The focal length of the Photo-Visual Telecompressor is 27.6" (700 mm). In order to obtain approximately .75x, please refer to the exploded diagram for various configurations. Although not shown on the diagram, the telecompressor is threaded for 58mm filters.

The S155EDFFF 4" Prime Focus Field Flattener was originally produced for the 155 f7 StarFire EDF with its 4" focuser and was included with those instruments. It is now available as an accessory for owners of the 155 f7 StarFire EDFS version who have upgraded their 2.7" focusers to the 4" model. It is also the perfect Field Flattener for the 140 f7.5 StarFire EDF when purchased with the optional 4" focuser (140EDF4). These 4" Prime Focus Field Flatteners come with two beautifully machined, velvet-lined aluminum covers to protect the valuable optics inside.

This optical marvel was originally designed to take full advantage of the medium format Pentax 6x7 camera, and will provide pinpoint stars all the way to the edge of its field with no vignetting! It is perfect for today's larger CCD cameras as well. We also offer an adapter that allows this Field Flattener to be used with the more conventional SLR's - either 35mm or digital (including a larger clear aperture version for the full format Canon EOS cameras). The S155EDFFF flattens the field across a full 4" circle without significantly changing the native focal ratio of the telescope - The 155 f7 operates at about f7.3 while the 140 f7.5 will operate at f7.8.

At the present, CCD cameras must be attached using a 2" adapter and nosepiece - see image below left - but we are currently designing a direct interface to the larger format STL series of cameras that will be similar to the ones available for the 155TCC Telecompressor Corrector, the other outstanding 4" imaging accessory for both the 155 f7 and 140 f7.5 StarFire EDF instruments.

Diagrams and Instruction Sheets:
Astro-Physics Prime Focus Field Flatteners- Exploded diagram showing the field flatteners with a variety of accessories. Note that this is a PDF file. Read hint for viewing this two-page diagram. Installing the CCD Adapter to Use the 2.7" or 4" Field Flatteners with a CCD Camera - Instruction sheet in PDF format.

LEFT - The S155EDFFF in place on a 4" draw tube with the A1261 CCD adapter (sold separately) and ADA2003 2" adapter (included with either telescope).

RIGHT - The S155EDFFF shown with its beautifully machined covers.

(67RT - - -, last 3 letters indicate t-ring)

Use this adapter with the 2.7" or 4" Prime Focus Field Flatteners to obtain the best possile results with your 35mm camera - pinpoint from edge to edge. I.D. painted flat and threaded for 48mm filters. See how this part fits into your photographic system in the exploded diagram (PDF file). Read hint for viewing this two-page diagram.

Owners of Canon EOS auto-focus 35mm and digital SLR's may wish to consider the larger, 1.875" clear aperture adapter below. (67RLEOS)

Purchase the adapter with or without the t-ring. T-rings thread easily into place. If you order your camera adapter with a t-ring, the three dashes in the part number will be replaced by three letters, i.e. 67RTNIK if a Nikon t-ring in included. Please specify the t-ring that you wish to use. Order an extra t-ring if you have two cameras. This part can be used with 2.7" field flatteners shipped after May 1994 and 4" field flatteners from any year.

If you have a field flattener that is an earlier model, please call.

This SLR Camera Adapter for Canon auto-focus 35mm and digital EOS SLR cameras with its large 1.875" (47.6 mm) inside diameter EOS bayonet minimizes vignetting on full frame chips and on 35 mm film by eliminating the restrictive 1.5” (38 mm) diameter standard T-thread interface. Since the introduction of Canon’s full 35 mm frame digital SLR’s, people have been asking for a solution to the vignetting caused by the small clear aperture of the standard T-ring interface that is universally used to connect telescopes to SLR cameras. This was especially true for Astro-Physics telescope owners who also had either our 2.7” or 4” Field Flatteners. What good were pinpoint stars to the edge of a wide field when the edge of that field was darkened by the T-ring’s vignetting effect? So, in keeping with our commitment to imagers, we introduced a solution!

