Getting started in Deep Sky Astrophotography

Almost once per week a new thread pops up in my favorite astro forum titled "Noob seeking help choosing first AP setup" or similar. (AP is short for astro photography.) Giving a short answer is not easy if not impossible. After writing down the same basic information several times I decided to write a short article so that I can post a link to it. Probably you put the question and followed that link. There are books written about the topic so indeed there is no short answer. I tried to boil it down to the most important topics but the complexity of the topic requires to go into detail now and then. To help you through the jungle of abbreviations I write to full term once and put the abbreviation in parentheses or vice versus. I live in the northern hemisphere so when it comes to popular targets I will be using examples from the northern sky. Astrophotography can be divided into several branches like photographs of the sun, the moon and planets, electronically aided photography, nightscapes, star trails and deep sky objects (DSOs). This article is about DSOs only. The technique for planets is quite different, the sun requires special equipment and nightscapes and star trails are more akin to regular night photography. Deep sky refers to any object further away than the members of our solar system (the planets and their moons). Deep sky objects are either stars, star clusters or nebulae within our own galaxy or other galaxies. Most images in my gallery are DSOs. It those photos are what you want to take yourself, read on!

The Earth is rotating

It is doing so quite fast. You may have heard of the 100 rule. Divide 100 by the focal length of your lens. That is how many seconds of exposure time you can use on a static tripod and the stars will not be elongated too much. For a typical beginner's telescope with a focal length of 400mm this is 1/4th of a second. For dim objects several hours of exposure time are required. That results in two things: first you need a device that compensates for the earth's rotation called a 'mount'. Second you have to take many single frames, so called sub frames or subs, and add them up for the exposure time required. The most surprising fact to a beginner may be that you have to spend by far the largest part of your budget for the mount. For visual astronomy you can come away with a low priced one. For astrophotography be prepared to spend about USD 2000 for a decent entry level mount. Really good mounts are 4-5 times as expensive. If you are not willing or able to invest that much you will suffer from various limitations that may cause frustrations. Don't be fooled by good images taken with a bad mount. You don't know how often someone failed until he or she finally produced one good image. People usually do not post the fails. The only way to take a decent photo with a cheaper mount or an astro tracker is to reduce the focal length and restrict yourself to the brightest objects. The mount rotates as fast as the earth does (360° in 23h 56m 4s, sidereal day) but in opposite direction so that the stars seem to stand still. First, due to mechanical limitations it will not rotate as smooth and constant as the earth does and the difference will show up as blurred images. Second the trick only works if the mount's axis of rotation is exactly parallel to the earth's axis of rotation. Aligning the two is called polar alignment because the earth's axis is defined by the two poles. If you live in the northern hemisphere and not too close to the equator there is a star that is close to the pole but not exactly on it. It is called Polaris. It can be used as a helper. A small telescope called the polar finder is in the mounts axis. By help of a reticle the star is placed in the right position of a clock dial. In the southern hemisphere there is no such star. If you are in the south or on the equator or if you are in the north and cannot see Polaris, from your place you can still align the mount using other techniques like drift alignment or electronic helpers that find the position for you.

