Used Skywatcher 250 won’t focus

[Timebandit]

 

Hello.

I would not start messing with the truss poles.

I would not start altering the primary or secondary mirror position.

You could make a whole lot of problems for yourself by "tinkering" with the above.

If you are gaining focus by extension pieces on the focuser, then go down this route. Just get the right length of extension pieces and your eyepiece will come into focus. Don't forget also different eyepieces/makers can come into focus as different lengths on the focuser position.

I hope this helps

 

 

[DeathWarpedUp]

28 minutes ago, Timebandit said:

 

 

If you are gaining focus by extension pieces on the focuser, then go down this route. Just get the right length of extension pieces and your eyepiece will come into focus. Don't forget also different eyepieces/makers can come into focus as different lengths on the focuser position.

 

 

 

I was going to mention that, I think he said it was a zoom. put the ep setting on its lowest mag (probably a 24mm)

[Avocette]

Hi @Daznok55 and welcome to the harrowed ranks of second-hand Sky-Watcher telescope owners! What has happened here is the unfortunate fact that the seller omitted to provide you with some of the accessories that were supplied in the new package. In particular there should be a 2" extension tube, and there should be a 2" to 1.25" eyepiece adapter. This thread and the responses in it represent a lot of accumulated wisdom, but also a certain amount of accumulated history! To my direct knowledge as a buyer in 2011 of a Skyliner 200p, in 2012 a Skyliner 250px and in 2014 a Flextube 300p (aperture fever now cured by local light pollution and an aging back) there were two different types  of eyepiece holder/extension tubes supplied. And I hear that a brand new SW flextube Dobsonian does have two clickstops as the tubes are extended, but the addition of the second clickstop holes in the truss tubes was a new feature perhaps 5 years ago. I never saw anything written up about this feature on sales websites nor in Sky-Watcher manuals, but heard mention of it in passing on this forum. The first clickstop is around 10cm from the fully open clickstop position and seems to have been intended for if you want to use binoviewers directly for your observing sessions. Your scope does not have two clickstops but don't worry - if you ever want to try binoviewers just tighten the truss rods at a point 10cm before the normal end stop position. With my 300p I found that the truss rods were quite rigidly mounted and moved as one piece without any particular flexing so I just judged the distance and didn't measure the offset with a ruler. By the way, binoviewers are a great addition for planetary and lunar observing since you've got plenty of light capture with the 250mm mirror and can afford to lose some of it in the binoviewers.

 

Edited July 7, 2020 by Avocette

[Avocette]

Just looked up the user manual https://inter-static.skywatcher.com/upfiles/en_download_caty01316546523.pdf and here is the relevant page for your scope showing the 2" and 1.25" eyepiece adapters.

[Carbon Brush]

A while back I was sorting a somewhat neglected SW 250 truss.

The poles were very stiff. Needing a good clean then a polish.

The spring loaded ball bearings had suffered from neglect.
They were very awkward about clicking to lock.
I took them apart. Just unscrew the cap but catch the bits!
There was a bit of rust on the bearings.
I bought a pack of (10 I think) balls the right size for a couple of quid from ebay. Cleaned the springs and housing, and sparingly applied oil.
When I put it back together it was like new.

In this case the previous owner had left the scope in a poor storage location for a long time.
But I guess any similar scope, brought in with dew that stays in the pole spring mechanism may suffer.

HTH, David.

[bomberbaz]

3 hours ago, Daznok55 said:

White dwarf and proto star

Guys took a few pictures of tubes Entended (as far as I can) and stowed.

White dwarf and proto star are a kind of forum ranking, if you look you are classed as nebula.

I am named bomber baz, but call me steve. Proto star is actually geoff barnes, whom I assume is geoff 😅

(btw you aren't the first to make this error)

Steve

Edited July 7, 2020 by bomberbaz

[bomberbaz]

2 hours ago, Avocette said:

Just looked up the user manual https://inter-static.skywatcher.com/upfiles/en_download_caty01316546523.pdf and here is the relevant page for your scope showing the 2" and 1.25" eyepiece adapters.

Blooming heck its all coming flooding back now. I remember I didn't like the stock skywatcher EP holders so I ditched them in favour of an extension tube with twist lock and then a 2" to 1.25" adaptor.

Can't remember what it was or from where I got it but you do need one.

Think it might have been a 2" extension because the SW supplied ones are about that long. Something along the lines of this https://www.harrisontelescopes.co.uk/acatalog/altair-50mm-tube.html#SID=627

Problem solved I hope

Steve

[cletrac1922]

On 06/07/2020 at 22:09, Daznok55 said:

Hi

Im at a loss as how to go forward, wife bought me a used 250 dobsonion with a 2” focuser and a badder 8x24 click eyepiece on eBay but I cannot get it to focus. After reading here on other people having the same trouble, I purchased a 1.5 inch extender from FLO. It didn’t work came close but no cigar. Do I continue extending it out or do I have some other problem?

Getting very frustrated can anyone shed more light on this.

 

Daz

First of all welcome from Land Down Under

Have enclosed a pic of the focuser of my 10" flex Dob

The Dob should had come with a 1.25" adapter, which just slips into the 2" mount

The eyepiece just slips straight into the 1.25" adapter

There is no need for extension tubes, and I occasionally use a 2X barlow

I also use 15mm or 17mm eyepieces, when viewing planets, and other DSO, very successfully

I also have a right angle finderscope as well, which saves having to lay on ground when spotting objects over head

As the base of the Dob is also chipboard material, always put down a small waterproof tarp, to protect the base from moisture in the ground

If have any issues, only too happy to assist

John

 

[JOC]

With experience although it may not contribute to the problem if you look at that picture posted just above I can vouch for the potential of twiddling that big grub screw between the two focus knobs by accident in the dark.  That locks the focus and then any amount of twiddling with the big knobs won't change it - make sure it has not been tightened by accident.  I also agree that the flex tubes seem to be correctly positioned.  FWIW you are looking for yours to look like my smaller one when it's ready to use - mind does actually do the two position clicks referred to above, but if yours doesn't then providing the rods are extended apparently as much as mine they should be correct:

[Daznok55]

Hi Guys 

Just a quick update. I bought a 2' extender works perfect focus on saturn was just a touch off the bottom end , absolutely amazed with the view. 

I have noticed its hard to keep focus and constantly needs a tweek, is this normal?

Are there adjustments to the focuser itself, it dosnt seem as........responsive as I think it should.

Thanks again for all your help.