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LondonSi72

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Posts posted by LondonSi72

  1. On 28/09/2020 at 02:59, Louis D said:

    I was out last night with my Dob and binoviewer.  I was able to verify that using a Meade 140 Barlow nosepiece as the reference distance that a Celestron Ultima type shorty barlow required about another 1/2" of in-focus while the above Orion long barlow required about 1" of additional out-focus.  This was also true with just an eyepiece.  The shorty Barlow required in-focus while the long Barlow required about double that out-focus.

    Thank you. That’s really useful to know for future. 
     

    However... The converter / adapter I ordered from eBay - as Dave spotted from another post in SGL - arrived last week (early) and I had a clear night so managed to try it out. It works a treat! 
    The eyepieces I have all worked with my short 2x Barlow (and even with the 2.25x - though it wasn’t an improvement in clarity)

     

    This setup is really nice. I’ve attached a photo of the converter and helical focuser. The converter is the first narrow black ring in the picture, attached to the silver thread on the focusing tube, and the helical focuser attaches snug up to this. 
     

    The helical focuser has three grub screws to tighten the compression ring and a fourth to lock focus in position. It’s a very fine adjustment and works well in conjunction with the normal rack and pinion focuser of the SW130. 
     

    Thanks for everyone’s help on this. 
    The icing on the cake would be if this works on a SW200 too...

    BB2FC141-7CEC-4EFE-B135-F5782D2AC65A.jpeg

    • Like 1
  2. 1 hour ago, PEMS said:

    As you say the 130 is a spherical 900mm mirror I would really not expect great results from it at the high magnifications.

    It comes out as F/6.9 and many would suggest that a 7mm was a good idea and maybe a maximum. Giving the scope the benefit of the doubt you could try a 6mm but I doubt that a 5mm would be worthwhile.

    The barlow is another vague area, they are not all equal and some may work with a scope and others may not. Throw in that the barlow works on the scope focal length, actually image size, not on the eyepiece. So the barlow is affecting the output of what is a spherical mirror. As that likely is not starting out good the barlow is likely just going to highlight the abberations from the mirror. Previous person may have had a selection of barlows to try and naturally selected the one that worked best.

    However for the nature of the mirror the use of a barlow and an 8mm eyepiece is I expect too much for the scope.

    A finer focus adjustment is likely to make no difference. What you have not indicated is that you get momentarily to a good focus but cannot stop at that place. Meaning to me that there is no good or sharp focus. Exactly what I would expect.

    I would say that a 6mm eyepiece is going to be in effect as good as it will get, that is 150x. Seriously doubt there is any more to squeeze out of the scope.

    Concerning 200P use if the 1000mm focal length version f/5 then select a 6mm carefully. The William Optics ones were said to be good but not best in an f/5 scope, worked well in an f/6 and slower. Altair sell a 6mm however I suspect, from the appearance, it is a rebrand of the WO item so may suffer in an f/5. Would suggest the f/6 200P if possible. The slower scopes seem a little easier to use. Other then that a 6mm should, focal ratio considered, be a good option in a 200P. The question being "Which 6mm?"

    Yes - I suspect I'm pushing my scope beyond its limit - which I'm sure every newbie has a tendency to do :).  Theoretical max magnification of the SW130 / 900mm scope is x260.  The 8mm with a 2x barlow is x225, which I thought would be OK as it's almost 15% less than the max magnification - if you follow me.  Maybe that was too optimistic.  (I have a Baader 2.25x Barlow as well - now that would be optimistic at x253 !)
    The Helical focuser works really well without the barlow - a very smooth, fine adjustment, so if I can't get this setup to work with the Barlow as well, I'll just go with the helical at lower magnification.

     

    One of the many challenges for a newbie working through the options in astronomy, is being able to truly understand what a view will be like in THEIR scope for various EPs and Barlows etc.  As I said - theoretically my scope could provide 260x, but if you're saying I shouldn't expect anything better than 150x, that's hard to workout until I see the result and determine if it's good enough for me.  Like most things, that comes with experience, I guess.

