Planetary observations with 4" apo refractors

[rmcconachy]

I agree with those who suggest trying to improve the motions on your current Dob first.

However, if you really want to swap your scope for something else I'd not recommend the 150mm Synta. The F/5 version has heaps of false colour (inevitable) and the F/8 version still shows much colour on bright objects, e.g., naked eye planets. Additionally, the F/8 version is ~4ft long, weighs ~10kgs (scope alone, no rings, dovetail or finder) and is very nose heavy (the balance point is ~1/3rd of the way from the objective lens to the focuser). That means the mount it sits on has to be strong to cope with the scope's moment arm and tall to keep the eyepiece far enough off the ground. I'd say something like an EQ6 at minimum. A 120mm Synta F/8 is a hugely more manageable scope in every way than its bigger sibling.

More manageable than both Synta scopes is something like my Vixen 4" F/9 ED refractor (similar size to a Synta ED100). My Vixen is about 38 inches long, weighs a little over 4kgs with rings and dovetail plate and can be used on a fairly light weight mount. It also requires almost no time to cool down. If you are happy with what you can see with 4" of aperture then I think a 4" ED refractor is about as hassle free a scope as you can get. I use mine when going out for quick looks.

Best of luck with whatever you choose!

[ausastronomer (John Bambury)]

Originally Posted by rmcconachy

That means the mount it sits on has to be strong to cope with the scope's moment arm and tall to keep the eyepiece far enough off the ground.

Hi Rich,

This was exactly my point about some of the mounts I have seen this scope mounted on. The last time I tried to use one of these scopes I distinctly remember crawling around in the long grass on my hands and knees with the brown and black snakes, will trying to split Acrux with Ken Charlwood up at Kurri Kurri. Not long after spending 5 minutes on my hands and knees I decided there were better telescope options available for use on the night, like 10",13" and 16" dobs, which I could use standing up, rather than lying down That scope was on an EQ4 clone which clearly was not tall enough for the scope and not remotely close to large enough to stabilise the weight and large moment arm and resultant inertia.

Cheers,
John B

[rmcconachy]

G'day John,

I owned a 150mm Synta F/8 for a few years (sold it last year during a clean out). In some ways the best mount I ever had it on was my car! Place a bean bag on the roof of the car and the scope on top of that. Only good for objects at lower altitudes but I defy you to find another motorized mount with as much torque The big Synta was too much scope for any real mount I had or wanted to lug around so it was sold. Very much not a grab and go scope as you said.

[Darth Wader (Wade)]

Thanks for the informative replies all. I've decided to suck it up and stay on the dob path. For the money they really are great value. I spent a good amount of time collimating as exactly as I could, and my hard work paid off the other night viewing Saturn. WOW. plenty of cloud band detail and 2 (or was it 3?) moons nearby.

The only problem now is that I want to go bigger, with a solid tube 12" - and then mod the hell out of it for super smooth motion. Hopefully it will take care of my aperture fever for a few years (until I start lusting after a motor-driven 16" - hey, they might be affordable one day!).

Thanks again guys.

Cheers
Wade