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Tuesday 30th. I was pleased with my new telescope optically. Though NOT the R&P focuser. Hours of fine adjustment would not allow smooth movement. If it was smooth, then the slow motion stopped working. Finding a balance was a nightmare! I emailed the dealer and they responded with a focuser instructions leaflet. It was useful guidance but didn't help me achieve smoother motion.
By the strangest coincidence I had a Feather Touch 2.5" focuser on my 6" H-alpha 'scope. The one I wasn't going to be using again. Because it was too big and too heavy. Could the FT focuser be made to fit the Tecnosky?It all hinged on the size of the rotation ring/focuser adapter. I donned clean and brand new rubber industrial gloves. For more grip and unscrewed both focusers. To discover an identical M95 [?] thread on both. Off with one and straight on with the next. My 102mm APO now sports an identical focuser but a Feather Touch instead of the original. The nominal 2.5" with 90mm drawtube movement have the same sized fittings!
It gets even better: The Feather Touch focuser is shorter than the Tecnosky by a whopping 50mm! When fully racked in. The same will be true for all the other 102mm f/7 FPL53 APO clones of course.
Which means 50mm more inward travel from focus. Binoviewing without a GPC or Barlow! While simultaneously allowing a wider range of diagonals, solar wedges, etc. Yet to be confirmed in practice but almost certainly true. Being able to use a focuser I already own is just a bonus. One less item to dispose of.More inward travel might mean a donor Lunt 60MT etalon. Can be ideally placed in the light path of an f/7 refractor. My f/7 refractor? Without having to saw a length off the main, telescope tube. We'll see.
I bored out an Omegon, 35mm extension to 52mm to a depth of 28mm. With the active length of the extension being 35mm. The added physical [optical path] length is only 7mm. It occurs to me that I could gain a further 10-12mm. By boring out the 2" push fit Feather Touch adapter to 52mm push fit. This has an M63 male thread and is only 19-20mm deep. The same adapter on the Tecnosky is 38mm deep. So there is nothing to be gained there.
The magic number we are looking for is 264mm spacing between the etalon and the focal plane of the telescope. The native focal length of my telescope is 714mm. The shortest I can make the telescope/focuser/etalon adapter is around 520mm. That still leaves 194mm. Even using the FT focuser and my mods to various parts leaves a shortage of 70mm. Which is not nearly enough for optimum etalon tuning. The 264mm figure is set by the power of the lenses in front of and behind the etalon. Which are supposed to send parallel light through the etalon. Then converge the exiting beam as if nothing was there.
M63 is a fairly common thread size. I'll see what else is available in a thinner format. Telescope-Service sells an M63mm male adapter to 2" push fit for €61. At a fraction of the cost of the Starlight original. The T-S example might be considered preferable to chucking a €230 part in the lathe! One slip and ouch!
It would be possible to remove a focuser completely from the equation. Just find an M96 male threaded part to fit the main tube. RAF do a thin, double ended M96 male ring. Then you just need to add whatever is required to make up the missing 50mm. I suppose a 3D printer could manage a shallow flange with a male 96mm thread and 52mm internal bore. Or something suitable for holding a 52mm clamping ring. M63?
Hang on! I have a ready made, threaded rotation ring on the Tecnosky focuser. Removing the centering screws will provide a fitting to go in the end of the main tube without a focuser. Or, leave the inner ring in place and unscrew the focuser body. Done.
There is a male M81 thread on the back of the inner ring. Where the focuser body fits. The two nested rings have a depth of only 26mm. More than enough shortening to fit the etalon. Now I need a 2" push fit adapter to fit the M81 male thread. Prima Luce make an M81 adapter but it only reduces to M63 male and costs over €100! Telescope-Service has hundreds of adapters but no M63 female to female connector to add the M63 to 2" eyepiece receptacle. Which would still need to be bored to 52mm for the etalon nosepiece.
I could turn plain adapters on my lathe but not the fine threads used on telescopes. Ideally there would be an M82 female to M63 female adapter. That would use the Tecnosky focuser fittings. Without the focuser body. I could turn a doughnut ring to accept the Omegon extension but that can't be copied by others. I was hoping for a commercial plug 'n' play solution.
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