Guiding

You will probably not succeed in a perfect polar alignment. Even if you do the tripod might sink into the ground and shift the axis. The difference is called polar error. It causes the stars to walk out of your image over time. The worse your polar alignment the faster they drift away. Keep this in mind while I point out a second problem: The mount's gears or pulleys are not perfect. Is will sometimes be a bit ahead and sometimes a bit behind the earth's movement. This is called periodic error. Only the most expensive mounts can compensate for it using high precision absolute encoders. All other mounts need some help. This is called auto guiding. A small telescope is mounted in parallel to your main telescope (scope for short) and a so called guide camera watches one star that you choose. If the star walks away from it's position either because less than perfect polar alignment makes it drift or because the mount is ahead or behind the earth's movement the auto guiding will send a command to the mount where to move in order to correct this. If you use a very short focal length for imaging like a camera lens with less than 50mm focal lenght you don't need guiding. If you image a very bright object with a small telescope below about 400mm of focal lentha and limit your single subframes to 30 seconds or less you may not need guiding on a good mount. Alas there is not much you can do with a short focal length and there are few objects bright enough for short exposure times. You will want to start guiding rather sooner than later. The guidescope can have a focal length about 5 times less than the main scope. The guide camera supposed to be a monochrome type. Most people connect the guide camera to the computer and use a free program called 'push here dummy', PHD for short. If you don't want a computer outside you have to spend more money and get a stand alone guider. The mount is either connected to the computer/autoguider or to the guidecamera. Instead of the guide scope you can us an item called off axis guider (OAG). It is between telescope and camera. A small prism reflects a small part of the image into the guide camera. This corrects for movement inside the telescope as well but it is more difficult to use. Most beginners go for a guide scope. Guiding is no magic wand. If you have too bad a mount it won't react properly to the guider's commands. It may delay movement due to backlash, it may overshoot or oscillate. The worse the mount reacts the more subframes you will have to sort out. Saving money on the mount is payed in lost subframes. One reason why you want to use auto guiding right from the start is that you no longer need perfect polar alignment. The drift is corrected by the guider. There still is a price to pay which is field rotation. The rotation is much less than the drift so a relatively coarse polar alignment is fine when you guide. This needs both axes to be guided and thus will not work with a single axis astro tracker. More vocabulary: the axis that corrects for the earth's rotation is called right ascension (RA) and the other one is called declination (dec). When polar alignment is perfect the dec axis will not move. RA is constantly moving. A guide command for RA causes the mount to speed up or slow down but never to stop or to reverse. For dec that supposed to stand still a guide command can be in either direction. This is where backlash comes into play. When reversing the little gears inside it takes some time until all cogs engage in the opposite direction and finally move the dec axis. Meanwhile the guider may have over corrected. This is why guiding cheap mounts is a difficult and sometime frustrating task.

What is an arc second?

Angles are measured in degrees. 360° is a full circle. One degree is divided into 60 arc minutes. One arc minute is divided into 60 arc seconds. So an arc second is 1/3600 of a degree or 1/1,296,000 of a full circle. In one single (time) second the earth rotates 15 arc seconds. The apparent diameter of Jupiter, the largest planet, varies from 30 to 50 arc seconds. Neptune, the furthest planet, is only a bit more than 2 arc seconds large. The apparent diameter of the moon is 30 arc minutes so 60 times larger than Jupiter in its furthest position. Our neighboring galaxy Andromeda is 3° long, 6 times larger than the full moon. Stars are incredibly small. The near by super giant Betelgeuse is only 0.046 arc seconds in diameter. Most other stars are much smaller. So stars appear as singular points without a diameter an general. One might expect they appear as single pixels in the image. This is not the case as we will soon see.

Resolution and Seeing

Let's assume you start with a typical beginner's scope with about 400mm focal length and a digital single lens reflex camera (DSLR) with a typical APS-C (Advanced Photo System type-C) sized sensor (22x15mm) and some 12-20 MPix. In that case one pixel in the image equals a viewing angle of about 2 arc seconds. This ratio of pixels per arc second is called the image scale and matching it to the equipment's and the sky's limits is essential. The laws of physics put a limit to the smallest thing an optical instrument can resolve. A decent beginners telescope can resolve 1.5 arc seconds. But for most of us the scope is not the limit. The air that we all need to survive keeps on moving all the time and it consists of layers of different temperature and density. This adds movement, the so called seeing that is perceived as twinkling stars by the bare eye. Under very good conditions it may be as low as 2 arc seconds. At some places it may be as much as 6 or 8 arc seconds. The seeing varies from day to day and it may even vary from minute to minute. For the rest of this article I assume that you have a seeing of 3 arc seconds on good days and 2 on very few excellent days. You have to find out if that is true for your place and correct my recommendations up or down accordingly. The following considerations are only relevant if you dare starting with a longer focal length because you want to image small objects like the Blue Snowball or the Ring in Lyra. In this case the focal length of your telescope and the size of your camera pixels must be matched wisely. The formula is pixel size in microns divided by focal length in millimeters times 206.3. If you get a telescope with a focal length of 1100mm and attach a DSLR with 4.25 micron pixel size your image scale is 4.25/1100 x 206.3 = 0.797 arcsec per pixel. There is no point in choosing a scale that is way less than the resolution of your telescope or the seeing. Well, almost. We are doing digital photography and there is a theorem by Nyquist and Shannon that tells us to sample 2 to 3 times better than the finest detail in the image. If your seeing is between 2 and 3 arc seconds and your telescope resolves 1.5 a resolution between 0.66 and 1 arc second is fine. Using an even loger focal length will make you oversample. A bit oversampling can help to give the stars the shape of a circle rather than a block of 4 pixels. Oversampling too much won't help. You loose intensity but you do not gain any additional detail. If you really go for less than 1 arc second that you will soon show you the limits of an entry level mount and you will be challenged by guiding. For the start a I recommend you stay near 1 arc second imaging scale. Be warned: this is the challenging path. Even if you succeed in bringing the high resolution to the sensor you need hours and hours of exposure time. Why is that? There is noise in the image. Noise is eating up the fine structures first. Even a technically sharp image will not show the detail if the noise covers it up. It needs 4 times the exposure time to reduce noise by a factor of 2. It needs 100 times the exposure time to cut it down by a factor of 10. If you have poor weather conditions or work and family life limits your exposure time it is quite likely you cannot collect enough data to get the noise down far enough to make the fine detail show up. Even advanced astrophotographers are often not aware of this fact. The most common error of beginners is to use a far too long focal length on a far too weak mount. Vice versus is much better!

