3rd July 2026 Etalon spacing.

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 Friday 3rd I set up the 102mm APO with 60MT etalon in the drive. It was blowing a gale from the NW. So this was the only real shelter where the sun was still visible. In between huge clouds.

 I am using the mini-PC indoors. So it was not readily available for astronomical duties and imaging. I had to make do with visual observation only. All I really wanted was confirmation of surface texture in H-alpha. I made a slight alteration of the spacing to about 18mm of the Omegon extension still visible. 

 The ZWOAM5N mounting is sitting on top of a PE200 pier extension. All mounted upon a Celestron Advanced tripod with 2" stainless steel legs. 

 

The tail end of the H-alpha set up. With the Lunt LS60MT etalon, housing and focuser. 

 I am using a 2x Shorty Barlow. To reach focus with a TS star diagonal and the Magnum 8-24x zoom eyepiece.  A solar wedge [diagonal] is not needed with an H-alpha set-up.

 

 

 

 

 

 

Close-up of  the tail end of the 102mm where the focuser would normally fit. Showing the bored out 2" x 35mm Omegon extension and the Lunt 60MT nose clamped in plumbing fittings.

 Ideally I need to introduce a threaded fitting to allow fine adjustment of the etalon spacing from the objective. Some sort of push-pull arrangement if possible.

 My ZWO174mm camera needs to be fitted in place of the star diagonal and eyepiece. So that I can use imaging software to confirm the best possible spacing between the telescope and the etalon. A much less cloudy day would reduce the considerable frustration of waiting for clouds to clear the sun.

 

 

  

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1st July 2026 Summary of the modified 102mm H-alpha telescope.

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 Wednesday 1st. Mostly overcast. I had to wait at home for a delivery. So used the intervening time to rebuild the 102mm TecnoSky APO refractor as a modified H-alpha telescope. Much of the detail here is a duplication of a number of earlier posts. Posted as I developed my ideas for modification. I have summarized the details here so they are hopefully much easier to follow in one place.

 After my last viewing of the sun in white light. I had left the Lunt 60MT etalon module and focuser unattached. The Feather Touch 2.5" focuser had proved to be ideal for white light and had the same thread size as the TecnoSky focuser. 

 I still wanted a more stable connection between the two major components. The Lunt 60MT etalon module and the TecnoSky 102mm APO telescope. Which involves removing the focuser from the APO telescope. To allow the Lunt etalon module to be attached more closely at the rear. The Feather Touch adapter ring is left in place. The TecnoSky focuser's base ring/rotation adapter is not as useful as the Feather Touch. Though it could be adapted if desired. The base ring is also deeper than the FT adapter. This might not matter. Provided there is still room for the Lunt 60MT etalon at the correct spacing.

 The etalon's nosepiece must be placed 264mm inside the APO's focal plane. The focal plane is 735mm from the front edge of the fully retracted dewshield. The focal length is quoted at 714mm. The APO's main tube is 460mm from the retracted dewshield tip. To the edge of the Feather Touch focuser rotation/adapter ring. So the Lunt etalon's nosepiece should be 11mm beyond the adapter ring.

 Or not? The focal plane is where it is relative to the dewshield. Regardless of any adjustments to this measurement for the exact position of the objective lens. So 735 - 264 = 471mm from the front edge of the retracted dewshield. This is where the nose of the etalon should lie. About 20mm more than the present position. Unfortunately I shall have to wait until tomorrow afternoon's promised sunshine to prove it. 

 The image [top right] shows my original assembly. With the etalon nose extension inserted and centered. By a marine plywood ring in the empty, FT focuser, rotation ring. The extension is a standard, short, 35mm, bored out 2" fitting from Omegon. The nose of the Lunt etalon is rather oversized for a 2" standard push fit extension. So I bored out this extension in my old lathe.  To increase the internal diameter to 52mm. Only to a depth of 25mm in the female half of the extension. I also had to increase the depth of the groove which houses the bronze clamping ring. Which was much more fiddly. 

 I really wanted to fit a permanent spacer. To ensure the two components would always be close to the desired spacing. Unfortunately there isn't room for a focuser in the gap between them. Which would have been preferable. To allow fine adjustment and more accurate centering. With a positive clamp on the 2" etalon nose piece once the best position was found. 

 It would take a brave and skilled man to shorten the APO's main tube and re-thread it to match the original. The old fashioned way of using radial fixing screws has been replaced by precision, CNC machining.

 My final solution will be to turn a thick, aluminium ring. To replace the temporary plywood ring with something more solid. Probably with a turned V-groove. To match the Feather Touch adapter and its nylon pointed rotation and clamping screws. Most Feather Touch focusers have this V-groove turned in the bases. To allow secure and silky smooth rotation of the entire focuser. With no sloppiness or loss of concentricity.

