Astro-Physics 3,5" Prime Focus Field Flattener

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Astro-Physics 3,5" Prime Focus Field Flattener

# 1405351

€ 1,075.00 Price excl. German VAT tax (19%): € 903.36
  • extends the focal length a little bit, the resulting is f/6.7
  • provides a field of view with 65 mm diameter without vignetting and delivers a diffraction limited image even at the edge of the image circle
  • is equal to a field of view with a diameter of 4.3 degree at the slightly larger focal length of 870 mm
  • it works perfectly, even with the large CCD-sensors which are currently used by amateur astrophotographers

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3,5" Prime Focus Field Flattener for Astro-Physics 130 StarFire GTX

Optical accessories for the 130GTX

Astro-Physics Prime Field Flattener

A special Field Flattener and a Focal Reducer/Correktor have been developed for the large 3.5" focuser of the Grand Tourismo 130 GTX. Both optical elements can be used once the 2.7" focuser of an older 130 EDF-GT has been replaced with the 3.5" focuser.

The Field Flattener extends the focal length a little bit, the resulting f/ratio is f/6.7. It provides a field of view with 65 mm diameter without vignetting and delivers a diffraction limited image even at the edge of the image circle. This is equal to a field of view with a diameter of 4.3 degree at the slightly larger focal length of 870 mm.

This way, it sets a standard for our time. It works perfectly, even with the large CCD-sensors which are currently used by amateur astrophotographers (like e.g. the Kodak KAF 50100 with a size of 49.1 x 36.8 mm and a diagonal of 61 mm at 8.208 x 6.132 Pixel and 6 mü).

Nebelregionen DWB-111 and DWB-119
Test image of the Propeller Nebula (DWB-111 and DWB-119), imaged with SBIG STL-1100 using Field Flattener

The following table shows the field of view of the 130 Starfire GTX combined with the Field Flatteners and several CCD-sensors.

Size [mm] Field of view [degree]
Fully Illuminated Circle 2.6" (65 mm) 4.3° (256 min.)
KAF-8300 18.0 x 13.5 mm 1.2° x .88° (71 x 53 min.)
APS-C 22.3 x 14.9 mm 1.5 ° x .98° (88 x 59 min.)
35 mm Full Frame CCD 24 x 36 mm 2.4° x 1.6° (142 x 97 min.)
KAF 16 803 36.8 x 36.8 mm 2.4° x 2.4° (146 x 146 min.)
Astro-Physics Primär Field Flattener

As with all optical systems which change the focal length, the distances between lenses and camera sensor have to be kept as exact as possible. This is why there are several camera adaptions available for this flattener. Please visit for detailed information the original website of Astro-Physics.

There is a special backspacer ring available for this Field Flattener. Its optical length is exactly 22.1 Millimeter. The necessary distance from the back of this backspacer to the image plane is 80.8 +/- 2.5 Millimeter. To attach your camera, you need one of the following five adapters. If you require more backfocus, you can leave out the backspacer - then, the required backfocus is 102.9 +/- 2.5 Millimeter.

Flattener and backspacer do end in a 3.3 inch male thread. The backspacer is included with the Reducer/Correktors.

Article number Camera Adapter
140 8478 (ADATCCEOS) Canon EOS
140 8479 (ADATCC1) SBIG STL with Five-Position Filter Wheel Adapter
140 8480 (ASACCT2/ADASCTLM ) SBIG STL with Eight-Position Filter Wheel Adapter
140 8480 (ASACCT2/ADASCTLM ) 2"Nosepiece Adapter
140 8423 (A 3513) QSI 500/600 Cameras
2408145 + 2458215 Zeiss M68 Adapter

pdf-file: Schematic showing Backfocus Spacer and Adapter spacing. Astro-Physics 130 GTX Field Flattener Spacing Requirements

If you have any questions about attaching your accessories, please give us a call or send us an email. For further information and useful accessories about the 130mm f 6,3 StarFire GTX Triplet Apochromat Refractor please visit the Website of Astro-Physics.

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Additional Information

Manufacturer Astro Physics
SKU (#) 1405351
Manufacturer SKU (#) 13035FF
Colour Black
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