Choosing
A telescope listing contains two kinds of number: the ones fixed by physics and the ones written by marketing. Telling them apart takes about a minute and saves the commonest bad purchase on this site.
Light collected goes with the square of the diameter. It is the one figure that cannot be improved by anything bought afterwards, and it is often printed smaller than the magnification claim.
Telescope focal length divided by eyepiece focal length. Without the first figure, no eyepiece can be matched to the instrument — which is why a listing that omits it is a real problem, and several on this site do.
A 1.25 in focuser opens the whole accessory catalogue. A 24.5 mm one closes it. It costs nothing to check and it is the difference between a telescope that grows and one that does not.
Professional, HD, high-definition, astronomical-grade. None corresponds to a measurement. Where a listing leads with them and omits the focal length, this site says so on the page.
70 mm aperture · 400 mm focal length in the title
A 70/400 refractor sold with two eyepieces, a 5x Barlow, a phone adapter and a stainless-steel tripod — and a listing whose own bullets contradict its title.
Best for: A buyer who will check the tube’s printed figures before ordering anything else for it
≈ £79 / €70
76 mm aperture · 700 mm focal length
A 76/700 Newtonian on an equatorial mount, supplied with three eyepieces, an erecting lens, a 3x Barlow, a Moon filter and a smartphone holder.
Best for: A first equatorial telescope that has to be light enough to move fully assembled
≈ £223 / €166
70 mm aperture · 300 mm focal length
A 70/300 refractor for beginners with two eyepieces, a 3x Barlow, a 1.5x erecting lens, a metal Moon filter, an aluminium tripod and a phone adapter.
Best for: A wide, bright first view of the Moon and star fields at low power
≈ €39
70 mm aperture · 400 mm focal length
A 70/400 refractor on an alt-azimuth mount with two 1.25 in eyepieces, an erecting prism, a phone adapter and a carry bag.
Best for: A first 70 mm where the eyepiece fitting and the focal ratio are both stated plainly
≈ €60
203 mm aperture · 1200 mm focal length
A 203/1200 Newtonian on a Dobsonian base — the largest aperture in this group, sold with an accessory set and a mount with nothing to align.
Best for: The observer who has decided that aperture matters more than portability
≈ €529
Because any telescope can reach any magnification with a short enough eyepiece. Beyond roughly twice the aperture in millimetres, the image is larger and no more detailed — so 675x on a 70 mm tube describes a calculation, not a capability.
Aperture, then focal length, then eyepiece diameter. Those three decide what is collected, what magnification an eyepiece gives, and what else will fit.
Several on this site do — a title and a bullet giving different focal lengths, a mass and a package weight that cannot both be right. Where that happens, this site prints both and resolves neither.
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.
Telescopes and mounts are discounted over and over through the year — hardest of all in the weeks before Christmas, which is exactly when most of them are bought — and a struck-through figure on its own says nothing whatever about what the same model was charged at four weeks ago. UniverTrack keeps a week-by-week record for each retailer, so a discount is measured against a figure somebody genuinely paid instead of one invented for the sale — and it says when the moment to buy has genuinely arrived.