    At least there's an active market in EPs so it's almost like loaning them, if you don't buy them from new :)

    Thanks.

  3. 2 hours ago, DaveL59 said:

    doing a search, turns out someone here already crossed the bridge of finding an adaptor:

    Looks like what you need to fit direct and then hopefully have enough in travel.

    You absolute STAR (excuse the pun)!  I looked on this forum - and many others - to try and find anyone else who had this issue, and this post didn't show up (my search criteria, I guess).  That's exactly the same setup.  Found and ordered on eBay.  Bit of a wait (20 October), but I'll let you know if it works.

     

    Thank you :)

    • Like 2
  4. 2 minutes ago, DaveL59 said:

    I believe on the SW130 the inner silver drawtube has a T-thread (or T2?) but I can't confirm for certain, having neither manuals or a T-thread to try on it. That would likely make a big difference tho as you'd gain at least half an inch of in travel which may be enough. Is your helical threaded, in which case its worth a try?

    The end of the EP holder has a T-thread - that's actually what the helical focuser screws on to - but the silver tube is different - much wider pitch, and slightly smaller diameter (I think).

  5. 18 minutes ago, DaveL59 said:

    sounds sensible, mine's a black tube 130/900 SW130 and I've had the cell out with no issues, but if the nut does come away for sure it'll be a challenge to refix them, epoxy would likely be better than superglue but either way allow a lot of time to outgas before refitting the optical bits. I was thinking about lifting the mirror to use a modified CCTV camera with it but I've other scopes so no real need. I did lift the mirror in the TAL-1 so it could use regular 1.25-inch eyepieces which was simple to do, just used longer screws and springs and it's been very stable.

    With the SW130 I've had no issue with eyepieces or barlows but I've not fitted a helical to it. I guess that's increased the length of the focuser tube which causes you to not have the in travel needed.

    Dave - yes - in-focus is exactly the problem.  That's what I was trying to work out - if there's some way you could calculate where the focal point would be for a given telescope, barlow, eyepiece combination based on the information the manufacturer's provide with these items.  It seems not.
    The helical focuser is probably about an inch in length, so quite compact.

    If you have the SW130 then you may be able to answer another question I have.  I noticed that the EP holder in the SW130 screws into the focusing tube, and the holder is just about the length of the helical focuser.  I was wondering if I could take the EP holder off the tube and screw the helical focuser to this other thread by a short adapter.  Perhaps getting someone to 3d print one for me, if there isn't one commercially available.  Is the thread on the focus tube that the normal holder screws into a standard size for telescopes?  I looked on eBay for adapters and there are so many different combinations I couldn't figure out what I might need.

     

    (And you're right - epoxy resin would be a much better choice than superglue!)

  6. On 08/09/2020 at 09:06, DaveL59 said:

    another option perhaps would be to raise the mirror using longer screws & springs if there's not enough travel left on the OEM ones. That'd move the focal point further up the focuser tube to allow you to reach focus. You would need to redo collimation but it's a relatively simple mod to do. Your eyepieces sans barlow would find focus a little further out from where they currently do, as in the amount you shifted the mirror. Trick would be to determine how much to adjust for to reach the barlow focal point. How much extra length does the helical add to the focuser compared to the SW OEM holder ring?

    Thanks Dave.  I saw a post from a guy who moved his mirror like that on the same scope as me - but it was like open heart surgery!  The primary isn't attached to the tube in a very user-customisable way on some of the SW130s - including mine.  There are non-captive nuts inside the tube holding the side bolts in place that hold the mirror assembly.  Undo the bolts and the nuts fall free and would have to be super-glued in place to allow you to screw the bolts back in securely.  I think I like the long Barlow option better (I'm a whimp!)

    I've started looking at the SW 200P as a nice upgrade to my current scope, so may just hold out for that before I change my EP and accessories set, as with the different focal length and aperture it will all be different.

