Troubleshooting
A soft image is rarely a bad telescope. Four causes explain almost every case, and three of them cost nothing to fix. Check them in this order: the air, the temperature of the optics, the alignment of the mirrors, and the focus.
Turbulence in the atmosphere blurs everything. Stars that twinkle hard mean poor seeing. Lower the magnification, or wait for a steadier night. See seeing scales.
A telescope brought from a warm house carries heat in its glass and tube, and warm air currents blur the image. Closed tubes are worst: a Maksutov such as the NexStar 4SE needs 30 to 60 minutes outside before the view settles.
A Newtonian’s two mirrors must be aimed at each other. After transport they drift. Fast mirrors are the most demanding: National Geographic’s 114/500 at f/4.4 needs careful collimation; the Heritage 130 needs an occasional check. A capped eyepiece tube or a laser collimator makes it a five-minute job.
Focus slowly through the sharpest point and back. On a light mount, touching the focuser shakes the image; let it settle, or use a mount with slow-motion controls such as Celestron’s heavy-duty alt-azimuth tripod.
The optics themselves. Check the four causes above before blaming the telescope.
An instrument brought straight out shows an unstable image. That is normal and temporary.
Rising warm air destroys the image whatever the instrument.
Dew settles gradually and the image degrades without anything having been touched.
| The symptom | The likely cause | What it is not |
|---|---|---|
| Soft at every magnification | The instrument | The sky |
| Soft at high magnification only | The sky | The optics |
| Degrading over the evening | Dew | Collimation |
| Unstable when coming out | Temperature | A fault |
Most softness comes from temperature and dew, not from a fault. An instrument stored in a warm room will always take time.
This site publishes stated specifications and diagnoses no instrument.
102 mm (4 in) Maksutov-Cassegrain · 1325 mm at f/13 · GoTo fork with built-in wedge · 21 lb with tripod
Celestron's NexStar 4SE: a 4-inch Maksutov-Cassegrain with StarBright XLT coatings on a computerized single-arm GoTo mount whose tripod has a built-in wedge, 21 lb with tripod.
Best for: A first computerized telescope for the Moon and planets that can also take short-exposure photos
≈ $649
130 mm (5.12 in) parabolic mirror · tabletop Dobsonian · collapsible tube · 94% reflectivity coatings
Sky-Watcher's Heritage 130: a 130 mm parabolic Newtonian with a collapsible tube on a tabletop Dobsonian base, delivered assembled with 10 mm and 25 mm eyepieces and a red-dot finder.
Best for: A real 130 mm parabolic mirror that stores in a closet and needs no assembly
≈ $269
114 mm (4.5 in) · 500 mm (19.7 in) focal length · f/4.4 · 19x and 51.5x · alt-azimuth mount · red-dot finder
National Geographic's 114/500 Newtonian: a 114 mm mirror at 500 mm focal length on an alt-azimuth mount and full-size tripod, with two eyepieces giving 19x and 51.5x, a red-dot finder and a smartphone adapter.
Best for: Wide, bright low-power views of large objects, by someone who will learn to collimate
≈ $75
32 to 45 in height · two slow-motion controls · slotted 1/4-20 plate · aluminum legs · no dovetail
A metal alt-azimuth head on two-section aluminum legs, with slow-motion controls on both axes and a slotted 1/4-20 plate for balancing a spotting scope, binocular or small telescope.
Best for: Giant binoculars or a spotting scope that needs geared movement rather than a dovetail
≈ $115
Look at a bright star at high power. If it boils and shimmers, it is the air. If it shows a steady but distorted pattern, it is the telescope or its temperature.
30 to 60 minutes for a closed tube such as a Maksutov or Schmidt-Cassegrain, less for a small refractor.
Check it each session after transport; adjust when the star test or a collimation cap shows it is off.
For observing: A first computerized telescope for the Moon and planets that can also take short-exposure photos
Where it is strong: Built-in wedge for polar alignment, which reduces field rotation in exposures
Where it is weak: 4 inches of aperture limits faint deep-sky objects
For observing: A real 130 mm parabolic mirror that stores in a closet and needs no assembly
Where it is strong: Parabolic 130 mm mirror with 94% reflectivity coatings, stated
Where it is weak: Needs a table, wall or stool outdoors
For observing: Wide, bright low-power views of large objects, by someone who will learn to collimate
Where it is strong: 114 mm of aperture for about $75
Where it is weak: f/4.4 is demanding: collimation and eyepiece quality show
For observing: Giant binoculars or a spotting scope that needs geared movement rather than a dovetail
Where it is strong: Slow-motion control on both axes, so a target can be kept centered at high power
Where it is weak: No dovetail saddle: most telescope tubes need an adapter that is not in the box
$75 – $200
7 models
$268 – $500
9 models
$649 – $1 699
7 models
Model against model, where the comparison is already published.
The models above are taken from the catalog of this site. Specifications are the ones the maker publishes and the ones on the Amazon page; prices are the Keepa reading for the date shown, and both change. Ranking uses declared specifications, the weight of stated strengths against stated limits, and price. Nothing here has been pointed at the sky by us, and the page makes no such claim.
Last checked on
Any figure written into the body of this page was true on the day it was written. The amount shown next to each instrument is requested from the retailer as the page loads, and it is that amount, not the text, that stands.
