| review: Cooled CCD Camera Starlight Xpress HX916 (appr. € 3900,-) |
The HX916 is just the size and weight of an average 2 inch eye piece.
With the suplied 1 1/4 inch nose it can be used in every focuser.
Or you can use the M42x1 (Pentax Thread) to directly screw it to telephoto lenses (second hand ones or the ones they still produce in Eastern Europe).
The appropriate adaptor to give the appr. 27 mm of distance (camera body to lens distance) is included.
With it the lens is in focus short before the eternity mark.
An adapter for piggy-back mounting is also included (see below).
Technical specification
- 1300 x 1030 pixel
- Pixel size: 6.7 x 6.7 uM
- Chip size: 8.7 x 6.9 mm
- Read out noise: appr. 12 e- RMS
- Dark current: appr. 0.1 e-/s/pixel
- Full-well capacity: appr. 30.000 e-
- about 50% overall quantum efficiency
- AD-converter: 16 bit
- not self-guide-compatible (Star 2000)
- Linear resolution parallel: 75 line pairs/mm (best case, lines parallel to pixel array)
- Linear resolution diagonal: 53 line pairs/mm (worst case, lines diagonal to pixel array)
- Maximum spot size for a useful lens would be: 0.019 mm (worst case, lines diagonal to pixel array)
This CCD comes with a fast USB connection.
A whole frame takes appr. 10 seconds to download (on a 1GHz laptop).
The USB cable is lighter than the printer cable which decreases the moving load on the telescope.
This camera is reliable in operation.
It has very low dark current so you can use exposure times up to 1 hour without a problem.
Well, if your mount and weather condition allow to do so...
This is reached with only one peltier element for cooling.
This cooler is not regulated for a constant temperature of the chip.
This means you have to take a dark frame for each specific outdoor temperature.
I am taking darkframes between the RGB and the luminance frames.
So the temperature is close enough to correct all the frames without a problem.
More and more I did not take dark frames at all and just subtracted a master bias frame.
This leaves more time for exposing the light frame and gives better SNR under alomost all conditions.
Thinks is thanks to the excellently low dark current.
There is no special element to prevent the chip from moistured air and therfore ice crystals inside the housing which degrade the image.
The good thing: this camera doesn't need it!
I work a lot in really moistered air so that sooner or later the water is dropping out of the tube of the Newton.
But I never was faced to ice crystals (at least in the camera ;).
The trick is, that the coldest area in the camera is the cooler and the ice is forming there - well away from the optical path.
This CCD has a very good blue response.
This is important for three colour work and gives exposure times close to 1:1:1 for R:G:B.
On the other hand the CCD is not very sensitive to infrared.
I never use an IR-blocking filter with it on APO-refractors.
This detector made by SONY is very robust against blooming.
You can hardly achieve it in practice.
This is reached *without* a big loss in sensivity or non-linearity (about 90% of full well capacity).
The sensivity is normally decreased on Anti-Blooming-Chips because the drain to eliminate the *blooming* electrons takes space in the sensitive area.
The SONY chip used in the HX916 user HyperHAD technology.
Actually this means every pixel has a micro lens in front to collect light from the non-sensitive drains.
Star 2000 self-guiding
This camera cannot be used for self-guiding.
I use my old MX516 as a guiding CCD instead.
Service / Support
Another thing I really should not forget about: The support of Terry Platt from Starlight Express is really fine.
There is quickest response for every question on his message board.
Very often by himself.
But more and more by the growing amount of skilled and motivated Starlight CCD users.
Conclusion
The HX916 is a very good megapixel CCD for that price.
The good color balance makes it perfect for RGB techniques.
The small pixels are perfect for shorter focal length telescopes and even camera telephoto lenses, but the small pixels are demanding for 0.019 mm spot size of the optics.
Ordninary 35 mm photo lenses very often have a spot size of about 0.03 mm.
Hence a slight amount of oversampling would result at 1x1 binning.
It is very good for high resolution takes of the planets and for deep sky because of the very low dark current and read out noise.
Search photos taken with the HX916
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