Using Sequence Generator Pro and Friends: Imaging with SGP, PHD2, and Related Software

By Alex McConahay

This guide is specifically aimed at those who are using—or want to use—Sequence Generator Pro. SGP is a “session management” software package that controls the telescope, mount, camera, and ancillary equipment to target and secure images during a night of imaging astronomical objects.
The book begins with a special tutorial to get up and running with SGP. With a comprehensive reference section, it takes the user in detail through the various aspects of user and equipment profiles, equipment definitions, the sequencer, and other essential elements of SGP. Finally, it focuses on how to get the most out of the ancillary programs—target databases, autoguiders, plate solvers, planetarium software, and other applications.
Oftentimes, technical guides can end up being far denser than the processes they intend to explain. Many of the insights provided by SGP expert Alex McConahay are beyond what can be found in the official program documentation. In this book, the reader will find in-depth, yet straightforward practical advice on how to automate nightly astroimaging sessions with Sequence Generator Pro.

• Language: English
• Publisher: Springer
• Release date: Sep 10, 2019
• ISBN: 9783030197193

Book preview

© Springer Nature Switzerland AG 2019

A. McConahayUsing Sequence Generator Pro and FriendsThe Patrick Moore Practical Astronomy Serieshttps://doi.org/10.1007/978-3-030-19719-3_1

1. Why Do I Need Sequence Generator Pro?

Alex McConahay¹  

(1)

Moreno Valley, CA, USA

Alex McConahay

Significance of Sequence Generator Pro

Tony Hallas, then and now among the pantheon of great astroimagers, was explaining why the St-4 autoguider was the most important development of all time for amateur astroimagers.

It was some twenty years ago at RTMC Astronomy Expo in Big Bear, California. Forty astroimagers piled into a tent to hear a panel of expert astroimagers tell about developments in their specialty. And Tony said the prize belonged to the St-4.

Remember, this was when CCD’s were replacing film, cold cameras were showing up on the swap meet table rather than on the retail shelf, and even Ektachrome was being phased out. But Tony claimed the St-4 was the one thing that had the greatest impact on astroimaging. Yes, the St-4 was a wonderful invention. It could track a star down to sub-pixel accuracy. It could follow that guide star more accurately, more quickly, and more smoothly than any human imager out that night. Curiously, though, it was not the improved guiding that made the St-4 such a monumental thing. According to Tony, it was the better image processing that resulted.

../images/472657_1_En_1_Chapter/472657_1_En_1_Fig1_HTML.jpg

Fig. 1.1

The St-4 autoguider did more to improve imaging than anything else in astrophotography. So said Tony Hallas (second in from right) as part of a panel on astrophotography at 1998 RTMC Astronomy Expo. (Inset image by Robert Stephens.)

How did an autoguider affect processing? Tony saw something that the rest of the hobbyists did not. Prior to the autoguider, he said, enthusiasts would fall in love with imaging. After all, there they were under a beautiful night sky. They were looking up at the wonders of the heavens, probably out with a few buddies, lots of cables, gears, buttons, glass, and other things that had some natural attraction for those who like that sort of thing. When it came time to image, one sat there for 45 minutes, an eyeball pretty much glued to the eyepiece, gently pushing one button or another to keep a star centered on a crosshair – like chasing a Mario Brother in super slow-mo. After the shots came back from the drug store, they were scanned and then processed with the earliest image processing programs, trying to bring out all the colors and details. Some people got pretty good at it. The longer they worked at it, the better they got at the processing.

It was fun, really fun – for a while. Then, they came to. It was cold out there. And boring. And awkward. An eyeball frozen to an eyepiece, especially a dim eyepiece in a perverse position, was not really fun. But they did it for a year, or two, maybe three. Those with three years of experience taking and processing images got better. They got pretty good. But far too many found it was a silly way to spend time – frozen to an eyepiece, knowing that an errant plane or satellite could ruin 45 minutes of work, fingers stiff from the cold and the monotonous clicking of the buttons. Most quit. Maybe they still liked the pictures, but they found it easier to look at other people’s pictures than get their own. The ones that quit never improved their processing skills.

