Going H-alpha: Connecting it all to the refractor & first H-alpha light.

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WARNING: SOLAR OBSERVATION REQUIRES GREAT CARE AND SAFE FILTRATION.
INSTANT PERMANENT BLINDNESS CAN EASILY RESULT FROM SIMPLE MISTAKES.
NEVER LOOK AT THE SUN THROUGH ANY LENS, MIRROR OR INSTRUMENT UNLESS IT HAS BEEN FULLY TESTED AND APPROVED FOR SUCH USE. YOU FOLLOW MY EXAMPLE ENTIRELY AT YOUR OWN PERIL!

With the D-ERF cell completed and the filter installed I just need to connect the star diagonal/etalon/filter assembly to the 6" OTA. While I could plug it straight into the 2" focuser that would push the etalon much too far out. Though I could shorten the main tube to compensate.

The cheapo 2" SCT Crayford focuser would be easy to fit to a simple plate but would struggle with the remarkable weight of the entire tailpiece filter assembly. Just over a kilo or 2.3lbs. I'd rather save my Vixen 2" Newtonian focuser for the 10" reflector when I am inspired to start working on that again. That focuser is about 10cm high when full wound in.

I was considering turning an adapter ring to replace the big Vixen 2" refractor focuser but that would need to be 110mm in diameter.  Some means of clamping the 2" nose of the front etalon adapter would then be necessary. Which would probably require very long threads for very long, radial pinch screws. That can't be done with normal hand tools. Nor do I have a stump of 110mm aluminium bar to make an adapter ring of that diameter. So I need to look at the OTA connection problem again.

A turned, birch plywood ring could plug the 6" refractor's tailpiece. The entire etalon/filter assembly could then be fitted to a 2" internal diameter adapter ring with a larger flange. The much smaller diameter of this flanged adapter would allow normal, radial pinch screws to be fitted.

It is probably unnecessary to have a focuser for the refractor because the PST etalon wants to be fixed at 20cm inside focus. The PST moved the pentaprism as its focuser and that lay between the etalon and the eyepiece filters. So the etalon to ITF/BF distance is obviously an acceptable variable, within reason.

The images show the result of turning an 18mm, 3/4" plywood adapter ring in the lathe. By carefully turning and boring the ring to size, both inside and out, I obtained a perfectly concentric, push fit exactly on axis. Because the plywood ring was turned in the chuck the surfaces are all perfectly square to each other. The 2" extension is a very firm fit with no sag or wobble.

I put a marked 120cm batten through the empty Celestron main tube first to confirm the exact position of the etalon relative to the 6" f/8 objective's focal plane. I just happened to have a 2" extension of exactly the correct length with a brass compression ring to avoid damaging the AOK etalon : 2" adapter. The 2" extension allows easy removal of the etalon/filter assembly for storage. It takes only a few seconds to release the components for use on other instruments.

Now I just need to fit the D-ERF in the correct position in the main tube and screw the tailpiece back on. Job done. I should now be able to observe the sun in H-alpha with a 120mm clear aperture. There is a risk of some sunshine tomorrow!


And sunshine there is! I've been too busy this morning to make a start and still need to drag the heavy mounting and its massive pier across the snow.

Success! I had to use a shorter 2" extender to reach focus. Then I tuned the etalon to reach an overall 'orange peel' with a few small prominences in the same view. The Cemax 12mm eyepiece offers about half a solar diameter in field of view. I tried a 26mm Plossl but that didn't help. It needed my eye to be held well back to get the full field of view. Back to the Cemax.

The sun's image is huge @100x but razor sharp on the limb. No sign of any spots so far but several prominences including an arch. The sun is regularly obscured by cloud and only 23° above the horizon. Going back out to try and capture some snaps with my short zoom, Canon P&S digital camera. Not sure how well that will work on a 12mm EP. Back soon.

It wasn't to be. After the sheer luck of earlier sunshine it has become heavily overcast. This was the best of only a few handheld snaps. Later the sky finally cleared to coincide with the sun dropping below the ridge of the house. I managed to snap one prominence but the contrast is far too wide for the camera to manage successfully. Unretouched image except for resize. Centering the camera lens on the 12mm Cemax is hard work.

Click on any image for an enlargement.

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