Grab'n'go: 102 or nexstar 114?

[WayBig]

I'm thinking about a grab and go setup, and have narrowed it down to

Nexstar 114slt

Advantages: I already own it

Disadvantages: Motorised mount is bulky, compared to a simple alt/az, needs a power tank, i don't really need the goto

102 achro such as a startravel

Advantages: smaller mount and ota, presumably more robust

Would a 102 be better for clusters, nebulae and galaxies? It's a smaller aperture, but would this be offset by the faster focal ratio - does that make the fainter fuzzies brighter.

Another thought, How much bigger is a 120 startravel?

[michael.h.f.wilkinson]

The big advantage of the 102 is that it sports a 2" focuser (at least some variants I have seen do). This means you can get wider fields of view (good for clusters, etc). Even with say a 24mm Hyperion, the 102 sports a 3.26 deg FOV. With a 26mm ultra wide angle you get a massive 4.26 deg FOV.

However, given a certain visual magnification, the brightness of the objects does not change with the speed of the scope. At say 25x the 114 will show a slightly brighter image, though this depends on the quality of coatings etc. The 120 is quite a bit bulkier (probably difficult in overhead storage on airlines). The 114 does have the edge at high magnifications, but is more sensitive to collimation issues.

[Donkeiller]

Just got an ST120 for DSOs and noticed a BIG improvement in objects like M42compared to my ED80.What is more it is only 2" longer and doesn't weigh much more.Tube + rings + RDF + diagonal + 25mm EP =4.4kg= 9.7lbs.I can mount it on my Synscan AZ goto mount, no problem, and still pick up the whole assembly and carry it with one hand.Yes there is false colour but objects like Jupiter can take up to 100X before it gets bad.I'd take the aperture of the 120 over the 102

[WayBig]

Thanks, i'm not too worried about false colour on planets, as i'll mostly be using it on DSOs.

My main question/concern is whether I would lose some of the fainter objects by stepping down from a 114mm newt to a 102mm frac.

[michael.h.f.wilkinson]

Not really as the 20-odd percent loss in aperture surface area is more-or-less compensated by the loss of central obstruction. Whatever the difference, it will be small.