  7. On 03/09/2020 at 19:47, Louis D said:

    Look for an older, long Barlow.  They usually require a fair amount of out focus rather than in focus.  My favorite very long Barlow is the 1.25" Orion Fully Baffled 2x made in Japan in the 90s.  Side by side testing on the Trapezium showed it is slightly sharper than my Tele Vue 1.25" 2x and Meade 140 2x, both of which are phenomenally sharp and mid-length Barlows.  The Orion is about 6 inches long and focuses about 2 inches out, IIRC.  I just don't insert it all the way into the focuser rather than crank the focuser that far out.

    spacer.png

    Thank you Louis.  I'll have a look for a long barlow and see if that does the trick.  They seem to be harder to find these days, as I guess the optical quality of short barlows has improved, and they're more convenient.  (I'm still intrigued as to how you can determine where a particular eyepiece / barlow combination would need to be in the focuser for it to focus)

  8. 6 hours ago, Rob_UK_SE said:

    Assuming that everything is setup correctly with the focuser, it sounds like you might need more inward travel in order to bring the eyepiece/s into focus. Barlows require more inward travel than simply using the same eyepiece alone.

    It would be worthwhile sending MackTheNight a message about the ‘winning’ combination and how it was achieved. I suspect that it’s probably the result of a specific eyepiece, specific barlow and possibly a small modification to the focuser?

    I have not used the 130 explorer, but some of the other Sky Watcher newtonian scopes include a short extension tube. If this the case for your one too, you would -at present- be missing sufficient outward focus to bring the eyepiece into focus. I am purely speculating with this suggestion though. 

    Can you achieve focus without using the barlow?

    Hi Rob.  I'll try Mak the Night - they last posted on the forum 2 years ago so suspect they aren't monitoring it these days.  Yes I can focus without the Barlow - though a large part of the point of getting the helical/fine focuser was to focus at higher magnifications.  I could buy a higher mag EP, and not use the Barlow, but that's not as flexible as having the Barlow / medium mag EP combination.  Mak didn't modift the scope - the helical focuser attaches directly to the T-thread that's on the focusing system and then accepts 1.25" EPs.  It just adds about 1" to the length of the focusing tube - and that's enough to prevent focusing for the Barlow/EPs I have.

    What I was trying to work out is the how to calculate where an eyepiece would need to be in the focuser to achieve focus.  There must be some optical calculation that would explain this, but i haven't found anything - nor any specifications on EPs that would help.  I wondered if eye relief may be a factor, but in reverse - if you know what I mean.  Longer eye relief may mean the focuser has to be closer to the OTA than eyepieces with shorter eye relief - or vice versa.  I know some ranges of EPs are described as being parfocal - you don't have to refocus when you switch between magnifications in the same set, so there is some maths being done there in terms of the focal plane.
     

    I guess there isn't some common knowledge telescope maths here that I'm missing.  I've just seen comments from other members about EP combinations that suggested they knew in advance if an EP and telescope combination was going to work - and not just in terms of maximum potential magnification, focal length and exit pupil stuff.

     

    I'll keep researching the setup Mak used to see if there's anything special about the combination.

     

    Thanks again for repsonding :)

  9. Thank you John and Rob. Sorry - My explanation of what I’m trying to work out was very poor. 
    I’m trying to work out why some eyepieces will work with the helical focuser and Barlow in place and others won’t. It must be something to do with where the focal plane is in the eyepiece, I think, but I haven’t been able to find anything that explains this. 
     

    MackTheNight managed to get a combination of The helical focuser plus 2x Barlow and 10mm eyepiece to work in the 130 scope. I have the helical focuser, the Barlow that came with the scope and the Super MA 10mm & 25mm  eyepieces that also came with the scope and also the 8mm BST Starguider I bought and can’t achieve focus at  all with any of them. The additional length the helical focuser adds to the focus apparatus together with the Barlow mean the eyepiece can’t achieve focus. I’d need to wind the focus into the scope beyond the hard stop.  I’ve heard of short barlows - maybe that would help. 
     

