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Cheap 100mm Ha scope??
Since getting the PST and "hooked" on Ha observations of the Sun, I couldn't help myself..............
Oldfield's ( Hong Kong) blog on El cheapo ERF and pulling the PST apart to use the etalon got me thinking; why not pull the PST apart and use it on the 4" Genesis. Great idea, 6 times the resolution WooooW!!!
Just needed to find a cheap ERF; they don't exist!!!!!!!!! We're talking 100's of dollars, but as you probably know by now I don't give up easy.
I think I've cracked it!!!!!
I needed to machine a couple of adaptors with M50 x 1 threads to mount the etalon ( BTW it doesn't want to be separated from that beautiful gold tube, you need to apply "excessive" pressure, believe me!).
From Oldfield's notes also needed a x2 Barlow, you need to be above f7 (the Genesis is f5), OK found one! A TV x2 "Big Barlow".
For the ERF ( Energy rejection filter) it needs two things:
To remove the UV/IR before it frys the etalon ( or your eye!)
To filter all the visible light other than an few Nm around the Ha
Oldfield just used an old Aerial red lens, but acknowledges the focus get toooo hot and you can't put any human tissue there!
I've found a supplier who does optical filters for stage productions which block the UV/IR ( to stop the make-up from melting....honest!) and bought a 125mm sq filter. This combined with a 4" Wratten #25 filter from Surplus shed will give about 30Nm wide transmission at Ha.
Won't get to put everything together until I get back next week, but I'll keep you posted.
Total cost to date, excluding the Genesis ( you could use an ED80, or the bottom of a Coke bottle; remember you're only transmitting a narrow piece of red light, so you definately don't need an APO!!)
PST $600 ( Can still be used on its own)
Adaptors - slab of VB, plus $11 for the aluminium bar
Red #25 filter $10
UV/IR filter $170
All up say $800 and you've got a terrific Ha scope with 100mm aperture, which would cost well over $4000!!!
I can supply details of specific addresses ( the machining might be a bit more expensive than "mates rates")
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