Starlight Xpress SXVF-H16
Submitted: Tuesday, 19th February 2008 by Dr Dietmar Hager
Features and Design
In manufacturing this monochrome large format CCD Starlight Xpress departed from their tradition of installing Sony chips, that are well known and appreciated for their very low dark current signal. A KAI4021M from Kodak was used in this CCD and the reason for this decision was that unfortunately Sony do not manufacture large mono chips.
In order to diminish the undesired negative effects of the higher dark signal, SX introduced a 2 stage Peltier element to cool down the chip to about 40°C below ambient.
Pixel size is 7.4 microns in a 15.15mm square area. This results in 2048 x 2048 pixels; a total of 4.19 Mega-pixels. Nevertheless the download time of a full resolution image is quite short, since the high speed USB2.0 interface does this comfortably in 2.8 seconds.
The H16-chip covers about 2/3 of the area of the very large M25C Sony chip. You can find more features and detail of technical specifications here.
I appreciate the low weight of only 390g. This is very convenient for my scope that has quite a long back focal distance. So the mechanical lever is really huge and therefore a "light" CCD is what I need in order to prevent differential bending in the mechanical axis. This might also be a huge advantage for any scope with long back-focus or in those that are lightly constructed such as some Newtonians.
The dark signal is very small as you can see in the 2 dark frames below. I have used only 1 dark frame for each exposure time in both, 1x1 binning and 2x2 binning. It is not necessary to take more darks...luckily.
This is also a big advantage in comparison to some Kodak-chips in other CCDs, where the accomplished imager has to recreate a huge dark frame data bank every 2 or 3 months, since all chips age over the time. Many Kodak chips in different CCDs have a disadvantageous signal to noise ratio, so the serious Kodak-chip-CCD user has to take at least as many dark frames as light frames. In case of SXV H16 I was very pleased to find that this effort is definitely not necessary.
Here is a comparison to 2 Kodak-chips:
Certainly those CCD Cameras are very sophisticated items and splendid images have been taken with those CCDs. Gorgeous results can be found all over the web. It is not my intention to offend anyone, but there is a significant difference in those chips and therefore pre- and post-processing is much more demanding and time consuming. (In order to hold down the noise, methods like dithered guiding, bias frames, a dark to light frame ratio of 1:1 etc become necessary...taking darks and bias frames and recreate them all 2-3 months to compensate aging of the chip finally accelerate the aging of those chips...) In using low noise chips, you can make every frame count for the image and lifespan will be longer.
Another important consideration is power-consumption of the device. For Astro-photographers like me, who run their observatory on solar power with rechargeable car-batteries (solar panels), low power consumption is an essential issue. I have found a very low average consumption of only 900 milliamps.
The anti-blooming is powerful. I have not seen "bleeding" stars yet. The spectral response is not really strong, as there are CCDs using Kodak KAF-1301E/LE Chip, that have a QE over 70%. That is very encouraging cos you gather the signal rather quickly as I have found in a test. I have also tested a one shot color chip KAI-2020CM. However on the downside of this chip the signal to noise ratio is really very bad: what you gain in signal you tend to lose in noise - so, many darks are vital to alleviate that problem. Anyhow, H 16-QE is quite good with a very nice 55% peak in green light.
As you can see in the first light image below the H16 has even imaged the H2 regions in the irregular galaxy NGC 4449 successfully, without using a H-Alpha filter.
Here is another result taken with SXV H16 - Sunflower Galaxy.
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