|
160mm f7.5 EDF AIR-SPACED APO REFRACTOR (6.3" aperture)
"the pioneer of a new high tech Apo design series"
Still proving "Made in The USA" can mean something great! This 160mm Starfire EDF is the pioneer of a new high tech Apo design series incorporating a brand new air-spaced triplet apochromat lens arrangement. The 160 EDF will be made available (at least initially) only with the improved 2004 model Astro-Physics four inch diameter focuser, and it may be followed soon by models in other apertures. This is the culmination of years of optical research by Roland Christen, President and optics designers of the Astro-Physics Co. It is made with the best available grades of optical glass to achieve exceptional image brightness and excellent color correction. And it incorporates the latest in high efficiency multi-coating technology to improve light throughput through the six air spaced surfaces.
Right: Astro-Physics 160 EDF telescope OTA with lens shade extended on optional 900 GTO German Equatorial Mount (103,954 bytes)
Click on image to see enlarged view (65,309 bytes)
Formally announced on 4 November 2004, this project aimed to develop a versatile and transportable telescope that will allow you to enjoy sharp, high-contrast images and capture images on film and CCD. The goals also included mechanical refinements of the Optical Tube Assembly and Focuser. Since production of the first lot was already well under way when these were announced, the first new production 160mm Starfire EDF telescopes are to be delivered in December 2004. The first of our instruments (with the Feather Touch® Micro Focuser option ) arrived in August 2005 and was placed on display in Company Seven's showroom collection for those who wish to see it alongside many of the other popular Astro-Physics telescopes.
PERFORMANCE
The EDF series telescopes are each superb as a visual or imaging instrument. These employ Super ED glass (ED stands for extra low dispersion, Vd> 90) that provides color free performance at this focal ratio. Images of stars and planets are presented in their natural colors, and daytime objects appear sharp and contrasting without annoying purple fringes. The 160mm EDF is easily capable of high-power observations of the moon and planets. The color correction is ideal for visual uses being completely free of false color; secondary spectrum is totally absent at any power and this allows the observer to discriminate the subtle color variations on the surface of the planets. Deep-sky views are equally impressive due to the broad range of possible fields of view (from low magnification to high), and very high transmission of the three glass types and advanced multi-coatings. With the optional Visual Telecompressor at f/5.6 one can enjoy fields of view of up to 2.9 degrees with a suitable eyepiece! Performance will rival much larger obstructed systems because the contrast is excellent; stars snap to focus, individual stars of globular clusters are sharply etched as intense diamonds against black velvet background - a beautiful sight!
The objective lens consists of a positive element of Super ED glass surrounded by two matching hard crown meniscus lenses. The two outer elements are chosen so that the combination is free of coma, spherical aberration and other higher-order aberrations. Under steady viewing conditions, you will see a hard white Airy disc at focus surrounded by the first diffraction ring. Inside and outside of focus, you will see an evenly illuminated, expanded disc with concentric Fresnel rings, the outermost ring brighter and wider than the rest.
Right: Astro-Physics 160 EDF lens design "Chromatic Focal Shift" data between .4046 to .7065 microns. Note the focus shift position for each wavelength (color of the spectrum) relative to the zero point, as well as the the Diffraction Limit Range. The total false color does not exceed plus or minus 0.053mm or 0.0045 percent of the focal length - quite extraordinary! (79,954 bytes)
Click on image to see enlarged view (121,427 bytes)
The close, air-spaced design results in rapid cool down during nighttime temperature swings and so this telescope is practical for use in temperate as well as very cold climates. On most nights, the settling down time for the lens is between ten to fifteen minutes, and even in subfreezing conditions it rarely takes more than forty five minutes to stabilize.
