Help needed: Sky Watcher 10" Dob can only focus on very close objects

[Ocellaris]

Hi, have brought my first telescope which is a Sky Watcher 10" collapsible dob. Currently having issues trying to focus with it. At night I have tried it on the moon which only appeared as a white featureless disk. Have been unable to even see out of focus stars.

Due to these issues I have tried the telescope during the day. Tried to focus on trees varying from a 100m to a few kms away but always have a very blurry view. Yesterday had it out looking at the moon. Once again very blurry and unable to make out even the shape of the moon. Really it was like looking at blurry blue with a hint of blurry white. When I was nearly finished trying to get it working I noticed I was able to focus on some fence wire a few meters away. So figure something must be up as I thought you should not be able to focus on close object.

Have looked through forums and checked I have not made the common mistakes people make when they cant focus. The telescope seems collimated to my uneducated eye. I have it fully extended. Am not using the the 1.25" eye piece adapter with the 2" adapter. Also used some high and low profile adapters to adjust focal length from a mate who looked at the telescope. He couldn't see what was going wrong either.

Any thoughts on what the issue could be would be appreciated

[tempestwizz]

If your scope will focus on close objects but not further away it must be because your objective lens is too far away from the primary mirror. Ie, it needs to be brought closer somehow. Usually the focussed does this for you, but if there is not enough 'in'travel, then there's something else wrong. Make sure there are no unnecessary extension tubes attached in your focusing train. As a last resort you can look at shortening the path by raising the primary mirror up the ota tube, but since this is a store-bought scope, you should not have to do that.
Hope this helps. Brian

[jenchris]

The legs on the collapsing part may be set to a longer length than required. Is there an adjustment for these?

[Ocellaris]

Have looked at a video of someone using the same telescope. Everything seems the same. There is nothing that allows the distance of the mirrors to be adjusted other than for the primary mirror. Top part of it clicks into place when you extend it.

[Allan_L]

Sounds very strange Steven.
Are you using the supplied eps (eyepieces), have you tried all supplied eps?

Sounds like a trip back to the supplier. :(
You don't want to do anything to void your warranty.

BTW Welcome to IIS :welcome:
You have chosen a great scope, very unusual to have this sort of problem.

[NoTan2]

Hi Steven,

From your comments, it looks like you've read my posts on a similar topic.

But just to be certain, the Skywatcher 12" collapsible has two clicks on the struts - it clicks when you initially extend it and then you have to give it an extra tug and it extends to the second click. Perhaps the 10" is the same?

[Allan_L]

Hi Paul,
I don't think that is the case with all SW flex dobs. :confused2:
Certainly not with my 12". Or my previous 10 Flex Dob.
But mine are probably older models.

[Ocellaris]

Yes I have tried both eye pieces supplied and a few of a mates.

Have been extending it fully to the 2nd click.

It's all very frustrating when its a telescope many people don't have issues with and brought from a telescope store. Hoping I dont need to get them to look at it as im in Canberra and dont want to make a trip to Sydney.

[Merlin66]

Steven,
I assume the secondary and primary mirrors look clean and bright.
When you look through the eyepiece holder. With no eyepiece- what do you see? I know you said the collimation looked OK but just double checking.
A couple of photos of the set-up. May be helpful.
I'm sure it's not a serious problem, we just need to get a better understanding.

[raymo]

How about a pic of how you have the focuser/eyepiece arranged. Never
heard of this problem, something must be set up wrongly.
raymo

[Ocellaris]

When I look through the focuser without the eye piece I see my eye and the 3 clips. Could say it may be the tiniest bit off but was struggling to get it any better.

Also tried moving the primary forward but didn't make any difference. still could only focus a few meters away.

Is it possible the wrong primary mirror was installed.

[Kunama]

If you have an extension tube between the focuser and eyepiece remove it to get the eyepiece closer to the secondary. (what suburb are you in?)

