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200P focuser annoyance


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I've just acquired a Skywatcher 200P, which looks like it'll be a great "grab'n'go" Dob. However, i've found one annoyance with the focuser. At the end of the silver focuser tube there's a black, screw-on adapter with two silver set-screws - pictures below. The problem is that the inner diameter of this adapter is slightly less than a normal 2" nosepiece, so standard extension-tubes etc. don't fit.

I'd planned on using a 2" Moonlite extension tube to provide a compression-ring fit for the focuser, as I hate set-screws scratching up my eyepiece barrels. However, thanks to the just-too-small Skywatcher adapter this doesn't fit. There's a solution of sorts in the supplied 2" eyepiece adapter, which is large enough to take normal 2" accessories including the Moonlite. However, this adds an inch or so extra distance and there's now not enough focuser in-travel to reach focus with some eyepieces. D'oh.

Anyway, my questions:

- is this typical for this adapter, or is the inner diameter of mine too small. I've owned both an 80ED and (briefly) a 250P DS and they appear to use the same adapter (?) but I didn't have problems with 2" accessories there. Or is it a different one in the 200P?

- if this is 'normal', is there a suitable replacement available or a compression-ring version of the Skywatcher-fit 2" eyepiece adapter (noting that normal extension tubes won't fit).

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Hi, you could reduce the length of the supplied 2" eyepiece adaptor ( from the EP end

of course, not the flanged end that fits the part in your pic ) that would give you

more in focus. You would need to drill & tap a new hole for the set screw.

Scopes n Skies had some of these adaptors if you want to try this, & still leave

the original if it doesn't work.

Hope this helps, Ed.

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How about using the part supplied (the 2 inch adapter you have) and fitting an Orion Precision adapter, that's what I have :-

I need to use 2" eyepieces - 1.25" is ok, as I have a spare 2"-1.25" compression-ring adapter to use with the existing Skywatcher 2" extension tube.

Hi, you could reduce the length of the supplied 2" eyepiece adaptor ( from the EP end

of course, not the flanged end that fits the part in your pic ) that would give you

more in focus. You would need to drill & tap a new hole for the set screw

Problem here is that it's no all that big in the first place, I could only remove about a half-centre before a normal 2" barrel would be longer than the extension and would hit the problematic focuser-tube adapter

Edited by Ben Ritchie
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Just use the 2" EPs in the 2" focuser? No need for an adapter and, unless you're Geoff Capes (once the World's Strongest man for those under 30), you're not really going to risk damaging you EP barrel with the grub screws!

Most 2" EP's have a cut in to prevent them falling out, so you just need to tighten the grub screws until they hold.

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Looking at the 250P DS, the adapter is a slightly different design and does directly accept a 2" nosepiece. So not sure if the adapter on my 200P is too narrow, or if they're all like that. There's fractions of a millimeter in it, but it's just too narrow...

Can somebody with a 200P check for me? With the focuser like the top picture above (i.e. without the supplied 2" extension tube) can you put a 2" eyepiece into the focuser? On my 200P I can't, on the 250P DS I can.

edit: new pictures attached. Note the different design of the 250P DS adapter compared to the one in the first post

Edited by Ben Ritchie
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Won't need to replace the whole focuser, but may need to try and source the new-style (?) adapter from FLO - the silver focuser tubes are identical, so the 250P DS adapter is a screw-in replacement for the standard 200P one.

Just curious really if this is by design, or if mine was poorly machined - seems very odd to make it literally a couple of tents of a millimeter narrower than the 2" format.

Edited by Ben Ritchie
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You're not alone in this. It is bad design!

I got round it by getting a friend with a lathe to - very carefully - take a little off the inside lip. Difficult to do properly without affecting the thread. I managed it but I wouldn't recommend it unless you know what you're doing (I didn't but my friend did) - or you have no other choice.

It works great for me. However, once you've done that the grub screws are then too far away to hold the 2" accessories in place. I got same friend to cut off the bottom part of the 2" adapter, put a split in it and then use it as a split ring compression ring. Works well for me - but again risky.

I had got to the point where it was either try it or spend £120 on a low profile focuser.

Does that make sense?

Mark

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Does that make sense?

Very much - it was exactly what I was thinking, and gave up on (as i'm bound to mess it up!). Mine's the singlespeed too.

I'm going to try the Mercury replacement linked above, if that doesn't work i'll see if I can get hold of the same part from the 250P DS as that fits fine.

Edited by Ben Ritchie
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sorry to butt in and offer no help but does this also effect standard use of 2" EP's? or is it only a problem when doing what Ben wants to do with an extension tube? as I was looking to get a 2" 28mm UWAN for my 250px dob

Edited by Daryl
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  • 2 weeks later...

Ben,

Question: Does the standard focuser on the 200P have enough back focus to allow a DSLR to be used at prime focus? It would need 55mm from the attachment point either a 2" nosepiece/ 1.25" nosepiece or a T thread if the focuser has one.

Just interested.....

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  • 3 weeks later...
The Skywatcher Coma corrector comes with a replacement adapter that accepts 2" barrels, it's called a D200-A00-02 on the instructions so maybe it can be ordered separately. If so, that would seem to be the cheapest/easiest fix.

As an addendum to this, FLO tried (thanks Martin!) and tell me it can't.

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