Webb Society Double Star Section

The Webb Deep-Sky Society - Double Star Section

RETEL Micrometer

Specification:

12 micron Tungsten Wires (subtend 1.2 arcsec at focal length of 2 metres)
One fixed, one movable wire in parallel plus a 3rd wire at right angles.
Micrometer graduations: 0.01mm (usable range about ą6 cm)
PA Circle 0 to 360 degrees in 1 degree graduations.
Vernier 29 degrees with 10 divisions. (Can read to 0.1 degree)
Red LED field illumination.
Choice 18mm or 25 mm Kellner eyepieces
Dimensions: 82 mm X 106 mm long made from HE30 Hiduminium Alloy
Weight : 0.8 kg.

Extras:

Other eyepieces
Barlow
Illumination Control

Current cost (at 2007 July) is 537 pounds sterling (micrometer plus one eyepiece plus illumination control). Post,packing and insurance in the UK is 10 pounds.

One of the two instruments belonging to the Webb Society and operated by the undersigned has been used with the 8-inch refractor at Cambridge (focal length
=114 inches) since 1990. Since then some 6,000 measures of double stars have been made with an average of about 15 settings per pair. The PA drive is a friction arrangement but seems to be repeatable within a few tenths of a degree on wide, bright pairs. It is recommended that the effective focal length of the telescope is sufficient to make the wires small - otherwise close pairs cannot be observed.

With the 8-inch, a x3 Barlow means that the wires subtend 0.3 arc seconds each and pairs as close as 0.6 arc seconds can be observed. A drawback is the bright field illumination, rather than bright wire illumination. This restricts the observation of faint companions to bright stars and stars around mag 9 are difficult to see in the 8-inch with the illumination on.

R.W.Argyle

2007 July

For further details contact the manufacturer:

Mr. D. Dolle, RETEL Ltd, 37 Banbury Road, Nuffield Industrial Estate, Poole, Dorset BH17 7UG. Tel: (01202) 685883

e-mail: retelemd@btconnect.com

Comparison between RETEL and van Slyke micrometers

The following comparison between the RETEL and van Slyke micrometers has been made by Andreas Alzner, in Germany.

Comparing the RETEL and the van Slyke is not easy. In the following I list the benefits (+) and the disadvantages (-):

RETEL:

+ stable 12 micron - tungsten wires (they will never break)

+ filars well adjusted

+ high quality of the Japanese micrometer screw for the distances

+ simple handling

- mechanics for position angle somewhat cumbersome (fast rotations are not possible)

- bad field illumination, has to be modified (my solution: remove it completely and put three red power-LEDs into the dew-cap, adjustable via a potentiometer, this gives a very good soft field illumination)

- 12 microns is too thick for the tungsten wires, 8 microns would work much better

- position angle difficult to read

van Slyke

+ high quality of the Japanese micrometer screw for the distances

+ the values for the distances and the PAs are easy to read

+ fast rotations for the position angles are possible

+ for the distances: one "wire" is a line, the other one is "dotted", hence distances for stars with a faint companion can be better measured than with two solid wires

- the apparent thickness of the wires (etched lines on reticles) are about 15 microns. This is too thick, a Barlow lens is always necessary

- I have the impression, that the reticles are not coated: this means a loss of light

- the wire-illumination is red, but wire illumination must be yellow as a rule. I measure the distances always with my self-made field illumination.

- the upper part of the micrometer is not fixed to the holder! This means you cannot work without a 90 degree prism, otherwise it simply falls out of the holder. No easy modification possible. The price for the van Slyke is about 2.2 times that of the RETEL.

In conclusion, I prefer the simple RETEL. With 8 micron wires and modified illumination it would be a very effective device for a good price.

For bright pairs and distances 0.5 to about 2.5 arc seconds the Meca-Precis double-image micrometer is far superior for the distances.

Andreas Alzner, 1999 April

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+	stable 12 micron - tungsten wires (they will never break)
+	filars well adjusted
+	high quality of the Japanese micrometer screw for the distances
+	simple handling
-	mechanics for position angle somewhat cumbersome (fast rotations are not possible)
-	bad field illumination, has to be modified (my solution: remove it completely and put three red power-LEDs into the dew-cap, adjustable via a potentiometer, this gives a very good soft field illumination)
-	12 microns is too thick for the tungsten wires, 8 microns would work much better
-	position angle difficult to read


+	high quality of the Japanese micrometer screw for the distances
+	the values for the distances and the PAs are easy to read
+	fast rotations for the position angles are possible
+	for the distances: one "wire" is a line, the other one is "dotted", hence distances for stars with a faint companion can be better measured than with two solid wires
-	the apparent thickness of the wires (etched lines on reticles) are about 15 microns. This is too thick, a Barlow lens is always necessary
-	I have the impression, that the reticles are not coated: this means a loss of light
-	the wire-illumination is red, but wire illumination must be yellow as a rule. I measure the distances always with my self-made field illumination.
-	the upper part of the micrometer is not fixed to the holder! This means you cannot work without a 90 degree prism, otherwise it simply falls out of the holder. No easy modification possible. The price for the van Slyke is about 2.2 times that of the RETEL.