MULTI-COATINGS
A multilayer coating is applied to the six air spaced lenses of this telescope to prevent light reflection off the surface of, or between the lenses. This helps to eliminate ghost images and flare and can improves color rendition, achieving a dramatic increase in image contrast. The coatings provided are a recently developed multilayer antireflection coating; this provides a cumulative light transmission greater than 97% across the peak visual wavelengths and improved durability over prior choices. While Astro-Physics has previously produced some air spaced lenses, these air spaced lenses tended to incorporate less efficient Magnesium Fluoride antireflection coatings or at times some then risky multi-coating technologies were tried. The very costly, precisely polished and figured ED glass lens elements undergoing these older processes were at risk by exposure to very high temperatures in the chamber as the coatings were flashed onto the lens. Heating or cooling a large piece of glass could produce immediate breakage or in some elements start in motion a problem that might become apparent years later. And after the process, these coatings could be damaged by something as simple as a grain of sand accidentally wiped across the lens surface. So among the reasons why Roland decided to move to oil spaced designs in the 1980's was to avoid the risks imposed by these older coating techniques.
Since the prior EDF design was introduced in 1989 a number of new low temperature coating technologies have been developed which produce a very hard and durable coating. These also can provide superior light throughput compared to what was previously available. So now the average loss due to reflections from a surface across the photo-visual spectrum can be less than 0.5%. Since these technologies have come about, it is now possible for Astro-Physics to produce air spaced lenses with acceptable throughput. And the durability is increased since the new coatings are actually fused into the glass surface.
The improvement of the new coatings over those provided with previous EDf models is apparent even to the naked eye. With the increase in light throughput and reduction of possible ghosting due to the new multi-coatings, the new 160 EDF spherical design becomes practical. Astro-Physics can eliminate the time consuming aspherizations process employed to make the previously EDF series, while continuing to produce a highly corrected lens.
IMAGING APPLICATIONS
This high degree of correction serves as well as for film or CCD imaging needs. This refractor can be used photographically with a 35mm Single Lens Reflex (SLR) digital or film camera at prime focus with only a simple camera adapter or even faster at f/5.75 with the new optional matched flat-field telecompressor. An optional matched field flattener is available for use with the Pentax 6 x 7 medium format camera with full coverage provided by the provided four inch focuser and optional field flattener.
As CCD camera technology has advanced the quantum efficiency has improved. These devices are now can have good sensitivity beyond the visual into the UV (400 nm) and the IR (700 nm) portions of the spectrum.
COMPARISON WITH PRIOR EDF
Right: Astro-Physics 160 EDF Telescope objective lens and cell with lens shade extended (40,735 bytes)
Click on image to see enlarged view (178,424 bytes)
Many will wonder how this telescope compares to the prior generation of the AP Apos which were announced at Company Seven on 1 December 1989 and then came to dominate the market from then until now. Astro-Physics chose to make the new Apo with a 160mm clear aperture instead of the prior 155mm f7 Starfire EDF 6.1 inch aperture. The 160mm EDF has a theoretical light gathering power of about 520X that of the unaided human eye (based on a 7mm exit pupil), while the prior 155mm EDF was about 490X. So the 160mm will produce an image that will appear about the same or marginally brighter to the most discriminating eye than that of its predecessor even after considering the loss due to the multicoated air spaced surfaces.
The new 160 EDF lens has slightly better visual color correction over the spectral range from 400 to 700 nm than the predecessor. The previous EDF lens had slightly worse visual correction over this range but somewhat better color correction to 1000nm in the IR, but this factor is not very relevant to most who are involved with CCD imaging since IR blocking elements or coatings are frequently employed in their imaging systems.
The 1,200mm (47.25 inch) focal length is still quite versatile, the differences in physical overall length between the stored 155mm EDF and the 160mm EDF OTA's should be only about one and one half inches. The f/7.1 and f/7.5 ratios permit the use of a full range of eyepiece designs - from relatively simple to complex as long as they are well made - to produce extremely sharp planetary images. This f/7.5 is a bit longer ratio than that provided with the prior 155mm EDF's 1,100mm (43.3 inch) f/7.1. The new air spaced design combined with the stretching the focal ratio from the prior f/7.1 to f/7.5 make this somewhat easier to produce (buyers of the prior 155 EDF averaged five or more years on our waiting lists) and so this may make it possible for Astro-Physics to actually meet the demand - unless of course even more people come to look through the new 160mm EDF!