Field of View (FOV)

If you want to take the save route to good images, you should follow a different philosophy. Many popular targets like the Rosette Nebula, the Great Orion Nebula, the Pleiades are about 2 degrees in diameter. The Andromeda Galaxy is about 3° x 1°. If these are targets that you want to image you need a field of view of about 2° x 3° or even larger. If you want Heart and Soul or North America and Pelican Nebula in one frame you need a 4° x 6° FOV. The formula is this: field of view in degree equals width of chip in mm times 57.6 divided by focal length in mm. For example a 420mm focal lengths scope and an APS-C chip of 22x15mm makes up a FOV of 22 x 57.6 / 420 = 3° wide and 15 x 57.6 / 420 = 2° high. (The formula is a simplification, it does not work for wide angle lenses.) Now your imaging scale is 2 arc seconds per pixel. If the numerical value of the scale is higher than the seeing or scope resolution you are undersampling. This may sound bad but there is nothing wrong with that. At 2 arc seconds per pixel you don't need to worry much about seeing. If you find yourself putting a short and small telescope onto a mount that looks oversized you are doing the right thing!

Focal length and f-ratio

Telescopes are usually sorted by aperture, the diameter of the front lens or mirror. People talk about 80mm or 8 inch and then say they image at f/10 or f/6. The f-ratio is also referred to as fastness. An f/3 is a fast telescope, an f/10 is a slow one. The f-ratio is focal length divided by aperture. If your telescope has got a front lens of 80mm diameter and a focal length of 480mm it is an f/6. The smaller the number the more light it collects in the same time. An 12 inch f/10 telescope has got a focal length of 12 x 25.4 x 10 = 3048mm (good for planets; an inch is 25.4mm in case you are not used to imperial units). For beginners I recommend to settle between f/6 and f/8. Why not get an f/3? Because the faster telescope needs very accurate focus. When the temperature changes by only a single degree centigrade the change in length may require to correct focus. The slower the scope is, the less critical it is to focus and the more change in temperature it can handle. A very slow scope on the other hand casts only dim light onto your sensor you you need hours and hours to image even a brighter target.

Camera lens or telescope?

It is difficult to find telescopes with a focal length of less than 400mm. A regular lens telescope, also called a refractor, consists a two or three lenses in the front and a long tube. This construction principle simply does not work for much shorter than 400mm. There are very few telescopes in the 250-300mm range that are Petzval designs consisting of two groups of two lenses. To go even shorter more lenses are needed and this is the construction principle of camera lenses. A decent 300mm camera lens can be as good or better than a 300mm (focal length) telescope. In any case you want to use a prime lens. Zoom lenses consist of as many compromises as lenses. They cannot deal with the high demands of astro photography. There are some nice vintage lenses available used for low prices. As a rule of thumb from 400mm up you are better off with a telescope. Advantages or telescopes over lenses are: They come with mounting rings and a dove tail that fits the mount. For a camera lens you have to find a lens collar or a set of rings. Telescope often have holes for the guide scope on top. Attaching a guide scope to a lens requires some tinkering or a side by side mount adapter. Very soon you spend more money for the rings, bars and adapters than for the lens. Telescopes have a longer back focus. You can put things like a filter wheel or an off axis guider between camera and telescope. You cannot do this with a DSLR and a camera lens. You can perhaps do this when you put an astro camera behind a camera lens. A telescope focuser either does not move accidentally or can be locked. Some camera lenses start sliding as soon as you point them upwards. You have to lock the focus ring by tape or rubber bands. Tape won't stick when the lens is wet. Filters are usually placed between the telescope and the camera. That means it can be as small as the sensor. A filter as large as the front lens is far more expensive or not available at all. There is one exception called clip in filter. It is put into the DSLR body and the lens is in front of it. This is not available for all camera brands and does not work in all cases. (For example it does not work if you have a Canon and an EF-S lens.)

