SBIG STT-3200ME

A new SBIG camera was delivered to me by Ad Matthijs (Astrotechniek) on 17 February 2013: a STT-3200ME with Selfguiding Filterwheel (FW8G-STT as it is called by SBIG).  You can find all details concerning this camera and accessories on the website of SBIG of course.  The camera comes in a Pelican case, a little larger and thicker than the Pelican cases for the ST series cameras but smaller than the STL camera cases.

This camera is to replace my SBIG STL-4020M (sold) and is complimentary to my SBIG ST-10XE with CFW-8.  The new camera has the same type of CCD as in the ST-10XE (KAF3200-E) but with the microlenses (KAF-3200ME) as in the ST-10XME.  These microlenses in the STT-3200ME should get more light into the pixels and make the camera more sensitive than the ST-10XE that has the sensor version without microlenses.

A surprise, that I only learned after submitting the order, is that the FW8G-STT does not have the "normal" T-thread connection (M42x0.75 metric thread) but the larger STL-camera type threads to connect the nosepiece or to connect to the telescope  (STL thread is 2,156"x24tpi).  This meant that I had to check and change the adapters that I used with the STL-4020 and ST-10, because off course the backfocus distance of the new camera with filterwheel is different as well (54 mm).

Drivers:
Together with the new class of cameras that SBIG has launched in the past years, they also updated the drivers so they can be used on 64 bit PC systems.  The utility that SBIG ships with the cameras (or can be downloaded from their website) is the SBIG DriverChecker, now renamed DriverChecker64.  If this is the first SBIG camera that you use, you will be using these new drivers of course.  Owners of older cameras, like me, must make sure to follow the instructions in the handbook, als the old DriverChecker program and older drivers must be removed from the PC before installing the newer types of drivers and camera.  After installing the new program and new drivers, you must also re-install the older cameras that you still have, I had to do this for my ST-10XE and my ST-402 cameras.

Software:
For imaging and basic image processing I am using Software Bisque's CCDSoft V5.  While I was waiting for the camera to arrive, I was astonished to read on the SBIG Yahoo!Group that CCDSoft did not support the STT series, although this program was still mentioned in the documentation. SBIG worked with Software Bisque so that, only a few weeks before the camera arrived, an updated version of CCDSoft was avaible that can connect to this new camera.  However, Software Bisque have announced on their webpage that they consider CCDSoft to be "legacy software" and as from mid 2013 it will no longer be supported!   So it looks that I will either have to upgrade my planetarium program TheSky6-Pro to the successor TheSkyX with its camera control extension (if this supports STT cameras), or change to MaximDL...

I use Software Bisque's TheSky 6 Professional.  One feature of the program is that you can superimpose the field of imager chip and autoguider chip over the starmap.  The program has the default data e.g. for the SBIG ST-10XE and it's autoguider.  For the STT-3200 the ST-10XE overlay will work for the imager chip but not for the autoguider chip because the user can change the position of the autoguider relative to the imager and the autoguider contains an extra compressor lens so that the image scale is different on the autoguider (different focal length).
In TheSky6, the user can specify or edit the field of view overlays, both for the imager chip and the autoguider chip.  I selected the ST-10XME+ST-237 overlay and edited it to read STT-3200ME + KAI-0340 (Mewlon) and a second instance STT-3200ME + KAI-0340 (TEC140).  Both these telescopes work at f/7, with the extra autoguider focal reducer this becomes f/5. So, instead of size in mm I used the f/7 field of view size in arcminutes for the imager and the f/5 field of view size in arcminutes for the autoguider, this for each telescope separately. The offset of the autoguider (Element 2 as it is called in TheSky6) was determined, after adjusting the pickoff mirror, by centering a star on the imager chip (oriented N/S E/W), noting the declination, then moving the star to the middle of the autoguider chip and noting the declination difference in arcminutes.  This was then used in TheSky6, detector data for field of view, in the STT-3200 the autoguider is in the same position relative to the ST-10, that is in the direction of the cables.
The offset measured for my Mewlon 300CDK with reducer is 23', for my TEC140 with fieldflattener it is 47'.  Note that the image of the autoguider is 180° reversed with respect of the image of the imager.  Also, it seems the KAI-0430 chip is an ABG sensor.  Below or two images taken with the autoguider.



Filterwheel:
There is a separate concise manual concerning the installation of the FW8S-STT/FW8G-STT filterwheel. To fix the filterwheel to the camera, this is simple: remove the cover and attach the filterwheel housing in its place.
Contrary to what its designation suggests, the CFW-8 filterwheel for the SBIG ST-10XE camera can contain only 5 filters, I have Astrodon LRGB filters and an Astronomik H-Alfa filter inside in the  CFW-8. These are screw-in filters of 1,25" diameter.
The FW8G-STT filterwheel, as its designation correctly suggests, has the possibility to hold 8 filters, my camera has a complete Baader LRGBC filter set plus Ha 7nm, O III and S II filters installed. These filters are unmounted and are 36 mm diameter, 2 mm thick.  Depending on the thickness of the filters, you have to use supplied O-rings either in front or behind the filters or no O-rings at all.  As I use Baader filters, I needed to put the filters in the filterwheel first, then on each filter an O-ring and then the plate that keeps everything in place.  Be sure to wear gloves to insert unmounted filters so you don't leave fingerprints, it is quite fiddly to do.
 
