D-ERF needed for a 120mm refractor (achromat) ?

[Radon86]

Hi all,
I have got a Skywatcher Evostar 120 (D=120mm, FR=8.33). When imaging with the Daystar Quark Chromosphere, do I need a front mounted ERF (e.g. like the Altair tri band ERF) or another type ?

I did ask Daystar who said a large front mounted ERF was not needed, just a UV-IR cut filter mounted before the diagonal etc.
Some others also agreed.

Please can someone confirm whether it is safe for the Quark and my camera and my eyes to do this ?
I have a 2 inch Baader 35nm H-alpha filter, and also 2 inch UV-IR cut filters for internal energy rejection.

Many thanks.


Magnus

[hopskipson]

Yes, you only need the internal erf. The full aperture derf would help in reducing tube thermal currents. I use both on my scopes to be double protected.

Make sure to move the internal erf as far up the light cone as possible to spread out the heat on it. You want it far away from the focal point. I would use the Ha filter for the erf.

[Radon86]

Thank you Hopskipson,

I will look at thermal protection of my OTA as well.

[TareqPhoto]

I am thinking about the same thing, i might buy 150mm aperture scope in future then reduce it to maybe 120mm or even more to 100mm, then i don't know if i need that front ERF for the reduced stopped down scope or not, maybe the question should be, what is the maximum aperture we can go with using the Quark Chromosphere without requiring that front D-ERF.

[Rusted]

At the risk of repeating myself:

An internal D-ERF reflects a burning hot [completely unfiltered] light and heat cone back out from the face of the objective.
This is even worse than the original light and heat cone formed by the larger objective.
Because the objective refocuses the original light cone to a much shorter focal length!

I wouldn't consider a solar scope, with an internal D-ERF, as safe in the presence of children or innocent adults.
I literally set fire to an aperture stop when using an internal D-ERF.
There were flames licking against the face of my 6" objective!

Those with domed observatories shouldn't even consider an internal D-ERF. IMHO.
It is very likely that would will eventually burn the inside of your dome.
I see the sun's reflection from my full aperture D-ERF on the inside of the dome all the time.
Usually as I am aligning the telescope on the sun. Imagine if I went away without closing the dome shutters.
What if that harmless bright spot was a searing hot, refocused cone of destruction?

[Radon86]

Thank you Rusted!
I never thought about the reflected light before.
I will take a look next time.
Daystar with their Quark filters say internal ERF and many solar imagers say its safe for smaller scopes. I will reassess the thermal,optical and electromagnetic properties of these systems anew.

Magnus