope, if not for the entire duration of your photography, but at least for some time. You may need to adjust the telescope position once in a while or use a guide-scope and guide camera (not shown in the picture) to correct course of  tracking.

Polar Alignment

To track objects of sky while Earth rotates, you need to do polar alignment of your mount before you point your telescope to the desired object in the sky and take pictures. What it means is that the mount should point to pole star or north star. Celestial pole is very close to it. For that, the mount provides some mechanism. Either manually look for the north star from the center of the mount and adjust its azimuth (along the direction of horizon). Its declination can be set to the latitude of your location. Some mounts provide another camera (my mount provides), either at its center or on the side, and provide software and a cable to connect to laptop so that you can do polar alignment by looking at the laptop screen.

In my case, north star is not visible due to a new building that came up in my neighborhood! So, I’m not able to use I-polar camera of the mount. I do approximate polar alignment using Google Sky Map and Polar Alignment app.

Software

Dedicated Camera Driver

Currently I use 1.2MP dedicated camera. It is ASI224MC colour camera. But didn’t see precise colours. Its drivers are available from ZWO company website.

Photograph Capture Software

ZWO also has a suite of free software for capturing images from its camera. It is called ASI Studio. You can download it from ZWO website.

Stacking Software

We take not just one or two photographs of objects of the sky but take a few hundreds to capture a lot of light from the objects. If the object is fixed, just taking one photograph would have been sufficient. As Earth rotates and tracking is not so precise, we can’t expose camera for more more than a few seconds or a few minutes at a time. So, taking so many pictures and stacking them is essential. Stacking software generates one final photograph from hundreds of photographs. The software also removes inherent noise generated by the camera itself, noise due to heating of camera and images of dust particles that might have settled on the lenses of telescope of camera. There are free and paid software for stacking photographs.  I use free software called Deep Sky Stacker (DSS).

Graphics or Image Editor

The final image generated by stacking software needs editing using software such as PhotoShop or GIMP.  Unless you edit and change image parameters, you may not be able to see the image you captured!

Process of Taking Photographs

Polar alignment of your mount is pre-requisite to have as much camera exposure time as possible. It is assumed that the mount you are using is capable of tracking celestial objects. Some mounts have various slewing rates to track moon, planets and stars. For photographing nebular and galaxies, you should set the slewing rate to stars, called 1X. The first thing to do is to look for the object you want to photograph. You can use an app such as Google Sky Map and search for the object. Then move your telescope in the required direction to get the object in the field of telescope. Use finder scope or red-dot finder to keep the object at the center of the telescope. If your telescope has GOTO functionality, you might have got a hand-held controller. Use this device to move telescope to the desired object. But you need to see the camera LCD screen or laptop screen to make sure the telescope points to the object.

The next thing is to adjust focus of your telescope/lens so that you get sharp picture. Camera lenses will have focus rings for the adjustment. Telescopes will have helical focuser or some other tool for focusing. Stars should look sharp. Make sure tracking is on your mount while doing this.

Set up suitable exposure time. The more exposure time the better the picture will be. If polar alignment is poor or your mount tracking precision is not great, you won’t be able to get good pictures with a lot of exposure time. The stars should be round and not like thick lines.  So far, I couldn’t use more than ten seconds of exposure time and usually I set just three seconds! I am not able to do precise polar alignment because a building obstructs view of pole star from the terrace of my house.

Use appropriate ISO level (term used for regular cameras) or Gain (term used for dedicated cameras) of camera. More ISO/Gain, the brighter the picture will be but also more grainer. Gain that I use for the dedicated camera ranges from 300 to 500. For my mirrorless camera, I generally use ISO level between 800 and 16,000. These are for conditions of my environment on the terrace of my home. You may need different values suitable for your environment. It all depends on the seeing conditions (light pollution, presence of moon, etc.)

Set up your camera or capturing software on your laptop to capture images at given interval. They allow you to setup exposure times, ISO levels or Gains. If the stars don’t look round, image stacking software is likely to fail. So, adjust focuser of your camera or telescope  to make sure you get good pictures with round stars. If you are not able to focus to get sharp stars means required back focus between your telescope and camera is not right. Either you have to reduce distance between them or increase by adding or removing various spacers. Some DSLR and mirrorless cameras come with an intervalometer gadget – wired or wireless – for capturing pictures without touching the camera to avoid vibration of the camera while taking pictures. In my case, my mirrorless camera didn’t come with an intervalometer. So, I use an Android app developed by Canon. Still, I can’t setup interval or number of pictures to be taken. I have to manually click a button on the phone/laptop to capture an image. This will be a pain to capture hundreds of pictures you need for stacking. Fortunately, I can set up interval and number of photographs to be taken for my dedicated camera. Consider these points before purchasing a camera. Once this set-up is done, start capturing a few hundreds of pictures. Make sure your object doesn’t go out of view on the LCD or laptop screen. If it goes out of the center of the screen a lot, stop capturing and adjust your telescope to point to the object again and continue to take pictures. These pictures are called light frames.

How many pictures you have to capture?  It depends on exposure time and number of pictures. I see people taking pictures with a total exposure time of  up to an hour or a few hours. Small exposure time means you have to take a greater number of light frames. Some photographers use exposure time as big as five minutes. For this kind of exposure, polar alignment has to be precise and autoguiding may need to be used (for a later article!). Fifty light frames might be good in this case. If it is small such as three seconds, you may have to take at least a few hundred light frames, say 200 or more.

