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Paulhenry85

Help!! My 2inch eyepiece doesn't focus

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I have a skywatcher 200p dob telescope, I recently purchase a 2inch 32mm skywatcher panaview eyepiece. Last night was the first opportunity I had to us it, so I removed the adaptor that is on the focuser and slid the said eyepiece in tightened the grub screws and ......nothing I couldn't see a thing !! Until I fully retracted the focuser where I could make out a fuzzy mess , so I loosened the eyepiece from the focuser and gently started to remove it and eventually the stars came to focus, but my focuser seems to be about 2mm to short, doh.

Is this right? I've seen since you can buy "focus extension pieces" but they come in to sizes , so which size ?and if I do need one why don't they mention this!!

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Welcome to the weird and wonderful world of newtonian focusers. Newtonian focusers often have a relativley small travel; I've seen some as small as 25mm, 50 is about standard and 60 is positivley generous. Could be just the way the tolerances line up. Could be your mirror is sitting a bit high in the tube; I don't know about this particular scope but it might be possible to set the mirror cell a bit lower by letting out the 3 collimation screws a few turns (be very careful, and you will need to re-collimate afterwards.) If you readjust the spacing like this you need to ensure there is still sufficient in-travel for your other eyepieces...it's a compromise. It's pretty much standard practise to collect a few bits and pieces to get round this issue, especially with low-profile focusers. The situation can get more complicated when you add barlow lenses and coma correctors into the mix as well. A lot of the the bigger Televue eyepieces tend to focus further out. This is one issue where SCTs and refractors have a genuine advantage, in that the focusers have a larger travel as a rule. Eyepieces that have the double barrell size give you 2 chances at getting focus without adapters.

Not sure this helps a lot....I've had exactly the same issues with an OO 12"F/4. Might be worth looking out for some s/h 50 and 80mm 2" extenders on astro b/s.

Regards, RL

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When you removed the 32mm adaptor, I am guessing that the 2" adaptor will go in its place.

The 2" extension tube should have been supplied in the box with the scope when it was brand new.

If you bought the scope second hand, you may need to source one.

50mm adaptor on the left / 32mm adaptor on the right

2inch.JPG

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what Reeny said. this is almost certainly the reason.

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Got same scope and eyepiece and definately need the extension which should have come with your scope.

Sent from my GT-I8160 using Tapatalk 2

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As above. If the scope was new then I'd contact the seller if you don't have one. However, if you purchased it second hand you may need to source your own. Something in the 40mm region will be fine... also, try and get either a self-centring or compression ring type, grub screws don't do your EPs any favours.
 

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You have to get a Skywatcher 2" adapter for this job - other brands (like the ones linked to above) just won't work in the Skywatcher focuser I'm afraid. This situation is unique to Skywatcher - other brands of dobs are more flexible in this.

This is what you need:

http://www.ebay.co.uk/itm/Skywatcher-2-Eyepiece-Adaptor-For-Explorer-200-/200960555156?pt=UK_Telescope_Filters&hash=item2eca2eb894

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You have to get a Skywatcher 2" adapter for this job - other brands (like the ones linked to above) just won't work in the Skywatcher focuser I'm afraid. This situation is unique to Skywatcher - other brands of dobs are more flexible in this.

This is what you need:

http://www.ebay.co.uk/itm/Skywatcher-2-Eyepiece-Adaptor-For-Explorer-200-/200960555156?pt=UK_Telescope_Filters&hash=item2eca2eb894

Thank you very much for this.

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You have to get a Skywatcher 2" adapter for this job - other brands (like the ones linked to above) just won't work in the Skywatcher focuser I'm afraid. This situation is unique to Skywatcher - other brands of dobs are more flexible in this.

This is what you need:

http://www.ebay.co.uk/itm/Skywatcher-2-Eyepiece-Adaptor-For-Explorer-200-/200960555156?pt=UK_Telescope_Filters&hash=item2eca2eb894

Not strictly true. It depends how old the scope is. For example my sw 200p takes standard extensions. In fact I use my 2" Barlow with the lens removed as mine then I just screw the lens onto my 1.25 adaptor to give 1.5 mag :)

If a 2" ep fits in the focuser then a normal extender will.

