Sky-Watcher Skyliner 250PX Dobsonian questions

[Taz777]

I'm building up a shortlist of telescopes from which I will make a purchase at some point later this year. The Sky-Watcher 250PX seems to be highly rated and good value in terms of 'bang for the buck'. I realise that this is a large, heavy and bulky telescope.

I've got some questions:

1. Is the optical quality of this better than the same-sized Flex Tube version? I know that the Flex Tube version can be made smaller for storage and transportation, but I'm wondering about dirt collection and accuracy/alignment of the Flex Tube.

2. What is the shortest practical height of a person to use the 250PX comfortably at a range of viewing angles? In other words, is it okay for short people (5' 6")?

3. How difficult is this telescope to collimate?

[Paul73]

Firstly, 10” is a great size. Big enough to see loads. Small enough to carry.

I believe that the optics are the same in both versions. I have the flex tube 250 with a shroud around the open part. This keeps out unwanted light and dirt. However, when stored in the closed position, there isn’t much space for dirt to get in.

Re. Portability. I’m an average size guy and had real problem lugging the whole thing outside to observe. The whole thing can be made easier by carrying to tube and base separately. It takes about 10 seconds to separate the two. At 5’6” you could manage the flex tube easily.

Re. Alignment etc. As long as you check that everything is fully extended, no problems. Collimating is a 30 sec job (once you’ve go the hang of it). I use a simple Cheshire collimator. Some folks like the laser versions.

The flextube version is a touch heavier, but the reduced tube length makes it a lot more manageable.

Paul

 

[Geoff Barnes]

Hi Taz777

I have the SW Flextube 300mm which is really high quality optically and mechanically. Dust is a real problem here so I've ordered this shroud from FLO which has the great benefit of being able to stay on the scope even when collapsed....

https://www.firstlightoptics.com/dew-prevention/astrozap-light-shroud-for-skywatcher-flextube.html

The 250mm version will be shorter than mine and I would expect fairly short people to be able to view quite easily apart from near vertical. A short 2 tread stepladder solves this problem simply and effectively.

Once you've got the secondary set up correctly it should stay pretty well set forever, so just a few seconds before each viewing session checking the primary with a simple star test is all I do with great results.

If you are still in doubt the 200mm version is very highly recommended on here by many and maybe would suit a short person better.

Hope this helps. ?

Edit: we posted at the same time Paul73, but we agree on everything! ^^^

 

 

[RolandKol]

1 hour ago, Taz777 said:

I've got some questions:

1. Is the optical quality of this better than the same-sized Flex Tube version? I know that the Flex Tube version can be made smaller for storage and transportation, but I'm wondering about dirt collection and accuracy/alignment of the Flex Tube.

2. What is the shortest practical height of a person to use the 250PX comfortably at a range of viewing angles? In other words, is it okay for short people (5' 6")?

3. How difficult is this telescope to collimate?

I  had SW250 Flex Goto, -  some answers:

1) not sure, I did not have 250PX, - my guess, if the mirrors are different, - the difference will not be essential (price tells it all);

2) I am 5.7 and had no problems with 250 Flex while watching. As per moving it around.... heavy.... I simply hated to move it out....  - especially because my doors to the garden were single and it was VERY difficult to squeeze out/in (the base is quite wide and was catching all door corners possible). Keep it in mind.

3) I have not touched the secondary, - Primary is easy, but due to the size, Lazer (a proper one, - which also can be collimated) is a better option as you will not be happy to: check Cheshire, -  later  "run" down the tube to collimate , - and "run" back to Cheshire to check what you done. In other words - you simply will not reach the collimating knobs while looking into the Cheshire. At least my hands were too short.

[Paul73]

I think that the GoTo element adds a fair bit of weight.

