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Optec MAXfield 0.33x Three Element Telecompressor
The MAXfield 0.33X telecompressor lens system offers the widest field of view available for CCD applications with f10 Schmidt-Cassegrain Telescope. This lens is designed primarily for use with medium and small format CCD cameras with chip of up to 11 mm across the diagonal. Those who are attempting astronomical CCD imaging can now achieve nine times more area than available using prime focus techniques so the MAXfield makes centering and composing an image easier than ever. The lens could be employed in terrestrial applications if the great light gathering power of the larger aperture SCT's is desired.
The MAXfield design has been particularly optimized to correct for coma and field curvature in commercially available f/10 SCT's within the spectral region most sensitive to CCD's. With the MAXfield, f/10 systems work at an incredible f/3.3. Note that this MAXfield system is not recommended for f/6.3 SCT systems, or for use with other telescope designs.
For tri-color imaging work the MAXfield's elegant design allows for easy removal and insertion of optional threaded 2" (48mm) diameter filters. These filters can be installed without refocusing!
The system is modular so that the MAXfield lens can be employed with a variety of CCD imaging systems.
Nine times more imaging area provided on a CCD than at f/10.
Shorter exposures times.
Can attach to either standard SCT rear-cell thread or slip fit 2" focusers.
Threaded lens cell accepts optional 2" filters.
Mounting Kits are available for most astronomical CCD cameras.
Moderate cost - MAXfield 2" systems starting at $325.
Those with experience using CCD cameras on relatively large, or extended objects soon realize the value of having a wider field of view. At prime focus, even the larger TC-241 chip of the SBIG ST-6 camera provides only about 1/14th the area of that provided by a the 35mm film format. So for digital astrophotography of larger objects, a good telecompressor can be a good alternative to buying another telescope that may provide the shorter focal length. The MAXfield provides the needed telecompression by acting as a 0.33X focal reducer, thus the f/10 Schmidt-Cassegrain telescope can performa as a fast f/3.3 optical system. While the field of view at f/3.3 now covers nine times the area than at f/10, corresponding to the change of Effective Focal Length the exposure times are also decreased to 1/9th the time.
The MAXfield design is a three-element lens system optimized and corrected for the region of peak CCD sensitivity: 550 to 850 nm. Star images are small and round to the very edge of the field. Mechanically, the MAXfield is designed to be extremely versatile and easy to use, yet it will securely hold an expensive CCD camera. The 2" barrel design with a dovetail groove is far superior to the standard 1¹" adapter present on most cameras. Available in the standard SCT version (stock no. 17400) with threaded SCT telescope mount and friction grip or in the less expensive MAXfield 2" design (stock no. 17402) without the telescope mount, the MAXfield lens assembly will slip perfectly into the Optec TCF Temperature Compensating Focuser or any other 2" focuser. Two side mounted thumbscrews hold the lens assembly in place and a precise alignment hole insures perfect alignment each time the lens assembly and camera are inserted. At the camera end, a rotatable CCD mounting plate attaches the CCD camera to the lens assembly. See the table below for the current selection of CCD camera mounting kits. When used with the
Table 1. Astronomical CCD camera mounting kits for the MAXfield telecompressor.
In use, the operator will first attach the Mounting Plate to the CCD camera. Next the telecompressor lens assembly is inserted into the mounting plate and secured by the three setscrews. The telescope adapter with the knurled grip (not included with the MAXfield 2") is attached to the rear cell of the Schmidt-Cassegrain Telescope. The camera with lens assembly is then inserted into the telescope adapter and secured by the two thumbscrews. Finally, the three setscrews located around the mounting plate are loosened carefully and the camera is rotated for proper orientation of the desired field to the monitor. You are now ready to focus and use the system to capture spectacular images.
For tri-color and other filtered imaging uses the lens assembly and camera can be removed from the 2" telescope adapter to facilitate the insertion of optional color filters. Standard 48mm filters can be threaded into the front end of the MAXfield lens assembly for tri-color, photometric, or LPR filter work. Using an alignment pin and precision keyhole, the camera is reinserted into the telescope adapter without losing registration. The image below was taken with the MAXfield and SBIG ST-6 camera and shows the what kind of image can be expected with only a 60 second exposure.
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