In production the prior 155 EDF objective is an oiled design that requires all the external and internal surfaces must be polished fully, and then the lenses are carefully matched and corrected to one other which includes a time consuming apsherization process. The 160 EDF design still requires a highly perfected polish as with the prior design however, the 160 EDF is spherical to a high degree and this makes it somewhat easier to finish than the 155 EDF. And the curves of the opposing elements differ.
The Astro-Physics company has evolved over the years to include several of the best experts in lens design and figuring. Their reputation for consistent perfection is unrivaled. And incidentally, as before Astro-Physics will continue figure the lens sets of the EDF to 1/50 RMS - these are nulled in the yellow-green portion of the spectrum where the human eye is most sensitive and the wavelength more revealing of any anomalies than testing in Helium Neon red light as is typical in many other factories. As related by Roland Christen:
"All polishing including hand correction is always done on a machine. Steep
curves are no worse to polish to high accuracy than shallow ones. In fact, very
shallow curves are the most difficult to get right. For an apo triplet, every
surface must be matched to a very high tolerance level to an interferometric
test plate. Only if this is done will the spherical and color correction come
out right. Apo doublets have slightly lower requirements, and achromats have
much looser tolerance for color correction than a triplet lens."
There are many ways to polish a glass surface, and the oft used words
"machine polished" really means very little. There is no-one in this business
that pushes glass around by hand. There is a vast difference between precision
polishing and rapid polishing of a surface. Rapid polishing can clear a ground
surface is 10 minutes or less. Some new processes can do it even faster - a few
seconds for a 6" part. The surface will not be very good in either case, and
will have machining marks and zones on a microscopic level. Precision polishing
takes many hours with specially made pitch laps. That's the only way to get
consistent high surface finish."
MECHANICAL CONSTRUCTION
As has been the case for more than a decade, these optical tubes remain the standard of excellence in mechanical design as well as in optics. The mechanical construction provides this telescope will be completely trouble-free, and the optics will remain permanently aligned unless it suffers some catastrophic injury. The gorgeous tube assembly is precision machined in the Astro-Physics shop with the most modem CNC equipment available; there are no fragile die castings in this telescope. Expert machinist transforms solid, aircraft-quality aluminum stock into a fully baffled tube assembly with no less than twelve knife-edge baffles in the focuser draw tube alone. Astro-Physics has has endeavored to achieve the highest absorption of stray light possible to give you the maximum contrast.
The exterior textured finish of the optical tube and dew cap will retain its deep, lustrous beauty for many years. The texturing also reduces the chances of the optical tube sliding in the rings or in your hands (particularly when wet with dew for example) than the original gloss white finish provided with the early 1990's EDF models. You will appreciate the unique design and fine craftsmanship of this telescope - even on cloudy nights you might be content to stay home and just look it over.
The objective lens resides in a push-pull cell that maintains its collimation even under conditions of vibration during shipping. The newly designed captive sliding felt lined dew cap (lens shade) features an integral baffle placed at the leading edge to help prevent dew accumulation as well as to block stray light.
Above: Astro-Physics 160 EDF four inch focuser with optional Astro-Physics "Maxbright" Mirror 2 Inch Diameter Diagonal and 8mm Super Planetary Series Eyepiece (89,994 bytes).
Click on image to see enlarged view (237,080 bytes)
The 160 EDF optical tube assembly incorporates an unrivaled four inch aperture focuser. This was developed by Astro-Physics to permit wide field astrophotography with their original 155 to 206mm EDF telescopes, and this focuser has been refined over the years to accept a broad range of heavy equipment while still moving smoothly without image shift. Our superb Astro-Physics four inch focuser is a finely crafted unit with several unique features:
- The inside diameter (I.D.) of the focuser draw tube is 109mm (4.3 inches). This allows the avid astrophotographer to employ optional Astro-Physics lenses and hardware to attach a medium-format camera to capture images in a 6 x 7 cm format with no vignetting.
