Quark or PST Mod

[garryblueboy]

What do you think guys I have a 120 Equinox with full ERF filter should I go Quark or PST Mod I'm mostly viewer but may do the odd picture 

 

[spaceboy]

I'd go with a PST mod personally. I have been lucky enough to look through a PST TAL mod on a fine day and the views are stunning. Quarks seem to offer up superb images but there has been many QC issues and the x4.3 barlowing factor of a quark has to be taken in to consideration.

[Stu]

Isn't the 120ED a bit fast to get the best out of a PST mod? The scope should be f10 or slower to avoid vignetting due to the etalon field stop (I think that's right anyway)

[Peter Drew]

Yes, Stu is correct, a PST mod requires a F10 focal ratio to benefit from the full aperture of the donor telescope. The PST etalon unit can be reconfigured to work at faster focal ratios but this involves removing the positive and negative lenses that sandwich the etalon and replacing them with ones of a different prescription. Not for the inexperienced!

[garryblueboy]

So looks like quark is the best option then 

[Peter Drew]

Just checked the focal length of the 120ed. 900mm so a PST mod would work at an effective aperture of 90mm. A bit of a waste of aperture but a good 90mm PST mod gives stunning results.

[garryblueboy]

Peter Other than a PST what else would I need and does it matter what model PST is old or new appreciate your expierance 

[Moonshane]

Bear in mind for a pst mod you need to place the etalon at 200mm inside focus point. This generally necessitates cutting a substantial part of this off the (donor scppe) tube. I'd find a 90-100mm f10 donor scope if I were you.

[Moonshane]

You definitely need to do more reading.

[Moonshane]

Eg http://www.photosbykev.com/wordpress/2011/11/29/pst-modifications/