 Before that happens I must absolutely confirm the required spacing. The quality of the H-alpha image depends entirely on this dimension being correct. Not just to tune closely to the H-alpha wavelength but to obtain even lighting and detail across the entire sun's disk. Or camera's field of view. 

  

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24.04.2026 White light solar observing.

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  Desite having hurt my back a week ago I dragged the new rig outside. Hoping to do some solar observing in white light. I did not connect the mini-PC. Just used the paddle.

 First I tried the Lunt 1.25" solar wedge. Then I fitted the Lacerta 2". Which provides dimming by rotation of the EP holder. I started with a single Meade 4000 26mm EP. Then my 2x Shorty Barlow, Zoom EP and finally TE binoviewers and a pair of 26mm EPs. 

 The latter was by far the most satisfying set-up. The sky was milky but there was no visible cloud crossing the sun. The seeing was mostly very soft  but with moments of tantalizing, razor sharpness. Most of the time I was focusing in and out. Just trying to get a sharper image. When there was often, literally none to be found. I did not bother to use my mobile phone to capture the fuzzy image. Nor bring out the ZWO 174MM. Which would have required a screen and mouse mat.

 Earlier plans to have a permanent pier in front of the greenhouse were never progressed. The endless cloud and cold wind did not give way to sunshine until this last week. I only had an hour free this morning before leaving for a heart scan at the city hospital. I still have plans to put one of my piers in the front garden. Unfortunately I hurt my back playing with heavy paving slabs a week ago. So I can't possibly manage moving the massive weight of any of my three piers. Each of which needs different adaptation to the ZWO AM5N base.

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1st April 2026 MkIV packing and parcel delivery delay.

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 UPDATE: 22nd April: Two of the parcels reached the recipient. The third, in the foreground of the image below has only just arrived after three weeks. Damaged at both ends but the contents remained intact. Largely thanks to my taping the axis shafts to the MkIV's huge, saddle casting. I also fixed the locking collars to the ends of the shafts. Even so both ends of the parcel were punctured.

 Wednesday 1st April. Sunny. I have been outside packing the MkIV for its trip back to Blighty.

Having taken the whole thing apart. So I was able to tape the main shafts and cradle together. Then place it in a long, narrow box with padding. I was hoping to avoid the heavy shafts shooting out of the box and causing damage. Taping the parts together also increases the cross sectional area. I also taped the box thoroughly. To avoid penetration. This parcel came to 14kg. So just under the 15kg postage step.

 The rest of MkIV just fits into an old banana box. However it came to just over 21kg once I had added lightweight packing materials.

 The weight limit is 20kg for handing packages into parcel centres in Denmark. So I will have to lighten the second parcel and make up a small third.

 16.30 I have just delivered the three parcels to the parcel office in the village. 2 x15kg and one of 10kg. 

 

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23.03.2026 MkIV dismantling.

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    Monday 23rd. Bright but cloudy. Rather cool. I have continued to struggle with the removal of the main shafts of the MkIV. I had fitted stainless steel shafts in place of the rusty originals. This was years ago. I had fitted clamping screws to ensure th safts didn't detach accidentally. The fit must have been close. Because the shafts didn't want out come out of the castings. 

 11.30 In the end I used a compact counterweight as a slide hammer. With two shaft clamps well tightened onto the end of the shafts. The castings were resting on 2x4s on a folding workbench. This has taken me a couple of hours but the shafts are finally free. I can now pack the MkIV into compact boxes. Or wrap the parts. Rather than have to cater for huge L-shapes. The Dec shaft is by far the longest and the saddle is quite a length. 

 I have started to weigh the components but decided I need a rest first. 

 Lunch over. I have weighed all the MkIV's components. The total comes to 28kg. There are parcel services which allow 30kg. Or I could split the load two ways.

 

 

 

 

 

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20.03.2026 Downsizing Pt.2. The MkIV is going.

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 Finally a reasonable day to be comfortable working outside. Warm sunshine [46F/8C] and no wind. Though there was a light overnight frost and thick mist. 

I have been using a tall, tripod ladder, chain hoist and slings to lower my old Fullerscopes MkIV telescope mounting down from its massive steel pier.  The pier was so embedded in the undergrowth that I needed the car and a long rope to pull it free! 

 I welded the pier together and placed the restored mounting on top while I was still at work. So at least 18 years ago since my retirement. I must have been much stronger, inventive and determined back then. I stripped and painted the mounting. Fitted stainless steel shafts and silvered the scales. 

 The mounting was used to capture the Mercury Transit with my 7" [180mm] F12 refractor on board. Which lasted so long that it fried a big transistor in the speed control electronics for the synchronous drive motors. 

 Now I am dripping with sweat and a bit tired from the effort required today. I still have to dismantle the mounting and pack it up for postage to its new owner. That should be fun! Everything is rusted. 

 

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