The St-4 came along, though, and changed the part about sitting in the cold. Get the St-4 going, set an egg timer for 45 minutes, and crawl back into the sleeping bag. Or head out to a friend’s house while the ST-4 and imaging scope gathered the photons. People could continue in astroimaging without questioning their own sanity. The more they did, the more their other skills improved. Image processers became better processers. And that, said Tony, is how the St-4 improved image processing. It allowed people to stick with the hobby more than the three or four years any sane human would subject himself or herself to manual guiding. And it took that long and longer to get good at processing.

Sequence Generator Pro does some of that. It makes astro imagers better in the first place by allowing them to get more data, and probably better data. But it also removes the drudgery and difficulties of gathering the data, and thus allows them to spend their time getting more out of those photons they record. It does so at a price that, along with less expensive DSLR’s and other cameras, brought many more imagers into the hobby.

Session Management Software

Sequence Generator Pro is also an example of what can be called session management software (although in computer sciences that term has a more specialized meaning). A session is the evening (or many evenings) under the stars gathering data. Management means SGP is controlling and coordinating many different pieces of equipment, and even other programs, which in turn are managing other equipment. Once the imager tells it what to do, SGP coordinates the equipment and software so that it takes the pictures the imager wants without further assistance.

What does it take to pull off an imaging session?

Equipment and Ancillary Software Selection

An imaging kit includes a mount, a telescope tube, a camera, a guiding system (a camera and either an off-axis guider or a separate guide scope), a computer (for running the software and storing the data), a focuser, other software to do some of the required tasks, and a myriad of wires, power supplies and cables. It is the session management program’s job to keep track of:

what is in the system,

how it all connects,

its specifications (field of view, resolution, download times, mounttravel limits, etc.)

Target Selection

The first thing an imager must do is to decide where to point the scope on any given night. To do so, the imager must know what is in the sky, where it is in the sky, how large it is (compared to his or her field of view), and several other things. This information is available in a planetarium program. The planetarium program may be part of the management software or (in the case of SGP) a separate program called by the management program. Other methods, such as looking the target info up in a book or catalog or matching an existing photo, will also produce the target coordinates. If the object is too large to get into one field of view, the imager must learn how to aim the scope to get a series of shots that can later be stitched together into one larger image. Having decided all that, the imager (or subprogram) must pass the celestial coordinates for the object(s) to the session management program.

Pointing

Knowing the target coordinates, the session manager must point the scope to the desired target. It does this by controlling the GOTO functions of the mount and perhaps the rotator. Alas, very rarely does the scope point precisely where it should. Therefore, the software must confirm the pointing by taking a picture and determining just where the scope is pointed. This is plate solving. Then, the software compares the solved location with the desired location. If the match is imperfect, the manager must move the scope and repeat the process until the match is sufficiently close.

At times, the target moves across the meridian, and this can be a problem for the most popular type of imaging mount, the German equatorial. Session management software must know when this is about to happen, flip the mount over, change the guide parameters, relocate the desired field, and restart the whole system. A final aspect of pointing involves rotating the camera in some setups for better composition or to acquire a better guide star. The session manager accomplishes all this by calling the plate solver, rotator, and mount mechanics.

Focusing

More sophisticated scopes are equipped with motorized focusers. The session manager can either by itself or with an ancillary program take a picture of a star field and calculate the size of the stars. It then moves the focuser a few steps and takes another picture. It goes through a series of such pictures and predicts the position for the focuser where the star will be the smallest. The focuser subroutines also schedule when focusing is to be done, and how it is to be adjusted based on filter or temperature changes.

Guiding

As the mount tries to track the stars, little imperfections in the equipment and how it is set up, and even the sky itself, mean that no human-made mount can track precisely. So, the autoguiding system takes a picture of one star over and over again. If the star is in the same place in each successive picture, it does nothing. But if that star begins to drift ever so slightly from one picture to the next, the autoguiding system sends signals to the mount to move so that the star is returned to its original location. More sophisticated systems can use whole fields of stars instead of just one, but the concept is the same. An autoguiding system can consist of a separate scope or an off-axis or on-axis guider that picks off some light from the main scope, a camera, connectors from the camera to a computer and back to the mount motors, and the software to manage the corrections.

