Optec - Model TCF-S, 2" Temperature Compensating Focuser.

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Mechanically, the TCF-S is a robust Crayford style motorized focuser with high repeatability,
SKU: OPT-17670
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Product Description

OPTEC - TCF-S Temperature Compensating Focuser

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. Optec's 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.


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 Celsius. This would make long exposures difficult at best.  Unique to the TCF-S focuser, an electronic controller system monitors the telescope's tube temperature and compensates the focus accordingly. A small temperature probe is attached to the side of the telescope tube and monitors temperature with a resolution of 0.1°C. For a typical Schmidt-Cassegrain of 8 to 11 inches aperture and f/10 focal ratio, the back focus will move approximately 0.010 inches for every 1°C change in telescope temperature. It is not unusual during an observing session for the ambient temperature to change by as much as 10°C within the time span of a few hours. This change in focus due to temperature is a serious problem for most telescope designs and requires frequent re-focusing during long exposures.  At the end of an observing session, the TCF-S focuser remembers the last temperature and position. When the unit is turned back on for a new session, the TCF-S computes a new position using the current tube temperature and moves to that position. Assuming no changes to the optical configuration, the object will snap into sharp focus.


  • If you wish to control the TCF-S via it's hand controller at any time, an Optec RJ-45 to DB-9 cable that connects the two is necessary.  




Name Optec - Model TCF-S, 2" Temperature Compensating Focuser.
Manufacturer Optec
Model OPT-17670


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