Refractor telescopes
Same 70 mm aperture, different focal length: which first refractor?
These two collect exactly the same light through a 70 mm lens. Everything that separates them follows from the focal length: 400 mm against 700 mm, which is f/5.7 against f/10. The short one frames more sky and shows more violet fringe on bright edges; the long one gives more magnification from the same eyepiece and a cleaner image of the Moon.
| Compared on | JUNIOR 70/400 (blue) | AC 70/700 AZ-2 |
|---|---|---|
| Aperture | 70 mm (2.76 in), stated | 70 mm (2.76 in), stated |
| Focal length and ratio | 400 mm (15.7 in) · f/5.7 · 20x to 100x, stated | 700 mm (27.6 in) · f/10 · 140x maximum, stated |
| Lens design | Refractor (lens telescope) | Achromatic refractor (AC) |
| Glass type | Not published by the maker. | Not published by the maker. |
| Focuser | Not published by the maker. | Not published by the maker. |
| Drawtube | Not stated on the US listing. | 1.25 in (31.75 mm) eyepiece holder for all standard eyepieces |
| Supplied accessories | H20, H12 and H6 eyepieces · zenith prism · 1.5x erecting lens · 5x24 finder · phone holder · tripod · backpack | AZ-2 mount and tripod · eyepieces not itemized on the US listing |
| Listed on amazon.com | Yes | Yes |
A tick means one listing published something the other did not, or published a better figure. It does not mean the product is better, and the column is not a score out of anything: a maker who says less loses lines here without losing a comparison. The two verdicts below are where the page is settled.
The one that arrives complete. Three eyepieces, a finder, an erecting lens, a phone holder and a backpack make it usable the evening it is unpacked, and f/5.7 gives the wide, forgiving view a child points at things with. Check the price: the blue version cost about $48 more than the same kit in its other color.
The one that grows. f/10 on a 70 mm achromat is where a two-element lens is at its best, and the standard 1.25-inch eyepiece holder takes any eyepiece, filter or Barlow sold today. It publishes less about what is in the box, and its stated 140x maximum is honest.
For the same magnification, yes: both collect the light of a 70 mm lens. What differs is the magnification each eyepiece gives, because that is set by the focal length.
No. f/10 controls false color better on an achromat; f/5.7 gives a wider field with the same eyepiece. They are different instruments for different users, which is why there are two verdicts here.
The Bresser: it is sold for children from eight, packs into a backpack and comes with everything. The Omegon suits an adult or older teenager starting with the Moon and planets.
70 mm (2.76 in) · 400 mm (15.7 in) focal length · f/5.7 · 20x to 100x · backpack · from age 8
The blue version of Bresser's JUNIOR 70/400: a 70/400 refractor on an azimuthal mount and aluminum tripod, with H20, H12 and H6 eyepieces, a zenith prism, a 1.5x erecting lens, a 5x24 finder, a phone holder and a backpack.
Best for: A child from about eight who will carry the telescope themselves
≈ $227
70 mm (2.76 in) · 700 mm (27.6 in) focal length · f/10 · 1.25 in (31.75 mm) eyepiece holder · 140x maximum stated
Omegon's AC 70/700 AZ-2: an achromatic 70/700 refractor on an alt-azimuth mount with a 1.25-inch eyepiece holder, assembled without tools, with a stated maximum of 140x.
Best for: An adult or older teenager starting with the Moon and planets
≈ $167
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.
