Sky-Watcher Explorer 130 — Field Reference

Aperture 130mm

Focal Length 650mm

Focal Ratio f/5

Max Useful Mag 260×

Mirror Type Parabolic

Mount Type EQ3 GoTo

01 Polar Alignment

Before you GoTo

Set up the tripod on level ground. Use the bubble level on the mount head — adjust legs until centred.

Loosen the latitude adjustment bolts and tilt the polar axis to match your latitude. Lock.

Point the polar axis north. Use a compass but offset ~2° for magnetic declination in most of the UK.

Look through the polar scope. Rotate the RA axis until the small circle marker is in the correct clock position for tonight's date/time.

Adjust azimuth bolts (left/right) and altitude bolts (up/down) until Polaris sits inside that small circle.

POLAR SCOPE

Quick tip: Rough polar alignment is enough for visual GoTo use. Only visual — within ~1° is fine.

02 Attaching the OTA

Slide the OTA rings onto the dovetail bar. Tighten evenly.

Insert dovetail into the mount saddle. Tighten the locking knob — do not overtighten.

Fit the counterweight partway up the shaft before unlocking the RA/Dec clutches.

03 Balancing the Mount

RA Axis (East–West)

Point the OTA east. Release the RA clutch. The scope should float — if it falls E or W, slide the counterweight up or down until balanced.

TOO LIGHT ← BALANCED → TOO HEAVY

Dec Axis (North–South)

Point OTA to horizon. Release Dec clutch. If it swings forward or back, slide OTA in rings fore/aft until balanced.

Why it matters: An unbalanced mount stresses the motors and causes tracking drift.

Before you align: Enter your location, date, time and UTC offset in the SynScan handset. Park the mount in the Home Position (counterweight down, OTA pointing north and level). Accuracy here is everything.

1-Star Alignment — Fastest, least accurate

Procedure

Select Alignment → 1-Star from the handset menu.

SynScan suggests a bright star. Choose one that is above 20° altitude and ideally near the meridian.

Press ENTER. The mount slews to the approximate position. The star should be in or near the eyepiece field.

Use the arrow keys to centre the star precisely in the FOV. Always approach the final position from south and east — this removes backlash.

Press ENTER to confirm. Alignment complete.

When to use

Best for: Quick visual sessions when you don't need precise pointing. Planets, Moon, bright Messiers.

Avoid for: Searching faint objects below naked-eye visibility — pointing errors of 2–3° are normal.

Backlash rule

Always make your final approach from south (in RA) and east (in Dec). Reverse past the target and come back. This removes gear backlash and is the most common cause of poor GoTo pointing.

2-Star Alignment — Good balance of speed and accuracy

Procedure

Select Alignment → 2-Star. Pick the first suggested star. Slew and centre as per 1-star. Press ENTER.

SynScan now lists a second star. Ideally choose one far from the first — at least 30° away, in a different part of the sky.

Centre the second star carefully. Again approach from south/east on the final tweak. Press ENTER.

SynScan calculates the alignment model. Any pointing error it reports is the residual — under 5 arcmin is excellent.

Star selection tips

Good pairs: Arcturus + Vega, Deneb + Altair, Capella + Rigel, Jupiter + Saturn (if available).

Spread them out: Two stars close together give a poor model. Aim for angular separation > 60°.

Best for: General deep-sky observing, most Messier objects, medium-faint targets.

Avoid: Stars near the horizon (atmospheric refraction) or directly overhead.

3-Star Alignment — Best accuracy for the whole sky

Procedure

Select Alignment → 3-Star. Complete the first two stars exactly as in 2-Star alignment.

Choose the third star from a different region of sky — ideally forming a wide triangle with the first two.

Centre and confirm. SynScan builds a sky model accounting for cone error, polar misalignment and flexure.

Test by GoTo-ing a nearby bright object. If well within 1° of centre, the model is excellent.

Why 3-star is worth it

Corrects for: Polar misalignment, non-level tripod, mechanical flexure, cone error.

Triangle geometry: Think of the three stars as vertices of a triangle that covers as much sky as possible. East, west and north of zenith is a good spread.

Best for: Long sessions, faint galaxies, planetary nebulae, objects you've never seen before — GoTo accuracy under 15 arcmin across the whole sky.

25mm

Wide Field

26×

Low power. Max exit pupil — perfect for large nebulae and open clusters.

10mm

Medium Power

65×

All-round workhorse. Planets, globular clusters, smaller nebulae.

6mm

High Power

108×

Planetary detail, double stars. Only useful in steady seeing.

