Much of the modern success in amateur astrophotography is dependent on the marvelous advances in telescope, mount, and sensor technology that have come about in the last twenty years or so. The contribution of new software advances and open source projects must be included in this as well and is equally as responsible for the successes of imagers. Below I present the hardware as well as software that I use, along with any links to product pages where appropriate. Clicking on any of the highlighted technical terms will give additional information in interpreting the bulk of techo-babble that's about to ensue.
My primary imaging rig is housed in a mini roll-off-roof imaging obervatory of my own design and build - Inner Light Observatory. The primary OTA is a Stellarvue SV105 apochromatic refractor. The stock focuser has been replaced with a 2" Moonlite focuser with high resolution stepper motors for computerized focus control. This is saddled on an Orion Atlas EQ-G mount, modified with a Rowan belt kit (Rowan Astronomy). The mount sits on a custom built 8" diameter steel pier and is coupled using a top plate adapter from Dan's Pier Plates. The primary imaging camera is a QSI683 (Quantum Scientific Imaging) with integrated 8-position filter wheel and off-axis guide port (wsg-8 model). This is outfitted with a Starlight Express Lodestar X2 guide camera. All equipment is connected via USB to a StarTech 7-port DC USB hub and powered by a PowerWerx 30 amp DC switching power supply (imaging camera is powered separately on it's own adapter). I use Anderson powerpole couplings for all power connections which are run to a Rigrunner fused power bank (including dew heaters). The entire assemply is connected to an APC battery backup and surge protector. The rig is controlled by an on-board Quantum Access fanless PC stick with built-in wifi (Intel BayTrail T quad-core, 2GB DDR3L ram and 32GB storage - built in micro SD supplies additional 64GB storage) runing Windows 10.
My secondary rig consists of a mobile setup for lightweight, wide-field imaging. For this rig, the OTA is an Astrotech AT65 EDQ apochromatic quadruplet. I'm using the stock focuser and typically use an Orion mini kit for guiding - a 50mm guide scope and Orion Starshoot Autoguider camera. This is saddled on a Celestron Advanced VX mount and controlled via laptop. I primarily use a Canon 700D (Rebel T5i) for imaging on the mobile setup, but sometimes use this camera on the main rig as well. The camera has been modified by Hutech (IR cut filter removed). I also will occasionally piggyback the 700D on these imaging setups to capture wide-field Milky Way shots while imaging other targets with the QSI (as seen in the main rig image to the right).
I use several, powerful pieces of software to manage image capture, guiding, and processing. These are commonly and broadly used by astrophotographers and are considered among the best available for the task. For image capture on the main rig I use Sequence Generator Pro (Main Sequence Software) - one of the best pieces of capture and control software in my opinion. The software controls all devices via EQASCOM and can handle image capture, autofocus, dithering, auto meridian flip, plate solving, multiple target capture, and even observatory control. I'm using SGP for just about everything except observatory control and my main imaging rig is fully automated. This allows two things - frequent and efficient imaging and something elusive and rare in amateur astrophotography... sleep! As much as I love being out under the stars, work nights and those bitter cold nights of New England winter can cripple an imaging run. The ability to quickly get up and going and have data waiting for me when I wake is worth much more than what Ken and Jared are charging for SGP (don't tell them that!).
A standard-bearer for a number years in guiding software has been PhD guiding by Craig Stark. Although there are other pieces of software out there, this is now open source and in its second major edition (PhD2). Many features of PhD guiding work well with SGP including automatic reversal of calibration data on meridian flip, auto guide star selection and the drift alignment tools in later versions. On my mobile setup I typicaly use BackyardEOS for DSLR control and image capture - a great piece of software, intuitive and powerful. This lacks built-in planetarium software or plate solving so I use Cartes du Ciel and Astrotortilla to patch those needs, respectively. I'll likely migrate over to using SGP on the mobile setup eventually.
On the processing side, DeepSkyStacker is an excellent, free piece of calibration solftware that I've used extensively. More recently though, I've been using one of the more powerful processing suites availble, PixInsight (PI). Though unintuitive and relatively cumbersome to learn, PixInsight is the go-to software in astrophoto processing. Having a deep background in Photoshop however, I find that many functions in PI can more easily and effectively be accomplished in Photoshop. Therefore, I tend to use both in tandem and find that this yields more flexibility with post processing in particular.
When light of different wavelenths passes through a lens, colors will disperse due to the varied refractive indices of the lens at those wavelengths. This causes chromatic aberration; different colors being focused at differnt points causing color separation and fringing of objects imaged. Apochromatic refractors typically have a three-element lens that refocuses the wavelengths of light (typically red, green and blue) such that they have the same focal length and eliminate chromatic aberration.
Optical Tube Assembly (a.k.a. telescope)
Telescopes that are pointed at the infinite cosmos experience radiative heat loss to the cold, dark vacuum of space. This means that it is possible for your telescope to drop slightly below ambient temperature and thus, on humid nights, condense water from the air on your precious lenses or mirrors. Although your dew shield (that extendable tube that protrudes from the end of the telescope - or an accessory extension for newtonians and catadioptrics) can stave off the dew for a time, a dew strap or dew heater is one of the best defenses against condensate as this resistive heat coil will keep your optics above the dew point indefiniely.
Apochromatic refractors have a three-element lens that refocuses the wavelengths of light (typically red, green and blue) such that they have the same focal length and eliminate chromatic aberration (see "apochromatic" above). This will remedy chromatic aberration, however field curvature remains an issue with photographic systems. Lenses and mirrors typically focus an image not to a flat plane, but to a curved surface. A quadruplet also has another lens that serves as a field flattener, correcting the focus to a flat plane for the image sensor. Other telescopes have field flatteners as an accessory that is added to the optical system.
The common image sensor found in most point and shoot cameras contains an infrared (IR) cut filter that limits the incoming light in this wavelength. This prevents images from having an overly red cast due to activation of the sensor from this proximal area of the electromagnetic spectrum. Unfortunately, for astrophotography, this limits the bandbass from red targets in space, the most prominent being light from hydrogen-alpha radiation - one of the most common photons emitted from deep space objects, particularly nebulae. Removal of this filter makes a sensor significantly more sensitive to H-alpha light.
A typical German Equatorial Mount system like those shown in the images here have an optical system on one side of the RA axis and counterweights on the other. As the mount tracks an object across the sky from east to west (if staring far enough east) it will cross the meridian - the imaginary north-south line that bisects the sky into two parts, passing though the zenith. As the mount passes this point, the telescope and counterweight assembly is horizontal and from this point forward will place the counterweights above the telescope which is now on it's way to a mount collision. A meridian flip reverses this orientation to keep the weights lower than the OTA.
This term is a throw-back from the heyday of astrophotography when images were captured on glass plates coated in photographic emulsion. Astronomers would layer and align the stars in sets of these glass plates to determine the relative positions of each image to the others. In a way, this is what plate solving algorithms do - star positions are extracted from an image and the information is queried to a database to determine the precise position of the image in the sky. This technology allows precision placement and automatic slewing of telescopes making target hunting and recentering of targets amazingly simple - a game changer in astronomy.
Accurate sky tracking requires that the RA rotational axis of an equatorial mount be precisely aligned with the celestial pole, which in the Northern hemisphere is very near polaris in Ursa Minor (the pole star, from where it's common name is derived). This is not a trivial task for imaging purposes as more precise alignment is required for long exposures. Drift alignment is a technique used to determine the accuracy of polar alignment by letting the mount track for a while (without guide corrections) to determine the amount of drift in either axis. A perfectly aligned mount would have decernable drift.
© 2022 D. Heilman