  10. Hi SGL,

    My lovely wife bought me a SW Explorer 130 with the basic RA drive for my 40th birthday 8 years ago, and I've enjoyed using it on and off ever since.  I've started getting more into it - it's a great beginner scope, but I'm - like lots of others on this forum - looking at upgrading.  One of the things I found tricky with the scope was getting the focus just right at high magnification (I'm sure that's kind of obvious!).  It does wobble quite a bit on the EQ2 mount when focusing.  I get pretty good - if small - views of Jupiter, Saturn, (the Moon, of course) and have had hints of seeing some DSOs.
    I bought a 8mm BST Starguider, and it's a great improvement on the standard 10mm that comes with the scope, but if I push the scope by adding the 2x Barlow and the 8mm it's a blur and the focus seems to keep missing the sweet spot.  I saw a post elsewhere on this forum by MakTheNight, (looks like they've left now - last post was 2 years ago) who added a Baader Helical Focuser that attached directly to the T-thread on the focusing apparatus on the SW. Link to that post is below. I got one and it is indeed a great improvement on fine tuning - the problem is I can't use it with the Barlow as the helical focuser is about an inch long and the focuser can't move far enough into the scope to focus with the Barlow and any of my eyepieces (the 8mm BST, or the 10 or 25mm standard eyepieces)
    .
    Clearly MakTheNight managed to get their setup to work with some specific eyepieces (a Luminos 10mm and 32mm Plossl) and a specific Barlow, so I tried looking up how I could work out what combination of eyepieces and Barlow would work, rather than randomly buying kit and having to return it because it won't work with my scope, but I haven't found anything useful yet.  So I thought I'd take the plunge and ask here :)

    Can anyone help me figure out how I can calculate what combinations of eyepiece and Barlow would work with this setup?  I'm also looking at upgrading the OTA and mount to a 200P and EQ5 at some point, so ideally would have a combination that could work with that too - the focal length and mirror is quite different - 1000mm on the 200P parabolic vs 900mm spherical on the 130.

     

    Many thanks!

    Simon

     

     

  11. On 31/08/2020 at 10:39, Pixies said:

    I'm finding a long Cheshire better as a "sight-tube" to align the secondary under the focuser (step 2 in the AB guide - with the coloured paper). But it is the FLO premium cheshire which doesn't have the 'lip' on the tube, so it can be inserted to any depth.  It all depends on the size of your scope.

    For step 3 - Aligning the secondary to the Primary Mirror - all you need to do with a Cheshire is to align the crosshairs with the doughnut centre mark on the primary, you don't have to use the mirror clips (unless you don't have a doughnut). I'm not sure why A-B doesn't mention this. If I have misunderstood, someone please let me know!

    Step 4 - Aligning the Primary Mirror - yep, so easy.

    I am lucky with my laser collimator that it appears to match my Cheshire and is stable when in the focuser. It's a BST Starguider one, and cost £18. I did check its collimation though and it needed a little tweak when I first got it.

    A challenge with the SW Explorer 130 is that it doesn’t have a centre mark/donut on the primary. I’ve seen articles describing how you can add one, but on my scope removing the primary mirror looks like a potentially terminal action!. I wouldn’t want to risk removing the mirror and damaging it or not being able to get it back in, just to get that very last tweak of collimation correct. 😁

    There are clearly a few variations on the SW Explorer 130, depending on when it was manufactured/purchased.  Mine was bought in 2012 and has captive nuts on the inside of the tube holding the primary mirror apparatus in place.  From the two other members of SGL who seem to have centre spotted similar 130s, it sounds like it's easier to remove the mirror from directly underneath the scope using the locking and/or adjusting screws.  Either way, it seems like a fairly major operation and think I'll only try that if I can see the collimation is off with a star test.  Haven't had a chance to do a proper test since I adjusted it with the cheshire and collimating cap - too much turbulence and the airey ring looked like it had been pebble dashed!  Still got decent views of Jupiter and Saturn, though.

