We have been asked from time to time to explain in more detail the similarities and differences between the STF-8300M and the STT-8300M since these two models both use the same CCD. For the beginner it can be a bit consufing to have to sort through all the specifications and try to determine which features are important and which ones might not be so important to the new user. This section is therefore designed to compare these two models and outline the differences and similarities and how they might apply to you. As a general overview, the two cameras have almost identical electronic specifications and will produce the same quality image at a given temperature. The primary difference between the cameras is that the STT, for a somewhat higher price, has better cooling, and more advanced features than the STF.
Lets’ start with a table covering the major specifications and features to be discussed:
|Dark Current||.02e- @ -15C||.02e- @ -15C|
|Download Rate||< 1 sec||< 1 sec|
|Full Frame Buffer||Yes||Yes|
|Internal Image Processing||Yes||Yes|
|Even Illumination Shutter||Yes||Yes|
|User Rechargeable Desiccant Plug||Yes||Yes|
|Lens Adapters for Canon and Nikon||Yes||Yes|
|Standard Filter Wheel||8-Position||5 or 8-Position|
|Self-guiding Filter Wheel||8-Position||N/A||*|
|Cooling||2-Stage TE||Single Stage TE|
|Cooling Delta (Max / Regulated)||-55C / -50C||-40C / -36C|
|Water cooling ready||Yes||No|
|Built-in RBI Pre-Flash||Yes||No|
|Remote Guide Head Support||Yes||No|
|Self-Guiding Filter Wheel Support||Yes||No||*|
|Adaptive Optics Support||Yes||No|
|Size||4.9 x 4.9 x 2.9 in.||4 x 5 x 2 in.|
|Weight||2.7 lb.||1.8 lb.|
|Power||12VDC @ 3.5A||12VDC @ 3.0A|
|Price of basic camera||$3,695||$1,995|
|Price of camera + FW8||$4,490||$2,890|
|Price camera + FW8 + Self-guiding||$5,290||$4,360||*|
|* The STF does not have “self-guiding” controlled by the camera like the STT. A similar configuration can accomplished by the addition of a custom OAG-8300 Off-Axis Guiding assembly and the ST-I autoguider. The price comparison takes these additional accessories into account.|
You will notice that the first eleven specifications are the same for both cameras. OK, so far so good. What this means is that the two cameras both use the same CCD, have the same read noise, the same dark current at a given temperature, the same download rate and some of the same basic features like a full frame image buffer and USB 2.0 electronics. The basic image quality will be the same from either camera, unless you need the additional cooling of the STT due to your location (high ambient temperature) or imaging application (e.g. long exposure narrowband).
Self-Guiding Filter Wheel
Where the two models start to differ is shown from the line of the table starting with “Self-guiding Filter Wheel.” The STT Series of cameras has its own unique Self-Guiding filter wheel. This filter wheel has the self-guiding CCD built-in to the cover in front of the filters. In addition, both the Standard and Self-Guiding Filter Wheels for the STT Series use a positive centering mechanism that yields micron-precision filter positioning. This makes it easy to acquire highly accurate flat field frames even after the filter has moved several times. This type of filter wheel is not available for the STF Series. However, a similar configuration can be created for the STF by adding an OAG-8300 Off-Axis Guider and an ST-i guide camera to the system albeit at an increased cost and with the additional control of the ST-i. [Read more about the Self-Guiding Filter Wheel]
The STF has a single stage TE (thermo-electric) cooler capable of cooling the CCD to a maximum of -40 degrees C below ambient. The STT has a two stage TE cooler capable of cooling the CCD to a maximum of -55 degrees C below ambient. If you live in a very warm climate, where it stays warm at night, then the additional cooling of the STT can help to improve your images by reducing the dark current noise more than the STF camera. This will matter less if you nights are typically cooler than about 20C.
The STT camera has the ability to attach water tubing for circulation of water to further cool the camera, or to cool the camera without the use of the fans. Water cooling is not available on the STF series.
The STT Series cameras have both USB 2.0 and Ethernet connectivity whereas the STF cameras have only USB 2.0. If you plan to operate the camera remotely, or over a long run of cable for any reason, the Ethernet interface can provide a more stable solution. It can also be operated over a local network or wirelessly using appropriate adapters.
The KAF-8300 CCD is relatively free of RBI (Residual Bulk Image) however other full frame CCDs like the KAF-1603 and KAF-3200 (also supported in the STT Series cameras) can exhibit this effect more often. Essentially the charge from a prior exposure remains trapped in the CCD for a period and can show up as a “ghost” image if not managed somehow. The pre-flash floods the CCD with IR light to mask this effect when it becomes objectionable.
Remote Guide Head
A Remote Guide Head is a separate guider, like the ST-I, but it connects directly to the main camera, eliminating extra cables running back to the computer. It is also lower cost than the ST-I. It requires a special port on the camera as it is an extension of the main camera’s electronics. The same Remote Guide Head port is used for control and power to the built-in guiding CCD of the Self-Guiding Filter wheel. This is available on the STT Series but not the STF. [Read more about the Remote Guide Head]
The AO-8T or AO-X Adaptive Optics accessories is controlled via a port on the STT Series camera and are not compatible with the STF Series. The AO is designed to help improve the seeing on long exposures taken through longer focal length scopes. The AO-8T can also significantly improve the results one gets when imaging through a commercial SCT by reducing vibrations. [Read more about Adaptive Optics]
Size, Weight and Power Requirements
As you might imagine, the STT is slightly larger and heavier and consumes slightly more power than than the STF. If you have a small refractor, the smaller size and lighter weight of the STF can be an advantage.
The additional professional features of the STT also come at a somewhat higher price. The STF-8300 alone or with an 8-position filter wheel is about $1600 less than the STT-8300. If you go all the way and want a self-guiding system including camera and filter wheel this difference is reduced to $930 due to the additional OAG and ST-i that must be added to the STF system.
For the beginner, it is difficult to beat the STF-8300 for value. A self-guiding system can be accumulated all at once or piece by piece over time. The STF camera is capable of images identical in quality to the more expensive STT-8300 at a given CCD temperature. For the intermediate and advanced imager, the self-guiding filter wheel and AO capability of the STT are found on no other camera. And for anyone living where it stays quite warm at night, the high cooling capability of the STT camera will definitely be appreciated.