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130 SLT mods

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#1 HenryVIII

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Posted 25 October 2012 - 07:38 AM

Hi,
I've got a 130 SLT that I find isn't a bad scope but I'm planning on making a few (hopefully) inexpensive mods to improve the shakiness of the mount and the flexing of the OTA that lead to the great difficulty of focusing at higher magnifications. The first is ditching the tripod and mounting the arm on a wooden surveyor's tripod. This should hopefully provide a good stable mount for a start. The other options I'm considering are tube rings for the OTA and an electric focuser.I'm after some advice about mods that others have already tried / made to improve this scope.
Also some suggestions as to some decent eyepieces for it. I'm still using the original 9 and 25 mm eyepieces along with a Celestron Ultima 2 x Barlow. I find I can get pretty good views of the moon and planets apart from the shaking that goes on trying to focus! I'm after some ideas for a better eyepiece for viewing DSO's. Perhaps I should be looking at a wide angle 2" eyepiece?

Cheers
H VIII

#2 hamdul

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Posted 25 October 2012 - 08:30 AM

Henry,
It sounds like you're about to take a dive onto that slippery slope. While the 130SLT might be a good scope It isn't so good as to deserve the cost of the Modifications that you propose. My advice would be to live with what you have until you can sell it and get something like a Nexstar 4, 5, or 6 SE. Better optics, better tripod, 100% BETTER SCOPE.
Fred

#3 core

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Posted 25 October 2012 - 08:51 AM

Welcome to Cloudy Nights, H8!

My thots on the matter (I have a 130SLT OTA only, will be acquiring a SLT mount soon):

* it seems that replacing the tripod of the SLT mount (either the whole tripod or just the legs) goes a long way to improving its stability.

* the added ring's weight may not work nicely with the SLT mount.

* I use the 130SLT OTA on a Vixen Porta mount and it's solid enough when focusing; as noted the main flexture comes from the small dovetail block 'warping' the OTA.

* I do not really like the high power views on the 130SLT and don't use it on moon/planets, keeping it in the lower range; I usually bring it out with a 2" 25mm eyepiece (WO SWAN) which works great for lower power sweeps (26x magnification, 5mm exit pupil, 2.8° field of view) and a 24-8mm Zoom (Baader or Vixen) - it basically covers everything I need to look at DSO-wise.

* There is a significant difference when upgrading from 25mm 1.25" ep to a 2" unit with ~70° apparent field of view; there may be some aberration near the edge of the fov, but the expansive view is really nice. I've also tried a 2" in the 33mm range, but the 6.6mm exit pupil is wasted on me.

* Nice eyepieces can be carried forward to the next scope that you get.

* the best mod that I did was to install 'milk-jug-washers' under the secondary collimation screws (from the flat sides of polypropylene milk containers, cut out a circle of the same diameter as the secondary mount where the 3 collimation screws are at, and install as a shimmed washer - make collimating much smoother).

#4 Arthur Dent

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Posted 25 October 2012 - 11:13 AM

The 130 SLT as it comes is a bit of a dog with so much vibration and slop as to be virtually unusable - particularly at higher mags.

The mirror and optics are generally fine but the flimsy aluminium tube, single arm and small diameter tripod legs don't do this scope any favours.

Using tube rings rather than the fitted dovetail bar, having the tripod at minimum extension, weighting down the tripod by hanging a weight off the spreader bar, fitting an electric focuser and using anti-vibration pads will all help.

Art

#5 barbarosa

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Posted 25 October 2012 - 01:37 PM

That little mount is surprisingly good when not overloaded. Celestron says it will carry an 8lb. payload, but less is better. A sturdier tripod will help, but is not a cure all.

You should give some thought to how you will attach the mount to the new tripod. The stock tripod top is a tapered cup that supports the perimeter of the mount. Without the cup, all you have is a single ¼”x20-bolt hole in bottom of the mount.

Using just that center mounting point may add unwanted flex in addition to the flex already in the arm.

I have seen a photo of a DIY adapter using a captive length of plastic pipe to hold the mount's perimeter. Presumably, a long bolt or threaded rod running up from a base plate on the tripod secured the mount in the pipe. Something like that should help.

#6 Paco_Grande

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Posted 25 October 2012 - 02:11 PM

I started down this road with mine, rings, new dovetail and electric focuser. The 130SLT suffers from the same problem as the 8SE: OTA too heavy for the mount.

However, the rings and dovetail did help some, but the rest of the stability issue is just pushed onto the mount arm and you can't fix that. Or at least it's not worth doing cost-wise.

The ring-mounted OTA works very well on the Porta II.

After seeing how the rings and dovetail didn't make sense economically (about $75 in parts), I picked up a used C6-N instead, and installed the focuser motor on the C6-N, which is use only on the Porta II.