Autoguider:
 The cover of the FW8G-STT contains the autoguider.  The covers can be interchanged, e.g. if you would want to use camera lenses with the filterwheel, you will need the FW8S-STT without the autoguider to be able to do so.  The FW8G-STT is to thick to allow the use of e.g. Canon EOS lenses.
While in the ST-10XE the main and autoguider sensors are built in the camera housing, in the STT-3200ME the guiding sensor is either integrated into the filterwheel and sits in front of the filters or you have to use an external guider.  The fact that in the FW8G the guider is in front of the filters is a bonus when imaging through (narrow band) filters.  Drawback is that the autoguider CCD is not cooled in this case.  
The pick-off mirror that directs light to the autoguider CCD can be moved in the lightpath so that the position can be adapted to different sizes of CCD Sensor and can be adjusted in the lightcone of the telescope.  After the pick-off mirror is adjusted, the autoguider can be focused separately, so after focus on the imaging CCD is achieved, one can adjust the focus of the autoguider CCD.  A 0.7x reducer lens is mounted in front of the autoguider CCD. Also, the manual states "the star images on the tracking CCD may not be as good as your imaging CCD, since the focal reducer reduces the F/number by 0.7x, and you are quite a way off axis.  This is not a problem for guiding".
If you use only one telescope, or telescopes with a equal F/D value, you will only need to adjust the pick-off mirror and focus once (similar light cones).  If you use telescopes with a large difference in F/D (e.g. f/10 and f/4) you will need to adjust the pick-off mirror for each telescope so you don't get vignetting.  As the KAF3200 CCD is the smaller one in the STT series, the pick-off mirror can be adjusted quite close to the sensor edge.  There are three screws used to adjust the autoguider: a locking screw, a screw that moves the pick-off mirror in/out and a screw that adjusts the focus.  These screw-systems are not what I would call "high precision", there is some play that one can feel when adjusting, but then they normally don't need to be used often.  So, on first use one needs to adjust focus of the imager, then take flat frames with the telescope and adjust the mirror so that the pick-off mirror does not induce vignetting on the underside of the image (as it is presented on the screen).  When this is done, point the telescope to a star again, make sure focus of the imager CCD is OK and then adjust the focus of the autoguider.   When taking images with the autoguider, a clicking noise is heard,  this is a shutter in the autoguider assembly so that the autoguider can take its own darkframes and can close the shutter between downloads.  While adjusting the autoguider, the screw on the side of the FW locks both the movement of the mirror and the focus position.  As mentioned in the manual, after adjusting the position, it is a good idea to put some tape on the screw that adjusts the position so you do not change position while you want to adjust the focus.

Power supply:
During the first use of the camera to check it out and to take dark frames,  I noticed that the camera lost power frequently when moving it.  I had read about this behaviour on the SBIG list, also with other cameras that have the same type of power connector.  All it takes is to spread the tines in the power connector a bit with a small bladed screw driver, so that this center pin makes better contact.  The power supply delivered with my camera is a transformer converting 220 V AC to 12 V DC.  The cables are thick and get quite stiff at lower temperatures (say below 5°C).  So make sure to attach the power cable in a way that it will not offset balance of the telescope.  My SBIG dealer provided an extension to the power cable, much lighter but without the locking screw. I just plug this in and fix the cable to one of the handles so it is secure during use, this puts much less strain on the combination than the original heavy cable.

Connections:
The connection between the filterwheel/autoguider with the camera is done with cables.  The filterwheel cable (too long) needs to be plugged into the  I2C connector of the camera, the autoguider connects with a HDMI type cable.  These cables then more or less protrude from the side of the camera, so take care they don't catch on something while imaging.  It is impossible to put the camera + filterwheel into the case with the cables attached, so you have to disconnect them to store the camera.  Then the combination camera + filterwheel fits nicely in the case. 

First use:
I waited to mount the filters until I had done some tests and after making a first series of darkframes to compile a darkframe library for this camera.  Installation of the new camera went well, the shutter and filterwheel worked OK, cooling was fast and the download of an image from this camera is FAST (about one (yes 1) second versus about 25 seconds on the ST-10XE.  The noise of the two fans on the camera is noticeable and varies during the cooling sequence.  This cooling is also remarkably fast.
On the first try to adjust the position and focus with my Takahashi Mewlon 300CDK and reducer, the imager chip had the star Pollux in it's center.  When taking images with the autoguider, I saw two very distorted images on the autoguider but could not focus on these - however clouds prevented more testing that evening.  The evening after, I put Castor on the imaging chip and focused, then moved the star until it appeared on the autoguider chip and focused, then locked the autoguider.  The distortion of the stars on the autoguider image was negligible, so I guess what I had mistaken for distorted stars the first time were probably reflections from bright Pollux!
Due to the different image scales of the imager and autoguider, I think you need to calibrate the autoguider using the autoguider chip only (with e.g. SBIG ST-10 you can calibrate both with imager or autoguider chip).
I did some autoguiding tests while the imager was taking a series of pictures with different filters, this worked very well - as the autoguider sits in front of the filters there is no change in luminance of the guide star anymore of course .  This second session was again over due to clouds, the "new equipment curse" is quite strong with this camera ;-).
On 29 March I could continue with some tests, below are two images each 1 minute exposure, these images are reduced 50% for this webpage.





Camera size:
The STT-3200ME with the FW8G-STT is noticeably larger and heavier than the ST-10XE with the CFW-8. On the photo below, you can see my old SBIG ST-10XE next to this new camera. The ST-10XE with CFW-8 weighs 1500 gr while the STT-3200M with the FW8G-STT filterwheel weighs 2400 grammes. The camera body of the STT-3200ME measures about 120x120x105mm (including the handles).  The FW8G-STT filterwheel measures 210x160x45mm.



Here is a picture showing how the camera fits in the Pelican case, the white disk is an aluminum plug to close the camera when not in use, I had this plug custom made:

This picture shows why the camera does not fit in the case with cables attached:

Some pictures of the camera from different angles:




Below is a picture taken when the filterwheel was open to add the filters in the filterwheel, you can also see the inside of the autoguider cover: