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Please Help, I've bought a triplet apo and something is wrong!

Chris

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Chris

Chris

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You can imagine my excitement when I picked up an Ascension (Meade 5000 clone) 80mm Triplet Apo off ebay for 350 quid. It was sold as being nearly new only having been used only the once and had been bought earlier on in the year, sounds great I thought!

Well it arrived today and looks the part, well apart from one or two airline stratches and missing the dovetail shoe that it comes with. I thought I can over look this and just buy some rings considering I got it for a good price. I then decided to check out the optics: The coatings on the front lens look good just a bit of dust. I popped the diagonal in plus 20mm eyepiece and looked at some distant trees which looked good (no chromatic aberration). It was only when I removed the eyepiece I noticed that the diagonal mirror wasn't an illuminated circle rather than an oval like a nearly full moon. I took the diagonal out and looked down the scope and the baffles don't look concentric with the rest of the tube, almost like the tube is bent but its not? I could see the same cut off that I could see down the diagonal! I estimate around 5-10% of light is being blocked through the scope! :(

I've tried to take some pics to demonstrate whats going on and I'm really hoping I'm missing something obvious I'm doing wrong or hopefully an easy fix. Its a beautiful scope apart from this but I'm not sure I can live with it if the optics are losing light?

Any suggestions folks?

Chris 

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Chris

Chris

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Thanks for you rery quick replies folk :)

Earl - Thanks for the suggestion, I'll just finish the washing up and I'll see if the focuser will unscrew ok to have a look before further action :)

Andy & Pat - Thanks guys, I agree :) If its not what Earl says it could be then I will message the guy. He said he bought it earlier on in the year so if its not a loose baffle in transit and is somethig more serious then he should beable to get a refund his self.

Thanks guys I'll rush the washing up so I can check out the baffles, I would be so relieved if its a simple fix :)

Chris

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ChrisLX200

ChrisLX200

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The baffles look concentric to me - perhaps the focuser is not sitting on the end of the tube correctly? I cannot imagine how the baffles could move, but a blow on the end of the focuser could knock that out of alignment. I'm always suspicious of stuff being sold through ebay...

ChrisH

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Chris

Chris

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I've found the problem!!

Its not the baffles, ChrisH was close. I unscrewed the focuser which was easy to remove and the problem is the draw tube inside the focuser is not running concentric with the focuser! Its miles out in fact. This coulsn't have been done in transit either because its well inside the tube, I've taken some pics, don't know if I can fix this or not? don't see how :(

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ChrisLX200

ChrisLX200

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You see those small black grubscrews? they may (if like the Revelation Crayfords) control the position of small bearings inside the focuser housing and upon which the drawtube runs. Slacken off the tension on the adjuster screw first - the one that presses the rotating rod against the tube - then adjust those grubscrews until the drawtube runs parallel. Then finally readjust the tension on the rod.

ChrisH

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Chris

Chris

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You see those small black grubscrews? they may (if like the Revelation Crayfords) control the position of small bearings inside the focuser housing and upon which the drawtube runs. Slacken off the tension on the adjuster screw first - the one that presses the rotating rod against the tube - then adjust those grubscrews until the drawtube runs parallel. Then finally readjust the tension on the rod.

ChrisH

Thanks Chris I'll give it a go, if it works I owe you a pint :)

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russ.will

russ.will

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It looks like the focuser is well out of collimation. My ES was, albeit nothing quite that drastic.

There are six screws on top of the focuser that adjust the Teflon pads the tensioner (underneath) holds them against. The central one does push, whilst the two either side adjust the tilt of the pads. back them all right off and it will all go very loose, but then you can incrementally tighten them up so the draw tube runs square. it took me a bit of practice, but using a good, perfectly collimated laser collimator (Farpoint) it's all pretty obvious once you get the knack - certainly easier (and more permanent) than Newtonian collimation.

Once it's done, the same laser will show you how far out your diagonal is....

Russell

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Chris

Chris

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YES!!! A very special thanks to both Chris and Russ, we have lift off! :icon_salut:

I've been upstairs for while with a bunch of Allen keys fiddling with screws trying to get all the adjustment right, very much like collimating as Russ says. The phrase easy when you know how springs to mind.

Basically its exactly as Russ said although I didn't use a collimator I ended up lining the end of the draw tube (the end inside the scope) flush with the end of the focuser (the bit that screws onto the tube). This presented me with two circles one inside the other so when I adjusted the screws I could see the whole thing pull into position and become perfectly concentric! :)

Here are some celebratory pics! She's a beaut! Just need to source some tube rings now and I can get first light! :)

I big thank you to everyone, SGL saves the day :icon_salut:

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andrew63

andrew63

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Glad you manages to sort it - looks a nice scope.  I was looking at one of these a couple of years back,  called a Maxvision - now where have we come across  that name before !  It would appear there is a factory in China where Meade sourced their scopes and eyepieces from and the in house version was Maxvision Ascension etc 

Hope you enjoy sweeping the summer Milky Way...

andrew

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russ.will

russ.will

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And now you know why the bloke who bought it new, only used it once. I'll bet the star shapes were all over the place at higher powers. ;)

Now that's done, you can start worrying about and start a thread on, how to collimate a triplet objective! :grin:

Russell

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Chris

Chris

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Glad you manages to sort it - looks a nice scope.  I was looking at one of these a couple of years back,  called a Maxvision - now where have we come across  that name before !  It would appear there is a factory in China where Meade sourced their scopes and eyepieces from and the in house version was Maxvision Ascension etc 

Hope you enjoy sweeping the summer Milky Way...

andrew

Thanks Andrew, good to hear a bit about the history of these scopes, and if its as good as my Maxvison EP's then I'm for a treat :)

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Chris

Chris

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And now you know why the bloke who bought it new, only used it once. I'll bet the star shapes were all over the place at higher powers. ;)

Now that's done, you can start worrying about and start a thread on, how to collimate a triplet objective! :grin:

Russell

I honestly don't think he noticed :D I got the impression that he had bought some imaging kit, gave it a go once then decided to sell up. He was selling a modded 450D at the same time. Although I'm saying this as someone who's been labelled gullible in the past :D 

I hope and pray I don't have to start the triplet objective thread :D

Cheers for your help Russ :)

Chris

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