- The components are machined to extremely high tolerances, assuring that there is no rotational or lateral wiggle between the draw tube and housing.
- More than a dozen knife-edge baffles are machined into the wall of the draw tube and painted anti-reflection black in order to maximize contrast by essentially eliminating any internal reflections.
- Recessed brass locking rings are installed at each thumbscrew location. As you tighten each thumbscrew, the brass locking ring clamps onto the part that has been inserted. Consequently, your focuser draw tube and accessories are held securely in place. This is particularly important considering the heavy and expensive accessories that you may use. As an added advantage,
the brass will not mar the surface of your accessories.
- The telescope is designed with the astrophotographer in mind and so it incorporates the Feather Touch dual-speed geared manual focus control. While the Focuser can be precisely rotated a full 360 degrees. These features allow more accurate focus, and the optimal composition of the image whether in the eyepiece or camera.
|
|
The built-in collar allows the user to loosen the focuser and rotate it smoothly on the optical tube throughout a full 360 degrees of travel to suit - all without the need of tools or loss of critical alignment.
- Advanced engineering eliminates the need to grease the focuser drawtube thereby eliminating a magnet for contaminants, and reducing "stickiness" when focusing which may have been encountered with other focusers on very cold nights.
- Two pair of tapped and threaded holes are provided located at the 10:30 and 1:30 clock positions on the Focuser Housing. These facilitate the attachment of accessories (finder telescope, etc.).
- Focus travel is a generous as the drawtube extends 105mm (4.1 inch). And the focuser is positioned on the optical tube so that the Baader Planetarium/Carl Zeiss Mark V Großfeld Binocular Viewer will come to focus with or without it's provided 1.25x compensator. This allows the user to see glorious wide field views with both eyes - a real treat.
- In 2004 Astro-Physics developed a new specially designed dual-speed pinion fine dual speed geared focuser assembly for their 2, 2.7 and 4 inch Focusers. Incorporating a 9 to 1 geared reduction knob, this is the Feather Touch® Micro Focuser option. You can order it factory installed in your new 160mm EDF telescope. It is also available as an retrofit kit for existing compatible Astro-Physics focusers.
Right: Feather Touch® Focuser shown option on Astro-Physics 155 mm EDF Apo telescope 2.7" Focuser, becoming available with the 4" model (54,384 bytes).
Click on image for higher quality, enlarged view (125,877 bytes).
You can use the larger or standard slip accessories on this focuser since it is provided with reducers to accept optional 2.7 inch accessories, and another reducer to accept 2 inch accessories, and a reducer of from 2 to 1.25 inch. For those who wish to employ the telescope in a straight through arrangement we also provide a 4 inch wide x 2-1/4 inch long extension tube which attaches onto the focuser drawtube bayonet mount.
There are a number of current and coming photographic accessories for CCD imaging, 35mm and medium format film photography for this telescope. In addition to an optional 4" Prime Focus Field Flattener for medium format or 35mm applications, we will offer a new dedicated f/5.75 Flat-Field Telecompressor that is diffraction-limited over the entire 35mm field; this is perfect for use with the new, larger format CCD systems available today including our Santa Barbara Instruments Group new Research Series CCD systems.
This giant four inch focuser is a versatile component of the 160 EDF which will allow you to enjoy many aspects of astronomy.
