Common 150mm (6 Inch) Aperture Telescopes

I was interested to look at what is commonly available in the 150mm aperture range. A list comparing telescopes that cost the same would probably be more practical for anybody interested in Cheap Astronomy, (as it would allow to judge what offers the best "bang for the buck"), but is a bit more difficult to compile – maybe one day…

Of course I looked at the cheapest ways to get a scope from each category – this is Cheap Astronomy after all! – so don't bother me with Takahashi-Astro-Physics-Something Super-APOs :-).

The prices are roughly what these cost here:

• "new"  are list-prices (more or less)
• "used" are typical prices I have seen, maybe a bit at the lower end

(With both: lower and higher prices are possible – go hunt for a bargain!)

	Advantage	Disadvantage
150/750 Newton/Spherical EQ-3-1 ~230€ new ~100€ used	- Cheapest 6-inch scope* (Cheapest to manufacture) - Compact and light (OTA ~3kg) - Relative fast (f/5) - Small obstruction (25% diameter)	- Secondary mirror is too small (vignetting leads to scope being somewhat stopped down and image degraded off-axis) - Fast spherical mirror (spherical aberration) - Mount is a bit undersized - Three vane spider - Second most quirks
150/1400 Newton/Catadioptric EQ-3-1 ~200€ new ~120€ used	- Second cheapest 6-inch scope* - Compact and light (OTA ~3kg) - Small obstruction	- Corrector lens ("Bird-Jones") can degrade image if not manufactured/assembled properly - Image will degrade if not properly collimated AND - Difficult to collimate (Cheshire and laser needed) - Mount is a bit undersized - Three vane spider - Most quirks*
150/750 Newton/Parabolic EQ-3-2 ~370€ new rarely seen used	- Compact telescope - Good mount	- Heavier (OTA ~6kg) - Heavy mount
150/1200 Dobson/Parabolic ~260€ new ~170€ used (rare)	- Best 6-inch optics* (probably) - Easy to use - Dobson mount (cheap, stable, intuitive, easy)	- Needs expensive wide angle eyepieces - An 200/1200 Dobson might offer slightly better bang for the buck - Heavier (OTA ~6kg) - No astrophotography
150/1200 Newton/Parabolic EQ-3-2 ~380€ new rarely seen used	- Best 6-inch optics* (probably)	- Mount may or may not be undersized - Somewhat long and unwieldy - Heavier (OTA ~6kg) - Heavy mount
150/1800 Maksutov OTA only ~600€ new ~300€ used (rare)	- 6-inch scope with longest focal length* - Compact	- Not well suited for wide-field - Heavier (5.6kg) - Needs stable mount - A 127/1500 Maksutov might be a better bargain
150/1500 Schmidt-Cassegrain OTA only ~600€ new rarely seen used (at least here)	- Compact and light (3.7kg)	- Not well suited for wide-field
150/750 Refractor/FH OTA only ~600€ new rarely seen used	- No obstruction - Best suited 6-inch scope for wide-field* - Compact	- Chromatic aberration - Somewhat heavy (7kg) - Needs stable mount
150/1200 Refractor/FH OTA only ~600€ new rarely seen used	- No obstruction - Most expensive 6-inch scope* (including proper mount)	- Some chromatic aberration - Most heavy 6-inch scope* (13kg) - Somewhat unwieldy - Needs good mount (expensive and heavy)

* Out of the scopes in this comparison 
(And yes, I know, 150mm are 5.9 inch)
(And yes, I know, some of these scopes have an effective aperture even less than 5.9 inch)


So, if you can live with the quirks (or even ameliorate some of the flaw with DIY): best bang for the buck is offered by the 150/750 spherical Newton, followed by the 150/1400 catadioptric (even if you include buying a Chesire and an laser for collimation of the catadioptric). With some investment in accessories you get a 6-inch scope for under 300€ (new) or even as low as 150€ (used) – a proper mount will set you back another 200€ (new) or 100€ (used). If you want more, you have to spend more…

Next in line in the 6-inch range: The 150/1200 Dobson is cheaper than the 150/750 parabolic Newton, but you'll need to buy some wide-angle eyepieces for the Dobson. The Dobson will (probably) offer the best views: the long focal length will minimize any aberrations, and only the diffraction spikes from the spider vanes are a problem for some people. For 400€ to 500€ (new, depending on accessories) or 250€ (used) you get an reasonably good 6-inch scope.

The 150/1200 on an EQ-mount is a bit obsolete when compared to the same sized Dobson. The scope is a bit long and unwieldly, and the mount could be a size larger. Will set you back about 450€ to 500€ (new) with accessories.

The 150/750 Refractor, the 150/1500 Schmidt-Cassegrain and the 150/1800 Maksutov are specialists depending on what you want: The refractor is at home as a wide-field scope, the others are better suited for higher magnification (planets and the like). But despite being more specialists, they retain some measure of being all-round scopes – and all three are somewhat compact. Together with an mount and accessories they will set you back about 900€ (new) or 500€ (used).

Together with an proper mount the 150/1200 Refractor is the most expensive and most heavy solution, while offering only small benefits (if any) over the other scopes – with accessories the long focal length refractor will set you back at least 1000€ (new).