My sense is, leave it alone and get another scope. If you can find used rings and dovetail, that mod is worth it as used parts. Otherwise, as mentioned already, you're dropping lots of money in a scope that is OK in stock form but really not worth spending much money to improve.

#7 HenryVIII

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Posted 25 October 2012 - 03:16 PM

Thanks All for your thoughts and suggestions. It's made me start thinking that I was probably about to start spending a lot of money to try and fix a scope that I guess was built as a budget scope. I'm going to try the mod to mount the arm on a surveyor's tripod as I've already got one, (I'm a surveyor). I'm replacing the mounting plate with 1/4" bolt hole with a new plate with a 5/8" threaded hole that the 5/8" threaded screw of the tripod will engage in without needing an adaptor. Then in the flat head of the tripod I'll drill / file three slots for the three small prongs on the bottom of the SLT 130 mount to engage in. Hopefully it'll tighten down onto the tripod nicely.It'll be interesting to see how it works or if most of the shaking is from the thin sidewall of the OTA flexing anyway.
Also I'm wondering if anyone's sucessfully mounted another OTA on the SLT mount as I presume that the dovetail mount will accept another scope? But maybe the mounting arm just isn't sturdy enough for anything bigger than the 130? I'm completely happy with the GOTO of the scope and have never had any probs getting a successful alignment. If the tripod mod I'm going to try does steady things up and the rest of the problem is with the 130 scope then perhaps just a better non flexing OTA is worth a try?

Cheers
Henry

#8 Arthur Dent

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Posted 25 October 2012 - 05:15 PM

Yep Henry,

My guess was that most of the vibration was due to the flexing of the 130 SLT's paper-thin aluminium sidewall, coupled with a rather small dovetail bar. Can't remember who it is on CN who has put tube rings on it, but they said it helped immensely.

I ditched my 130 SLT because it had faulty tracking but I feel that had I kept it, I would have got rid of it anway because I reckoned that it would cost a fair amount to fix it to be come usable.

Going down the tube rings/electric focuser route means spending $$, whilst the mount is rather overloaded with the 130's OTA. Personally, I'd probably not do this but put the money into a different scope.

The mount itself is OK and will accept other dovetailed scopes - just don't overload the mount. I'd agree with Paco G's assessment though - forget the 130 SLT and get a NexStar 4/5/6 SE instead. The mount - especially on the 6SE - is far better and under less loading than the poorer mount on the 130 SLT, so more stable.

Just a personal view you understand. YMMV.

Art

#9 Paco_Grande

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Posted 25 October 2012 - 07:20 PM

Henry, the SLT mount would likely work very well for a small Mak or SCT, 90mm-100mm for sure. Or a small refractor.

No doubt, the main flex is due to the small dovetail attached without any reinforcement to the thin walled main tube. The rings make a noticeable improvement but again, that's $75 in new parts. I considered installing a backing plate inside the main tube and would have done it if I'd had access to the proper tools. That would be a cheap and effective mod.

Oh yeah, fitting other scopes: The SLT mount requires the scope be slid in, it won't accept tipping the dovetail into place as is normal for a Vixen style mount. So, one of the dovetail bolt heads needs to be counter sunk into the dovetail so it will slide into the mount. No big deal if you have the tools.

#10 herrointment

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Posted 25 October 2012 - 08:01 PM

For use with a surveyors tripod I think the mod posted in the photo in this link would be a great choice.
LINK

#11 SDTopensied

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Posted 05 November 2012 - 09:58 PM

I use an old surveyor's tripod for mine. The mount secures with a 1/4-20 bolt which can be easily found in a variety of lengths at your local hardware store.

-Steve

#12 *skyguy*

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Posted 06 November 2012 - 01:14 AM

I took my SLT mount and placed it on a CST/Berger Surveyor Tripod (~$55) with a homemade wood wedge. The largest scope I use on this mount is a 7 pound 5.5" Celestron Comet Catcher. It makes a pretty solid combination.

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#13 *skyguy*

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Posted 06 November 2012 - 01:15 AM

... and a close-up shot of the wedge:

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#14 Astrosetz

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Posted 01 December 2012 - 07:50 PM

I've designed some replacement tripod legs for the Nexstar 102GT, which I believe has the same tripod as the 130SLT. I'm building the prototype this weekend; details are on my blog: http://astrosetz.wordpress.com

#15 core

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Posted 02 December 2012 - 03:00 AM

Astrosetz,

Looking forward to a report on your new leg mods!

#16 Chucky

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Posted 02 December 2012 - 07:06 AM

Nice job on the tripod. My first real scope was an SP-C6 back in the 1980's. I see you mentioned this scope in a recent blog. Wish I still had the thing!






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