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.

#17409 - NextGen Ultra WideField NGUW 0.50X Telecompressor Lens

The Optec NGUW 0.7XL (Next Generation Ultra WideField) telecompressor was designed specifically for systems with well corrected optics and flat fields such as can be obtained from apochromatic refractors and the new coma free and correctly named LX400-ACF telescopes. The speed of a f/8 telescope would be increased to f/5.6 with this reducer and the optics would still be nearly diffraction limited. This four-element system also maintains the parfocality of the telescope since these types of telescope have more limited focus compared to SCTs. The image field is highly corrected to 18mm diameter so that large format CCD cameras can be used. The performance of this reducer would be impaired if used with a SCT type telescope.

The Ultra WideField 0.7XL is a coupler from Optec and is designed specifically to speed up the focal ratios of highly corrected telescope systems. This design assumes that the image formed by the telescope is reasonably flat and aberration free. If so, the resulting image will also be highly corrected and nearly parfocal with the original image. Optimized for an f/8, the Ultra WideField 0.7XL will work for any focal ratio in the range of f/5.6 to f/20. The field is highly corrected up to 18mm in diameter and would work well even with larger fields with only slight degradation near the corners.

Like the other reducers in the NextGEN series, all surfaces have a broadband multilayer coating optimized for the 450 - 650 nm pass band of the optic. Filter mounted in front as with the IFW are compatible. In fast systems, it is always better optically to mount the filters in front of any reducer optic to keep the incoming rays closer to being normal (collimated) to the filter surface.

The Ultra WideField 0.7XL was redesigned and improved in late 2006 and now has a much longer back-focus distance and uses the same mounting plate adapters as the 0.33X and 0.50X models. This allows use of this reducer with SBIG cameras having the CFW-8/10 filter wheels mounted.

Specifications

The optical design of the NextGEN  0.7XL was done with 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 an idealized telescope of f/8 and with perfect optics. 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 below for currently supported cameras.

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