Reflector telescopes
A fast 114 mm or a parabolic 130 mm?
Sixteen millimetres of aperture separate these two, and rather more than that separates what their listings say. One publishes a mirror figure and a focuser size; the other publishes a box of accessories. On a Newtonian, the first pair of facts outlasts the second.
| Compared on | Pluto EQ 114/500 | Advanced 130/650 EQ-320 |
|---|---|---|
| Aperture | 114 mm (from the title) | 130 mm (from the title) |
| Focal length | 500 mm (from the title) | 650 mm (from the title) |
| Focal ratio | f/4.4, the quotient of the two figures above | f/5, the quotient of the two figures above |
| Optical design | Newtonian reflector | Newtonian reflector with parabolic primary, stated by the maker |
| Mirror coating | Not published by the maker. | Not published by the maker. |
| Focuser type | Not published by the maker. | 1.25 in, described as compatible with other makers’ accessories |
| Collimation access | Primary and secondary both adjustable, stated by the maker | Fully adjustable, stated by the maker |
| Mount supplied | Equatorial, with aluminium tripod | EQ-320 equatorial with tracking gear |
| Supplied accessories | 20 mm and 4 mm eyepieces, 3x Barlow, LED finder, smartphone camera adapter, accessory tray | Illuminated LED finder |
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 fuller box. Two eyepieces, a Barlow, a finder, a phone adapter and a tray, at the shorter focal length of the two. What the listing never says is what shape the primary mirror is — and at f/4.4, a spherical mirror does not bring a star to a point. The omission is the finding.
The one that says what its mirror is. A parabolic primary at f/5, a named focuser size, and a mount with a tracking drive. Almost nothing is listed as supplied beyond a finder, so eyepieces are a separate purchase — but they are the part that can be bought later, and the mirror is not.
A spherical mirror focuses light from its centre and its edge at slightly different points, and the faster the mirror, the wider that gap. At f/4.4 it is visible; at f/8 it is not. A parabolic mirror does not have the problem at all.
The light collected goes with the square of the aperture, so about thirty per cent more. That is a real difference on faint objects, though not a transformation.
No. A tracking drive keeps an object in the eyepiece once found; a GoTo mount finds it. They solve different halves of the problem.
114 mm aperture · 500 mm focal length
A 114/500 Newtonian on an equatorial mount, supplied with two eyepieces, a 3x Barlow, an LED red dot finder and a smartphone camera adapter.
Best for: Wide, bright views of extended objects rather than high-power planetary work
≈ €199
130 mm parabolic mirror · 650 mm focal length
A 130/650 Newtonian with a parabolic primary on an EQ-320 mount, with a 1.25 in focuser, a tracking drive and an illuminated LED finder.
Best for: A first serious deep-sky instrument for somebody prepared to collimate it
≈ €409
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.
