3.5" Prime Focus Field Flattener for 130GTX serial #130GTX-600 to 130GTX-885, 889 & 890 (13035FF-2)

December 2022 - Two new field flatteners were introduced to optimize performance of all 130GTX scopes and 130GT scopes (upgraded to the 3.5" focuser).

Field flatteners are designed to accurately compensate for the inherent field curvature of a refractor lens. For each lens design there is an optimal spacing that works best for sharp focus over the specified field size. When the refractor lens design changes even slightly, the field flattener may need to have different spacing for highest performance. This is now especially important when using the newest CMOS cameras with pixel sizes of 3.76 microns and smaller.

When producing refractor objective lenses we produce the best design possible using the glass index data supplied to us. For the first 3 runs of the GTX lenses (serial# 600 to 885 and 889-890) the glass was the same and we designed the field flattener for those lenses. In the latest runs (serial# 886-888, 900 and higher), the glass data was slightly different and produced a design with slightly different field curvature. Therefore the field flattener for these later production lenses is internally adjusted to produce the same high correction over the specified field size. This allows the external spacing to the camera chip to remain the same at 80.8mm with the optional EXT327-17.0 back-focus spacer. 

Choose the appropriate version for your refractor

For the 130GTX, look closely at your dew shield, in most cases, to determine which version you need. You may also refer to your original sales order. The serial number is difficult to see on the scope. 

Part # 13035FF-2

• 130mm StarFire GTX serial # 130GTX-600 to 130GTX-885 (shipped from 2015 to Dec 2019) and 130GTX-889 and 130GTX-890 (shipped 2024). The dew shield does NOT have a thumbscrew for lockdown.

Part # 13035FF-3

• 130mm StarFire GTX serial # 130GTX-886, 130GTX-887 and 130GTX-888 shipped in Fall 2019.  The dew shield does NOT have a thumbscrew for lockdown.
• 130mm StarFire GTX serial # 130GTX-900 and higher. These were shipped from October 2020 to the present. The dew shield INCLUDES a thumbscrew for lockdown. 
• 130mm StarFire GT scope that has been upgraded to our 3.5" focuser. (04-22-23: Correction made to show that 13035FF-3 is the correct version for these scopes)

 13035FF-2 Includes

• Field Flattener housing with optics optimized for this version. The barrel design uses a unique dovetail for quick attachment to the focuser without introducing tilt into the optical system. 
• Two beautifully machined and black anodized covers
• 13035FF-2 Decal to differentiate from similar assemblies

 Back-focus spacing from the rear flange 

• Back-focus distance is 97.8mm - measured from the back flange to the camera sensor.
• Back-focus distance with the optional EXT327-17.0 is 80.8mm. We offer adapters for popular CMOS cameras as well as Nikon and Canon EOS DSLR and mirrorless camera. These adapters are described below. 

Use with CMOS Cameras up to 35mm Chip

Adapters are available for use with CMOS cameras with thread sizes of 48, 54 and 68mm. These are designed for the popular CMOS cameras currently available that utilize the 55mm standard spacing. The EXT327-17.0 Back-focus Spacer is required for this image train. Refer to the 130GTX CMOS System Diagram.

ADA327-48, 3.27" to M48 Adapter (new July 2024)

ADA327-54, 3.27" to M54 Adapter (new July 2024)

ADA327-68, 3.27" to M48 Adapter (new July 2024)

Use with Canon EOS and Nikon DSLR and Mirrorless Cameras

We recommend the optional 17.0mm Back-focus Spacer (EXT327-17.0), which will provide back-focus spacing of 80.8mm for coupling directly to our camera adapters below. Refer to the 130GTX DSLR and Mirrorless Camera System Diagram. 

• Canon EOS DSLR Camera Adapter with large 1.875" (47.6mm) diameter stainless steel bayonet. (ADATCCEOS)
• Nikon DSLR Camera Adapter with large 1.73" (44mm) diameter stainless steel bayonet. (ADATCCNIK)
• Canon EOS Mirrorless Camera Adapter with large diameter stainless steel “RF” Lens bayonet. (ADACAN-RF)
• Nikon Z Mirrorless Camera Adapter with large diameter stainless steel “Z” Lens bayonet. (ADANIK-Z)

Custom Adapters

If you need an adapter for a configuration that is not described above, we recommend that you contact PreciseParts. You may also review the following diagram that shows additional components you might find useful. Keep in mind that some are legacy parts: Field Flatteners, TCCs & QUADTCC Imaging Train Options

Diagrams and Instructions

Current recommendation:

• 130GTX CMOS System Diagram
• 130GTX DSLR and Mirrorless Camera System Diagram
• Optimizing Your Field Flattener / Lens / Camera Combination

Legacy documents for your reference in case you own some of these components:

• Field Flatteners, TCCs & QUADTCC Imaging Train Options

• If you own items not shown in the diagrams above, please refer to the Discontinued Products section of this website and Technical Support for Legacy Products that are No Longer Available. 

Astro-Physics 80.8mm Back-focus Spacing Distance

For more information regarding the concept for the 80.8mm back-focus spacing distance, refer to this webpage: Spacers & Extensions