  12. I bought the Astro Essentials Cheshire and a collimating cap, having had problems using a laser collimator that I got when I first got my scope. I’ve started getting back into using the scope recently, and figured it probably needed collimating.  I followed the instructions in AstroBaby’s guide and she recommended using a collimating cap for the secondary mirror alignment so you can see the primary mirror clips more easily, and the Cheshire for the primary mirror alignment. This seemed to be easier - and more consistent - than using the laser collimator, which seemed to change every time I removed it and reinserted it.
     I have the SW Explorer 130.

  13. 18 hours ago, John said:

    The optical tubes can be bought for around £120 used and the EQ5's for around £100 (undriven). Worth bearing in mind.

     

    Hi John,  Where have you seen them for that price?  Every advert I've looked at so far (Astrobuysell, Ebay, Gumtree, and the private ads forum here) has been ~£350 for a complete scope and mount or about £250 for scope and £250 for the mount if sold separately.  Are there other good places to look?

     

    Thank you :)

    • Like 1
  14. 19 minutes ago, Jm1973 said:

    The seller said it was an 'old eq5'. I did some googling and apparently there was an eq5 that was released sometimes between Helios and Skywatcher, that is the same as the eq4. So it's not as solid as an Eq5, but it seems ok for now. Possibly it won't hold up too well in windy conditions etc. and probably no good for AP, but good enough to get some planet shots and stuff and for visual observing. 

    I just saw what looks like the same telescope on sale, just the OTA, on ensoptical for £240, so I guess this was still a bargain.

    But yeah, I'm seeing stuff all the time, but usually on the other side of the country. What made this atractive as well, is the guy was visiting near where I live and was able to deliver. Saving me a 4 hour round-trip which would have added 40 or 50 quid onto the price.

     

     

    Yes! That’s what I’m finding. A few 200ps have been available but all seem to be a 200mile round trip away. I’m also not sure if upgrading to the 200p from my 130 will allow me to see that much more, so a little reluctant to take a punt. I just found there’s an astronomy shop about 40mins drive away so I think I’ll go there and hopefully check out a few scopes to see for myself. I’ve kind of set my self a £300 limit for my upgrade, but think that’s too optimistic!
    (A boxed pretty much mint condition 200p +EQ5 went on EBay for £250 early last week - whoever got that was very lucky!)
     

    Hope you enjoy the scope and have some clear skies soon! I’d be really interested in hearing what you think of it. 

  15. 1 hour ago, Jm1973 said:

    Well thanks again for all the replies. I did buy it, and I am very pleased with it. 

     

    I am still not quite sure whether it is worth upgrading the tripod to the 1.75" stainless steel version, if it fits.

     

    There is a used one currently on sale at a reasonable price (£55).

     

    My thinking is that at the price it is a nice cheap upgrade... if it will make a noticeable improvement.

     

    And I haven't really seen any EQ5 or NEQ5 mounts for sale second-hand, and I can't really justify shelling out another £350 for a new one.

     

    Incidentally, all afternoon there have been clear skies and beautiful sunshine, now after putting my daughter to bed and coming back down, the skies are completely cloudy. Typical!

    Ha! I was just looking at that scope on Astrobuyandsell. I asked the seller what the mount was as I couldn’t figure out if it was an EQ2 or EQ2-3. At £265 I thought it was probably too much of a bargain to be an EQ5 and it didn’t look quite right. 
    I have the SW 130 and am looking to upgrade but can’t justify the £480 that the 200P and EQ5 are brand new. The score is still listed as for sale so I guess they didn’t get around to updating the listing yet :(
     

    Guess I’ll keep looking.  There have been a couple on eBay recently, but they disappeared before auction end. Probably because the seller found someone local to sell them to. Shipping a large scope is not really practical for second hand...

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