Quick Look at the "Roegger PEGASUS" 150/750 Newton

On Sunday I bought another scope: An Newton reflector, called "Roegger PEGASUS", with 150mm aperture and 750mm focal length (which works out to f/5 focal ratio) – a big mirror in a cheap package. 

Prices range from 90€ (used on eBay) to 140€ (new on eBay), and up to 230€ (if you buy new from an "proper" scope shop on the internet) so I was lucky to get one for 70€. With prices about twice of an 70/700 refractor, will this be twice as much fun? It is cheaply made, but has some potential as a fun scope. :-) I will use it less on planets (my long focal length refractors are probably better suited here) but more on Deep Sky objects.

My scope was branded as "Roegger PEGASUS", but can be found here under various other "brand-names" (and color schemes). There are different versions floating around:

• The version without an corrector (focal length 750mm), available as an "Roegger PEGASUS". Seems very similar to the "TS Optics Starscope 1507", and somewhat similar the "OMEGON N 150/750 EQ-3".
• The version with an corrector (focal length 1400m), available as an "Seben Big Boss", "TS Optics Megastar 1550" or "Bresser Pollux N 150/1400 EQ-2".
• And then there are hugely better versions: Three is e.g. the "Celestron OMNI 150XLT", or the "Sky-Watcher Explorer 150P EQ3" (and possibly the GSO). These have an parabolic mirror and much much better EQ-3-2 mount (aka "NEQ-3"). These telescopes are for all practical purposes completely different scopes.

Beware: Even if the numbers are the same, there can be differences between the brands!

What was included with mine:

• The OTA with 1.25" focuser (rack and pinion)
• A corrector lens ("Bird-Jones") was not included
• An EQ-3-1 mount An EQ-2-2 mount
• Two mounting rings and one "screw on" rail (that almost looks like a thin dovetail rail)
• One Plössl 25mm eyepiece (1.25", non-standard filter size) 
• One Plössl 6.5mm eyepiece (1.25", non-standard filter size)
• One 2x Barlow (plastic housing, singlet glass lens, lots of stray light, same Barlow as the one supplied with my 76/350 table-top Dobson)
• One "1.5x erecting eyepiece" (ignored)
• A "6x30" finderscope (which I ignored mostly, for now) with 30mm aperture and achromatic lens
• A flabby finderscope-bracket

Some of the things worthy of notice:

