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Marvin Jenkins

Replacement focuser upgrade

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A couple of years ago I was fortunate enough to be bought a 130mm newt on an eq2 mount. Opened my eyes to what is up there and got me thoroughly hooked on astronomy, to the point that my wife says I speak of nothing else, which is of course a load of nebula.

The newt concerned is an Orion Space Probe 130 ST which I like a lot. The mount on the other hand I did not. I very quickly found that anything but guessing polar alignment is out of the question. It wobbles like a jelly. The RA mechanism is rough, that it occasionally binds slightly and squeaks it's disapproval whilst wobbling! Time to upgrade. NEQ5 pro with a synscan upgrade kit version five. Outrageous difference in everyway, this mount has a polar scope which is useless at night as it needs to be illuminated, ordered one of those little plastic jobs that light it up nicely. The main difference with mount beyond all the motor control and goto is that it is so stable it was like I had upgraded the OTA at the same time. I started to see objects that before were impossible without adding anymore aperture.

This got me thinking.... How much better could this OTA be if Orion had put in some effort. I drew inspiration from some of the threads on here and in particular from the SW 130 PDS club. Firstly flocking which ironically seems far harder in a smaller tube than a larger one. On this model the base of the tube has a metal cover plate held by three small screws to prevent dust entering the primary mirror area. I have removed the plate as it covers the collimation screws for the main mirror. Try collimating in the dark and getting the plate back on without loosing the screws, plus I figured quicker cool down with the base of the tube open.

As the upgrades started to make a difference I found that the 1.25 inch focuser supplied with this model is a horrible plastic chrome thing, the focus tube of which can be moved from side to side easily, so far from accurate. Next decision was to buy a laser collimator, bit the bullet and bought a Hotech. Absolutely no point on this OTA as the focuser moves so much it renders the accuracy of the laser redundant.

Now the reason for the title. Big decision! Do I just not bother with the OTA and buy an SW 130PDS and upset my wife by making all of her kind present unwanted? I think not, and besides, I am now emotionally attached to this little tube as up till now it can lay claim to all my astronomy firsts. On to FLO for the PDS focuser order, fingers crossed I can modify the tube enough to fit it and gain focus, here goes.

First picture the existing focuser urrrrr.

Second picture is the tube stripped with the urrrr at the bottom.

Received the PDS finally, after the French postal system disappeared it for ten days. First job to remove the base plate from the focuser body (pic three). Please note black paint around the inside of the plate! Now I am all for productivity but the good people at Skywatcher could at least let the paint dry before assembly. I then used the base plate as a template for enlarging the hole in the OTA. After much grinding with dremmel tools and hand files I had the desired hole size and position and drilled the tube for the new bolt positions. It was during this stage that I realized that flocking the tube after all the mods would have been far better. It took ages getting all the metal fillings out of the flock (hoover, compressed air and sticky tape). Picture four is the end result.

I am going to post more on the remaining work tomorrow.






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Stage two. Installing the focuser mounting plate. First thing is, the plate is made for a larger diameter tube than mine so the radius is larger. In essence I have a big gap on two sides of the focuser, so I have to add spacers to allow the fixing bolts to bind up on something. The fixings are simple metric threaded, conical headed bolts. I did have to cut them to length as mine were over long. (couple of pairs went in the bin after cutting too short)

Now the base plate is in place I realise that the shoe for the finder scope will have to be moved. Only one hole to drill as one existing hole is used. You can see the redundant hole between the shoe and the focuser base plate. I will have to close this somehow, black tape for the time being.

Now before refitting the OTA I turned my attention to the secondary mirror. I have seen a few mentions on here of blackening mirror edges to remove light splatter and I can see why. The second pic is the item in question and it has a ground edge with quite a large surface area which light has to pass over to reach the primary. The second picture is with the edge and back face blackened with matt paint, simply applied (carefully) with an artists paintbrush. The paint is still wet so looks gloss.

Once all was dry the re-build begins. Once back together but before the secondary mirror goes in, I blacken the focuser base plate nuts inside the OTA. Secondary mirror back in place and then the focuser body re-attached via the three small grub screws. Wow that is a big unit compared to the urrrrr that it came with. I pop in the laser collimator and do some basic alignment checks and smile, no focuser tube movement! ten minutes and it is collimated. (Still using allen keys, no B knobs yet)

Next instalment, first light, or at least a daylight alignment on a distant pylon to see if anything needs adjusting, you know it will........... Next instalment.







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Instalment three. Day light check on my most distant terrestrial object, a pylon about a K away. Turns out I have zero distant focus, the focuser is racked all the way back into the OTA and it is not enough. Now I start to worry as it's not like I can put the original focuser back on as I have cut and ground a huge hole in the OTA!

For obvious reasons I am not using the 2 inch or 1.25 extensions that come with the focuser, what are they for? I remove all the 1.25 fittings from the focuser just leaving the 2 inch fitting that a t ring would screw onto and simply hold an eyepiece in the hole to see where it would have to be to attain focus. Seems the 1.25 ext tube is three cm's too long, think about cutting it right down to just retain the two thumb screws that secure the eye piece. Then have another idea.....

The old focuser has a short section at the end for the eyepiece to go in. Why cut one down when I can unscrew the end of the old one and join it to the 2 inch fitting with a slim section of grey plumbing pipe (picture above). Tried all my eye pieces and problem solved, the eye piece is now closer to the center of the OTA by 4 cm's and focus has been achieved. That very night it is clear so Jupiter beckons, what better target to test it on.

The following is from my diary, and I think proves that the unit is a massive improvement, not just because of the DS aspect, but I can finally collimate this scope. Jupiter at dusk. Lot's of heat distortion, but all four moons clearly visible. Two weather bands showing and fortunate to see the GRS. Can just see some southern features, I would only dream of seeing all that once it is truly dark and it is not.

The last thing I need to do is focus my attention to the gap around the focuser due to the radius problem. I have found some 10mm thick medium density foam which I will use as a light sealing gasket, simply cut to shape and size with scissors and pushed into the gap to stop light leakage. I think I have now reached the limit with mods unless anyone has any suggestions. The last picture is 'it' finished. The grey bit around the bottom of the tube is light shield made from camping bed roll that cost 3 euro, is even baffled in texture on the inside.

Collimation knobs, and an anti dew band as winter is approaching and my work here is done. Next time I am out observing I will try and get a picture and add it to the thread on here about showing your scope in action.



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You could try a lower profile 2" to 1 1/4" adapter.  Televue make one (part ACF-2125), and probably others.

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On 05/09/2019 at 20:31, Oldfort said:

You could try a lower profile 2" to 1 1/4" adapter.  Televue make one (part ACF-2125), and probably others.

Indeed, bit strange they make them so high.

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