Telescope Guide

1Removeaccessories

Remove the eyepiece, Barlow lens, and any other accessories from the eyepiece holder. You should be able to see directly inside the tube.

2Checkthe centering of the secondary mirror

When looking through the eyepiece, you should see:

• The secondary mirror centered in the tube
• The reflection of the primary mirror in the secondary mirror
• The central disc of the primary mirror

If the secondary is not centered, adjust the 3 screws on its bracket (rarely necessary).

3Adjustthe tilt of the secondary mirror

The secondary mirror must be tilted at 45° to reflect light toward the eyepiece holder. Adjust the three tilt screws until you see the primary mirror perfectly centered in the reflection of the secondary mirror.

4Centerthe primary mirror

This is the crucial step. The primary mirror usually has 3 adjustment screws (collimation) and 3 locking screws.

• Loosen the 3 locking screws slightly (1/4 turn).
• Adjust the 3 collimation screws to center the primary mirror spot with the center of the Cheshire
• Make small adjustments (1/8 turn maximum).
• Tighten the locking screws without forcing them.

5Complete visual inspection

When everything is aligned, you should see (from the outside in):

• Main tube circle
• Centered oval secondary mirror
• Circular reflection of the primary mirror
• Reflection of secondary school in the center of primary school
• Your eye at the absolute center

6Star Test

This is the final validation. Point to a bright star (magnitude 2-3) at high magnification (150-200x):

• Defocus the star slightly (intra- and extra-focal).
• Diffraction rings must be perfectly concentric.
• If asymmetrical, finely adjust the collimation.
• Once focused, the star should be a perfect point.

1Installthe mount level

Place your tripod on stable ground. Use a spirit level (or smartphone app) to check that the plate is horizontal. Adjust the length of the legs if necessary.

2Orienttoward true north

• Use a compass to find magnetic north.
• Apply the magnetic declination for your region (in France: ~0-2° East)
• Orient the right ascension axis (RA) toward this North.
• Required precision: ±5° for observation, ±1° for astrophotography

3Adjustthe latitude

The mount has a latitude adjustment (angle to the horizontal). Set it to the latitude of your observation location:

• Paris: 48.9°N
• Lyon: 45.8°N
• Marseille: 43.3°N
• Brussels: 50.8°N
• Montreal: 45.5°N

Find your exact latitude on Google Maps or GPS.

4Verificationwith Polaris (simple method)

Once the latitude has been set and the mount has been oriented north:

• Look through the polar finder (if your mount has one)
• Adjust the Alt/Az knobs until Polaris is centered in the crosshairs.
• Polaris must be in the small central circle (not exactly in the center).
• Use an app (Polar Scope Align) for the exact time position.

5Drift method(astrophotography precision)

For maximum precision (required for long exposure astrophotography):

• Point to a star near the celestial equator, toward the south (declination 0°).
• Observe at high magnification (200x+) for 5 minutes.
• If the star drifts northward: adjust the azimuth screw toward the east.
• If the star drifts southward: adjust the azimuth screw westward.
• Repeat until drift is zero

6Follow-up test

Final verification:

• Point to Jupiter or Saturn
• Center in the high-magnification eyepiece
• Turn on the tracking engine
• Observe for 10-15 minutes
• The planet must remain perfectly centered.

70-80mm telescope (f/10-12)

• 20-25mm: Overview, searching for objects (35-40x)
• 10mm: Versatile use for the Moon/planets (70-80x)
• 6mm: Maximum useful planetary (115-135x)

Budget: €100-150 for three decent eyepieces

130-150 mm telescope (f/5-7)

• 25-32mm: Deep sky wide field (25-40x)
• 15mm: Versatile Moon/M13/M42 (50-65x)
• 9mm: Planets and planetary nebulae (85-110x)
• 5-6mm: Planetary details (130-165x)

Budget: €200-300 for 4 eyepieces (2025 price)

200mm+ telescope (f/5-6)

• 30-40mm 2": Extreme deep sky (30-50x)
• 20mm: Wide intermediate field (60-80x)
• 12mm: Versatile (100-130x)
• 7-8mm: Standard planetary (150-185x)
• 4-5mm: Planetary details (240-310x)

Budget: €300-500 for 5 high-quality eyepieces (2025 price)

Plössl (optimal value for money)

• Apparent field of view: 50-52°
• 4 lenses, good contrast
• Price: €20-60 depending on focal length
• Ideal for beginners, excellent less than 15mm
• Less than 20mm (short eye relief)

Wide angle 68-72° (intermediate)

• Brands: Explore Scientific 68°, APM HDC XWA
• Excellent immersion
• Price: $80–$150
• Perfect for deep sky
• Comfortable eye relief

Ultra wide angle 82-100° (high end)

• Brands: Televue Ethos/Nagler, Explore Scientific 82-100°
• Total immersive experience
• Price: $200–$600 per unit
• Reserved for discerning enthusiasts

Zoom Eyepieces ⚠️

Features: Variable focal length (e.g., 8-24 mm) - single eyepiece = full range

Advantages: Practical, compact, no changes during sessions

Disadvantages:

• Often mediocre optical quality (edge aberrations)
• Reduced field of view (~50°), variable eye relief
• Price similar to a good fixed eyepiece

Verdict: Not recommended for serious observation. It is preferable to use 2-3 fixed focal lengths rather than a low-end zoom lens.

