90mm refractor or 6" dob as Grab and go

[Crusader]

I've got to decide between a 90mm refractor or a 6" dob as a grab & go companion to my XT10.

The specific models are both from Skywatcher.
Skywatcher 90mm Evostar F/10 refractor on Alt-Az mount.
Skywatcher 6" Dobsonion F/7.8

I need something I can grab and take outside without much fuss for a quick viewing session of an hour or two. It will strictly be used for visual and I enjoy observing all objects so something that will do a good job on planets and the bright DSO's will be a plus.

I haven't used refractors before (aside from a department store one as a kid, which I think put me off of refractors for life). I can't afford a APO and am limited to the brands available over here.

Anyone that can give me some feedback/input would be welcome.

[francis]

Hi. I have a 90mm x 1200mm refractor having recently sold my 8" dob. I like the focal length of the refractor, the lack of maintanence, and being able to take it into dusty locations on windy nights with little or no cool down time. Perhaps you would consider the 102mm x 500mm achro on an az? I find that is my best grab and go, and that it works great with high powered eps (3.8mm, 5mm, 6mm) You could achieve these powers with a cheap ED GSO barlow. The 102mm also gives great low powered wide views.

If you can mount either the 90mm or a 102mm on a GSO or Vixen porta mount, then you will be in 'grab and go heaven' as far as zipping around the sky at full alt /az goes. I have dovetail bars on my 102mm and 90mm and they work great on the GSO Vixen clone.

You could get a 90mm refractor cheap on ebay and tip the savings into a good GSO or Vixen mount.

Other wise, the dob is cheap, light, and has more light gathering power as you would be well aware. They take up a lot of car space though. It's tough call. Best wishes!

[Crusader]

With your 90mm, how does the views compare with the dob? Obviously you wouldn't expect the same brightness and details, but obviously you'd still like to see the cloud bands on Jupiter, and Saturn's rings. Are you able to do so with ease using only the 3" of the refractor?

[rmcpb (Rob)]

Don't even try to compare the views from either the 6" or 90mm to your 10". You will be disappointed. Either of them will be fine instruments but for a real grab and go I would chose the refractor, no cool down time needed. If you want to go deeper then its time for your 10" to come out.

[Crusader]

The choice has been made. No stock for the 6" dob, so I went for the refractor. Looks like fate has come to my rescue again, the same thing happened when I had to choose between a 8"/10" dob. I'm happy with how it turned out then, so I hope I'll feel the same with this one.

I haven't used a refractor before so is there anything special advice I need to keep in mind? The slow motion controls will be something new. Weighing in at around 8kg total (I'm not sure about the weight of the mount so I'm guessing) it will be a heck of alot lighter than the 10"

[rmcpb (Rob)]

Make a dew shield to stop the objective lense from fogging up too soon. Other than that, have fun with it

[Crusader]

Well, the scope finally arrived last night at around 9:30 pm. I nagged the courier company to deliver at that hour since they were running late.

The scope came in one large box containing to separate boxes. One for the OTA and one for the AZ3 mount. Once again I underestimated the size of the scope. It's pretty big and would fall in the upper limits of a grab-and-go scope. It is easy enough to carry around fully assembled using both hands.

I struggled to get everything set up, since this is my first non-dob scope and the instructions were a bit vague on some points. Finished at around 11pm just when I had to go to bed since I had to work today.

I did play around with the mount and it seems stable enough. The only problem is that close to zenith the slow motion control cables tend to get in the way, bumping against the finderscope bracket. The coarse adjustment of the altitude is also a bit of a pain. You need to take hold of the scope itself and force it up and down... not the smoothest of motions. I'll definitely be looking to add some kind of altitude adjustment handle to make it esier.

The slow motion controls seem to work nicely after that and the azimuth motion is basically the same as a camera tripod. You loosen a locking knob and then move it around quite easily.

Will hopefully get a first light in tonight if everything goes to plan.

[Crusader]

Had the scope out two times so far. The initial first light was a bit of a disappointment since I found the mount a bit frustrating. The slow motion control cables get in the way if you want to view closer to zenith (60°+). Obviously it was also a bit difficult to not compare the views to my 10" dob. CA doesn't seem too bad, but Jupiter is pretty low so I couldn't really test the planetary capability of the scope.

On the second viewing session during the conjunction I did get some better views of Jupiter and could make out the central cloud bands, which I couldn't in the initial test. Details on the Moon were very clear with only a slight yellowish fringe/coloration visible when moving your head. Venus and Jupiter both show some purple fringing with it being more severe on Venus. Couldn't resolve any stars in 47 Tucanae and M42 looked very nice.

For the price I can't really fault the scope. The AZ3 mount will get some getting used to and the 45° diagonal it came with is a pain in the neck. I've ordered a 90° diagonal which will should arrive tomorrow, hopefully it will make viewing and using the mount more comfortable.

[rmcpb (Rob)]

Yep, the 90 degree diagonal will make a HUGE difference. I use that almost exclusively over the 45 on our refractor. As for the slow motion cables at high altitudes, I use the same fix as for the dobs hole. Make the leg of the tripod under the eyepiece shorter so its not so great an angle relative to the tripod. give it a go.

[Crusader]

Thanks for the tip, I'll definitely try it once the clouds decide to go away.