Description

Telecompressors / Focal Reducers

Optec has a long history of designing and manufacturing exceptional optical correctors and focal reducers beginning in 1995 with the original MAXfield 0.33X corrector/reducer for Schmidt-Cassegrain telescopes.  Coupled with the ST-7 camera, the original MAXfield yielded an effective imaging area nine times larger than the native f/10 SCT's could achieve alone. 

Optec continues this tradition with the NextGen series, the 3-inch NGC corrector line, and the new Lepus long-backfocus telecompressors for the Meade ACF telescopes. 

The NextGEN Series is the second generation of telecompressor lens systems designed by Optec. The first generation was available for the early CCD cameras such as the SBIG ST-6 and Meade 416. Improvements in CCD designed has warranted a complete redesign of our telecompressors which we offer now. These designs have been optimized by the premier Zemax optical design program and are made to the highest optical standards. All optical surfaces are polished to a 60-40 cosmetic quality and coated with a hard broadband coating for maximum transmission and durability. No finer telecompressor is available.

#17403 - NextGen MAXfield NGM 0.33X Telecompressor Lens

The Optec NGM 0.33X (Next Generation MaxField) telecompressor increases the effective speed of the Meade and Celestron Schmidt-Cassegrain telescopes from f/10 to f/3.3. This 3 fold reduction in focal length allows for 9 times greater field area and 1/9 reduction in exposure time for extended surface objects such as bright nebulae. The system is optimized specifically for the classical f/10 Schmidt-Cassegrain telescopes to allow for the correction of field curvature and spherical chromatism that afflicts these types of instruments.  At f/3.3, the maximum corrected field has a diameter of 11 mm at the image plane which makes the unit suitable for CCD cameras with imaging chips of the same diagonal dimension or smaller.

The second generation NGM 0.33X MAXfield telecompressor is perfect for the SBIG ST-7 class CCD cameras with or without a color filter wheel. The NGM is especially well-suited for most C-mount cameras including the Mallincam Video CCDcameras.

Designed specially for the classic Meade and Celestron SCT's, the NGM yields an incredible f/3.3 effective focal ratio (EFL) on native f/10 systems. When used with an f/11 classic C-14, the NGM will yield an EFL of f/3.7. Results may vary slightly depending upon the imaging train configuration.  Best results will be obtained when used with the TCF-S Temperature Compensating Focuser.

Specifications

Optical Design

The optical design of the NextGEN 0.33X was performed using Zemax and optimized for four field points using wavelengths of 450, 550 and 650 nm.  The goal was for the smallest blur diameters for the four field points. The system was modeled using the actual optical prescription for a SCT with the inherit aberrations of this telescope. The resulting lens curvatures of this designed were made without adjusting the radii to the optical lab's tool list. Custom tools were made for all surfaces.  The Zemax results are shown on the left.

Telescope-Side Compatibility:

• TCF-S focuser,
• Any 2-inch focuser or receiver.

Camera-Side Compatibility:

• NextGEN Camera-specific mount. See table below for currently supported cameras.

Historical Perspective

The original 0.33X Maxfield was first introduced many years ago and was designed for cameras such as the ST-6 and 7 with CCDs deficient in blue sensitivity. The design wavelengths were 500, 650 and 850 nm and was not really intended for RGB imaging which was in its infancy. You can still see on the web a report comparing the old MAXfield to the Meade telecompressor here. While the reviewer gave the Meade a slight edge over the Optec unit primarily because of cost, it is important to note that the NGM is now priced competitive to the Meade unit and has been completely redesigned to perform better optically. The same quality mechanical mounting noted in the review has not changed.

NextGEN Mounting Plate Finder

These mounting plates fit on the back dovetail of the NextGEN and are secured in place by three setscrews located in the mounting plate 120 degrees apart. It is important that the back-focus distance be set as closely as possible for the NextGEN reducers which is why each mounting plate has a unique length for every model camera. Backfocus distance should be known to +/- 0.04 inch (1mm) for best performance. Use the table below to find the appropriate mounting plate for your camera. If your camera is not listed below and you know the back-focus (BF) distance and thread type for your camera, you can find the stock number as follows:

1. Take the base stock number for your camera's thread: 
   T-thread #17392 
   Pentax-thread #17395 
   SCT-thread #17396
   QSI 500wsg #17397 
   C-thread #17399 
2. Add a dash
3. Add the tube length, which is equal to 2.39 - BF, with BF measured in inches.

Note: The minimum tube length available is 0.52 inches for the NGM (0.33X), and 0.67 inches for the NGW (0.5X) and the NGUW (0.70X).

* vignetting WILL occur with NextGen Reducers