Sky-Watcher BK 705AZ3 is a compact lens telescope with a 70 mm objective diameter and a focal length of 500 mm. The telescope is supplied with a Sky-Watcher AZ3 alt-azimuth mount with micrometer screws on two axes. The device is designed for beginner astronomy enthusiasts, provides a direct image (without inversion and reflection) and can be used as a spotting scope.
Characteristics declared by the manufacturer:
Telescope type | refractor |
Optical scheme | achromatic |
Coating | fully multi coated |
Lens diameter (aperture), mm | 70 |
Focal length, mm | 500 |
Maximum useful magnification, times | 140 |
Focal ration | f/7 |
Eyepieces | 25 mm, 10 mm |
Mounting diameter of eyepieces, inches | 1,25 |
Finder | red dot |
Tripod | aluminium |
Accessory tray | yes |
Telescope control type | manual |
Mount type | azimutal, AZ3 |
Fine tunes mechanism | dual axis |
Extras | There is a standard T-thread (M42) for mounting a SLR camera |
Tube material | aluminium |
Tube dimensions, mm | 380 length |
Weight of tube, kg | 1,25 |
User level | for beginners |
Observations objects | Planets of Solar System |
APPEARANCE, EQUIPMENT
The telescope comes in one cardboard boxe – it contains the tube in mounting rings, the tripod, shelf, fine movement handles, and a separate box contains accessories – two eyepieces 10 mm and 25 mm, a 45-degree erecting prism, a red dot finder, a screwdriver and several wrenches. The workmanship is good, no defects were found.
The tube is wrapped in shipping paper. The length of the tube with caps is 52 cm. The weight of the tube without fastening rings is 0.83 kg. The tube is metal, there is a non-standard mount for the finder. The detachable plastic hood, length 132 mm, external diameter 97.7 mm, internal diameter 94.9 mm, thickness 2.4 mm. The length of the tube without the hood is 41 cm, the diameter of the tube is 75.5 mm. The tube is closed at both ends with plastic caps. In the large lid there is a hole with a diameter of 42 mm.
The objective is glass, two-lens achromatic with an air gap, between the lenses there are three gaskets. The measured aperture is 69.7 mm. The lens frame is plastic, attached to the tube with three screws. The diameter of the frame is 82.34 mm. The objective is fully coated, the color of the coating is blue.
The focuser is plastic and threaded. The focuser stroke is 70.9 mm. At the output of the focuser there is a T2 thread (M42x0.75) for connecting adapter rings and accessories.
The mounting rings are metal, the inner diameter is approximately 73 mm, the weight of the rings is 220 grams.
The erecting prism is uncoated, the axis is bent at 45 degrees, and there is a 19.6 mm diameter hole in the front part of the prism.
Finder with a red dot, plastic body. The meniscus lens for transmission is blue, orange coating on the outside. The finder is powered by a CR2032 battery. There is an adjustment of the dot position, as well as a switch with brightness control. Before use, you must remove the plastic plate near the battery.
Eyepieces with a focal length of 10 mm and 25 mm, made according to the Köllner scheme. Coated, the color coating is blue for 10 mm and light blue for 25 mm. The eyepiece bodies are plastic, the skirts are metal.
Fine movement handles are flexible, length 32 and 28 mm, handle diameter 49 mm.
Metal accessory shelf with three mounting screws, weight 0.45 kg, width 28 cm.
The mount is structurally connected to the tripod and is non-removable. The tripod is aluminum, the length of the legs is 78-132 cm. The weight of the tripod with the mount is 3 kg. The clamps on the tripod fixing mechanism are plastic. The junction of the tripod and the tripod base is also plastic.
The head of the mount is metal, with two micrometer screws with a limited stroke. At the bottom of the mount there is a handle with a screw that fixes the mount along the azimuth axis. There are two holes for mounting rings. The axes rotate quite tightly. If the stroke of the micrometer screw has ended, it is necessary to stop observing, unscrew the micrometer screw in the opposite direction until it stops, re-point the telescope at the object and continue observing. The stroke of the micrometer screws depends on the location of the object in the sky. The mount together with the tube can be rotated manually in height, and after preliminary loosening of the screw with the handle – in azimuth.
ASSEMBLY OF THE TELESCOPE
Assembling the telescope is very simple.
After that, we turn on the red dot finder, check its alignment with the tube against a distant ground object, a bright star or the Moon.
When transporting, it is not necessary to unscrew the tube together with the rings each time – it is enough to simply remove the tube from the rings and remove the handles with fine movements.
TEST
The aperture of the telescope is not cut by diaphragms or a focuser tube. With the erecting prism installed, the entire objective is visible.
For ground objects, the image in the central area is clear, for branches, longitudinal chromatic aberration (a bluish tint) is noticeable, as is expected for an achromatic lens with similar parameters. Lateral chromatic aberration is noticeable across the field.
On the Moon, chromatic aberration is noticeable along the edge of the disk, as well as in the blue tint of the lunar disk. On Jupiter, chromatic aberration is noticeable as a fairly wide blue halo. On Saturn and Mars, chromatic aberration is almost invisible. To reduce the visibility of chromatic aberration during visual observations, you can use an ocular yellow filter #8.
For astronomical observations, it is advisable to purchase a 90-degree 1.25-inch mirror – it will provide better image quality at high magnifications, a more convenient eyepiece position due to the 90-degree axis bend, and will also eliminate vignetting when using long-focus eyepieces (32 or 40 mm). For terrestrial observations, the complete erecting prism is quite sufficient.
SUMMARY
Sky-Watcher BK 705AZ3 is one of the best telescopes for a beginner amateur astronomer. Compact tube, good image quality with moderate chromatic aberration, stable mount with micrometer screws on two axes will provide pleasant impressions during astronomical observations.