Data Gathering (Light Frames)

The main job of the imager is to gather light frames. These are the longer frames, from 30 seconds to 30 minutes and more, where the main imaging camera is gathering light to make an image. The imager wants to capture dozens of these a night. The more he or she has, the better for noise reduction and other purposes. So, the session manager software must know how many shots the imager wants, the ISO or gain, the length of each, in what order they should be taken, which filters to use, how to name them, and where to store them. When it knows all that, it starts the session and keeps track of progress. As part of its functions, it might need to know when to start and stop for the evening.

Data Gathering (Calibration Frames)

As part of the eventual processing, the imager will need to calibrate with bias, dark, and flat field frames. The session manager may handle them the same way as the light frames. The program may also help to determine how long they should be for proper exposure.

Data Analysis

Session Management software may also help the imager monitor the session. SGP, for instance, can immediately analyze every downloaded light frame to determine star size and support (number of stars that stand out in the photo) to help the imager monitor sky conditions, change in focus, and other things. Another function of data analysis is to determine the overall quality of the shots. With that known, the imager can determine which shots will later be processed, and which rejected.

Image Visualization

A digital exposure coming directly from a camera is a dim, dark, uninspired thing. To see any detail, the data must be stretched and manipulated. Many imagers like to look to see how things are going after each shot. A good session manager program provides screen display utilities that will temporarily zoom in on or stretch the data (without changing the original) so that the imager can change data-gathering parameters as necessary. The most powerful software systems (however, not SGP) may also include true processing capabilities so that one may also process an image nearly completely.

Other Equipment

Some imaging kits are part of observatories with weather sensors, roof-closing mechanisms, electroluminescent panels for taking flats, and other devices. These total systems can be automated such that even if the weather changes, the system knows to shut down and close the roof, or in other ways accommodate the problem. The session manager software must know how to communicate with the controllers for all this equipment.

Error Handling

When something goes wrong, like a passing cloud that blocks the target and guider, or the telescope is not being pointed correctly after a meridian flip, what should happen? An intelligent session manager will know how to take care of this. Perhaps it will temporarily halt operations, wait for a cloud to pass, and try a restart after fifteen minutes. Perhaps it will just restart the image. Perhaps it will know whether to try to retarget the scope with a complete plate solve and repointing. It should certainly know if something is not set up correctly (a device is missing or not connected) and should know how to connect to it or otherwise remedy the situation.

User Communication

Finally, the session manager must know how to communicate with the imager. On screen displays are of course part of that. But many session managers can send messages or even phone text alerts to users.

Sequence Generator Pro does all the major tasks of a session manager either by itself or by controlling ancillary software. It will help pick and program targets and keep track of equipment and help run it and various other pieces of software. The imager can trust it to do its job while he or she does something else (like sleep). Then, the next morning, a stack of data is ready to process.

SGP Is One of Several Session Managers

Sequence Generator Pro was not the first session management software package to come along. MaxIm DL from Diffraction Limited was one of the pioneers and is still a leader in the field. Images Plus, The Sky X (with a camera control add on), Astrophotography Tools, Nebulosity, Backyard EOS and Backyard Nikon, and a few others were also created. In addition, several other programs, such as the ACP Observatory Control Program, CCD AutoPilot, and CCD Commander add layers of power to existing programs such as MaxImDL and the Sky X by calling those as needed. Few of these programs do it all. Most have one feature or another the others do not have.

Prices vary widely. A fully configured system in one, including the other programs it calls, is somewhere near $2,100. Others, which can be had for as little at $35, do not generally come with the features of the more expensive cousins.

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Fig. 1.2

A search will find many session manager software packages. (Google and the Google logo are registered trademarks of Google LLC, used with permission.)