160mm f7.5 EDF OVERVIEW:
Measurements based on the first production sample delivered to Company Seven in August 2005
| SPECIFICATIONS |
| Color correction: |
Less than 0.005% focus variation from 706nm to
405nm (h to r) see table above right |
| Clear aperture: |
160mm (6.3") |
| Focal length: |
1,200mm (47.2") |
| Resolution: |
0.7 arc seconds |
| Coatings: |
Multilayer broadband, total transmission greater than 97% in peak visual wavelengths |
| Magnification range: |
12x to 600x |
| Tube assembly: |
White finish aluminum tube; fully baffled,
permanently aligned cell construction; engraved focuser |
| Focuser type: |
4" Astro-Physics rack and pinion focuser, 4.1" travel;
2.7, 2 and 1.25" adapters; 4 x 2.25" extension tube |
| Telescope overall length: |
44-1/2" (1,130 mm) w/dew cap retracted |
| Telescope Tube diameter: |
6-1/2 inches |
| Dew Shield diameter: |
6-1/2 inches |
| Weight with dew cap: |
27 lbs. (12.3 kg) |
| Carrying Case: |
Foam-fitted, vinyl-covered plywood case |
| Carrying Case dimensions: |
49 x 11-3/4 x 11-1/4 inches |
| Carrying Case weight: |
17 lbs (7.7 kg) |
| Packaged dimensions: |
50-1/4 x 13 x 12-1/2 inches |
| Packaged weight: |
62 lbs (28.2 kg) |
| 35mm prime-focus field: |
1.6 x 1.1 x 2 degrees |
| 35mm telecompressed field: |
1.5 X 2.2 degrees at f/5.75 |
| 6 x 7 cm prime-focus field: |
3.3 x 2.6 x 4.2 degrees |
* Specifications are subject to change without notice.
Right: Astro-Physics 160 EDF Telescope objective lens and cell with Dew Shield/Lens shade extended (15,134 bytes)
Click on image to see enlarged view (173,595 bytes)
ACCESSORY SUGGESTIONS
- A suitable German Equatorial Mount and mount attachment hardware such as those developed by Astro-Physics. These portable mounts are perfect for visual and photographic studies in either the Northern or Southern Hemispheres. Good, less costly alternatives for visual and light duty imaging uses include the intuitive Vixen SPHINX SXW Equatorial Mount with the STAR BOOK "Go To" system. Or, for those who wish a capable astrographic mount that is not as sophisticated or costly as the Astro-Physics mounts we recommend the Losmandy G-11, or the Losmandy Titan "Go To" German Equatorial Mount.
- Mounting Rings:
For the 160mm EDF these will be the 6.5" Rings, sold by the pair as P/N 65RING.
- Mirror Diagonal:
Prism diagonals may introduce aberrations which degrade perceived image quality. Since this is especially noticeable in telescopes with fast focal ratios, we recommend use of the Astro-Physics "Maxbright" Precision Mirror 2 Inch Diagonal.
- Eyepieces:
Astronomers will wish to own at least a few 1.25" or 2" eyepieces initially to set up this telescope to address:
- Low magnification: for views of the faint deep sky objects a 32mm to 35mm focal length eyepiece.
- Middle Magnification eyepiece - usually between 80 to 120X, for views of the full Moon, Star Clusters, etc.
- High magnification: 200X or more for views of the planets
Astro-Physics and Company Seven recommend the eyepieces of advanced designs such as those pioneered by Al Nagler, founder of the TeleVue company. TeleVue's advanced designs include the "Nagler", "Radian", or "Panoptic" series eyepieces. These oculars will provide the widest angle clear, and flat field images bringing out the most in this (and many other) telescopes.
And for those who seek the most detailed images of the planets or close double stars, you should also consider the new Astro-Physics Super Planetary Eyepieces.
Examples of some popular eyepiece choices:
| Eyepiece |
Magnification |
Actual field of view |
Exit pupil |
| 55mm Plossl |
22x |
2.2 degrees |
7.3mm |
| 41mm Panoptic |
29x |
2.2 degrees |
5.5mm |
| 35mm Panoptic |
34x |
1.8 degrees |
4.7mm |
| 22mm Nagler Type 4 |
55x |
1.5 degrees |
2.9mm |
| 10mm Radian |
120x |
0.5 degrees |
1.3mm |
| 9mm Nagler |
171x |
0.6 degrees |
0.9mm |
| 6mm Super Planetary |
200x |
0.2 degrees |
0.8mm |
| 3 to 6mm Nagler Zoom (at 6mm) |
200x |
0.24 degrees |
0.8mm |
| 5mm Nagler |
240x |
0.3 degrees |
0.7mm |
| 3 to 6mm Nagler Zoom (at 3mm) |
400x |
0.12 degrees |
0.4mm |
You may slso consider using our Astro-Physics 2" (2X) Barlow to double your magnification and increase overall versatility.