[Merlin66]

Steven,
You seem to have a 40mm or so spacer fitted between the eyepiece and the focused. What result do you get when this is removed?
I don't think it needs to be there.

[Merlin66]

Matt beat me to it!

[Ocellaris]

What looks like a spacer is the adapter for 1.25" eye pieces. Instructions say to use it. Can't see anyway to make the eye piece fit into the focuser without it

[raymo]

The flat fronted plate with a bevelled rear face is correctly mounted into
the open end of the focuser. The front face has a male thread that the eyepiece holder screws onto, which appears to have been done, but from the pic I can't see if it is screwed hard up against the flat face. The eyepiece holder is indeed about 35-40mm long, and is intended to be in that position.
It can't have an f/4 mirror installed because the focal point would be radically different, so nothing would come to focus. Perhaps a member
with knowledge of these scopes who lives near you could come to your place to check it out.
raymo

[raymo]

After further study of the pic it looks like the eyepiece holder is fitted
inside the male threaded stub rather than screwed onto the male thread,
and therefore doesn't go far enough in. The eyepiece holder should have a female thread. I think you have the wrong eyepiece holder.
raymo

[NoTan2]

Here's what my 25mm EP (1.25) looks like on the 12".

[raymo]

I was remembering wrongly, the eyepiece holder does screw in as shown
in NoTan2's pic. The male thread screws into a T-ring. Ocellaris's set up
is correct, so the problem lies elsewhere. Maybe the extension rods are
incorrectly adjusted.
raymo

[Ocellaris]

Just my luck to be having an issue with this. My son is getting so desperate to see saturns rings. Takes me 30mins to get him to sleep because he keeps asking questions about space.

Has anyone had any issues trying to phone Bintel. Have been trying but calls have not been answered. Though have only tried yesterday and today as I wanted to wait until a friend looked at it incase I was doing something dumb.

[Kunama]

Sent you an SMS reply Steve, unfortunately Saturn's rings will have to wait until it returns to our night sky, at the moment Saturn is keeping the Sun close company... it will become an early morning target around the 10th of January....

[space_balls]

HI Steven like you I am new to astronomy i brought the exact same scope six months ago first do not try to clean your mirrors if you can see your refection in them they are fine if they ever get dirty use compressed air to clean them and with a collapsible dob scope you will need a light shroud will give you much better viewing as for the problem you are having i think it is to do with your focusing knob when you turn the nob does the eye piece move in and out if not there is a screw in-between the two focusing knob that need to loosened hope this works i will have a play with my scope tonight to give you more suggestions

[Ocellaris]

The focus is moving and have not touched the mirrors. They look clean. Have had a mate (with 12 months experience with astrophotography) look at it to rule out any silly mistakes so something uncommon is going on.

[Ocellaris]

Btw thank you to everyone who has replied. Think this is only the 3rd time I have ever posted on any forum and this is the only time I have had people wanting to help. Dispite my setback with my telescope, my early impression of the community adds to my interest in pursuing this as a hobby.

[doppler]

Hi, I have the 10" solid tube Skywatcher and my 2" to 1.25" adaptor looks much shorter than yours. It might be as simple as the wrong adaptor supplied?

[raymo]

His eyepiece holder is the same size as mine, so I'm guessing either the
solid tube version has a different adaptor, or the later 10" ones have changed to the shorter one that you have and he has the wrong one.
raymo

[Allan_L]

Hey Steven,
Got a tape measure?
When fully extended, what is the total length of the scope?
Specs say it should be 1120.
Just a thought!

Next, take out the eyepiece and show us a photo down the focus-tube.

[Kunama]

Hi Steve,
I have a shorter Takahashi/Baader adapter that we can use to test the scope to see where the problem lies. If you want to show things to the kids before the weekend I can call by sometime this week.