One comment sometimes heard about SGP is that it relies on other programs, and imagers would prefer to work with just one program. To work SGP, they say, one may need AstroPlanner or Starry Nights to select the targets (MaxIm has a planetarium program built right into the interface), and PhD Guiding to guide (MaxIm has a built-in guide routine). All this is true. But consider a few points. First, few programs stand alone. MaxIm, for instance, needs Pinpoint or another solver to do a plate solve, and another program, such as CCD AutoPilot, to automate imaging more than one target per night. Secondly, just because a program is bundled as a subroutine for another does not mean it easily works with the master program. One astute imager has called a popular session manager program a weird collection of subroutines that calls itself a program! Finally, the issue should not be whether the software and the routines it uses all came from the same software engineer and have a visually matching interface but whether the software routines work well together. In that respect, SGP has proven itself powerful and flexible while working with its ancillary programs. The fact that it uses software from other places should not be held against it.

What is different about SGP is that imagers can get much of the power, features, and control of the expensive products for a relatively low price.

How SGP Works

Sequence Generator Pro first gathers the information it needs about all the equipment that it will manage, and information about how the equipment is connected. This includes cameras, telescopes, and mount, of course. It also includes focusers, rotators, dome control devices, roof openers, thermometers, and all that. The program also gathers instructions for what to do when something goes wrong. It stores this information, and information about the user, in profiles.

Then it needs to know where the imager wants to point the telescope, how many pictures are to be taken, when to start or stop the session, and the guidelines for the pictures (exposure time, ISO, filters, number of sub-exposures, etc.). It also needs to know what the imager wants it to do when it gets finished with taking those pictures. It stores all this information in a sequence. When the imager pushes the run button, the program starts and stops the equipment either directly or by calling on other programs (guiders, focuser drivers, camera drivers, and so forth) to run the equipment. It waits for tasks to be done and then goes on to the next.

Typical tasks are:

Pointing the scope at a specified position in space.

Using the plate-solving program, making sure the scope is pointed at the right place, and if not, adjusting the mount until it is.

Starting the autoguider program and waiting until it reports it has settled to less than the acceptable error.

When that is done, stopping it, and starting the focusing program.

When the focusing program is done, taking a test exposure to make sure it is focused as was expected.

Restarting the autoguider, and checking that it is stable.

When the autoguider is stable, starting the main camera and running it for the specified time.

And more. All night long it monitors the sub-programs (such as the guider) to see it is all going well (the guide star is tracking). Or, if something is not going well, it falls back on pre-planned set of instructions to do something about it.

This goes on for as long as needed. The final instructions may be something to the effect of park the mount and close the roof. The system logs the many instructions it issued through the night and the reports back from the devices it was controlling. This log measures thousands of lines, many pages.

What Sequence Generator Pro has done is break down the entire imaging process into a set of instructions, executed them one by one, checked that they were going well, and if not, corrected the errors and then carried on.

What Sequence Generator Pro is NOT

SGP is meant for hobbyists or professionals who want to manage a session of imaging deep space objects. These include galaxies, nebulae, clusters, and other targets that require a large number of long sub-exposures. It is therefore specialized to manage a GOTO tracking mount, its scope and focuser, long-exposure camera, a guide camera, and so forth. It is not designed to be used for nightscape images, which require single exposures of 30 seconds or so, often on a fixed tripod. It is not for imaging planets, the Moon, or the Sun, which usually require a tracking mount and a video-based camera. Gathering the raw data for those targets is better done with other software.

And, to emphasize, as a session management package it does not do much more than gather the raw data. It collects raw sub-exposures for one night or several nights on one or more deep space targets. These sub-exposures are later stacked together and processed in a different program or programs to produce a final image. True, SGP does have limited image visualization routines, such as the screen stretch and the image history , to allow the imager to see how the data gathering is progressing. But this is no replacement for an image stacking or processing program.

Learning Sequence Generator Pro

With any complex product, it is easy to be dazzled by the many choices. Sequence Generator Pro can scare people off. It has too many buttons, switches, graphs, pull downs, profiles and all that. It was as if the new operator were staring at the cockpit of a 787. Even with shelves of instructional manuals, and the knowledge that it could be flown, the newbie can be intimidated by the control panel of a 787.

