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Astro-Physics 27TVPH 2.7" Photo-Visual Telecompressor 0.75x

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0.65 kg
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including VAT 20.00 % ( £51.33 )


Astro-Physics 27TVPH Poto-Visual Telecompressor (0.75x)

The telecompressor or focal reducer shortens the focal length of the telescope to 75% and thus increases the speed. An RC telescope with the aperture ratio of f/8 is boosted to f/6. The exposure time is almost cut in half.

The reducer is suitable mainly for Ritchey-Chrétien telescopes, but also for refractors. The very well corrected system offers high contrast and especially no bothersome reflexions of bright stars.

We recommend the compressor for medium-sized camera sensors up to full-frame size.

Connection to the telescope:

Customised adapters to your focuser are available, the item number is ADA-27TVPH.

Working distance and camera connection:

The working distance is quite flexible. A distance of 118 mm from the camera-side lens surface gives the wanted compression factor of 0.75x. A shorter distance of 83 mm would increase the factor to 0.8x.

With the 2" adapter ADA2003, you can get a short - only 19.56 mm - adaption to 2" with brass compression ring which allows hassle-free further adaptions and also 360° rotation.

Manufacturer's Product Description

We have increased the versatility of our telecompressor (also called a focal reducer) by designing a variety of accessories for photographic, CCD and visual applications. The effective focal length will be approximately 0.75 times the focal length of the instrument, i.e. our f6 refractors will operate at a very fast f/4.5! Deep-sky objects are recorded on film in a fraction of the time needed 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 130mm 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.

This well-corrected accessory lens preserves the high contrast and superb color correction of the main objective. 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. For the very best edge star images, we recommend the prime focus 2.7" or 4" field flatteners, which have been specifically designed for each focal length of our StarFire refractors. If you own one of our 175, 160, 155 or 140 StarFires and plan to take CCD images, we suggest our dedicated CCD Telecompressor Correctors that are optimally corrected for these scopes.

Here are a few examples of images from our gallery that were taken with our telecompressor:

IMPORTANT INFO: Astro-Physics have designed the telecompressor so that it threads directly into the drawtube, thus placing the optics forward in the optical system. As a result, the telecompressor can only be used with Astro-Physics 2.7" and 4" focusers (27FOC3E-FT and 4FOC3E-FT) and Starlight Instruments 3" and 3.5" focusers that have an end-cap adapter for Astro-Physics 2.7" accessories. Two additional adapters greatly increase the versatility of this Photo-Visual Telecompressor. The 2.7" adapters that thread onto the 3.25" rear plates of larger Meade and Celestron SCT's (ADASCTLM27 and ADASCTLC27) make this telecompressor available to owners of Meade and Celestron SCT's.

Note: Celestron EdgeHD scopes recommend a 146 mm back spacing distance (reference Celestron Tech information). Contact Celestron for further information.

In addition to AP refractors, Astro-Physics focusers are featured in several popular Ritchey-Chretiens (the telecompressor produces very fine results with these scopes) and are available for telescope makers.

The 6x7 Outer Bayonet Adapter (ADA2767), introduced in August, 2008 allows larger imaging platforms like the SBIG STL Series cameras or full frame DSLR's to be attached to the Photo-Visual Telecompressor without the vignetting effects of a 2" nosepiece or a T-ring and allow rotating the camera!

You may prefer a sturdier cover than the included plastic plug. Astro-Physics also offers an optional aluminum cover that will accommodate this part, depending on your storage needs. Please review the information regarding the Threaded Cover for AP 2.7" Drawtubes and Accessories with 2.7" Female Threads (A1005). More information can be found on our Accessory Reference Chart for 2.7" Threaded Covers.

Diagram and Magnification Info: The focal length of the Photo-Visual Telecompressor is 27.6" (700 mm). In order to obtain approximately 0.75x, please refer to the exploded diagram for various configurations. To calculate the compression factor and coverage for your particular setup, please refer to our Telecompressor Spacing, Compression Calculation and Coverage document or to the CCDT67 & 27TVPH Telecompression Graph.


35 mm Camera - Either our Canon EOS Camera Adapter (PFCLEOS) or our 35mm Camera Adapter (PFCT---) and your favorite 35 mm camera will produce very fine images in no time at all. They are both optimally spaced for 0.75x compression. If you desire a bit less compression, use our 2"/T-2 Secure-Grip Nosepiece (AP16T) in place of the Prime Focus Camera Adapter for closer to 0.8x compression.

CCD Camera - Choose the appropriate adapter (A3502-A, A3503-A, A3504-A, A3505, A3506, A1008-A) to space the telecompressor properly with your CCD camera for up to 0.75x compression.

Visual - Slip in a 2" diagonal, such as our MaxBright Diagonal (PMDMAX), with most eyepieces (some eyepieces may not focus). While it is fun to use the telecompressor in this manner, your best wide field results will be obtained with a high-quality eyepiece rather than a telecompressor/eyepiece combination.

The telecompressor is threaded for 58 mm filters.

Below image shows ADASCTLC27 adapter with 27TVPH Photo-Visual Telecompressor. (Only for demonstration purposes.)

Below image shows ADASCTLC27 adapter with 27TVPH Photo-Visual Telecompressor plus the ADA2767 6x7 Bayonet Adapter screwed into the top of the telecompressor. Screw it onto the 3.25" back of a large Celestron SCT, then we only need the appropriate length extension and a camera adapter to attach a camera.  (Only for demonstration purposes.)

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