Edited by Spec-Chum

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Not strictly true. It depends how old the scope is, for example my sw 200p takes standard extensions. In fact a use my 2" Barlow with the lens removed as mine then I just screw the lens onto my 1.25 adaptor to give 1.5 mag :)

If a 2" ep fits in the focuser then a normal extender will.

Does yours have the older rack and pinion focuser or the single speed crayford ?

Actually both the above, on the scopes I've used that had them, needed the 2" adapter that had the flared base (as per the link I posted). For some reason Skywatcher chose to use a focuser drawtube that was slightly larger than 2". You can actually fit a 2" eyepiece into them but the fit was not tight and 

Anyway, I hope my suggestion sorts out the OP's issue.

I wish Skywatcher had adopted a straightforward 2" focuser drawtube which would accept a standard third party 1.25" - 2" adapters like, for example, GSO scopes do.

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I don't think focusers are Sky-watcher strong point, the one in my M/N 190 is the pitts, one of the down-falls of having a Feathertouch and a Moonlite, something to compare to.

Alan 

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Ive got a Skywatcher 250PX and have the same lens as the OP.  Works fine,,,,using the 2" adaptor

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I think SkyWatcher have corrected the focuser fit with newer models. I can use 2" eyepieces and 2" accessories (Baader MPCC) straight into the draw tube without any problem. Both the 2" and 1.25" extensions that came with my 150P and 250PX have short straight barrels, not the the old flared-taper design.

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I've ordered the skywatcher 2" adaptor that John so kindly added a link too.

The adaptor that should of come with the scope doh, but I accept this happens when you buy second hand goods, I've also ordered the 80mm revelation self center adaptor as well, I'll test them both and give my feedback.

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Depending on the EP, you may find the 80mm too long. I use a 35mm extension with my 250PX.

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Does yours have the older rack and pinion focuser or the single speed crayford ?

Actually both the above, on the scopes I've used that had them, needed the 2" adapter that had the flared base (as per the link I posted). For some reason Skywatcher chose to use a focuser drawtube that was slightly larger than 2". You can actually fit a 2" eyepiece into them but the fit was not tight and

Anyway, I hope my suggestion sorts out the OP's issue.

I wish Skywatcher had adopted a straightforward 2" focuser drawtube which would accept a standard third party 1.25" - 2" adapters like, for example, GSO scopes do.

Hi John :)

Its the single speed crayford that came with the scope.

I'm not sure exactly when they changed but mine is definitely a standard 2" fit as the Barlow is snug in the tube.

I do agree tho, it was silly of them to provide a non standard one in the first place.

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For some unknown reason, my Vixen LV 30mm doesn't focus with the adaptor, you need to take that out and attach it directly... All my 1.25" eyepieces focus fine with the adaptor, so I don't see why the LV should be so different.

I agree with Rik, it's better to use a shorter extension - try measure how much you actually need :).

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My 150p I bought two years ago had a single speed crayford focuser that accepted standard 2" fit accesories.  I have an Altair Astro 35mm 2" extension living in that focuser permanently.  I find that focuser pretty good in fact.  I upgraded it with a Lacerta dual speed but the remainder of the focuser is stock and works well.

In contrast the standard PD-S focuser on the 350 is not good.  The nobs are too close to the OTA which means my fingers get jammed between the focuser nobs and the OTA when I'm focusing.  Also there is an annoying friction where the focuser binds on itself every couple of turns, it gets very stiff like its grinding on itself and then slackens off, only to go back into this again.  It's not every revolution of the focuser spindle either, its every couple fo turns which is odd.  I keep thinking I should replace it with a moonlite but I'm reticent to drop £250 on another focuser when this one, although annoying, does find focus easily enough - its just annoying.

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you could try replacing the spindle with a suitable diameter stainless rod.

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