Astro-Physics 2.7″ Photo-Visual Telecompressor 0.75X

Astro-Physics has produced a splendidly high quality focal reducer that is very effective and adaptable. They have increased the versatility of their focal reducer (also called a Telecompressor) by designing a variety of accessories for photographic, CCD and visual applications. Installing this focal reducer to your focuser will alter the focal length to approximately 0.75 of its original value. As an example, an f/6 instrument would be altered to a very fast f/4.5. This alteration makes it possible to capture deep sky objects on film in a fraction of the time required at prime focus. In addition, you can more effectively capture a large object or cluster of objects with the telecompressor. For instance, if you photograph at prime focus with a 35 mm camera on a 130 mm f/6 StarFire, you will achieve a 1.7 x 2.4 degree field. If you use the telecompressor, the field size increases to 2.3 x 3.3 degrees at f/4.5. This greatly increases the versatility of your refractor for imaging a wide variety of objects. The accessory lens is well corrected so as to preserve the high contrast and superb color correction of the main objective, sacrificing none of the quality of whatever you’ve chosen to install your Telecompressor onto. While the telecompressor flattens the field to a certain degree, you may still notice some slightly elongated stars in the corners. This is less of an issue with CCD imaging when the chip size is smaller than a 35 mm negative. The Telecompressor was designed to thread directly into the drawtube so as to place the optics forwards in the optical system. As a result of this design choice, the telecompressor can only be used with Astro-Physics 2.7-inch and 4-inch focusers and Starlight Instruments 3-inch and 3.5-inch focusers that have an end-cap adapter for Astro-Physics 2.7-inch accessories. Information on how to calculate the compression factor and coverage for your particular setup (along with connection options adapter drawings in their links): SeeHere

Magnification/ Telescompression Graph:SeeHere

Manufacturer Product Number: 27TVPH