• The primary is in all likelihood spherical.
• [Update 2013-11-01] The diameter of the primary is 153mm (6 inch), it has a grinded bevel of about 1mm width, and the edge of the primary is 14.5mm thick. (BTW: I used a black marker to darken the bevel.) 
• [Update 2013-11-01] The adjustment of the primary cell is done via three sets of push/pull screws, but no springs – longer screws and a set springs will greatly benefit the collimation process. BTW: The scope was only "screwed together" (one could see that all three "pull screws" were screwed in first, and the "push screws" were barely threaded out) – but collimation was somewhat OK, I have seen worse.
• [Update 2013-11-01] The secondary needs slight adjustment – I will have to do a proper collimation.
• [Update 2013-11-01] The full diameter of the back of the primary is covered by a foam pad, a piece of cardboard and on the outside a piece of camera leather (together about 6mm thick). I removed all three and put in some small DIY pads underneath the clips of the mirror cell.
• The secondary mirror is rather small (roughly 38mm, about 25% central obstruction) and does not fully illuminate the primary. I suspect that the effective aperture is more likely to be 120mm to 130mm (very rough estimate). [Update] I've done the numbers and a 38mm secondary (at an distance of roughly 560mm from the mirror) will fully illuminate 150mm (on axis, that is). Some off-axis vignetting will occur however: to illuminate a diameter of 20mm at the eyepiece one needs an secondary of about 52mm diameter. (If used with a Barlow the vignetting will be reduced. One needs however to make sure that the Barlow itself does not add vignetting…)
• The spider holding the secondary has three vanes which are rather thick (5.5mm). But people who done tests write that it won't hamper contrast much (if it is noticeable by me anyway) – collimating (and a good figure of the mirror) is more important.
• The diameter of the OTA tube seems to be a bit too small.
• At the outside of the OTA one can see that the scope is cheap: The seam of the OTA protrudes a bit, and when you rotate the OTA in the mounting rings you the OTA seam will "bump" against the hinges of the rings… But that is only a minor problem.  
• The OTA tube is deformed at the end of the mirror. O.o This is caused by the OTA end ring being too large, and the screws connecting the end ring with OTA tube cause the tube to be deformed. (Furthermore some light can get inside the tube through the gap between end ring and OTA tube.) [Update] For each screw holding the rear cell to the OTA, I put some one washer inbetween the OTA and the rear cell.
• There is a thread at the inner end of the focuser's tube, probably for an Bird-Jones corrector to double the focal length to 1400mm. (With this corrector the secondary might fully illuminate the primary – don't know, sure would like to know.)
• The focuser itself is quite nice. Only major problem was that the focuser's tube was loose! The tube had at least a couple of degrees play! However with a bit of flocking material I took take care of it. Otherwise the focuser's tube does protrude a bit into the OTA, if fully racked in (but not too much). The eyepiece retaining ring is made of metal and quite solid (nice), the focuser's tube is made of metal (nice), the focuser's casing is plastic (but OKish), the tube has lot's of travel (nice), the knobs are large enough (nice).
• The filter threads of the eyepieces is non-standard. (At least the barrels are interchangeable with the eyepieces from the 76/350 – those have a standard thread at one end and a "coarse" thread at the other. So I could exchange the 1.25" barrel from the useless H20mm eyepiece and put in on the PL25mm – now I can use standard filters with PL25mm)
• The supplied "Moon filter" is the most nonsensical piece of astronomical equipment I have ever seen. It is a (heavily over-engineered) disc of solid aluminium painted in black, with about 8mm thickness (!) and 30mm diameter. The filter is held by an screw-in plastic retaining ring with an clear aperture of about 12mm. The filter itself has about 15mm diameter. And now comes the real kicker: The green plastic filter has curved surfaces in the center and flat on the periphery of the filter! This thing looks like the bottom of a green Coke bottle… With the non-standard filter-thread, it doesn't even make sense to replace the filter glass, if you happen to have an 15mm diameter filter lying around.
• The PL25mm eyepiece has an "additional" section between the 1.25" barrel and the optics. This section seems to be designed to hold an reticle (again heavily over-engineered).
• The finderscope bracket is very awful.
• An EQ-3-1 EQ-2-2 mount (and tripod) was not made for such heavy scopes. The problem is that the axis have to much play and I haven't found a way to reduce the play any further. My EQ1 (adjusted, with DIY wooden legs) seems more up to the task… But the legs of the EQ-2-2 are better than those of the the EQ-3-1.
• The counterweight rod is 10mm (like my EQ-1/EQ-2) and not 12mm (like my other EQ-3-1).
• The counter weight is one piece of about 2.9 kg.
• The counter weight rod does not rotate (like my other EQ-3-1 mount).
• The "north adjustment" of the EQ-3-1 EQ-2-2 is slightly different than my other EQ-1/EQ-2/EQ-3-1 mounts: Normally there is a machine screw at the bottom (that you don't need to touch), and a tommy screw at the side to fix the north position. But here there is only one tommy screw at the bottom. The advantage is that you can easily separate the mount from the tripod.
• The tripod legs are more stable than those from my EQ-3-1 (from my 70/700).
• The mounting rings seem quite sturdy. Opening the rings requires completely unscrewing two screws, which is a pain in the proverbial behind.
• I have mounted the scope on the dovetail and mount from my 70/700 – but without a supplied quick-release the combination of scope and mount is quite unwieldy.

  Enough written today, hopefully more once I played around with it a bit.