Telescope Types

A telescope is also referred to as an optical tube assembly (OTA) There are different types. Refractors are made of glass lenses. They are good entry level scopes. (There are high priced high end refractors available as well.) Glass refracts the light (thus the name refractor) but alas it handles different colors in a differently. This effect is called dispersion. The unwanted result is called chromatic aberration (CA, from greek chroma = color and latin aberrare = go astray) showing up as often pink color fringes at stars. Telescopes with just a single lens are not good enough for photography but guide scopes usually consist of just one single lens. Using two lenses of different kinds of glass (crown glass and flint glass) as a combined element, a so called doublet or achromat corrects the problem for two colors. All other colors are still not in the same place. Using special glasses (extra low dispersion, ED) can reduce the problem further. Better than two are three lenses, so called triplets or apochromats (APO). There are some very good doublets that are better than some very poor triplets but the general rule is you should get a triplet for astrophotography if you can afford it. In any case the image of a refractor is not flat. If you put a curved surface like the inside of an egg shell behind the telescope you will have a sharp image there. As camera sensors are flat an element is needed that flattens the field. As you may have guessed this is called a field flattener. It must match the telescope so you have to follow the manufacturer's advice which one to buy. An exact distance between sensor and flattener is specified. If you fail to match the exact distance it does not work well. If you calculate the price of a refractor you have to think of the telescope and the flattener and perhaps the spacer rings to get the distance right. There are reducer/flattener combos as well. They reduce the image size and thereby the focal lengths. Many refractors make up an image (almost) large enough to illuminate a full frame sensor for 24mm x 36mm. If you use a smaller chip quite some light gets lost behind your sensors edge. A reducing flattener shrinks the image down, usually to APS-C size. The image gets brighter in that case. That is a good thing. Remember to multiply the telescopes focal length by the reduction factor (0.8 or 0.67 in many cases) when you calculate field of view or arcsec per pixel. There are some refractors called astrographs, flat field telescopes or quadruplets that come with the corrector inside the tube. This might be a cheaper option compared to a regular refractor plus a corrector. They are easy to handle: camera in, done. You don't have to worry about a correct distance. All you need to do is focus and you are fine. Curved mirrors also create an image. Mirrors do not suffer from chromatic aberration. There are several telescopes that consist of mirrors only or combinations of glass and mirrors. A newton telescope consists of a curved mirror at the end of the tube and a flat mirror at the front that throws the image out of the side of the telescope. The camera is mounted to one side of the telescopes front. Newtons give you by far the largest aperture for the money. They have a problem called coma that stretches stars to comet like things. You need a group of lenses called coma corrector to get proper stars. Next problem is the sensor must be close to the tube. In a DSLR the sensor is relatively far away from the front flange and you may not come to focus with a newton. If you consider one, make sure someone is imaging with the particular scope and the same camera as you want and a coma corrector. There are coma corrects that slightly enlarge the image in order to give you more back focus. Such a thing can easily cost more than a budget telescope. Newtons are quite large. They are as long as the focal length. A slight breeze might already challenge your mount. A special type that is made especially for imaging is the Maksutov-Newton. It does not need a coma corrector. Instead there is a glass element, the correction plate, in front of the tube. Of course the large glass plate is heavy. If your mount can deal with the size and weight of the instrument it is a very nice imaging scope. Be warned, like a refractor the front element can fog up if you have damp conditions. Electric heaters, so called dew heaters prevent fogging. Telescopes without a front element often can be used even under damp conditions without dew heaters. There is an endless list of folded designs. The all have a mirror with a big hole at the end of the tube. The light falls on this one first and is reflected back to the front where a second mirror reflects it back down through that hole onto the camera. They all have a rather large secondary mirror, much larger than the one in a Newton telescope. The size of the secondary mirror is required to create an image large enough for the sensor. The amount of light taken away by the secondary is called central obstruction. It can be as large as 30% in some cases. A Ritchey-Chretien design consists of two hyperbolic mirrors. The field is curved but not too much so a large part of the image can be used without a flattener. They have quite a long focal length and thus are often used with reducers, reducers that only shrink but not flatten in this case. RCs need collimation, the correct adjustment of the mirrors and this can be a difficult task. Some people fail and regard the RC as a pest sent from hell others take fantastic images with them. Small RCs are cheap and offer good quality for the price if you get them collimated. The cheap ones tend to have internal movement and can be used for short exposures only or with an off axis guider. A close relative is the classic Cassegrain design which is not recommended for DSOs. It comes with a small image that is sharp in the center only. Putting a glass correction plate in front makes it a Schmidt-Cassegrain telescope (SCT). These come with a flat and sharp image but they have a very long focal length like 2000mm and more. This is why you would use them with a reducer and a camera with a large pixels. For beginners it boils down to this: get a small refractor like 80mm f/6. Get a triplet if you can afford it. If you are on a budget get a newton plus a coma corrector and make sure you come to focus with your camera. If you think you can handle the collimation get a small RC with a reducer and keep the exposure time below 2 minutes.