- 4" Field Flattener for medium format photography - matched to the performance characteristics of this instrument.
- Flat-field Telecompressor f/5.75 for 35mm photography and large format CCD imaging - matched to the 160 EDF, diffraction limited over the entire 35mm field.
- Visual flat-field Telecompressor f/5.6 for use with 1.25 or 2 inch eyepieces - enjoy fields of view of up to 2.9 degrees with a suitable eyepiece!
- Feather Touch® Micro Focuser. A dual-speed pinion fine dual speed geared focuser assembly incorporating a 9 to 1 geared reduction knob. You can order it factory installed in your new telescope.
Right: Astro-Physics Traveler 4 inch telescope with optional Feather Touch® Focuser Pinion and Gear Reduction Assembly similar concept to what is coming for the 160 EDF's 4 inch focuser (53,738 bytes).
Click on image for higher quality, enlarged view (151,858 bytes).
- "Starbeam" Finder: Beautifully machined and black anodized aluminum, on a quick release machined hardware. Battery powered illuminator is adjustable in brightness; it projects a 10 arc minute diameter red dot onto a transparent 40mm clear aperture window so that the dot appears to be over wherever the scope is pointed. Six arc minute accuracy make "star hopping" easy.
- Red LED Flashlight such as the Rigel Skylite to help one set up and use a telescope, and to read charts or a planishpere without adversely impacting the observers night vision.
- Telescopes such as this often put the eyepiece at position that is only about 3 or 4 feet (0.9 or 1.2 meters) from the ground. Since most of our customers are taller than that, they will find it uncomfortable to stand bent over to observe for extended periods. For a much more enjoyable and comfortable observing experience, Company Seven recommends the Observing Chair; this is our most comfortable, flat folding, adjustable height seat. It is not inexpensive, but is so practical and can be used for camping or other times when a comfortable portable seat is desired.
- Company Seven's ATA Transport/Shipping Case: the case provided by Astro-Physics with each optical tube assembly is a reasonable balance of economy and performance for routine storage of a telescope in a temperature and humidity controlled environment. However, if you plan for long term storage, or if you intend to ship the telescope by commercial carrier or transport it as check in baggage on an airliner (observing oversize and overweight restrictions) then your peace of mind and telescope will both be better served with a custom engineered solution - an ATA case by Company Seven.
Right: Company Seven ATA Case custom fitted for a Astro-Physics 160cm EDF Apochromat Telescope with 2.7 inch Focuser (101,693 bytes). This case features full ATA requirements and upgrades by Company Seven including removable lid (eliminates risk of scraping telescope moving it in and out of the case), hand-laid velour linings to eliminate marring from conventional foam interior, weathertight construction, roller wheels (just below and out of sight in this photo) at one end to facilitate handling; the wheels and bumper pads may easily be removed when shipping the case.
Click on image to see enlarged view (230,560 bytes).
Features include:
- custom fit to accommodate the telescope optical tube with or without accessories (Rings, Focuser, etc.)
- hand fitted velour lining over foams of varying densities to deal with anticipated loads
- weather resistant construction
- combination lock and hasp
- Fedex/UPS label plate
- choice of interior and exterior hard shell material and colors
Left: Astro-Physics Model 900 Mount in optional Company Seven ATA case.
Case 1 of 2 shown here, with Declination housing (left side shown) with GTO Keypad Controller
and Counterweight Shaft (94,326 bytes).
|
|
Contents Copyright 1994-2005 Company Seven - All Rights Reserved
|
|
C-7 News 
