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Optec WideField 0.5X Telecompressor

Optec WideField 0.5X telecompressor (Positive Lens)
Above: Optec WideField 0.5X telecompressor. (187,490 bytes)

The WideField is a three element 0.5X telecompressor lens system has been designed to provide a wider field of view with quicker exposure times for CCD applications with either Meade Instruments, or Celestron f10 Schmidt-Cassegrain telescopes. Note that this lens system is not recommended for use with f/6.3 SCT systems, or for use with most of the other telescope designs. The lens could be employed in terrestrial applications if the great light gathering power of the larger aperture SCT's is desired.

Those experienced with the use of CCD cameras on extended objects realize the need for a wide fields of view. At prime focus, the TC-241 chip of the SBIG ST-6 camera provides only about 1/14th the area of a typical 35mm film. For digital astrophotography, there is an obvious need for a telecompressor. The WideField provides the needed telecompression by acting as a 0.5X focal reducer, thus the f/10 Schmidt-Cassegrain telescope becomes a fast, well corrected f/5 optical system. The field-of-view now covers four times more area while the exposure times are correspondingly decreased.

WideField is compatible with larger format CCD cameras than its 0.3X cousins including the MAXField and New Generation MaxField. It has been specially designed for use with f/10 Schmidt-Cassegrain telescopes employing CCD cameras such as the SBIG ST-8E cameras. This telecompressor provides a wide, flat field across CCD chips having diagonals up to 18mm so the WideField provides an unvignetted image with these larger CCD systems.

All air spaced lens surfaces each have a multilayer broadband anti-reflection coating to diminish undesirable reflections, and to improve light throughput. The WideField design is optimized and corrected for the full range of CCD sensitivity (from 450 to 850 nm). Star images are small and round to the very edge of the field. It also features improved blue color correction (compared to the MAXfield 0.33X telecompressor) making the WideField lens system an ideal choice for use with the enhanced blue response Kodak CCD chips.

Similar in mechanical arrangement to the MAXfield system, WideField is a three component assembly consisting of; 1. the fully multi-coated three element lens assembly, 2. an optional telescope mount to attach the system onto the telescope, and 3. a camera mount designed specifically to accommodate the most popular CCD camera models.

Above: Three components of the WideField Telecompressor (left to right): telescope mount,
WideField Lens Set, CCD Camera Adapter (160,671 bytes)

This optics group is engineered to allow for improved correction of the field curvature and spherical chromatism that afflicts the f/10 SCT instruments. When used with the f/10 Schmidt Cassegrain telescope, the WideField offers very low distortion and minimal field curvature. This system is quite appropriate for high precision astrometry applications too where residuals of 0.2 arc seconds or less are common when centroids are matched to GSC star positions with common astrometric programs such as "Project Pluto's Charon".

For tri-color and quad-color work, the WideField is fully compatible with the Optec 2" automatic filter selector systems including the IFW. And like the MAXfield, the WideField lens assembly is threaded for manual insertion of 2" (48mm) diameter threaded filters. However, unlike the MAXfield, the improved blue correction of the WideField means the use of a violet light rejection (#12 or #8 Yellow) filter is not necessary. For color imaging when attached to the optional MAXfilter 2", we do recommend the Model #17440 IR blocking filter be threaded into the WideField lens assembly. The #17441 IR/UV blocking filter is recommended for use with the MAXfield.

Benefits and features include:

    Provides unvignetted images of up to 18mm diameter.

    Improved color correction from the Blue through to the Infrared.

    Fully Multi-Coated three element optic sytem.

    Four times the imaging area of f/10 systems.

    Shorter exposures times.

    Can attach to either standard SCT rear-cell thread or slip fit 2" focusers.

    Threaded lens cell accepts optional 2" (48mm) filters.

    Mounting Kits are available for most astronomical CCD cameras.

Mechanically, the WideField is designed to be extremely versatile and easy to use, yet will securely hold an expensive CCD camera. Available in the standard SCT version (stock no. 17405) with threaded SCT telescope mount and friction grip or in the less expensive WideField 2" design (stock no. 17407) without the telescope mount, the WideField lens assembly will slip perfectly into the JMI 2" Motofocus or 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 MAXfilter 2" Automatic Filter Selector easy, tri-color imaging over a wide field of view is now possible. Consult our current price list for telecompressor, mounting kit, and 2" filter prices.

Camera ManufacturerCamera ModelOptec Mounting Kit
Apogee Instruments, Inc. AM-4 Stock No. 17427
Axiom Research, Inc. AX-1, AX-2, AX-5 Stock No. 17426
Celestron/SBIG PixCel 237 & 255 Stock No. 17415
LE21M Hi-SIS 22 (T-Mount version)Stock No. 17428
Meade Instruments Corp. Pictor 216XTStock No. 17413
Meade Instruments Corp. Pictor 416XT/1616XT Stock No. 17414
Santa Barbara Instrument Group ST-4, ST-5Stock No. 17412
Santa Barbara Instrument Group ST-6 (old style)Stock No. 17410
Santa Barbara Instrument Group ST-6B (new style w/ T-thread)Stock No. 17411
Santa Barbara Instrument Group ST-7/ST-8Stock No. 17422
SpectraSource Instruments Lynxx PC, Lynxx 2000, Lynxx-2 Stock No. 17416
SpectraSource Instruments HPC-1 Stock No. 17418
SpectraSource Instruments Teleris Stock No. 17420
Starlight Xpress Starlight Xpress SXFStock No. 17424
Starlight Xpress Starlight Xpress MX5 & HX5Stock No. 17425
various manufacturers C-mount cameras Stock No. 17415
Table 1: Astronomical CCD camera mounting kits for the MAXfield telecompressor.

In use, the observer will first attach the mounting plate to the CCD camera. Next the lens assembly is inserted into the mounting plate and secured by the three setscrews. The telescope adapter with the knurled grip (not included with stock no. 17407) 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 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 on the video monitor. You are now ready to focus and use the system to capture spectacular images.

Elliptical galaxy M105 (at right) with NGC3389 and NGC3384, part of the M96 Group.
WideField image using an SBIG ST-6 camera with track & accumulate (twenty 30 second exposures) using a clear filter. (190,199 bytes)

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