But, unlike flying a 787, one can take bits and pieces of SGP as they come, learning what is needed at first and then incorporating more later. One can start with a few simple images and gradually incorporating other parts, refining and perfecting as one goes.

After a few days or a few months, people figure it out (SGP, if not the 787). You will, too. But hopefully, it will happen a little quicker with this handbook. It will help you to start using the program and be a resource for some of the finer points after you get started.

We Will Not Cover It All

It is difficult to address in one volume all the needs of relative newcomers, as well as provide a comprehensive guide for most other users. This book will not do so. Seriously advanced users equip their observatories with weather monitors and roof closers. They program scripts that handle special situations or one-off equipment. They control their scopes wirelessly. All this and more can be done with SGP. But the number of users doing all that are a very small fraction of SGP users and could probably write the book themselves. Other control modules are rather clear, easy to use, or repeat what is done with other tools. Specifically, we will not cover the modules devoted to Observatory, Rotator, Flat Box, Environment Data, and Rotator or the use of API.

Organization of this Book

It seems on the surface that the most useful way to describe a software program is to march lockstep through the menus and toolbars, explaining what each item does in turn. Unfortunately, an imaging session does not march that path. Certainly, somebody learning a program for the first time does not. Instead this book approaches SGP the way an amateur imager would approach it. It covers the essentials lightly, then goes back through explaining the details at a deeper level. A section goes very deeply into the theory behind some of the parameters and choices. Finally, it covers some ancillary programs not otherwise covered.

Part I of this handbook, Meet SGP, introduces SGP, tells about the equipment it controls, and tells how to get equipment connected and the computer ready. Then there is a short tutorial about getting started with SGP. It will not teach all there is to know. But it will get the imager started. Part II, the Handbook, is an extensive resource base describing each of the various functions of the Sequence Generator Pro program itself. This large section will help the user understand some of the configuration choices made in the program and help customize SGP. Also included here is a description of the simpler, or less frequently used, wizards and other tools that make imaging easier and more productive with SGP.

Part III, Topics, contains deeper discussions of the finer details of the most important wizards, tools, and ancillary programs called by SGP. This theoretical background and detailed description of settings will help the imager get the most of those sub-programs and routines. If the sub-program or parameter was rather easily explained, or rarely used, it is probably in Part II. If the sub-program is crucial and complicated, it is likely described lightly in Part II, but in much more depth in Part III. Finally, Part IV, Friends, tells about ancillary programs used to select targets for SGP.

This book is not meant to be read from cover to cover. At times, particularly in Parts I and II, it glosses over issues, giving just enough information to give the user what is needed at the time. At other times, as in Part III, it goes very deep into a topic so that the user can see what is happening under the hood and tune the parameters of his or her own installation of SGP. As a result, concepts recur from time to time.

This organization means that there will be repetition. That is, something glossed over in one chapter will be deeply explored in another. Topics will revisited. This is by intent. When somebody is working on one aspect of the program, he or she does not want to get bogged down in what is at that time a tangent. But that same tangent may be the meat and potatoes of a different part of the book. So, in all cases, one is given enough to keep going but is referred to a deeper discussion someplace else.

Some sections can be skimmed the first time they are read; other times these same sections may need a slow dissection. It is up to you.

Good luck! Stick with it, and soon you will be a Sequence Generator Pro yourself.

© Springer Nature Switzerland AG 2019

A. McConahayUsing Sequence Generator Pro and FriendsThe Patrick Moore Practical Astronomy Serieshttps://doi.org/10.1007/978-3-030-19719-3_2

2. Can SGP Run My Equipment?

Alex McConahay¹  

(1)

Moreno Valley, CA, USA

Alex McConahay

Overview of an SGP Imaging Rig

Sequence Generator Pro works with most of the equipment you will find in observatories and at star parties frequented by amateur astro imagers. To start with a basic setup you will need a telescope on a GOTO mount, an imaging camera , a guiding system, and of course a computer to coordinate it all. To get even more out of SGP, add a motorized focuser. And to really optimize SGP, consider a flat screen panel, a rotator, a cell phone to wake you up when something goes wrong, and even a full observatory with a weather sensor to close the roof when the clouds come in. One major requirement is that any equipment that does not work with SGP native support should be ASCOM compatible, as nearly all amateur astro equipment is.

