Question about min. aperture needed for DSO

This is a subjective thing. Obviously bigger is better for serious DSO observing, but I am wondering what is the SMALLEST scopes that you would bother seeking out some DSOs with.

I find that scopes are all about compromise, period. I have an 8" dob. That's a good compromise between price (excellent), optics (good), ease of use (excellent), portability (excellent around the house, not great for travel), tracking (terrible / non existent), light gathering (good).

so now the three areas I lack most in the above are: portability, and tracking and to a lesser extent light gathering too. That indicates a small scope that tracks. Such as a Nexstar 4 or 5 (or 8) or ETX 125 (may as well throw in goto for fun and easy of use on the road I guess).

Well, I can only imagine re-running my analysis on such a scope: price (high compared to aperture), optics (cel & meade reportedly make great SCTs and MakCasses right?), tracking (yes! but not for photography unless you are on a wedge right?) and finally aperture*

*well, this is obviously down the drain at 4 or 5 inches not counting the relatively HUGE central obstruction. I then wondered how truly portable a Nexstar 8 or 8gps would be since that is what I would consider the minimum aperture for DSO fun. The nexstars are lighter than the meade 8" and above, so that's why I lean towards them. But if 4 or 5 inches can still be used to see structure in m51 at a DARK sight, then that may fit the bill better because of how portable they are.

I also like the idea of attaching a laser pointer to a goto scope in my back yard, switching it on after a goto slew and just fixing my bigger dob telrad circles on the green laser thereby TRANSFERING goto abilities to my dob or anybody else who happens to be set up with me so a small goto scope may be just the ticket, but my question (AT LAST) is this:

How LARGE a small goto scope should I get to even hope to see structure in some of the brighter messiers? is 4 or 5 enough, or is 8 truly the bare minimum?

Also, what do you guys think of my green laser plus cheap goto scope for use as an easy goto sky pointer for all the big dobs in the area idea?

What do you mean by "see" structure?

I would be astonished (and disappointed) if my 4-inch TV-102 would not outperform an ETX 125 for seeing structure on M51, but I am guessing that not too many people would think the views the TV-102 provides would qualify as good-quality deep-sky views. From a dark site you can see at a glance that M51 has structure. You have to look a long time, use averted vision, relax your gaze, rest, do it all again, etc. before you become confident you know what you are seeing. I think that rules out scopes smaller than 6 inches for what you are trying to do, but I have no idea where the limit ought to be.

I really want to see what others say about your cool laser pointer suggestion. Isn't parralax going to be a problem?

Steve

Well Allison, is there such thing as "minimum aperture" I wonder? When I look at some of these DSO (and planetary) sketches from this guy who uses a 60mm refractor, I truly marvel and wonder indeed!
http://skytour.homestead.com/sketch.html

Personally, I need a 4" refractor minimum ;-). BTW, mine
is setup on the SP EQ mount with tripod legs all spread out ready to go in seconds. The diagonal and 30mm Ultima are
all there setup as well.

Ron B[ee]

First, the 8" dob is a great compromise. I think that many people get an inexpensive 8" dob as a first scope, and then feel that they need some else (which is normal enough). But, what you may actually want is a better built 8" dob, possibly with setting circles. My 8" dob weighs 38 lbs, and I can carry it around in one piece. There's a 10" Discovery dob in today's listing for about what I paid, but the tube weighs 57 lbs and the base another 24.

I also have a 5inch MakNewt because it is the largest scope I could afford to put on a GEM and carry as one piece. It has wonderful images, but not the structure in say M 51, 81 or 82 that I can get in the 8". It shows the veil and N.A. nicely though, and the Rosette nebula. In a 3 degree field of view I can actually see M31, and the Orion, Swan, and Lagoon all show structure.

Steven O'Meara used a 4" apo for his books on the Messier and Caldwell objects, and based on his sketches and notes, saw more than I do out with an 8"!