Baader Planetarium

Fluorite Flatfield Converter Barlow (BPFFC) and Related Accessories in the FFC System

Baader Fluorite Flatfield Converter Barlow (BPFFC)
FFC Basic Set - Recommended
Threaded 2.7" Extension with Internal T-thread (A3511)
Achieving Various Powers with the FFC
Tips for Using the FFC System with Various Telescopes

Baader Fluorite Flatfield Converter Barlow (BPFFC)

The Baader Fluorite Flatfield Converter was designed by a top German optical inventor to cover up to a 6x7 cm format at magnifications up to 8x. The 4-element fluorite design provides a diffraction-limited, apochromatic flat field over a 90 mm image circle. It produces a sharp, color-free image for any projection photography need. It can be coupled to 35 mm cameras, 6x7 cameras (adapters are available for various camera models), as well as any CCD camera using 1.25" or 2" nosepieces or threaded custom adapters. The BPFFC also can be used visually for critical high-power lunar/planetary/double star viewing.

The fluorite lenses do not add any chromatic aberrations or other optical defects to the image. The lenses are corrected from deep violet to the IR regions, and present an excellent match to the new extended-wavelength CCD cameras.

The BPFFC is fully multi-coated with a hard 7-layer design, each layer exactly matched to the material index. The result is very high transmission while suppressing stray light. Looking into the front of the lenses shows a black tube with the elements barely visible as shown in the photo. All optical surfaces are polished to the highest optical standards of 1/10 wave accuracy, in order not to disturb the incoming wavefront from your telescope's optics.

For projection photography, the BPFFC is unmatched for image fidelity. Unlike eyepiece projection systems, the BPFFC is free of the common defects such as chromatic aberration, pincushion/barrel distortion, astigmatism, coma, and vignetting of the light cone.

This design works equally well on all optical systems - be it Newtonians, apochromatic refractors, Schmidt-Cassegrains, Ritchey-Chretiens, etc.

FFC Basic Set and Extensions
The FFC System (also known as the Astro T-2 System) offers a wide array of adapters to suit a variety of needs (also see: Standard FFC Combinations). We have also manufactured a 2"/T-2 Adapter with brass locking ring (ADAT2) to simplify the system (it takes the place of several components). The Basic Set couples the 2"/T-2 Secure-Grip Nosepiece (AP16T) to the front of the BPFFC optic and the 2"/T-2 Adapter with brass locking ring (ADAT2) to the back, allowing a simple method for using visual and photographic accessories.
Shown from left to right:
AP16T - 2"/T-2 Secure-Grip Nosepiece (fits into 2" openings). This item helps you to come to focus when the FFC is inserted directly into your refractor or SCT (not used for Newtonians).
BPFFC - Fluorite Flatfield Converter Barlow
ADAT2 - 2"/T-2 Adapter with brass locking ring (manufactured by Astro-Physics, not shown on FFC System diagrams)

Assembled unit: ADAT2, BPFFC, AP16T. Shown with the following three extension tubes threaded together on the right:

BP25A - T-2 Extension Tube, 15 mm long
BP25B - T-2 Extension Tube, 40 mm long
BP25C - T-2 Extension Tube, 7.5 mm long

Threaded 2.7" Extension with Internal T-thread (A3511)

Realize the full potential of the Baader FFC (or Astro-Physics 2" Convertible Barlow, part # BARCON) when imaging by using the A3511 Extension. The internal T-thread on this extension allows you to attach your BPFFC, BARCON or other accessory with male T-threads INSIDE the 2.7" extension tube. In this way, the camera, filter wheel, off-axis guider, and/or other accessories are all supported by the much more robust and rigid 2.7" tube system, and the Barlow only needs to support its own weight inside the extension tube.

This is particularly important when imaging at some of the higher magnifications achievable with the BPFFC where over a foot of extension may be used between the Barlow optic and the focal plane. The maximum OD of the T-thread accessory is 2.5". Please see the A3511 System Chart for component options.