Of course, any book would have a hard time keeping up with the changes in what equipment SGP can use. After all, the SGP website (http://​www.​mainsequencesoft​ware.​com/​Products/​SGPro) itself is very generic and is frequently in need of an update. It says rather sweepingly that " Sequence Generator Pro is compatible with a wide variety of Astronomy’s most popular brands!" It lists some compatible popular equipment and programs, and then invites anyone with a specific inquiry to contact them by email. For now, just remember that if you want to know if your hardware can be used with SGP, just ask if there is an ASCOM compliant driver for it or it has SGP native support. Or write directly to Main Sequence Software. Their address is on the webpage given above.

This chapter will discuss in some detail what to look for in this equipment. The next chapter will discuss details about how to connect it and get it to work together.

ASCOM and Star Trek’s Universal Translator

Let us take a moment to consider how equipment communicates. The various pieces of equipment are manufactured by dozens of companies from around the world. Each company, whether from the United States, England, China, Japan, Germany, Italy, or another country, speaks a native language. This could be confusing enough. But each manufacturer generally runs the product in that company’s software language, not their competitor’s or some universally agreed upon standard language. We are not talking about Japanese and Chinese and Italian here. The software that runs a Canon camera is not the same as runs a Sony or Nikon. And both differ from SBIG or Starlight Express.

SGP can communicate with some devices in their native language, but for much of this polyglot, if SGP is going to communicate, it needs Star Trek’s universal translator for imaging equipment. Luckily, with a few assumptions, we have just that in the ASCOM system.

../images/472657_1_En_2_Chapter/472657_1_En_2_Fig1_HTML.png

Fig. 2.1

The third column of this illustration, from the ASCOM website, describes how ASCOM works. Control programs (A) such as SGP and others communicate with the ASCOM driver layer (B). This is a universal translator. This layer in turn can speak to each device (C). In traditional schemes, monolithic and extensible, manufacturers must write different drivers for each different program.

Let’s assume for a moment that each of the cameras does the same thing. In whatever language the manufacturer uses, every camera must have a command that says something to the effect of Start an exposure… And another that says, "Continue the exposure for X seconds…. And another that says, End the exposure."

Along comes ASCOM. It is a universal translator that has its own list of commands, as it were. To oversimplify, each manufacturer supplies a translation table that translates the language of the manufacturer into an ASCOM command. Now, SGP can just speak ASCOM, and the computer translates this ASCOM command into something understood by the manufacturer’s device.

However, that simple assumption is not enough. A second assumption is that the equipment itself is different. So, different equipment can do different things, and some can respond to a larger set of ASCOM commands. For instance, with the development of CMOS (versus CCD) technology users can more often select gain when planning their shots. Other differences include that some cameras can be binned, and others cannot. DSLR users can specify ISO settings. SGP must know this and expand the range of commands it can send to these devices.

This is all done through drivers. Manufacturers (or sometimes individuals) provide drivers for each of the devices. Users must download these drivers and use them to configure the device for their computers. It is as if the user must download a translation table for each of the devices he or she is to use with the computer. The driver knows the capabilities of the device, can inform SGP of the capabilities, and has a way to translate the SGP (or other program) commands into the native instructional language of the device.

Although this all sounds very simple it is, in fact, very complex. New devices, especially devices with new capabilities, can present problems. Device and ASCOM drivers may simply not yet be released when the product is. It takes a while for them to come down the pipeline and get through the testing and trials to which any new product is subject. And, if there are new capabilities, the developers at SGP may be required to rewrite part of their interface to deal with the new capabilities.

