In my search for a grab and go scope of reasonable aperture and portability I came to a decision to purchase a Vixen Porta mount bundled with a Vixen R130sf newtonian. A few weeks later it finally arrived last Friday giving me a new toy to play with for the weekend
Porta mount.
As can be seen its a single arm alt-azimuth mount on an alumium tripod. This mount can be manually pushed in both axis with adjustable tension and has full 360 degree slow motion controls. It accepts a standard Vixen or Synta dovetail.
Underneath the rubber pad in the base the included allen keys needed to adjust and dissassemble this mount are held by small magnets.
The Portas' height at full extension is sufficient that the little newt had an ideal standing eyepiece height for me, and a little too tall for my observing friends last night. Im am 6ft 2"
What can I say, this mount performs beautifully and is clearly a cut and a half above over cheaper offerings like the AZ-3. Tracking Saturn in this scope at 162x with a 4mm ortho was a breeze using the slow motion controls with the stability of this mount at full extension a nice surprise, with damping time of about two seconds. Everybody in our observing party last night was very impressed with this mounts smoothness, ease of use and stability. It has a real "premium feel" to it.
If you are looking for an alt-az mount for a small scope, say a 100mm refractor, they dont come much nicer than this
There are limits and the geometry of the arm means ota size is limited to about 170mm diameter without hitting the ota at zenith.
R130sf Newtonian
The R130sf is a 130mm f5 newtonian of Chinese manufacture. Unlike most other small newtonians, this one has a real metal spider and fairly decent components including a collimatable mirror cell with hex grub lock screws.
The exception is the focuser, being entirely made of plastic, which lets down the general quality of this scope.
The scope came with two silvertop plossls, 20mm and a 6.5mm. They both work very well in this scope and amongst cheap plossls, I quite like the silvertops so these were a nice surprise
First light star testing showed astigmatism from a pinched primary, so it was time to strip down the scope and loosen off the mirror clamping blocks. I also took the opportunity to centre spot the mirror.
After sorting out the collimation, the optics were found to perform quite well for the size and price of this scope. On Saturn, cassini was well visible with banding visible on the planets globe. Later on details were visible on the equatorial belts of Jupiter at 162x and still I was limited by the seeing.
Not too bad for a small rich field newt
About the focuser and design of this scope, you can see that it sticks out a long way from the ota. The design is such that you use the extension tube for visual, or remove it with the focusers top being threaded, designed to take a camera fitting. This might even work with a binoviewer ( I wish Steve was there
).
The plastic focuser does flex when you put heavy eyepieces into it and the image shifts as you adjust focus. It is annoying when trying to focus at high power and this focuser is certainly the weak point of this scope.
The secondary is quite large at 45mm, giving a 35% central obstruction. The dual role photograpic/visual design of this scope with the focal point so far out of the ota means that the secondary is so close to the primary to only just catch the light cone. I am tossing up whether to get a new ota tube made so that I can push the primary back, or to just mount a better focuser on a high self made adapter.
To put all this in perspective, the OTA including two plossl eyepieces, dovetail and tube rings (nice I might add) only added about $240 over the price of a Porta mount on its own. Considering its optical performance, I still reckon I got a good deal
As it is, it's a great grab and go package. If I get a better focuser, it will be close to perfect for my needs as a lightweight grab and go travelscope
Many thanks to Steve at
http://www.myastroshop.com.au