What about visual?

In general there is no telescope that is good for visual and photography. Refractors may be the best choice if you want to do both. The folded designs have large secondary mirrors that put a black spot into the exit pupil that can be very annoying at low magnifications. They lack contrast. For visual contrast is king. Flat field astrographs often have too little back focus for a diagonal. Straight viewing works but is a pain in your neck. The best advice I can give is you get an AP rig and some separate solution for visual. For example a low priced Dobson telescope. This is technically a newton and it rests on a big square box. It is moved by hand. Use the dob to show the planets to y our kids while the other rig is taking the photos. I got myself a pair of decent binoculars for observing. Binoculars are literally grab and go. For hand held operation choose a magnification from 6.5 to 10. For larger magnifications you probably need tripod or a monopod.

Cameras

If you own a DSLR or a mirrorless for daytime use this is a one shot color (OSC) type. You may be surprised now. In astronomy as well as in many other applications monochrome cameras are used. The chip is monochrome by nature. If you want to take a color image you have two options: a) use a red, a green and a blue filter and take three images of the object. Of course neither object nor camera may move while you do that. b) place millions of tiny red, green and blue filters on top of the pixels and take only one shot. All DSLR and mirrorless cameras are following b). There are dedicates astro cameras with OSC sensors as well. Astro cameras often come with cooling and with better electronics. They lack any buttons to press and the display so that you need a laptop computer or computer like device (like a Raspberry Pi or the ZWO ASiair) to operate them. Astro cameras are build for the purpose and they consider the nature of some DSOs. More on that soon. Astro cameras are also available as mono cameras. This is the pro's choice because apart from red, green and blue a lot more filters like luminance and all sorts of narrowband filters can be used. The monochrome camera offers all options but also challenges you when you have to combine the different images to a color image. The filters are put in a manual or electronic filter wheel. The usual way is to set up a sequence in the computer that takes the images and changes the filters according to a plan that you have to set up. With a mono camera you can use any sort of filters. The nebulae in our Milky Way consist of gas that emits lights of very specific wave lengths. Using filters that let pass a specific wavelength send out by a nebula while blocking almost all light from the stars and the l ight polluted background. This allows for dramatic images of faint objects even under a light polluted sky. The downside of this technique - narrow band imaging - is the need for l ong exposure times and long subframes. If you want to go this path you need a mono camera and a filter wheel and a computer and a mount that can deal with exposure times of 10 to 30 minutes. Be prepared to invest $5000 minimum for a decent narrow band setup. What about OSC? It is the easy way. No need for filters, no need to combine images. If you use an astro camera it is sensitive the the most important and strongest emission line H-alpha, a deep red color created by hydrogen gas. Hydrogen gas is the most common element in space and you find it in your milky way as well as in special regions in distant galaxies. The deep red is close to the limit of what our eyes can see. If you use your daylight camera you might be lucky that it picks up a bit of this H-alpha (Ha for short) or it may block most of it. The sensor is sensitive to quite a large range in the electromagnetic spectrum. As the camera supposed to take images similar to our human vision the manufacturer puts filters in front of the sensor that keep the ultra violet and the infra red light out. Ha is just at to border to infrared. That is why some companies o ffer a service to replace the infrared filter inside the camera by a different one just remove it. If you dare you can do this yourself. You can also try to get a used modified camera. Sometimes it sounds like a stock DSLR cannot be used for astro photography at all. This is not the case. There are many objects that contain little or no Ha at all like star clusters. There are objects with strong Ha emissions that are picked up even by an unmodified DSLR like the Rosette Nebula or the Great Orion Nebula. If you have a DSLR, use it! If you think about modification be prepared that you cannot use it for daylight any more. Not only causes the removal of the filter a strong red color cast but also will it ruin the autofocus unless you put in a glass of the same optical thickness. I recommend to use your unmodified DSLR if you have one or get a used modified one for astro while you keep yours for daylight. If you want to invest in an astro camera and don't mind the computer OSC is the simple way. If you think you can deal with the complexity of combining several images shot through several filters get a mono camera. Using a technique called LRGB (luminance red green blue) you can get an image with the same noise level as an OSC image in a shorter time. You can either boost your natural color images with narrowband data or you can create false color narrowband images. OSC cameras, no matter if astro, modified DSLR or stock DSLR cannot take luminance images. They are not really well suited for narrowband. There are attempts of dual narrowband filters for OSC cameras. Some people like them, some don't. In any case the narrowband capabilities of OSC cameras are very limited compared to a mono camera. Mono adds a lot of complexity. If you don't know how deep into the rabbit hole you want to go, start with an OSC camera and upgrade to mono later.