However, before long, all this happens. A manufacturer cannot long survive if the equipment cannot be managed. So, it becomes imperative to have an ASCOM driver. When it is developed, SGP can run your equipment.

Computer

SGP, of course, needs a computer. Luckily, it does not need much of a computer. The demands on the central processor are relatively small. The computer spends much of its time sitting doing nothing while waiting for the camera to absorb photons. Even guiding, which is constantly taking small pictures, analyzing them, and issuing corrections, takes very few processing cycles on a computer. SGP and all its friends do not take a fast processor, or lots of memory.

../images/472657_1_En_2_Chapter/472657_1_En_2_Fig2_HTML.jpg

Fig. 2.2

SGP does not demand much in the way of a computer. Here are the author’s observatory computers. At home, the Outhouse Observatory is run from a twelve-year-old Lenovo (A). At GMARS, the rig runs off a refurbished desktop (B). The nice thing about old desktops is the native RS232 and lots of slots (C) for other cards.

Computer Suitability

Any Windows compatible laptop or desktop from the past ten years or so can run it. Although it is generally a good idea to update to newer software releases for compatibility and security reasons, the SGP Forum specifies that program will be supported at least through 2020 on Windows 7, and until 2025 on Windows 10. And, as with all programs, once a program is working on a computer, it tends to stay working. So, even though Microsoft may be updating Windows, and Main Sequence Software is updating SGP, your own copy of SGP on your old computer will continue to run as it always has even if you skip updates. (Well, as long as you use the same equipment and nothing breaks, etc.)

Data Storage

One function of the computer is to store the collected data. A night’s imaging can easily run to perhaps a gigabyte of data. This should not challenge any modern computer with a modest hard drive. However, if you tend to store the data on the acquisition computer, or if you use the machine for other functions, a hard drive can fill up. Those with smaller hard drives should consider removing the data occasionally to a larger storage system by means of a USB thumb drive, flash card, or some other method. Another solution that has worked for some, but not for others, is to save the data files directly to a thumb/flash drive during the imaging session. Then the thumb drive data is transferred to a larger, more powerful processing computer. Give it a try if you have limited hard disk storage. But be prepared to make room on the hard drive if the thumb/flash drive does not work well with SGP on your machine.

Ports and Connections

Another consideration for the computer is how it can connect to the various devices SGP manages. At a minimum, you would have an imaging camera , a guide camera, and a mount interface. Perhaps your system would also have a separate filter wheel. As the system develops, the imager would add focus motor control, temperature sensors, weather sensors and observatory control cables, and various other cables to the computer. The world of imaging hardware is still very traditional, with good-old RS-232 connections found on many devices. Other devices run on USB ports, both 2 and 3. Your computer should have as many native USB ports as possible, and if you can find a computer with RS-232, you can be ahead of the game. But, let’s face it, finding a laptop that can go into the field with four USB ports is rare enough, and RS-232 – virtually impossible nowadays.

RS-232 ports can be connected to USB ports through serial converters. There are many on the market. Some work all the time, others may work only when they feel like it. In general, avoid the bargain brand. By sticking to the Keyspan, with the FTDI chips, the imager can avoid many frustrations.

Another way to make up for lack of ports is to use a multi-port USB adapter. These also come at a variety of price and quality points. Some are powered (with a separate power supply) and some rely on the power from the computer itself. A four outlet splitter can be had for as little as $5. Or one can spend $65 for the same number of ports. If you want to avoid trouble in the long run, in general spend about $30 or more, and make sure any multi-port adapter has its own power supply.

Many imagers have found the greatest success by connecting the imaging camera to a dedicated port, the guide camera to its own dedicated port, and then using a splitter to accommodate the other devices as necessary. But no matter what one does, experience and experiment is often required to get all those cables connected to the machine.

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Fig. 2.3

In choosing your computer, also do what is necessary to control light at your imaging site. Any computer screen puts out too much light for an observing field. The screen need not be all that large. Be careful with your computer screen to see it is fully shielded and covered so that excess light will not escape.

