Astrophotographers who regularly travel to remote observing sites require a reliable power source to last an overnight imaging session. In this article, I will describe how to construct a DIY field battery — the most essential component of any portable imaging setup. I will also discuss how to calculate the total power requirement of your system in order to determine the recommended battery capacity (ampere-hours) that will provide continuous power that will last overnight (longer than 12 hours).
A DIY field battery to power my DSLR camera, mount, laptop, and dew heaters
Passive anti-dew system (i.e., requiring no power like a lens/corrector hood) may be able to help but only up to a certain extent (it delays the formation of dew, perhaps for a few hours, but will not completely stop it). As soon as the temperature of the scope drops below that of the dew point, dew will start to form and you will have no choice but to end your observation early. Without an active anti-dew system (heating by using electricity), it is simply impossible to completely eliminate dew. In this article, I will describe how an inexpensive DIY dew heater could be constructed using nichrome wire as the heating element.
DIY dew heater using nichrome wire
About a year ago (November 2011), I started constructing a home-built autoguider, a setup astrophotographers use in imaging galaxies, nebula, and many other deep-space stuff. The setup is no different from what is used by observatories world wide, except that this one was built entirely from scratch. Feel free to browse the details of the project here.
A home-built autoguider setup showing the key components: (1) imaging telescope, (2) imaging camera, (3) guidescope, (4) guide camera, (5) tracking mount, and (6) a computer.
This part of the DIY guide focuses on the actual guiding operation and the drift-alignment method for precise polar alignment. We begin by first assembling the telescope along with the guidescope. We also attach the imaging and the guiding cameras and connect all the necessary cables leading to and from the computer.
Screenshot during actual guiding operation
Now that we have already devised a simple contraption that allows a computer to convert guiding commands into light pulses, our next task is to devise a way for a telescope mount to “read” these pulses and translate it into actual east-west movement. This part of the DIY guide will describe the wiring diagrams that will enable any computer to talk to any type of telescope mount (i.e., with or without an autoguider port).
Wiring diagram of a DIY autoguider
Guiding commands from the computer are sent through a port called ‘LPT1‘, or the parallel port (or sometimes called printer port). It is a kind of interface that allows a simple way for a computer to communicate with other devices. We will try to convert these ‘commands‘ into a form that can be easily interpreted by your telescope mount. The simplest way to do that is to convert the commands into light pulses using Light-Emitting Diodes (or LEDs). These light pulses in turn will be used to drive what is called a ‘light activated switch‘ that we will connect directly to the autoguider port or hand controller. In this DIY guide, we will focus first on how a computer (with the use of the guiding software called GuideMaster) can generate light pulses, by connecting LEDs to the computer’s parallel port.
The parallel port is mounted on a socket called DB25F(F stands for ‘female socket’) or DB25M(M stands for ‘male socket’). It has 25 pins (1 to 13 top row, 14 to 25 bottom row). For this project, we are only interested in pins 4, 5, and 25 (other pins will be utilized however in future upgrades). Shown below is a photo of my laptop’s parallel port.
A female parallel port (DB25F). Note the location of pins 4,5, and 25 (see arrows).