Achieving Various Magnifications with the BPFFC

The magnification of the BPFFC will vary depending on the distance to the focal plane behind the Barlow. As the spacing increases, so does the magnification. However, remember that as you increase the spacing (magnification) you also will need to shift the BPFFC forward in the focuser. The amount of in-travel available becomes a consideration as you reach towards the higher magnifications. The following is a list of the magnifications and the back spacing required: 2x = 42 mm, 3x = 96.2 mm, 4x = 150 mm, 5x = 206.4 mm, 6x = 259 mm, 7x = 314 mm, 8x = 368 mm.

Link to BPFFC Magnification Explanation.
Link to BARCON & BPFFC Magnification Graph.

When using the Astro-Physics Maxbright Diagonal, we suggest one of the following configurations:

  • Basic Set: AP16T (2"/T-2 nosepiece) + BPFFC (FFC) + ADAT2 (Astro-Physics 2"/T-2 adapter)
  • FFC system components: BP16 (T-2 nosepiece) + BP6/7 (T-2 changer system) + BPFFC (FFC) + BP28 (expanding ring) + BP17 (2" adapter)

Magnifications as low as 2x can be achieved by placing either the “Basic Set" or the “FFC System Components" into the AP Maxbright Diagonal and then adding the eyepiece. The magnification will vary somewhat with eyepiece design.

Using either the "Basic Set" or the "FFC System Components" in front of the AP Maxbright Diagonal will yield approximately 4x magnification. Various extension tubes can be added to increase the magnification to 8x, assuming that your telescope focuser has sufficient in-travel to allow this configuration to achieve focus.

DSLR/SLR cameras have a 55 mm spacing distance to the film/sensor plane when using a T-ring system. The lowest magnification of approximately 2x is achieved by threading a standard T-ring directly to the back of the BPFFC body (without a 2" adapter).

3x to 8x magnifications are achieved by adding 50 mm to 320 mm. It is recommended to use the A3511 and 2.7" extension tubes to achieve these lengths. As above, this assumes that your telescope focuser has sufficient in-travel to allow this configuration to achieve focus.

CCD Camera
The FFC system allows you to achieve various magnifications with your CCD Camera. If you thread the BPFFC directly into your camera (without the 2" nosepiece or with a custom low profile adapter) the lowest possible magnification will be approximately 2x.

Similarly, 3x to 8x magnifications are achieved by adding 50 mm to 320 mm. It is recommended to use the A3511 and 2.7" extension tubes to achieve these lengths. Again, it is assumed that your telescope focuser has sufficient in-travel to allow this configuration to achieve focus.

Tips for Using the FFC System with Various Telescopes

There are several options for attaching the BPFFC to your telescope.

  • Basic Set: If you have an 8 or 9.25" SCT, use our ADASCT, which was designed for 2" slip-in accessories and features our brass locking ring. We have also developed the ADASCTLC and ADASCTLM, which are larger versions designed for SCTs that are 10" or larger. This adapter takes advantage of the 3.25" opening of these scopes.
  • FFC System: If you prefer to thread the FFC System components directly onto your visual back, you can use BP21 (2" SCT Short T-adapter for the standard visual back) or BP18 (adapter for the larger SCTs).

When inserted into a 2" focuser on a Newtonian telescope, the Baader FFC Barlow will require an additional 1 inch of in-travel to allow focus at 2x magnification. More travel is required for higher powers. To use, slip the FFC directly into your focuser. Tighten the focuser screw on the smooth surface of the FFC between the ridges. You will also need our ADAT2 (and possibly a 1.25" adapter) for your eyepiece.

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This page was last modified: November 9, 2017

Astro-Physics, Inc.
11250 Forest Hills Road, Machesney Park, IL  61115, U.S.A.
Phone: 815-282-1513   Fax: 815-282-9847