Meade RCX400 Instruction Manual download pdf (Page 60)

ting circle and slightly

loosen the two bolts located under the knob. Now turn the circle

unit until it reads 89.2°, the Declination of Polaris. Then tighten down the two bolts and

replace the kn

urled knob.

Should you wish to use the manual setting circles, the R.A. setting circle (

Fig. 51) must

be calibrated manually on the Right Ascension of a star every time the telescope is set

up. (The R.A. setting circle has two sets of numbers, the inner set is for Southern

hemisphere use, while the other is for Northern hemisphere use.) Locate a star with

which y

ou're familiar. Look up the R.A. for the star in a star chart or other aid. With the

star centered in the telescope's eyepiece, move the R.A. setting circle, using one of

knobs (

C, Fig.

), so that the R.A.

of the star lines up with the tick mark on the base

of the telescope (B, Fig. 53).

Precise Polar Alignment

It should be emphasized that while doing casual observing, precise alignment of the

telescope’s polar axis to the celestial pole is not necessary. Don’t allow a time-con-

suming effort at lining up with the pole to interfere with your basic enjoyment of the tel-

escope. For long-exposure photography, however, the ground rules are quite different,

and precise polar alignment is not only advisable, but almost essential.

Even though the

RCX400 telescopes offers a very precise and sophisticated drive sys-

tem, the fewer tracking corrections required during the course of a long-exposure pho-

tograph, the better. (“Long-exposure” means any photograph of a celestial object that

last for 10 minutes or longer). In particular, the number of Declination corrections

required is a direct function of the precision of polar alignment.

Precise polar alignment requires the use of a crosshair eyepiece. The Meade

Illuminated Reticle Eyepiece (see

OPTIONAL ACCESSORIES, pages 48 - 50) is well-

suited in this application, but it is also preferable to increase the effective magnifica-

tion through the use of a 2X or 3X Barlow lens as well. Follow this procedure (partic-

ularly if the pole star is not visible), sometimes better known as the “Drift” method:

1. Obtain a rough polar alignment as described earlier. Place the illuminated reticle

eyepiece (or eyepiece/Barlow combination) into the eyepiece holder of the tele-

scope.

2. Point the telescope, with the motor drive running, at a moderately bright star near

where the meridian (the North-South line passing through your local zenith) and

the celestial equator intersect. For best results, the star should be located within

±30 minutes in R.A. of the meridian and within ±5° of the celestial equator (see

CELESTIAL COORDINATES, page 57). Pointing the telescope at a star that is

straight up, with the Declination set to 0°, will point the telescope in the right direc-

tion.

3. Note the extent of the star’s drift in Declination (disregard drift in Right Ascension):

a. If the star drifts South (or down), the telescope’s polar axis is pointing too far

East.

b. If the star drifts North (or up), the telescope’s polar axis is pointing too far

West.

4. Move the wedge in azimuth (horizontally) to effect the appropriate change in polar

alignment. Reposition the telescope’s East-West polar axis orientation until there

is no further North-South drift by the star. Track the star for a period of time to be

certain that its Declination drift has ceased.

5. Next, point the telescope at another moderately bright star near the Eastern hori-

zon, but still near the celestial equator. For best results, the star should be about

20° or 30° above the Eastern horizon and within ± 5° of the celestial equator.

6. Again note the extent of the star’s drift in Declination:

a. If the star drifts South, (or down) the telescope’s polar axis is pointing too low.

b. If the star drifts North, (or up) the telescope’s polar axis is pointing too high.

7. Use the altitude adjust control on the wedge to make appropriate changes in alti-

tude

, based on your observations above. Again, track the star for a period of time

to be cer

tain that Declination dr

ift has ceased.

The abo

e procedure results in v

y accur

ate polar alignment, and minimizes the need

or tr

king corrections during astrophotography.

Fig. 54: RCX400 mounted on an

equatorial wedge.

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Meade RCX400 Instruction Manual Page 60

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