Some info I collected on subject ;
I measured my TV paracorr 2, and it is 45.60 mm from lense to shoulder at setting A.
From TV it is told focus point is 56 mm from lense.
The total adjustments is 0.7" or 17.78 mm. ( setting A-H, so each step is 0.1" or 2.54 mm )
-Note. Whatever this will be correct or not vs best coma, need to be tested out.
This is info from TV.
# Ethos 21 mm whit 2" barrel is told from TV to be at setting A.
That EP has a measure at ( -0.38" ) or 9.65 mm above shoulder.
45.60 + 9.65is = 55.25 mm.
So it need to be turned out 0.75 mm.
# Ethos 17 mm whit 2" barrel has is also told to be at setting A and has ( -0.39" ) or 9.90 mm above shoulder.
45.6 + 9.90 = 55.50 mm.
So it need to be turned out 0.5 mm.
# Ethos 10 & 13 mm whit 2" barrel is told from TV to be at setting H.
Thoose EP has a measure at ( 0.27" ) or 6.85 mm belove the shoulder.
45.60 + 17.78 - 6.85 is = 56.53 mm.
So it need to be turned in 0.53 mm.
( I personally don't like the paracorr at setting H, as design is weak ( sag )
# Ethos 6 & 8 mm whit 2" ( 1.25" ) barrel has no info from TV regards the 2" barrels.
Thoose EP has a measure at ( 0.7" ) or 17.78 mm belove the shoulder.
I use a TV extender barrel ring at 30.5 mm and has a stop-ring at 10.4* mm and use setting H.
45.60 + 17.78 - 17.78 + 10.40* is = 56 mm.
# Ethos 3.7 & 4.7 mm whit 2" barrel is told from TV to be at setting H.
Thoose EP has a measure at ( 0.25" ) or 6.35 mm belove the shoulder.
45.60 + 17.78 - 6.35 is = 57.03 mm.
So it need to be turned in 1.03 mm.
# Nikon 17 mm HW whit 2" barrel has focus point 10 mm below the shoulder.
At setting A and add a stop-ring ar 20.4* mm.
45.6 + 20.4* -10 = 56 mm.
( there will be no room for the barlow lense to get the EP be a 14 mm, as it are placed in the bottom of barrel and are 10 mm thick )
As I don't like the design of the turned top I work now on a new idea.
All EP has different barrel diameter ( many under 50.75 mm ) and the inner diameter of my top is at 50.92 mm.
That alone cause sag. Rotate design cause sag.
Then the thread from top to lense package is very loose. So if one take it off/on it will be out of roundness.
I will machine a adapter that has cloose to zero clearance from EP into adapter.
This one will make up the 56 mm from lense to EP focal point.
Then I screw it on at the lense package.
This mean EP will be parafocal and no sag.
Only thing I don't like is weight is hang on the lense package.
My next construction will be a corrector like the SIPS style.