TCF-S: Temperature Compensating Focuser
| TCF-S: Temperature Compensating Focuser
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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 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. A typical RGB exposure sequence can last one hour or more making it imperative that the focus be checked and corrected after each filter change. A simple learning procedure is used to find the temperature coefficients specific to the user's telescope system. The TCF-S system allows for two different coefficients (corresponding to two different f-ratio configurations) to be calculated and stored in the EEPROM memory. Once learned, either coefficient can be selected with a simple slide switch. A manual mode allows the user to set the focus manually at any time. Above right: TCF-S 2" and 3" I.D. focusers.
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Below right: The TCF controller.
The digital nature of the TCF-S allows opportunities for truly intelligent focusing. With the TCF-S focuser, programmers can communication directly with the focuser's controller (located in the hand control) via any serial port. The simple ASCII protocol is easily programmed and has been implemented in many popular imaging and camera control software packages. For example, CCDSoft Version 5 offers the @Focusİ routine which communicates with the TCF-S via a serial port to provide truly automatic focus control. MaxIm DL/CCD version 3 and above provides remote and automatic focus control with the TCF-S focuser. 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. It is possible to observe many days without the need to focus again. The TCF-S comes with its own PC control program for Windows. The source code for the program is available in the TCF-S folder after the install program is run. Users are encouraged to write their operating program using the TCF-S.bas routines as examples. You can download the setup program for TCF-S_Control by going to our Software Download page. The navigation button is on the left. |
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Big Brother: The TCF-S3 3" I.D. Temperature Compensating Focuser!
The TCF-S has a new big brother - the TCF-S3. This 5 pound focuser has all the same features of the TCF-S but is just bigger and stronger. With the every increasing size of CCD cameras and associated instruments, the need for a precision digital focuser that can take the weight and is compatible with most of the camera control software available is now met.
No corners were cut with this model. The massive drawtube has a 3.00-inch I.D. and is made from 7075, the strongest of the commercial aluminum alloys. To prevent any slippage common to Crayford style focusers, the drive rod is pressed onto the drawtube with a force of about 500 pounds. The TCF-S3 can take this extreme pressure because the drive rod is made from a ground bar of high speed steel with a diameter of 0.375 inch. Hardened rails of stainless steel are embeded in the drawtube to engage the drive rod and take the strain. The total linear travel of the drawtube is 1.00-inch with a resolution of 0.0001-inch. Like the TCF-S, a control box with IN and OUT pushbuttons, serial computer interface and digital display control all functions of the TCF-S3. All other features of the TCF-S3 are similar to the TCF-S. It uses the same cables, temperature probe and the new remote keypad. It is also compatible with the current Optec control software TCF-S.exe. Only a small number of telescope mounts are available to fit the 3" and 4" Meade thread and the Celestron 3" thread. Other telesope mounts can be made custom in our shop. This focuser is only intended for large scope with massive mounts. See price list for a list of available mounts. A 3-inch to 2-inch adapter is available to fit Optec and other standard 2-inch accessories. See stock number #17804. Future 3-inch products from Optec will include optical telecompressors and field rotators. |
Optional TCF Remote Keypad The plastic control box for the TCF-S focuser was never intended for frequent use at the telescope using it in a manual operating mode. The intended use was for complete computer operation with the control box located in some safe area near the computer. With three cables going to the control box, it was difficult to use as a hand paddle in any case. To allow manual control of the TCF-S and TCF-S3 at the telescope, a remote keypad with IN and OUT pushbuttons is available. The all aluminum device comes with a 3-foot cable (other lengths are optional) which plugs into the temperature probe connector located on the focuser. Neither the serial control or auto temperature compensation modes of the TCF-S focuser are operational when the remote keypad is in use. This keypad accessory is for manual hand operation of the focuser only. The connection is hot swapable so that the temperature probe can be plugged back in and normal TCF-S operation resumed at any time without a reboot. The remote keypad measures 1 x 1 x 6 inches and has two pushbuttons for IN and OUT functions. A stainless steel hook allows the unit to be stored by hanging on any available handle such as the hand hold on many Meade telescopes. The remote keypad is identified by stock number 17680 and requires firmware version 2.32 and above in the control box. The firware upgrade is available separately for $20 and is listed under stock number 17565. Batteries are not required since the remote keypad receives power from the focuser. |
| TCF-S System: Typical Package | |||
| Stock No. | Description | List Price | |
| 17670 | Model TCF-S Temperature Compensating Focuser w/RS232. | CDN $ | 820.56 |
| 17455 | 3" diameter mounting ring for Meade 10/12/14" | CDN $ | 61.36 |
| 17662 | 2" to 1¼" Adapter (for attaching camera to TCF). | CDN $ | 57.20 |
| 17471 | 12-ft. Cable, Hand Controller to TCF Focuser. | CDN $ | 40.56 |
| 17672 | 12-ft. Cable, PC Control RJ-12 Reverse (connects controller to computer). | CDN $ | 18.72 |
| 17695 | PC Serial Port Converter DB-9 to RJ-12 (adaptor for reverse cable). | CDN $ | 15.60 |
| Total Package Price: | CDN $ | 1014.00 | |