(I deleted your text by mistake and lost your number)

Cheers,
Matt

[ausastronomer]

I wouldn't recommend cleaning your telescope mirrors in this manner. There is some good information in the projects and articles section (http://www.iceinspace.com.au/63-345-0-0-1-0.html) on how to clean telescope mirrors.

Cheers
John B

[AEAJR]

I do recall reading of this kind of thing before with the skywatcher dob. It had to do with the eyepiece holder/adapter. I don't have one but if I recall there are two pieces or two adapters for the 1.25 and you don't use them together.

This is all from memory but that is what I recall. Seemed there was an extension tube included for some reason and this had to be removed for normal use.

Again, I don't have one but that is what I recall from reading of a similar.

Have you called Sky Watcher?

Have you spoken to the seller?

[Ocellaris]

Just checking that the focal length is measured from the primary mirror to the secondary. Just checked and it measures 970mm when focal length for this is 1200mm. Thinking maybe the rods for extending the telescope are from a small telescope.

[doppler]

You have to include the distance from the secondary to the end of the eyepiece for the total focal length. My 1200mm fl solid tube is 900mm from the mirror to centre of focuser tube and 300mm from centre of diagonal to eyepiece tip.

[Allan_L]

Thats why I quoted the specs for the extended length of the tube itself. (Not focal length, just tube length)
Straight forward and easy to see if something is adrift.

[AG Hybrid]

When I have in focus issues with my Skywatcher collapsible dob I just lower the top OTA cage by an inch, tighten the screws then collimated. It used to be an issue for me with coma correctors and things like that. Not so much any more since I replaced the rubbish stock focuser with a lower profile gso 2 speed focuser. Which is surprisingly good. Can handle at least 1.6 kilo's of corrector and eyepiece without problems.

[raymo]

I don't know why anyone has to play around with the extension tubes; both
mine worked fine with or without a coma corrector, but the coma corrector
is made for the SW f/5 scopes, and doesn't require any mucking around
with spacers.
raymo

[Merlin66]

Ian,
I'd hazard a guess that the 90mm difference is to accommodate the difference between visual and getting enough back focus to fit a camera.

[bigjoe]

Were here to help Ocellaris.
You could even ask for help by PM'S if need be.

bigjoe.

[75BC]

I had a SW 10 inch solid tube and the 1.25 inch adapter I had looked like the one in Ricks photo. Much shorter than the one you have Steve.

I'm sure someone here knows if the solid and flex tubes require different length adapters. :question:

[astro_nutt]

Hi Steven. I hope you've sorted out everything. I was going to suggest trying a full optical alignment. This process precedes collimation. A carpenters square, tape measure, straight edge, bamboo skewer and a pencil is needed. Using the square and straight edge, check that the optical tube sections ends are squared against the tube.
Place the top tube section upside down on a flat surface. Place the square against the tube and check for any variances other than the thickness of the end ring. Do this at various points around the tube. This is to see if the tube ends are seated square with the tube.
(Do the same with the bottom section but primary mirror facing up.)
Turn the top section right side up. Place the straight edge across the top of the tube above the spider vanes. Measure the distance from the spider vane to the straight edge. Using the skewer, place this on the spider vane with one end against the inner wall of the tube and mark the skewer where it sits above the screw which holds the secondary mirror. Rotate the skewer and check that each spider vane is the same distance.
Check each strut against the straight edge.
With the scope assembled, measure from the top edge of the secondary section to the top of the primary section at various points around the tube.
Just a couple of other things to try. Without the 1.25 adapter in the focuser, try looking through a 1.25 EP starting from right inside the focuser itself then gradually moving further away.
Check and see if the focuser is squared with the tube.
See if you can swap the secondary mirror over with another.
Apologies if you'd tried all this already and hope it does work out.
Cheers!

[astro_nutt]

Oh! I almost forgot. Check to see that the clips holding the Primary mirror in it's cell are just touching the mirror's surface. If they're too tight, pinched optics will result.
Cheers!