/Review STL11000M

First light impression of the SBIG STL-11000M

Updated: July 29, 2004

After waiting for approx 6 months a big Pelican case arrived.
The wonderfully machined silver camera impressed from the first moment. The installation of CCDOPS and the link to the PC proved well on the first try. For the connection of the camera to CCDSoft an update from the Software Bisque website had to be installed.
Maxim DL v4.0 perfectly matches with this camera (universal SBIG driver).

The STL11000M uses a 36 x 24 mm interline antiblooming chip with microlenses. The quantum efficiency peaks at 500 nm with 50% and drops off to 31% at 656 nm (H-alpha).
See the absolute and angle depending quantum efficiency curves here. Even fast systems at f/2.8 stay within the 10 degree angle and so do not loose efficiency.

The primary net resolution of 4008 x 2672 pixel can be binned 2x2, 3x3 and 9x9 to shorten readout time for previewing.

The mechanical shutter operates between 3600 and 0.1 sec, the electronic shutter operates down to 0.001 sec using the latest driver update.

Due to severe vignetting and distortions my setup with the 4" TMB refractor had to be changed, the 2" feathertouch focuser is exchanged against a medium format Borg helical focuser, the Televue 2" reducer flattener is exchanged against a medium format TMB flattener.

What could be improved:
* The DB9 to RJ11 adapter is bulky and difficult to secure in dark or cold environment. A direct RJ11 connection would be great.
* The original power supply cable is very stiff, I exchanged it against a super flexible cable 3m long.

The power consumption of the camera is quite low without active cooling: approx. 0.8 A, peaking at 1 A during filter change.
The dependance of the power consumption (current drain at 12V supply voltage) from cooling output and the cooling performance is shown in the graph at right.

It can be seen that the optimum cooling is reached below 100%, due to the high heat dissipation at 100% cooling.
For the field operation the battery life can be prolonged sigificantly by adjusting the proper setpoint. Only 1-1.5 A camera drain at a cooling of 30 degree C below ambient proves the high efficiency and good design of this camera.

The use of Canon EF lenses is made possible by using a EF bajonet from an old disposed body that was attached to a 3mm base plate. This distance of plate plus bajonet is parfocal with the EF lenses. Installing the lens securing bolt is very important when fixing the lens to the mount instead of the camera. Vignetting is not an issue with this connection. Image of the EF connection at right.

However the aperture setting can be adjusted by a trick, so even well corrected lenses like the Canon EF 100 f/2.0 USM or the 300 mm f/2.8L can be stopped down one step to improve star tightness:
Connect the EF lens to a Canon body, select manual setting, select bulb or long exposure mode, set the desired aperture. Then press the shutter and during exposure disconnect the lens from the bajonet, the aperture will stay in the selected position. Then use the lens for the STL with the shown bajonet.

Light test with the STL-11000

A cropped 10 min dark frame at -15C setpoint in full resolution as zipped fits file:
here (971 kB)

The same dark minus a second averaged masterdark at same conditions as zipped fits file:
here (933 kB)
(both taken after firmware fix May 2004)

Flat field frame To evaluate the evenness of illumination I have used my new setup with the big TMB flattener and focuser that allows full illumination of the chip, check out the setup: here The stretched flat to the right shows an even illumination, only 2 small shadows in the left corners deriving from the internal 2" filter that is not exactly centered. Instead of my threaded filters I recommend to use directly the 50mm unframed filters.
New image calibration frames To evaluate the repeatability of the darks I shot 2 darks at minus 15C, 600 sec, added 1000 ADU to the first one and subtracted the second one. The cropped result is shown at right. The problem of the "unreliable pixels" - they show up as dark or hot pixels in the calibrated image has been solved in May 2004 by a firmware update of SBIG, it can be downloaded from the SBIG beta-download site. This fix avoids these deviating pixels effectively already during imaging, see image at right after installing the fix.
Dark versus Temperature To check the CCD temperature influence on dark noise a series of 60 sec darks has been taken, each of them Bias subtracted, the analyzed in Astroart. The table at right shows the average value and the standard deviation for the full frame at 1x1 after installing the fix for the unreliable pixels.
Bias frames A cropped bias at -25C is shown at right with the statistics of the whole frame. To check the CCD readout noise 2 Bias frames have been taken at -25C, then added 500ADU to the first one and subtracted the other one, then analyzed in Astroart. The image below shows the center with the histogramm and the statistics.

S/N comparison with Canon 10D

In a dark environment a wall was imaged at identical conditions: 50mm lens at f/4 and ISO1600, 20C ambient for the 10D 50mm lens at f/4 and 2x2 bin at -10C for the STL 0,25 sec exposure, images stretched to same contrast	full frame reduced size	crop 100% size
Same conditions 1 sec exposure Comparing the images resul ints approx. the same S/N ratio for 0,25 sec exposure with the STL as for 1 sec exposure with the 10D	full frame reduced size	crop 100% size

At near full moon and bad transparency between clouds a comparison on the central Orion area with the Sigma 50mm f/2.8 lens.

Even fully open the lens shows very good sharpness for a field of approx. 30mm diameter.

The data for the 10D were: ISO800, 60 sec exposure; raw mode converted to 16 bit tiff, stretched.

The data for the STL: 1x1 bin, clear filter, 15 sec resp. 60 sec exposure.

The animation shows a central 100% size crop of the image including a 60 sec each LRGB filter.

animation

A direct comparison with the 4" TMB refractor at equivalent pixel scale on M45

Data for the STL:
f/6.5, mag 5 sky, single 5 min L exposure cooled to -25C, dark calibrated

Data for the Canon 10D in winter conditions:
f/5, mag 5.5 sky, single 5 min unfiltered exposure at -2C and ISO400 in jpg-fine.

The animation shows the central portion in 100% size in b/w.

The gain in S/N is obvious, much more fine details.