Optec NextGEN MAXfield 0.33x Telecompressor Reduction Lens
What's Included With This Item:
- Telecompressor Lens
- #17430 Violet Light Rejection Filter
- (CCD Mounting Plate NOT included, REQUIRED)
The Optec NGM (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 great field are aand 1/9 reduction in exposure time for extended surface objects such as bright nebulae. The optical system comprises a set of 3 lens elements with two air spaces. All surfaces have a multilayer broadband anti-reflection coating.
The system is optimized specifically for f/10 Schmidt-Cassegrain telescopes to allow for correction of the field curvature and spherical chromatism that afflicts these types of instruments. At f/3.3, the maximum corrected field has adiameter of 9 mm at the image plane which makes the unit suitable for CCD cameras with imaging chips of the same diagonal dimension or smaller.
With regards to color imaging, the NGM is was primarily optimized for the wavelengths of 450, 550 and 650 nm which are the center wavelengths for the commonly used RGB system. Secondary weight was given to 850 nm light during the optimizing process.
Thus, use of the NGM telecompressor with no filter except the violet light rejection filter, will give will corrected images using the full spectral sensitivity of the CCD. As in all refractive systems of this type,the violet wavelengths are the least corrected. As a result, a violet light rejection filter is supplied with the NGM which blocks all light with wavelengths shorterthan 415 nm.
In order to achieve the proper 3 times reduction and the best correction, the back focus distance of 55 mm (assuming 3 mm for the CCD window) must be maintained. Optec supplies various length adapters which match the NGM to a particular camera and thread. While other reductions are possible by varing the back focus distance, the best corrected image is obtained with the 55 mm distance.