2× BAR

Barlow Lens

×2 any EP

Insert before eyepiece to double mag: 25→52×, 10→130×, 6→216×

Selected: 25mm Wide Field 26× WIDE — 1.9° true FOV

Exit Pupil 5.0mm

Magnification Calculator

Focal length
650mm fixed

─────────── 650mm

650

Eyepiece FL
2 – 40mm

Barlow

1×

26×

Good for wide-field views and faint nebulae

Exit pupil: 5.0mm True FOV: 1.9°

1× (LOW) 260× MAX

When to Use Each Power

Low power (20–50×) — 25mm or 25mm+2× not quite

Best for: Milky Way star fields, Pleiades, Orion Nebula (M42), Andromeda (M31), open clusters (Hyades, Double Cluster).

Medium power (50–120×) — 10mm or 25mm+2×

Best for: Jupiter's cloud bands, Saturn's rings, globular clusters (M13), planetary nebulae (Ring Nebula M57).

High power (120–260×) — 6mm or 10mm+2×

Best for: Mars surface markings, lunar craters, tight double stars — only in steady seeing.

Seeing limit: On most UK nights the atmosphere limits useful magnification to 130–180× regardless of the eyepiece you use. If the image shimmers, drop power.

Using GoTo

After alignment, press MENU on the handset. Select Select and Slew.

Browse by catalogue: Messier, NGC, IC, Stars, Planets. Enter the object number and press ENTER.

Mount slews. Object should be within 1° of centre after a 3-star alignment. Check with a low-power eyepiece first.

Shortcut: Solar system objects — press MENU → Planets → target. SynScan knows current ephemeris.

When GoTo Misses — Tap to fix

What went wrong?

Manual Star Hopping

Finding M13 — Hercules Globular (example)

η Her

ζ Her

M13 ✦

1/3

→

General technique

Start from a bright naked-eye star near your target. Identify it on a chart (SkySafari, Stellarium).

Use low power (25mm) — you get a wider true field and the finder chart scale matches better.

Move in small hops following star patterns from the chart. Note which stars appear in the same field as the target.

When you reach the target field, a faint fuzz or stellar point will be visible. Confirm its shape against the chart.

Hint: Averted vision (looking just to the side of the object) reveals objects ~1 magnitude fainter than direct viewing.

TRACKING

Stars drift out of view / not tracking

▶

Cause	Fix
Polar alignment is off	Redo polar alignment, especially azimuth (left-right). Even 2° error causes drift in RA.
Wrong hemisphere set in SynScan	Check Setup → Hemisphere. Northern hemisphere = North.
Mount not balanced — motors straining	Balance RA and Dec axes before observing.
Time/date/UTC offset wrong	Even 1 min error causes sidereal rate drift. Re-enter time carefully.

GOTO

GoTo is wildly off — object nowhere near FOV

▶

Cause	Fix
Home position wrong at start	Park mount: counterweight shaft pointing down, OTA pointing north and level. This is the critical starting point.
Alignment stars identified incorrectly	Use a planetarium app to confirm which star is which. Arcturus vs Capella are commonly confused.
Backlash not removed during alignment	Centre alignment stars by approaching from south (RA) and east (Dec) only. Never push back from the correct direction.
Location entered incorrectly	Check lat/long in SynScan Setup. Longitude sign matters (negative for West).

IMAGE

Image is blurry / stars have halos or spikes

▶

Cause	Fix
Scope not cooled down	The mirror needs 20–40 min to reach ambient temperature. Warm air currents inside the tube degrade the image.
Focuser not at the right position	Focus carefully using a bright star. Stars should collapse to a tight point, not a disc or ring.
Poor atmospheric seeing	Check a seeing forecast (Astrospheric). If seeing < 3/5, drop magnification below 100×.
Eyepiece dirty or dewed up	Inspect eyepiece — breathe on it gently. Carry a dew strap or hand warmer near the focuser.

OPTICS

Collimation check — stars look like comets or off-axis blur

▶

What to look for — defocused star test

Good collimation: Defocused star shows concentric rings with the central shadow (secondary mirror silhouette) perfectly centred.

Out of collimation: Rings are off-centre or egg-shaped. The central dot is not in the middle of the rings.

Adjustment	How
Primary mirror (back of tube)	Three collimation bolts with locking rings. Loosen lock ring, turn adjustment bolt. Small movements only — check after each quarter turn.
Secondary mirror (spider vanes)	Central screw tilts secondary. Use a collimating eyepiece or Cheshire — adjust until secondary is centred in the focuser drawtube.
How often needed	Check after any transport. A parabolic mirror holds collimation well — a small offset won't ruin planetary work, but affects stars at high power.

POWER

SynScan hand controller not responding / mount won't slew

▶

Cause	Fix
Battery low	EQ3 SynScan needs 8× AA batteries at full charge or a 12V DC supply. Weak batteries cause erratic behaviour before total failure.
Hand controller cable loose	Check the RJ-11 connector at both ends — mount socket and handset. Click firmly until it seats.
Mount clutches locked — manual slew blocked	For manual movement, release the RA and Dec clutches (friction knobs). GoTo slewing requires them locked.
Motors slipping / stalling	Usually caused by mount imbalance. Balance the mount and check the worm gear tension screws are not overtightened.