UK prices for Ha blocking filters are nearly double what US folk pay for the same thing.
Nobody takes my hard earned money that easy, so I decided to make my own.

Whether you've a Lunt, Solar Spectrum, SolarScope, Coronado or Quark they all employ "blocking filters".
They help block energy and other superfluous wavelengths.

Within that mystical tube of stuff called a "blocking filter" is one key filter - the "trim" or "block" or "selection" filter.
Its job is to allow through a narrow band of light centered around Ha.
You could see lovely prominences with just this filter alone, but not the wispy gaseous ethereal Ha clouds in the chromosphere.

For that you need even narrower selections of light which is the job of the "etalon".
But etalons also allow through "sidebands", typically some multiple of the wavelength they're centered on.
This would bleach out the Ha experience.
https://luntsolarsystems.com/were-proud-of-our-etalons/

The "trim" filter and etalon work hand in hand. The trim ensures there are no sidebands for the etalon to let through.

The EO 656.3 / 0.5nm cost me £1300. I could have bought a complete off the shelf blocker for that!
But I was in the mood for tinkering and learning.

My "blocking filter" is not in a single convenient tube but in various places.
1. Altair D-ERF on the front of the scope. Allows through about 40nm of Ha. A "cool beam of light".
2. KG3 "heat blocker" up to about 2200nm. This is inside my 2" focuser tube.
3. UV/IR inside this "trim filter". The D-ERF already does this, but also adds cheap scratch protection for the EO.
4. The EO trim filter
5. The Lunt etalons from the LS40Tha still have their own red ERF on the front - so I should be 2x-4x safe

EO state this 656.3 is ">45%" transmission. Alluxa are stating ">90%" for theirs.
If I'd used Alluxa it'd be too bright for visual so I'd have to add ND filters or variable polarizers.
Plus the EO was ready to ship in 2-3 days while the Alluxa wasn't in stock, and Solar Maximum means no time to waste!
EO do a range from 0.2nm - 2.0nm. Here's a link to mine: Edmund Optics 656.3 / 0.5 FWHM filter
EO customer care was excellent - as a first time private buyer their head of sales reached out to me to confirm my delivery details were correct and I had knowingly purchased this rather expensive filter. 10/10 for caring about the person not just the purchase.

On my Vixen 80mm f/11 with DERF + KG3 + "Eds Trimmer" + single Lunt 40 the image is a tad too bright and needs ND 0.5 for my liking.
On my Skywatcher 150mm f/8 it'd be even brighter. I need to tread carefully.
I'm using the 80mm for dress rehearsal before the 150 is allowed on stage.

I'm thinking the quoted EO transmission value (">45%") was pessimistic. I received "S/N 01". I don't know if that's serial number #1 which got special attention, but my system transmission % seems more than I'd calculated from all the combined transmission charts I could find. That's a good place to be, I suppose.