Not only light frames of actual object, you need to take some other kinds of photographs. These are called dark frames, flat frames and bias frames. Dark frames are photographs taken by closing lens or telescope by capping it. These photographs contain noise introduced by the sensor when it heats up while taking light frames. So, you should grab these photographs with the same exposure, ISO or Gain levels and in the same environment.  Flat frames are photographs taken while its lens is lit with uniform bright light so that the photographs contain information about any dust particles that might have settled on the lenses. The photographs can be taken by putting a white cloth or t-shirt over the lens or telescope opening end and pointing it towards a light-source such as laptop screen. Or, put a  mobile phone or tablet with bright screen over the lens/tube opening. Stacking software eliminates the information about dusts while generating one image from the light frames. The last kind of frames are taken with as minimum exposure time as possible for the camera. These photographs are taken by capping its lens or telescope with the same ISO/Gain levels. This is to get inherent noise generated by the camera sensor in the photographs.

How to Process Photographs

To generate one final image from light frames, dark frames, flat frames and bias frames, you have to use software such as DSS (Deep Sky Stacker). There are many such software packages available for free as well as for a price. I use DSS because it is free and found an article that explained how to use it clearly!

What you have to do is, load all these four kinds frames into DSS, register them and stack them. Depending on the number of frames, it may take a few minutes or maybe hours to complete its job of stacking and generating one image.  The image it generates may look pretty bad initially! For example, the stacked images of Orion and Flame nebulas are as following:

Orion nebula image shows the nebula but Flame nebula is not at all visible in its stacked image. Therefore, just stacking is not sufficient but it needs a bit of postprocessing.

Postprocessing

Tools such as PhotoShop, PixInsight and GIMP are used for this job. The tools allow you to adjust various parameters of the image such as color levels, light levels and many other features.  The tools also allow you to crop the object of interest to the center and remove unwanted things such as noise in the image.  Here are the images of the nebulas after minimum postprocessing using GIMP:

Photographing Objects Not Directly Visible

Sometimes, it’s very difficult to see the exact location of deep space objects such as nebulas and galaxies. Then, how do you photograph them?  You can take photograph if you know approximate location based on nearby stars.  For example, Flame nebula and Horsehead nebulas are not visible to the naked eye, at least it is true in my case. To know the location, search the web and find out photographs or articles on the objects. Or search in the apps such as Google Sky Map. For example, Flame nebula is very close to the star Alnitak on its left side. The star itself is the bottom most star of Orion’s belt as seen from Bengaluru. Horsehead nebula is below the star but not visible even after stacking light frames. Of course, this is true only in my case with the prevailing conditions - city center with a lot of light pollution. Further, I used a very low-end camera. So, I simply aimed my telescope to point to the star knowing the nebulas are around the star and obtained many light frames such as the following:

Neither Flame nor Horsehead nebula is visible in the photograph. But don’t worry. You need to stack all the photographs, usually a few hundred, into one final image using software such as Deep Sky Stacker (DSS). It combines all photographs, aligns them, removes noise generated by camera, removes distortions due to dust particles on lenses and generates one single final image. Even after this, you may not be able to see the objects till you set color levels using Levels tool of GIMP or PhotoShop. The image after postprocessing using GIMP is as following:

I observed that GIMP doesn't handle big image files of high resolution cameras such as ASI071MC. Also, the software is not as versatile as others in terms of editing capabilities. So, you may have to use PixInsight or Photoshop.

Notes

I bought things that I needed on a piecemeal approach because I wanted to reuse existing telescope equipment parts. If you want to get into astrophotography, you need to buy a telescope with tripod, mount and OTA (Optical tube assembly) as one unit. You may go in for a GOTO mount to make life easier but it will be costlier. Though I bought a mount of iOptron, there are a few other choices as well – mounts from SkyWatcher, Orion, CellStron, Meade and many others.

The other option is whether to go in for refractor or reflector telescope. My first telescope was a reflector telescope. Refractor telescopes are small and costlier compared to reflector telescopes. It is convenient to carry refractor telescopes.

There are a few vendors of telescope equipment in India. Of prominent and reliable vendors from whom I bought are Tejraj of Mumbai, GoScientifics of Madurai, Galileo Telescopes of Mumbai, Tanotis of Bangalore (Koramangala 6^th block) and Vorion Scientific of Ahmedabad.

Some parts are also available from various other e-commerce sites such as EasyCart, Shop2India, Felzon, EssayMall and Amazon. You will not find all components in a single store!

One caution: Always check prices of telescope or its parts at multiple e-commerce sites as I found exorbitant prices for the same part at some sites.

References

1. For the meaning of threading types such as M48 and M42 used for telescopes, cameras and various adapters, refer to the article https://agenaastro.com/articles/guides/astronomy-threads-explained.html.
2. You must read the following excellent article to understand the whole process of kinds of pictures (light frames, dark frames, flat frames and bias frames) you have to take, stacking using DSS and postprocessing using PhotoShop or GIMP:  https://www.lightstalking.com/photograph-orion-nebula/?unapproved=3763137&moderation-hash=9b10e88562a70123b03401869394351a#comment-3763137

You can learn a lot by seeing You-Tube videos about various aspects of astrophotography.

- Vidyasagar Mundroy, Jan 18, 2022, May 1, 2022