Going H-alpha. The Baader D-ERF heat rejection filter.

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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!

I spent the morning preparing a 10mm thick ring for my 90mm D-ERF [Energy Rejection Filter] expecting it to be 8mm thick. Baader's own website says 6mm glass. Now it has arrived it clearly says 5mm on the box and is confirmed with vernier calipers. Should I ask Baader for a 1/6 discount? Later, I was able to confirm that 5mm is normal thickness for the 90mm D-ERF thanks to a resident optical expert on Stargazer's Lounge.

Superbly packed in a neat box, bubble wrapped bag inside a lip sealed, polythene bag and then lens tissue. 

The D-ERF filter shows very different reflections and transmission colours with changing light and angles of viewing. Upper image with flash. Lower image natural north facing daylight with computer screen behind.

I can now seek a suitable [household] object to house the expensive heat rejection filter. I do have a rather nice, stainless steel lid which is 92mm internal diameter but only 10mm deep. I would prefer something deeper to make room for radial fixing screws as well as the glass itself. Then there is the cork padding to allow for.

Cutting out the base to [say] 88mm Ø would be quite hard work in
stainless steel. Aluminium is a very much nicer [and softer] material to work with. Though stainless steel lasts forever out of doors.

Chain drilling is a quick way to make a large hole in metal. Which can then be turned smooth in the lathe once the circle has been broken or sawed out. Or one can evenly file the hole smooth if one doesn't own a lathe.

I would prefer metal for this task because the heat of the sun is fiercely concentrated by the large objective. More so, because the filter [and its holder] will be placed halfway down the main tube. So plastic or wood must be deleted from the list of possible building materials.

Click on any image for an enlargement. 

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