The adapter body is precision-machined aluminum and is anodized black. The bayonet is machined stainless steel, and both the body and the bayonet are baffled and painted flat black on the inside. The adapter is intended to be used exclusively with Astro-Physics 2.7" and 4" Prime Focus Field Flatteners (except the 160FF). It will position the chip (or film) at the correct distance from the Field Flattener optics for pinpoint stars. If you received your 2.7" Field Flattener prior to May 1994, you will need new aluminum parts to use this adapter. Please call Astro-Physics for details.

The most discriminating CCD imagers with large chips may wish to use our field flatteners for the best possible results at the edge of the field. These adapters will preserve the correct spacing from the field flattener to the focal plane of your CCD camera. Choose the correct length for your system.

Important: There are now a huge variety of CCD cameras, filter wheels and other accessories on the market, and all of them have different dimensions in terms of their optical backfocus or light path distance. Even different filter choices will affect the optical distance because of the indexing effect of the filter itself. It is important that you know the specifications of your own particular equipment before deciding on an adapter. The information below provides guidelines - NOT inviolable laws.

Diagrams and Instruction Sheets:

Astro-Physics Prime Focus Field Flatteners
- Exploded diagram showing these CCD adapters with the field flatteners and a variety of other accessories. Note that this is a PDF file. Read hint for viewing this two-page diagram.

Installing the CCD Adapter to Use the 2.7" or 4" Field Flatteners with a CCD Camera
- Instruction sheet in PDF format.

The design allows full corner-to-corner illumination of the ST10E chip with most catadioptric telescopes. This design does not add coma to the wavefront, and thus can be used with all flat-field and coma-free telescopes such as Maksutov-Cassegrains, Schmidt-Cassegrains, Ritchey-Chretiens and refractors. The inherent resolution of the telescope is not compromised when using this compressor.

Please review the exploded diagram to see how this item will fit into your imaging system. If you want a higher compression ratio, but do not use the color filter wheel, you can add two T-2 extension rings that we offer from Baader Planetarium. Thread both the 15mm T-2 Extension Ring (part # BP25A) and 7.5mm Extension Ring (part # BP25C) between the CCD camera and the nosepiece. This will approximate the length of the color filter wheel. You can also experiment with a single extension or other combinations. Although it may be possible to use additional T-2 extensions (there is also a 40mm version, part # BP25B) to gain even further compression, you may not have enough backfocus to do so. Also please note that as you increase compression, you decrease the size of the fully illuminated circle at the focus point. At 0.67x, the CCDT67 will cover the chip of the ST10E. It can never cover the chip of an STL series camera or the newer large size digital SLR chips, because its clear aperture is no larger than their CCD chips.

• Clear aperture is 1.75", designed to screw into our 2” Tapered Nosepiece (AP16T) or any other 2" nosepiece with 48mm threads that is designed for CCD cameras. It will not thread all the way into the nosepiece provided with SBIG cameras since the threads of that nosepiece are not deep enough.
• 0.67x Compression ratio for SBIG ST7/8/10 + Color Filter Wheel, when used with refractors. Fully illuminated circle: 30mm
• 0.75x Compression ratio for SBIG ST7/8/10 (without Color Filter Wheel or T-2 extensions), when used with refractors. Fully illuminated circle: 34mm
• Approximately 5 inches of back focus is needed to achieve focus on the CCD chip. It will not work with the AO7.
• The focal length of the CDD Telecompressor is 12" (305 mm)

We highly recommend our 2" Tapered Nosepiece (AP16T) for your CCD camera. When used with the brass locking ring of most of our adapters, this unique barrel will seat your valuable CCD camera squarely and solidly into place. Even a single thumbscrew interface will be improved. If you are using the thin 2" adapter (part # ADA2013) or the 2" adapter of the 92mm f5 or f7 Stowaways, we suggest that you use the 2" nosepiece that came with your camera or the 2" nosepice from Baader Planetarium (we offer as part #BP16).