SW 2" ED Barlow in SW 200p woes.

[russ.will]

I may be being a bit thick here, so would appreciate comment from anybody using this combo, or with experience of the same problem.

With the standard SW focuser, there is insufficient outward travel to bring an EP to focus without an extension tube in place. However the internal diametre of the 2" extension tube nose is obviously smaller than 2". Thus, you can't insert the 2" ED barlow all the way in. Now the focuser can't rack in far enough to bring the EP to focus with the barlow in place.

Take the extension tube off and it fits a treat, but now the focuser lacks outward travel again *unless* you faff about only half inserting the barlow.

Do you just put up with this? If not, what was the solution and if it's 'Buy a £200 focuser' I'll be disappointed, but not surprised!

Russell

[John]

I'm sorry to say it Russell but I've heard about this issue before. The problem is that the SW ED 2" barlow has quite a long barrel and there is a ridge inside the focuser drawtube that prevents it's full insertion. I noticed this when I owned a Skyliner 200P but my barlow then, as now, was an Antares 2" 1.6x which has a short barrel so it does not contact that dratted ridge. This must be an issue with the other SW newtonians that use the same focuser I would think

It does seem ridiculous that these two pieces of equipment, both from the same brand, are not quite compatible

The irony is that the older rack and pinion focuser that SW used to use on these scopes did not have this issue !.

I'd be pleased if someone has a solution - off hand I can't think of a simple one though.

[russ.will]

The obvious one would be that the 2" EP socket, actually screws onto the focuser tube. If it were possible to gat a male, female threaded tube to insert between them, then the problem would be solved and you could do away with the extension tube altogether.

Can I find one? Can I 'eck!

On the plus side, I find simply screwing the ED objective into the end of the EPs, sidesteps the issue, gives a moderate magnification without pushing the eye relief out to ridiculous distances and, unless I'm mistaken, makes the edge of field look sharper?

Russell

[John]

This might work:

2' adapter with brass compression ring for Skywatcher Newtonians

[rwilkey]

It's a long time since I used this combo, but I don't recall having this problem, I'll have to try it again.

[russ.will]

Hopefully, this picture will explain it better:

The extension tube is at the bottom, up turned, with the nose of the barlow sitting on it. It will fit in the top of the extension tube, but not pass through it - As you can see, nose to nose, they're the same diametre. The top of the draw tube, into which the extension fits, is shown half way up the barlow, to illustrate that it fits just fine.

I may have made some progress however. One of my suppliers in real life, supplies metal work to the construction industry. After about five minutes of trying to explain what I wanted, he asked what it was for. A telescope I said, getting ready for the derision. Why didn't you say you idiot (or a construction phrase that approximates to that sentiment). I've got a Meade blah, blah. He's on this forum, goes to Kelling Heath, etc, but I'll let him 'out' himself if he feels like it.

I'm Google Sketchuping some drawings as we speak, to see what's possible.

Russell

[russ.will]

This might work:

2' adapter with brass compression ring for Skywatcher Newtonians

If I can get the male to female extension made, I may top it off with that, or a similar, compression ring. They seem like a better engineered solution than a pair of thumbscrews.

What I need is something like this, but with M54 male and female threads.

Russell

[FrankieValley]

This might work:

2' adapter with brass compression ring for Skywatcher Newtonians

John is correct. That will do the trick. I just bought one and was very disappointed with the quality and it doesn't hold very tight for rotational forces that filterwheels, cameras, oag's will exert. It will do for eyepieces though. Very expensive as it cost me £45 incl. delivery to the UK!

Another solution is the SW coma corrector, which has a straight through collar with no ridge - Sky-Watcher Coma Corrector 2in for Newtonian Reflectors

(FLO sell it cheaper, but their pic doesn't show all 3 parts). However, I couldn't see any difference using the coma corrector visually - with or without the SW 2" barlow and I reckon it was visually worse with the barlow. It works for DSLR for imaging though.

The coma corrector collar is the same collar that is fitted to my 250PDS..... so 3rd option... buy a PDS ;-)

[russ.will]

Spending £90 just to get the extension seems a little a little stiff.

Russell

[Moonshane]

could you get someone to use a lathe and turn off the ridge? would be the cheapest option I'd wager.

[russ.will]

I've measured as closely as I can and as far as I can see, if you bored the extension out, the nose would fall off.

Russell

[russ.will]

.... so 3rd option... buy a PDS ;-)

Is it just me, or are people getting a bit 'free 'n' easy' with my budget?

Russell

[Moonshane]

I think the cheapest solution in that case is live with it and with the extension removed when using the barlow.

in reality, the barlow is going nowhere as long as the thumbscrews are tightened enough but I understand your concerns. if it makes you feel better, my 13mm Ethos won't fit all the way in with the 2" skirt I use on it and it also sticks out a little. I am not worried as the thing is always carefully tightened before use and has 'no chance' of dropping out.

[russ.will]

Absolutely agreed; It is perfectly possible to live with it. It's just not very elegant and is precisely one extra adaptor to drop/loose in the dark.

