26.10.2025 PT. 2 102mm H-alpha APO Lunt 60MT etalon.

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 Sunday 26th. Wet and windy with fleeting sunshine after 15.00. Sadly it is far too cloudy to be worth trying the telescope on the sun. With only a few second visibility in the last hour.

 I shall share some images of my Lunt 60MT H-alpha conversion of the 102mm Tecnosky APO refractor. It is all mounted on a PrimaLuce 50cm long [Losmandy style] dovetail plate. The APO uses its original tube rings. Though only the single, M6 central screw holes can be used. The spacing of the holes does not match between these rings and the dovetail plate. 

 The obscenely high price of PrimaLuce tube rings. Prevents me from buying a pair. Just to ensure the correct spacing. To allow pairs of screws to be used for attachment. A spacer block adapter with suitably spaced holes. Would allow two screws, per ring, to be used for extra security. I'll see if I have the patience to make a pair of adapter blocks from aluminium.

 The bosses of the tube clamps can be seen bolted directly to the dovetail plate. As mentioned in previous posts: I needed to buy 6 to 10mm thread inserts. To adapt the 6mm screws for the dovetail plate. To match the 10mm pipe clamp threads. Note the thick rubber gaskets. Which nicely protect the high quality finish on the Lunt telescope parts. 

 The plywood ring was turned on my lathe. To centre the Lunt 60MT etalon on the OTA focuser ring. Except, of course, I have removed the complete focuser from the Tecnosky OTA. The focuser ring shown is from a 2.5" Feathertouch focuser. 

 I sent the Tecnosky focuser back to Telescope-Service for "adjustment." It was far too rough to be used as supplied. [Brand new!] They promised me a few days turnaround. It has been three weeks. 

 Fortunately I am in no hurry. I am not using a focuser in this H-alpha modified refractor. It was sheer luck that the FT ring also fitted the APO tube thread of M91. The main focuser had to be removed anyway. To allow the etalon to function correctly at 461mm inside focus of the APO. Which has a stated focal length of 617mm.

 I have retained the Lunt 60MT R&P focuser behind the etalon housing. The knurled thumbscrews are an addition. To replace the pointed grub screws supplied by Lunt. More pointed thumbscrews would have been better. 

 The focuser houses the Lunt BF1200S blocking filter. Which has a nominal 2" body. Most solar telescopes employ a blocking filter based on a star diagonal. I chose a straight through model when purchasing it alone. To obtain a larger clear aperture. The tail end of the adapters has a T2 thread and 1.25" clamping ring to hold en eyepiece or my ZWO ASI174MM mono astro camera.

 

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