Moravian instruments, Inc., source: https://www.gxccd.com/art?id=515&lang=409, printed: 14.12.2018 4:19:30
Main page Products CCD & CMOS cameras Articles
|Gx Cameras Mark II||Updated: 11.6.2018|
|Gx series of cooled astronomical cameras evolved through many revisions, each bringing improvements, new features or just more aesthetic design. We are proud these cameras are now used to capture state-of-the-art astrophotographs (just see our Gallery section) as well as to acquire professional-grade research data. Now we introduce redesigned cameras with important enhancements, so they deserve denotation Mark II.|
Gx Mark II cameras inherited all proven design concepts and features from the previous generation cameras (we now call them Mark I). To hint such inheritance, Mark II cameras look similar to Mark I (camera head shape, allowing optimal placement of internal components, also belongs among the proven concepts). But still, Mark II cameras look differently, with modern design hinting they are significantly enhanced compared to their predecessors.
Mark I cameras already reached read noise very close to the CCD sensor limit, so there is no room for significant improvement here. Also the response linearity was limited by the sensor, not by the camera electronics. Cooling was enhanced with the introduction of EC (Enhanced Cooling) option for Mark I cameras and users capture single exposures up to 20 minutes long, so the need for even better cooling it not that pressing. Overall modular mechanical design, allowing stacking of various internal or external filter wheels, off-axis guiders and telescope adapters with exceptionally low back-focal distance, also fulfilled requirements of majority of users.
Mark II cameras brought two major enhancements compared to their predecessors. The first one is the download time lowered around 2.5× in the low-noise read mode and around 2.7× in the preview mode. For example, full resolution (no binning) preview image of the popular G2-8300 camera is now downloaded in 3.5 seconds instead of 10 seconds, necessary to download image from Mark I model.
When a single exposure spans 5 or even 10 minutes, download time in the order of tens of seconds is not very important. But when the target object is being centered within the field of view, camera is being focused, or when a series of short exposures is acquired e.g. during the course of photometry measurement, faster download is always beneficial. Take for instance a series of 30 seconds long exposures performed with G4-16000 camera (such short exposures are normal when capturing photometry of some bright object). While the Mark I camera needs ~60 seconds to perform one clear-exposure-read-save cycle, Mark II G4 camera performs the same cycle in just ~45 seconds. This means Mark II camera can gather 33% more data during the observing session.
The speed-up depends on the camera model and it can be between 2.4× and 2.6× for low-noise read mode and between 2.5× and 2.9× for preview mode. Exact speed-up for various cameras are summarized in the following table:
What is very important, we made sure not to harm any other quality parameter when downloading images faster. Typically a read noise increases with faster download, so we paid big attention to keep the read noise at CCD sensor limit (in fact, Mark II read noise is even very slightly lower compared to Mark I). Because low read noise is sometimes achieved artificially, at the expense of some other parameter, we also took care to preserve camera linear response, a very important feature for scientific and research application.
Despite careful alignment of the sensor to be perpendicular to the optical axis during camera manufacturing, some users could experience slight misalignment (sometimes caused by imprecise sensor position within the camera head, but often caused also by external filter wheel, telescope adapter, used corrector, focuser etc.). All Mark II cameras are equipped with adjustable telescope/lens adapters. Adjustable adapters can be mounted directly to the camera head or to the external filter wheel front shell.
The adapters are designed to allow easy adjustments of the optical axis. They contain ring-shaped spring, capable to hold even the heavy G4 camera with EFW in position, defined by three precision pulling screws. Pushing screws are also present, but not necessary for adjustments — they are included to fix the position after the alignment finished.
And yes, the last enhancement is not functional, but aesthetic. It is upon every user to judge whether our effort was fruitful.