Russell

[Moonshane]

true enough but it's possibly the best option for now. I have to say that some of the aftermarket crayfords also have this problem http://stargazerslounge.com/discussions-scopes-whole-setups/162426-gso-focuser-2-eyepieces.html so beware if thinking of a replacement.

[John]

For what it's worth, I believe this problem was caused by Skywatcher switching from a male to female thread on the end of the focuser draw tube. Simple as that. The old rack and pinion focusers were male threaded and did not have the issue. When they switched to the single speed crayford focusers, they switched to a female thread they had to redesign the 2" adaptor that screws onto the end of it and that included a raised section which impedes the insertion of long barrelled accessories.

When I had a Skyliner 200P with this issue I actually thought about getting an old R&P focuser to replace the crayford

PS: I've just checked the OC1 crayford focuser on my Orion Optics newtonian and that has a similar issue so it's a common one, unfortunately.

[FLO]

The problem is that the SW ED 2" barlow has quite a long barrel and there is a ridge inside the focuser drawtube that prevents it's full insertion.

John is right, it is a known problem connected with a single batch of 2" ED barlows that 'catch' on a ridge inside the focuser. Ask your supplier to collect/replace it with the correct version.

HTH

[russ.will]

It's a bit late to explain further, but the barlow slides into the draw tube without issue and secures just fine using the the thumbscrews. It's not the draw tube or the compression ring at the top.

The issue is the 40mm extension tube, which fits into the top of the draw tube, in place. As it also has to fit inside the 2" diametre of the draw tube top, it stands to reason that it's internal diametre must be narrower than 2" and so the barlow will not pass.

Have a look at the picture above. The ring midway up the barlow IS the top of the draw tube, inside which is acres of space. It's the constriction caused by the extension tube (upside down at the bottom of the pile) that is the issue.

I've just had the cheapest thought of all - I could just get a 2" parfocalizing ring and use the barlow as the extension tube set to the right depth. With the nosepiece unscrewed it is just an extension tube, which handily has a 2" and 1.25" compression fitting at the top. The nose piece, when attached direct to a 2" eyepiece, gives 1.5x magnification and will fit in the top of the barlow.

I shall experiment if this damned wind ever drops.

Russell

[Did Faux]

Hi Russ, oddly enough I thought of the parfocalizing ring solution on my way home!!!!!!!!

Personally, I like the idea of a bespoke adaptor, and i have been given permission from the highest Authority at B.I.G to investigate and experiment (cheers Kev)

I reckon I can sort it, most likely i would manufacture it from aluminium, possibly stainless (i have some solid round bar to hand).

I will have a play and keep you posted.

Naturally this will cost you dear, keep those enquiries rolling in!!!!!!!

Colin

[russ.will]

Evening Mr. Faux,

Back in post number six, I referred to a supplier of mine in the real world. Mr. Faux is that man. He's a lifetime astronomer who has loitered around these parts for far longer than I, albeit he is less vocal, because he has forgotten more than I have yet to learn and is thus, less prone to talking about it.

It is a matter of construction industry etiquette that I refuse to vouch for his integrity, given that I know him and because he has lifted my leg on umpteen orders. He is, however, extremely knowledgeable on all issues regarding matters pertaining to engineering metal and thus, if I want my solution cheap, I'd better shut up sooner, rather than later.

In spite of the full moon, I've been outside tonight and experimenting. The use of a parfocal ring on the tube of the 2" ED barlow, unfortunately won't work. Yes, the ED barlow tube works well as an extension piece and indeed, it copes with the 2" EPs, even with the barlow nose attached.

However, if you decide to screw the nose, back into it's rightful home, the setting depth of the, now complete, barlow is much deeper than the point the parfocal ring would be set at. Bummer. The 40mm mm M54 male/female extension is still the solution of choice.

On the plus side, I had some fantastic views of the moon tonight and one of my workmates coughed the £120 I was owed in cash. Thus, I'm off to buy a Panaview 26mm just as soon as my hangover clears tomorrow...

Russell

[frogdr1ver]

Just bought one of these also and was struggling to get the eyepieces to focus, had to pull the barlow right out the focuser so it was only just inserted to get enough travel to focus on a 200p DS. Can anyone show me a image of the best way to set it up so everythin seems secure? I have the skywatcher coma corrector also but couldnt see how that would help.

Sorry for the newb question!

[Anweniel]

worth keeping an eye put here for pocket saving adaptors.

AstroBoot

[frogdr1ver]

Yeah i keep an eye on there for bits and bobs. You would think it would come with the bits you need though. I have some extensions that came with the 200 and the coma corrector but none seem to fit properly.

[rwilkey]

Hi Frogdr1ver, I have the exact same setup, but not had any real problem, a bit of teething problem adjusting the focuser, yes, but it soon fell into place. No worse than getting used to a new eyepiece though. The 2" ED Barlow is a great piece of kit, I have to say.

[frogdr1ver]

Thanks for the reply, how do you connect it all up? Did you use any adaptors to get the focus travel?