Hi, I note that most if not all CCD cameras lack of memory (eg. SBIG STL-11000M) and therefore, it takes some time (30 s) after each shot to download the image to the computer before taking a new image, and thus the computer must be connected to the telescope dirtectly or remotely to collect images. Is there a reason and which one for which SBIG does not develop a CCD with an internal RAM memory, using for example high capacity and high-speed flash cards (SDXC Class 10 or UHS) ? Thanks in advance Thierry
There have been a lot of changes since the old STL models, which had only a line buffer and used USB 1.1. Modern SBIG models have RAM memory. That is volatile memory, which is used to isolate the CCD from variations in computer download speeds. Unlike older models the memory is large enough to buffer the entire image. Higher-speed USB 2.0 interfaces in the new models also download the images much faster, to the point where the limiting factor for most models is CCD readout speed. (Some of the sensors are capable of higher speeds, but reading them out faster results in higher read noise. Other sensors are simply not capable of higher speeds.) SD cards are a possibility for future models. A computer or other interface device would still be needed for the user interface, so it is not clear that there would be a large benefit to using the cards.
Thanks Doug, I have read that STL-11000 series have no ram (only a buffer, right, as can do DSLRs), what explained the 30 sec delay between pictures. I think that we could resolve this delay in using e.g. flash memory (an external storage device) but at the condition to prefer downloading all pictures later, and the end of the session. I understand that the computer remains mandatory to perform initial tasks (lock on the target, focusing, etc) and thus that the possible interest of a SD card doesn't seem obvious. But who knows. Although it is a out of context on this forum, could it be possible to made a wireless CCD with a flash memory and SD card (like are DSLR) ? This solution could eliminate the forced task of downloading data after each picture and could also eliminate 50% of the cabling system. So, at start of his session or even during the session, the amateur could select to download pictures either on the internal flash memory or on the SD card (or automatically on both if a SD card is available) and then download pictures only at the end of his session. Or, being close to the ccd, he could extract the SD card and plug it into his computer once at home. Of course, the hard link to the CCD as it is currently 'd always remain an alternative. At a time of further miniaturization and Wi-Fi links affect all devices, this flexibility seems a nice plus. Is it something somewhat planned to SBIG ? (I know that many remote telescope use SBIG ccds and control them via a remote computer too. So we are not far from the proposed solution). Thanks for your lights. Thierry
STL was slow because of USB 1.1. We are of course actively developing new products. We're not ready to make any announcements at this time.