[spike95609]

Speaking as a 250px owner, it's a terrific scope, and hits a great balance between price, power and portability. I've never used a flextube dob, but I wouldn't think there's any difference in optical quality, it should be the same mirror surely? I went for the solid tube because space wasn't an issue, and naturally there's no messing around with shrouds or worrying if extending the tube has an impact on collimation or not. I check the collimation now and again, and as I just take it into the back garden so it never gets bounced around in a car, I haven't had to adjust it once since I bought it 4 years ago. The solid tube is also lighter than the flextube, and even though it is pretty chunky, if you have an average amount of strength about you it's not a problem to lift it around. I lifted it in one piece from one end of the garden to the other a couple of nights ago, weight isn't so much of a problem as sheer bulk in that instance as it keeps hitting your legs as you walk. But doing it the sensible way and carrying it in two pieces it's perfectly fine.

I'm 5' 9" and don't have any problems with the height of the scope other than bending knees. Even when pointing vertically, it's bang on 4 feet from the floor to the eyepiece, so the shorter you are the better I'd guess.

As for collimation, when I was deciding whether to buy the 250px or the 200p I got very worked up about collimation and imagined it would be a lot harder. As it turned out, the basic process is the same for any dob, and as I said I've only had to do it once. Make sure the spider vanes are equal (mine were), then move the secondary up or down the tube until it's level with the focuser, then adjust the secondary until you can see all the mirror clips on the primary spaced equally around the edge, and finally get the dot into the centre circle of the primary. If you've never done it before it sounds rather complicated, but take each process one at a time and understand what you're doing and it's quite simple really.

Providing you're comfortable with the weight (not that an 8" is all that much lighter), you'll enjoy this scope and may not want another. My skies aren't awful with light pollution but they're certainly far from brilliant, nevertheless I've managed to glimpse about 150 galaxies with this thing so far, which is much more than I thought it would do. I don't feel the urge to upgrade to something bigger. Sure a 12-16" would show more, but it also starts to cost a lot more, weigh significantly more, and carrying it between doorways and over tables like I have to becomes a problem. If I had to move something like that about, I'd probably talk myself out of using it and decide I wanted to watch TV instead, whereas I can comfortably set up my 10" outside in a couple of minutes and still marvel at what it shows me.

[Taz777]

@spike95609 Thank you for your post. I'm hoping the weight will be okay as it will need to be moved to a shed for storage - a distance of 3-8 metres depending on where I decide to do the viewing from.

I've heard the diameter of the base (the widest part of the 'scope) is about 50cm. Would you be kind enough to confirm this? I have double doors on my shed but I'm hoping I only need to open one as the other one is nearly always jammed!

[spike95609]

I've just measured it and it's a little bit wider, 53cm I make it.

[Size9Hex]

8 hours ago, Taz777 said:

I'm building up a shortlist of telescopes from which I will make a purchase at some point later this year. The Sky-Watcher 250PX seems to be highly rated and good value in terms of 'bang for the buck'. I realise that this is a large, heavy and bulky telescope.

I've got some questions:

1. Is the optical quality of this better than the same-sized Flex Tube version? I know that the Flex Tube version can be made smaller for storage and transportation, but I'm wondering about dirt collection and accuracy/alignment of the Flex Tube.

2. What is the shortest practical height of a person to use the 250PX comfortably at a range of viewing angles? In other words, is it okay for short people (5' 6")?

3. How difficult is this telescope to collimate?

Some great answers above, but I’ll add another thumbs up for the 250PX which was my first scope a few years ago and I can see it staying for around for the foreseeable future. It’s fine for folks at 5’6". Don’t let collimation worries put you off. It’s not tricky to do and once you’ve got the hang, it only takes a minute. It holds collimation well too - most sessions it doesn’t need fettling at all.

[Astro-Geek]

When I bought my 250 Dob I mused over flextube vs solid as well.

The base is the same weight on both and the flextube is slightly heavier even though it can retract to a little over half of the rigid's length.

One slightly obscure advantage of all of the flextubes is that there is almost unlimited "in focus" because of the simple ability to not fully extend the front tube assembly.  This easily enables prime infinity focus with cameras and even binoviewers, which are usually impossible on Newtonians without the handicap of a Barlow and it's usually unwanted extra magnification.

