Manual Bresser AR-152S-L (page 20 of 44) (English)

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ma I n t e n a n c e a n d se r v I c e

Alignment (Collimation) of the

Newtonian Optical System

All Bresser Newtonian telescopes are precisely collimated at the factory

before packing and shipment, and it is probable that you will not need to

make any optical adjustments before making observations. However, if

the telescope sustained rough handling in shipment, you may need to re-

collimate the optical system. Such re-collimation is not a difficult procedure

in any case.

The collimation procedure for the short focal length-Newtonians is slightly

different from that of other Newtonian reflecting telescopes, because of the

„fast“ f/5 focal ratio of the primary mirror. In typical Newtonian reflectors with

more conventional focal ratios (i.e. longer focal ratios), when the observer

looks down the focuser tube (without an eyepiece in the focuser), the images

of the diagonal mirror, primary mirror, focuser tube, and the observer‘s eye

appear centered relative to each other. However, with the short focal ratio

primary mirror of the Newtonian, correct collimation requires that the diagonal

mirror be offset in 2 directions: (1) away from the focuser and (2) towards the

primary mirror, in equal amounts. This offset is approximately 1/8“ in each

direction. Note that these offsets have been performed at the factory prior to

shipment of your telescope. It is only necessary for you to confirm that the

telescope has not been badly jarred out of collimation, and to perform the

final fine-tuning of Step 4, below.

Fig. 31a shows a correctly collimated Newtonian telescope, as it appears

when viewed through the focuser with the eyepiece removed.

To check and, if necessary, set the optical collimation, follow these steps:

1. Observe through the focuser and orient your body so that the telescope‘s

primary mirror is to your right. The diagonal mirror will appear centered

as shown (2, Fig. 31a). If the diagonal appears off center, then adjust the

4 collimation screws on the plastic diagonal mirror housing.

2. If the reflection of the primary mirror (3, Fig. 31a) is not centered on the

surface of the diagonal mirror, adjust the 4 collimation screws on the

plastic diagonal mirror housing to center the reflection. As described

above, the 4 collimation screws (Fig. 31b) on the plastic diagonal mir-

ror housing are used for two different adjustments during the collimation

procedure.

b c d e f g

Fig.31a

Note:

The AR-(refractor) models do not

need any collimation

Focuser drawtube

Secondary mirror

Reflection of primary mirror

Reflection of secondary mirror

Reflection of observer’s eye

Primary mirror clips

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Bresser AR-152S-L Manual

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