DSLR Astrophotography by David Ahn

Telescopes
Skywatcher 200mm f/5 Newtonian Reflector
My imaging scope, this is a typical open tube newtonian reflector with secondary mirror held by spider vanes. Its relatively low price range makes it a good entry level telescope for astrophotography, but requires some modifications to fully utilise its optical potential.

Aftermarket modifications done
--Rack&pinion focuser replaced with crayford type
--Crayford focuser tube cut down to length flush with inside of OTA.
--Motorised the focuser for software based focusing
--Added light baffles inside the tube
--Replaced rear steel mirror cover with velcro foam for easy access to collimation screws, better cooling times and weight reduction.
--Rectified TDE(turned down edge) by covering edges of the primary mirror.
--Added foam dew/light shield
--Added mounting rings for guide scope
--Finder scope removed during imaging for weight reduction.

Skywatcher 70mm f/12 Achromat Refractor
Achromat refractor used as a guide scope only. It's long focal length matched with a ccd video cam makes it an ideal guide scope. However, it can be a little tricky finding a bright enough guide star on some targets due to its small aperture and relatively insensitive sensor of the Neximage ccd camera. I have added a flip-mirror with a par-focal eyepiece to aid in guide star acquisition and focus.

Mount
Skywatcher EQ6 with Skyscan Goto
A German equatorial mount made by Skywatcher. It has a claimed carrying capacity of 25kg, but for imaging the payload should be kept on the far lower side of this figure as possible. It comes with a typical worm gear PE (Periodic Error) and I wouldn't consider imaging without the aid of an autoguider to compensate. The Skyscan goto offers an option to train the drive for PEC (Periodic Error Correction) for preemptive correction. Backlash compensation is also available in the Skyscan on both RA and DEC Axis.

Cameras
Canon EOS 350D is an excellent candidate for DSLR Astrophotography. Just like its predecessor 300D a lot has been documented on modification for astrophotography, particulary replacement or removal of its factory low-pass filter. The low-pass filter removal will allow full exposure to Hydrogen alpha spectrum, an important stuff in astrophotography.

Celestron Neximage
This is a planetary imaging ccd cam by Celestron, basically a repackaged Philips webcam. Although it is possible to do SC(long exposure) mods on it but I have left this cam unmodded. The use of realtime stacking in PHDguide makes the mods unnecessary.

Logitech Quickcam 4000
A heavily modified webcam I built few years back. It has SC2 mod with active peltier / water cooling. I don't get to use it much now days, but it's good for a laugh now and then.

Filters & Optical Accessories
Astronomik UV-IR
After the removal of factory low-pass filter out of the Canon, I need to use an external IR filter. I have mounted the filter on the T-thread of the MPCC, this protects the MPCC and any other filter i want to stack.

Astronomik UHC-E
Filter used for blocking out bands of spectrum from mercury and sodium vapor based street lamps. Very useful for imaging from light polluted areas like my backyard.

Multi purpose coma corrector (MPCC)
Used to correct coma in DSLR newtonian setup. when correctly spaced from the imaging chip it produces nice round stars all the way to the edge of FOV.

Telescope control
Starmate
LX200 (Meade) command interpreter/emulator. This box allows me to send LX200 command to my mount and focuser. It also comes with a wireless controller with remote slew, focus and dslr timed shutter control functions.

LX200 Emulator
Home-built LX200 emulator based on Atmel programmable chip. I built this one to keep myself sane during a long period of cloudy nights. It basicalyl recieves LX200 commands down the serial channel and converts it into optically isolated ST4 signals for autoguiding, pretty much what the starmate does.