Having said that, I ended up buying the GSO solid tube 250, because it had two speed focus, adjustable pivot balance, a proper ball bearing lazy susan, and a primary mirror fan.  I'm very pleased with its performance and usability, but I do slightly regret not having the flextube's greater flexibility with binoviewers. 

(I often suffer from the "grass always being greener on the other side of the fence" syndrome though.... ?   )

[Paul73]

You have no storage issues. So, if you are going to take it in the car to dark sites from time to time (Recommend). Go for the flex tube. If not, go for the solid tube.?. You’ll enjoy either scope.

Paul

 

[Taz777]

Thanks for all the replies.

Is there a safe way to lift a fully-assembled 250PX? I cannot see a convenient and safe way of lifting the telescope without causing undue stress on the structure. I can see from pictures and videos that there are two handles on the side but they seem quite flimsy and I'm wondering whether they would bend or break if I were to lift the entire telescope using them.

[John]

With the 250PX I'd lift and move it in two sections to save my back as much as anything else. The tube detatches quite easily and quickly from the mount / base and goes back on just as easily.

 

 

[Geoff Barnes]

Before I put my 12inch Dob on a dolly board to wheel it around as one assembled unit, my wife and I used to carry it out using the two fitted handles and they were perfectly strong enough to take the considerable weight.

[spike95609]

There's no other sensible way to lift it in one piece without holding on to the handles. They are fairly solid though as there's a 10mm thick steel bar inside them which screws into the base. That said the metal component of it stops I reckon about 10mm along the length of the plastic handle, which isn't much of a problem because a lot of the weight will be resting on your index fingers and the metal will be under them at that point and therefore supported. Although I think the possibility of a stress failure in the plastic is pretty low, and as the bar is so short I think you'd have to apply pretty extreme pressures to it to risk a fracture, I would still only really want to rely on the handles for short hops now and again, relocating the scope from one position to another, rather than carrying it that way all the time.

[Taz777]

A very big thank you to everyone who offered advice and opinions in this thread. Any opinions on how the Sky-Watcher fares against the more expensive Bresser Messier 10" Dobsonian?

[niallk]

1. Same

2. Yes it's fine

3. Same procedure as any dob really; Astro Baby's guide covers it thoroughly. 

The tricky part of collimation is the secondary.  It comes with 3 Allen key hex bolts plus a central bolt: if you get a mental picture of how they are arranged to hold the secondary tilt + position along the optical axis + rotation, then it starts to make sense.  The tricky thing is tightening down and the flex in the spider vanes/ holder assembly.  This leads to lots of iterative tweaks - just takes patience. 

The good news is my solid tube 250px holds secondary collimation ridiculously well!  Rarely needs a tweak.

I shift it sometimes in one piece via the handles, but it takes only a min to separate and carry in 2 parts - makes it easy and safe.

 

The Bresser dob has large alt bearings and a tube ring mount.  This looks really very attractive, imho - I've only seen pictures of it, not used one.

A nicely moving well balanced scope is a joy to use manually at high powers.  Being able to move a fraction of the fov without overshoot or droop or flexure makes an enormous difference.

 

[Taz777]

So with a Dobsonian, in order to adjust its view, do you literally just grab the body and move it in the vertical axis against the handles and the horizontal axis against the base? (Apologies, not sure of the correct terms to use here!).

[John]

Basically, thats it. Some are fitted with a knob on the underside of the top of the tube which is handy to grasp when moving the scope up and down. It's a gentle, subtle business when tracking a target but you soon ge the hang of it. I use the approach of nudging the scope to put the target slightly to one side of the field of view and then observing as it drifts across then nudging again and so on. Trying to keep the target right in the centre of the field at high power would be a chore which is why "nudge-observe-nudge-observe" works.

The basic movement of the scope is like a canon - up-down-left-right. Its an alt-azimuth mount in fact with alt(itude) being the up-down movement and azimuth being the left-right movement.

It really does work and the mount design holds the scope surprisingly steady for viewing at high powers.