Phase 1: Getting started (1-2 eyepieces) - $50-$100

Start with the eyepieces provided + purchase a missing focal length:

• If you have 25mm and 10mm → buy 6mm (planets)
• If f/5 telescope → opt for a wide field of 20-25mm

Phase 2: Complete range (3-4 eyepieces) - $150-$250

Add 2-3 high-quality Plössl eyepieces (Budget: $230-$420 in 2025)

Phase 3: High-end upgrade - $200-$500

Replace your favorite eyepieces with wide-angle 68-82° versions

1Choosingthe right night

• Check the weather (cloud cover less than 30%)
• Check seeing on Meteoblue (reliability ~60%, good general trend indicator)
• Moon phase: New moon for deep sky, Moon visible for planets
• No strong wind (vibrations)
• Temperature not too cold (comfortable for 2-3 hours outdoors)

2Plantargets

• Download Stellarium (free) on PC/smartphone
• Set your exact location (GPS)
• Simulate the predicted night (date/time)
• Note 5-8 easily visible objects (Moon, Jupiter, M31, M42, M13, etc.)
• Print out a map of the sky or prepare a paper list.

3Testequipment during the day

Crucial! Never uncover your equipment at night.

• Assemble/disassemble the telescope 2-3 times to memorize the steps.
• Test all mount movements
• Check seeker (alignment with distant terrestrial object)
• Test all your eyepieces
• Time the assembly (aim for 15 minutes max)

1Arrive1 hour early

• Set up telescope before nightfall
• Assembly time: 15-20 minutes at a leisurely pace
• Allow telescope to adjust to temperature (30-45 min)
• Check collimation if Newtonian
• Perform approximate stationing

2Firsttarget: The Moon

Always start with the Moon if visible (except New Moon)

• Easiest item to find
• Allows precise adjustment of the searcher
• Guaranteed entertainment, even for complete beginners
• Start with medium magnification (50-80x)
• Gradually increase to 150-200x

3Nighttime adjustment(30 min)

• Avoid any white screens (smartphone in red night mode)
• Use only very low red light
• Full adaptation = 20-30 minutes (saturated rhodopsin) minimum
• One white light = everything needs to be redone
• Observe bright objects during adaptation (Jupiter, Saturn)

4Deep sky

Once fully adapted, explore nebulae/galaxies:

• Start with easy objects (M31, M42, M13, Pleiades)
• Use offset vision (look "beside" the faint object)
• Be patient: it takes 2-3 minutes for the eye to reveal details.
• Spend at least 10-15 minutes per item.
• Don't expect the colors of Hubble photos

All year round

• Moon: Craters, seas, lunar Alps
• Jupiter: Disk + 4 Galilean moons + bands
• Saturn: Spectacular rings (April–October)
• M31 Andromeda: Large galaxy (best viewed in fall/winter)
• Pleiades Cluster M45: Magnificent (fall/winter)

Winter (Dec-Feb)

• M42 Orion: Easy nebula, visible details
• M44 Beehive: Open cluster Cancer
• Double Cluster h/χ Perseus: Spectacular low magnification

Summer (June-August)

• M13 Hercules: The king of globular clusters
• M57 Lyra: Ring Nebula (small but visible)
• M27 Dumbbell: Easy planetary nebula
• Milky Way: Magical wide-field scan

Small diameter (70-100 mm)

What you will see:

• Moon: Craters larger than 40 km, seas, lunar Alps
• Saturn: Rings visible, Cassini Division difficult or impossible to see below 80mm
• Jupiter: Disk + 4 moons, 2-4 cloud bands
• March: Orange disk, polar cap (very difficult, less than 100 mm, requires opposition + excellent seeing)
• Double stars: Albiréo, Mizar-Alcor
• Open clusters: M45 Pleiades, M44 Beehive, M7
• M31 Andromeda: Elongated blur
• M42 Orion: Visible structure, no colors

Total accessible: ~30-40 Messier objects

Average diameter (5.1-7.9 inches)

In addition to 70-100mm objects:

• Moon: Craters less than 20 km, faults, domes
• Saturn: Cassini Division visible, cloud bands
• Jupiter: 4-6 bands, Great Red Spot, shadow moons
• March: Dark spots (Syrtis Major), seasonal variations
• Uranus/Neptune: Small blue-green disks
• Galaxies: M81/M82, M51 Whirlpool (spiral structure suggested if 150mm+ dark sky)
• Nebulae: M27 Dumbbell, M57 Ring, M1 Crab
• Globular clusters: M13 resolved into stars, M3, M5, M15

Total accessible: ~80-90 Messier objects + hundreds of NGC objects

Large diameter (250 mm+)

Extreme performance:

• Moon: Craters less than 1 km, Hadley valleys, central peaks
• Saturn: Multiple ring divisions, 5-6 moons, storms
• Jupiter: 8-12 detailed bands, festoons, ovals, structured GRS
• Galaxies: Spiral arms M51/M101, numerous NGCs
• Nebulae: Fine structures M42, Cygnus Laciniata, Rosette
• Globular clusters: All Messier resolved center, NGC faint
• 🪐 Pluto: Stellar point magnitude 14 (challenge!)