What else?

There are a few more things you need. A head lamp helps a lot, especially one that can be turned from white to red light. For focus a Bahtinov mask is a great help. If you use a computer anyway you can think about an auto focus. If your scope is very small or you use a camera lens the mounts counterweight may be too heavy and you have to get a smaller one. For larger equipment you can improve guiding by using two counterweights at the upper end of the shaft than a single one on the lower end. This reduces the inertia, the force that occurs when the mount needs to speed up or slow down when guiding. If you have damp conditions you need dew heaters. If you image near the house you can power the rig from the mains. Remember that electricity in a wet environment is dangerous. Make sure you have a residual current device (RCD, also RCCB, GFCI, GFI, ALCI or LCDI) installed that saves your life in case something goes wrong. If you go to a remote dark place you need a battery. 12-14 Ah is fine for a mount and an autoguider when the camera is a DSLR with it's own battery. For a cooled camera and/or a computer you need rather 30-50Ah. For a DSLR you need a second battery or even a third one for a whole night. Unless you control it by computer you will find that it cannot exposure longer than 30 seconds. An intervalometer connected to the trigger port lets you take a given number of longer exposures automatically. To align the mount you have to point the telescope to a few bright stars. A red dot finder or a finder scope helps you to do that. If you have a guide scope you can possibly use it by replacing the guide camera by a cross hair eye piece for the alignment. A bubble level or a level app on your smart phone helps to set up the tripod level. This is required if you do polar alignment with a polar scope. It also helps the mount to place the first alignment star in your field of view. If you use a computer you can replace the mount alignment by plate solving. That is an image is taken by the camera and the computer can calculate from a star catalog where the telescope is pointing to. As you can see the number of programs on the computer can be large. While some people recommend to use all computer aid available and perceive it as a great help others say to keep things as simple as possible. You have to decide which way fits your needs best. If you are troubled lifting heavy weights or carrying things you might choose a mount that is not too heavy or can be taken into parts for transport. Some build small trolleys to move mount and tripod on wheels out of the garage. For imaging the trolley must rest on solid feet like big screws that lift it up from the wheels. If you don't have to worry about theft in your community you can keep the rig outside under a cover. If you have the space and money you may think about a dome or a cabin with a slide off or fold away roof. During the image processing you need calibration frames, one of them is called a flat frame. It is created by putting an evenly lit light source a so called flat field to the front of the telescope. Although some people use laptop screens or copy panels for this task I recommend you get a decent flat field that is designed for the task. It may not be obvious but it will save you from a lot of problems during image processing. I was thinking about listing some example setups. I decided not to do so. As soon as you have a basic understanding I recommend you make a list and post it in an astronomy forum alongside with what you want to image and what limitations you have to deal with (visibility of Polaris, access to a dark site, time, physical abilities, budget limit, level of light pollution) and a hint in which part of the world you live. Experienced user will probably see if you missed something or can point to special offers in your region. Stay away from people who try to convince you that the onlymway to go is this or that. Rather listen to those who can describe different approaches and tell you the pros and cons of each. Then find your way.