Optec - Model TCF-Si, Integrated Temperature Compensating Focuser.
Optec has created integrated variants of their main line of focusers: the new TCF-Si and TCF-S3i. Unlike their predecessors (the TCF-S and TCF-S3), these focusers feature an integrated control board that allows direct connection between computer and focuser.
You can see the differences between the TCF-S (left) and the TCF-Si (right) in the photo of both below.
Unlike the predecessors, the TCF-Si focuser features an integrated control board that allows direct connection between computer and focuser, thus eliminating the necessity of the external TCF-S/S3 control box.
Mechanically, the TCF-S is a robust Crayford style motorized focuser with high repeatability, no play and nearly zero backlash of only 0.0013 inch. Optecs implementation is ideal for applications which require exact focus such as CCD imaging or film astrophotography. A geared stepper motor rotates the drive shaft with one step rotation of the motor equal to a 0.000086 inch movement of the drawtube. The unit adds 3.5 inches to the telescope's back focus as measured from the front to the end of the drawtube when at the mid-focus position. The total travel of the drawtube is 0.6 inches or 7000 steps. A pair of pushbuttons control the direction of focus and the DRO (digital read-out) displays the current position. The TCF-S focuser can easily handle cameras and instrument packages weighing up to 10 pounds. The TCF-S can be used by itself or with a PC for automatic focus with some of the popular camera control software.
- Heavy-duty Crayford style 2" focuser
Compensates for focal shift due to temperature
- Supports instruments up to 10 pounds
- Easy to use control box
- Use with or without a PC
- 4-digit readout for position
- Simple Learn procedure for determing TC
- Shut-off procedure remembers last position
- Compatible with major camera control software for autofocus
- Free control/interface program with open source
The most important advantage of the TCF-S is its ability to compensate for the focal shift of the telescope due to temperature change. The image plane of the common SCT telescope with aluminum tube can change as much as 0.01 inch per degree Centigrade. This would make long exposures difficult at best.