Monitors

For a monitor, consider the situation. The imager will be out on a dark night. Perhaps the imager is alone and does not mind a glaring screen. But, often, the imager is at a star party with lots of dark sky enthusiasts, or even letting SGP run the imaging scope while he or she is snuggled up to a big telescope star hopping across the sky. No time for more light than necessary. A netbook does not have a big enough screen, in general, to see all the details of an SGP session. A 27-inch-wide-screen makes a very impressive display but is totally unnecessary and probably counterproductive. The main advantage is that you can have full-size planetarium programs, the full PHD2 Guiding screen, and the SGP screens and windows all operating at the same time. However, it is not necessary to have these separate programs visible at the same time during an imaging run. The simple 17-inch laptop-sized screen is more than adequate. But, at a dark sky site even its screen should be darkened (dim the brightness control) and shielded with a red screen to prevent light leak to the imager’s camera system and to all the dark-adapted eyes at a star party.

Non SGP Requirements

Finally, it should be said that the computer described above is for running SGP, and not for processing images or other tasks. SGP users often load other programs into the computer and use them while imaging. Some surf the web while imaging. Others process images. It is not at all unusual to load PixInsight ® and Photoshop® into the acquisition computer so that the imager can do interim processing just after the images come in. What if the imager simply wants to use the same computer for finish work? No problem for SGP. It can run in the background while the user is doing those other things. But those other things will undoubtedly require more powerful computers and more storage. So, in selecting the computer, be sure to factor in other uses besides SGP.

Software

The next few pages give an overview of the types of software that must be loaded into this computer to run SGP. After this brief introduction, this handbook will spend a chapter commenting more specifically about how to download, install, and coordinate these software packages.

What software should one load into the computer? Well, Sequence Generator Pro of course. But there are other packages that the imager will want.

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Fig. 2.4

Sequence Generator Pro comes in two versions, as described on their website.

And even with Sequence Generator Pro, there is a choice to make. It comes in two editions: Sequence Generator Lite , and Sequence Generator Pro. This book is about the Pro edition so we will only refer to Lite by referring you to the website (http://​www.​mainsequencesoft​ware.​com/​Products/​SGProCompare), which has a long list of features available in both editions. You may peruse it at your leisure. Both can be used to take a series of guided pictures on various targets on a given night. But the Lite edition requires more attention during the session, requires re-entering of hardware data, and misses out on meridian flips, automated focusing, the power of plate solving, and other tools and wizards.

The software downloads with the Pro edition and becomes Lite after 45 days if one does not upgrade to the Pro. The Pro edition offers full functionality for 45 days for free. If you do not license the Pro edition at the end of the 45 days, it is possible to get an extension by writing a request to SGP.

Behind the scenes at SGP, the program is calling on subroutines in the operating system, add-ons to that operating system, and apps that allow the various programs to work together. These programs are generally highly dependent on one another. Before using one’s computer to run SGP, one must install these other programs, and if they are already installed, they should be updated so they are all at the same level of compatibility. These include Microsoft.NET and the ASCOM PLATFORM.

Plate Solver

Sequence Generator Pro relies on a plate solver. A plate solver is a program that analyzes an image and picks out the stars. It finds patterns among those stars, analyzing the angles and distances between sets of stars. It then matches this data to information in its database. When it finds patterns that match, it knows where the picture is in the sky. Plate solving is critical to the imaging session because with it, SGP points the camera, rotates it if necessary (and possible), makes sure the composition is what the imager wants, completes a meridian flip so that all the subexposures are centered at the same point of the sky, and so on.

SGP can be used with various plate solvers, including PlateSolve2 from Planewave, Pinpoint from DC-3 Dreams Software, Astrometry.net , Local Astronomy.NET server (ANSVR ), and Elbrus . PlateSolve2 is free, included in the SGP package, and very fast and powerful. Since the PlateSolve2 included with SGP interfaces directly with SGP, the user should not separately download the program itself. However, the user must download the appropriate database that PlateSolve2 uses. The user may also want to do blind solves, which do not need much in the way of hint (information about image scale and probable location). With an Internet connection, no additional software is needed. But the functionality