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

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

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 35mm 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 35mm 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 Telecompressors that are optimally corrected for these scopes.

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

M42, 105mm Traveler at f/4.5 taken by Ray Gralak with an SBIG ST8E.
Gamma Cygnus Region, 105mm Traveler at f/4.5 taken by Ray Gralak with an SBIG ST8E.
M8, 130mm StarFire EDFS at f/4.5 imaged by Loke Tan with an SBIG ST10E.
IC 5070 - The Pelican Nebula, 155mm StarFire EDFS at f/5.2 taken by Ray Gralak with SBIG ST-10XE

We 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 and Starlight Instruments 3" and 3.5" focusers that have an end-cap adapter for Astro-Physics 2.7" accessories. In addition to our 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 (27FOC3E and 27FOC3E-FT) .

Two additional adapters released in 2007 and 2008 respectively have greatly increased the versatility of this Photo-Visual Telecompressor. The 2.7" Adapter that Threads onto the 3.25" Rear Cell of Larger Meade SCT's (ADASCTLM27), introduced in July, 2007 now makes this telecompressor available to owners of larger Meade SCT's. 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.

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. Although not shown on the diagram, the telecompressor is threaded for 58mm filters. 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.

Applications:

35mm Camera - Our Prime Focus Camera Adapter PFCT--- and your favorite 35mm camera will produce very fine images in no time at all. It is best to use the Astro-Physics Camera Adapter since the length is appropriate to achieve approximately 0.75x for optimal results. If you desire a bit less compression, use our 2"/T-2 Tapered Nosepiece (AP16T) in place of the Prime Focus Camera Adapter for closer to 0.8x compression.

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

Pentax 6x7 Camera - For a 2" fully illuminated circle on 6x7 film (results in approximately 55% more field than 35mm film!), a special camera adapter (ADA67P) interfaces with the Pentax 6x7 medium-format camera.

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.

Diagram:
Astro-Physics Photo-Visual Telecompressor - We suggest that you review this exploded diagram, in PDF format, showing the telecompressor with a variety of accessories. Read hint for viewing this two-page diagram. We also recommend that you review our Telecompressor Spacing, Compression Calculation and Coverage document - PDF format - before trying to assemble an image train.

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.