Total accessible: 110 complete Messier objects + thousands of NGC objects

Winter (December-February)

Most visually spectacular sky:

• M42 Orion: The easiest nebula to see with the naked eye
• M45 Pleiades: Magnificent open cluster, low magnification.
• M31 Andromeda: Visible until January
• M35 Gemini: Rich open cluster
• M1 Crab: Taurus Nebula (diameter 200mm+)
• Sirius: Brightest star
• Orion's Trapezium: 4 close stars M42

Planets: Jupiter/Mars often well positioned

Spring (March-May)

Galaxy season:

• M81/M82: The Great Bear Galaxy Duo
• M51 Whirlpool: Spiral arms (200mm+)
• Lion Triplet: M65/M66/NGC3628
• M104 Sombrero: Mexican hat galaxy
• M3 Hunting Dogs: Bright globular cluster
• Virgo Cluster: Hundreds of galaxies (challenge!)

Planets: Saturn returns in late spring

Summer (June-August)

Spectacular Milky Way + bright objects:

• M13 Hercules: The king of the northern sky's globular clusters
• M57 Lyra: Ring Nebula
• M27 Dumbbell: Easy planetary nebula
• M8 Lagoon: Nebula + Sagittarius Cluster
• M20 Trifid: Trilobed nebula
• M22 Sagittarius: Giant globular cluster
• M11 Wild Duck: Dense open cluster
• Milky Way: Wide-field scan of Cygnus-Sagittarius

Planets: Saturn/Jupiter opposition in summer

Fall (September–November)

Return galaxies + miscellaneous items:

• M31 Andromeda: Zenith, optimal conditions
• M33 Triangulum: A challenging but large galaxy
• M15 Pegasus: Dense globular cluster
• Double Cluster h/χ: Weak grossing show.
• NGC 7331: Pegasus Galaxy (200mm+)
• Albiréo Cygne: Gold/blue double color

Planets: Jupiter opposition often in fall

Seeing (atmospheric turbulence)

Definition: Image stability caused by air turbulence

Impact: Blurring, flickering, distortion of planets/Moon

Scale:

• Excellent (less than 1"): Image stable for more than 10 seconds, fine details of planets, fine details of planets
• Good (1-2"): Stability 5-10s, planetary observation possible
• Moderate (2-3"): Moderate turbulence, deep sky OK
• Poor (3-5"): Constant bubbling, planets unusable
• Terrible (more than 5"): Image dances, no serious observation

When to observe:

• 2-3 hours after sunset (cooled ground)
• Calm nights without wind
• After the passage of a cold front
• Avoid nights after heat waves

Transparency (atmospheric clarity)

Definition: Light absorption by moisture/dust/pollution

Impact: Magnitude limit (faint objects visible)

Limiting magnitude scale for the naked eye:

• City center: Mag 3-4 (50 stars visible)
• Suburbs: Mag 4-5 (200 stars)
• Nearby campaign: Mag 5-6 (1,500 stars, faint Milky Way)
• Dark site: Mag 6-7 (5000+ stars, spectacular VL)
• Exceptional location: Mag 7+ (desert/mountain)

Adaptation process (3 phases)

• 0-5 min: Pupil dilation (3mm → 7mm)
• 5-15 min: Sensitivity x10 (bright objects visible)
• 15-30 min: Sensitivity x1000-10000 (saturated rhodopsin) (max rhodopsin)

Result: Gain of 2-3 magnitudes (x10-20 sensitivity)

Preserve adaptation

• ❌ Never use white light (smartphone, lamp)
• ✅ Red light only (wavelength >650nm does not affect rhodopsin)
• ✅ Stellarium night mode (red background)
• ✅ Screen brightness set to minimum
• ⚠️ A single 1-second exposure to white light = 15 minutes of adaptation lost

Averted vision

Principle: The peripheral area of the retina has more rods than the center.

Technique:

• Look "beside" the weak object (10-20° offset)
• Optimal direction: nasal side (toward the nose) - left for the right eye, right for the left eye
• Object suddenly appears brighter at the edges
• Try different angles (top/bottom/left/right)
• Alternate between direct and offset vision

Gain: +1 to +1.5 magnitude (20-40× fainter objects detectable)

Tapping

Principle: Lightly tap the telescope tube.

Effect: Micro-movement of image stimulates motion detection in retina

Usage: Reveal very faint objects (mag 12-13 galaxies)

Patience and persistence

• Eye reveals details gradually (2-5 minutes)
• Spend at least 10-15 minutes per deep sky object.
• Breathe calmly, relax your eyes
• Blink regularly (to prevent dryness)
• First details = encouragement, keep going!