Sweet spot, banding and tilted etalons ...where are the limits ?

[MapleRidge]

Hi Christian...

Thanks for the completed math on the calculations.

I had always though the 'sweet spot' on my mod was less than optimum since the etalon/collimators are designed for a f7 scope, but I have it on a f8 OTA.

My original mod with this etalon was on a 100mm, f10 scope and I think the sweet spot increased as the focal ration move closer to what it was designed for. When I run the math on the 100mm scope it shows the radius is smaller, close to 0.16 deg by my math.

Brian

[LeoD]

Very informative thread!

BTW, there is also a possible combinaison with a double stack Lunt 80 mm internal etalon. I don't remember what is the actual diameter of this etalon.

The Lunt LS80MT has 51mm tilted internal red ERF in front of 45mm clear aperture etalon and DSII-SFPT module of 36mm c.a., joint next to it.
The same as Marty, I'm curious to pair the Lunt, in my case DS rear system, with a bigger frac f/7. Seems promising, though.
With my given 130/7 according to Christian's formula, I have 0.34° diameter of the 'sweet spot' i.e. 2/3 of the disk.
How to calculate a lens in front of the etalon? with detached native collimation lens or as it is?

Leo

[christian viladrich]

I think George9 on Cloudy Night Forum has a double stack configuration with his 155 mm Astrophysics. I am pretty sure he has at least one Lunt 80 mm etalon, but I don't remenber whether the other etalon is another Lunt 80 mm or a Quark.
I don't remember if George9 is also on SolarChat ?

[christian viladrich]

Here is an example of double stack Lunt 80 mm on a 204 mm refractor :
http://www.astrosurf.com/topic/144876-s ... m-h-alpha/