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Reporting on my experience inserting a Lunt DSII into my Quark optical train:

Baader 160mm D-ERF and cell
AP 155EDF f/7 with 4" focuser
Precise Parts AP 4" to Lunt 78mm adapter (0.25" thick)
Lunt DSII intended for LS80
Lunt 78mm to Feathertouch adapter
Feathertouch 2" focuser
AP 2" extension (borrowed from Barlow)
DayStar Quark Chromosphere model
DayStar 2" top for Quark
AP Maxbright 2" diagonal
AP 2"-to-1.25" adapter
Denkmeier II binoviewer with PowerSwitch at neutral (middle)
Denkmeier 21mm eyepieces

It produces very high contrast, similar to my Lunt LS80 DSII. Tuning was easy and not too sensitive to exact positioning. The view is noticeably darker, but not too dark to view. Normally in my very nice, narrow Quark, I see very little in poor seeing other than proms and the most obvious disk detail. With the new double stack, the filaments and other structure pop out even in terrible seeing. Hopefully, I will get some better seeing soon.

The sweet spot is significantly narrower, probably only half the field of view. I need to do more experimentation with spacing. The AP 4" focuser and PP adapter place the DSII about an inch or two too far from the objective even when that focuser is all the way in, and that may be part of it. Perhaps a DSII for the LS100, which has a longer nose, would work better.

I think the D-ERF is sufficient to protect the DSII. I can put my hand where the DSII is indefinitely with just some warmth.

George

Thanks George, any chance of an image of the setup.

Here is a shot from the 4" focuser down. Looks like I forgot to mention that I left the Lunt 78mm-to-78mm spacer between the DSII and the adapter for the FeatherTouch; let me add that below. George

Baader 160mm D-ERF and cell
AP 155EDF f/7 with 4" focuser
Precise Parts AP 4" to Lunt 78mm adapter (0.25" thick)
Lunt DSII intended for LS80
Lunt 78mm to 78mm extension that comes with the LS80
Lunt 78mm to Feathertouch adapter
Feathertouch 2" focuser
AP 2" extension (borrowed from Barlow)
DayStar Quark Chromosphere model
DayStar 2" top for Quark
AP Maxbright 2" diagonal
AP 2"-to-1.25" adapter
Denkmeier II binoviewer with PowerSwitch at neutral (middle)
Denkmeier 21mm eyepieces

Thanks George looks good and the most important thing is it gets results

Here is some follow up on the Quark DSII. When seeing is bad, it makes the biggest difference. The Quark by itself in poor seeing shows limited detail. With the DSII unit in series, the disk lights up in more detail despite the seeing.

In good seeing, the Quark by itself shows lots of detail. The DSII unit has more contrast, but doesn't show more detail. The darker view with a smaller sweet spot in the DSII version is not worth the extra contrast.

George

Thanks for the write up George.

Nice setup and write up!

I also tried a 2A prom filter (a tunable Prom15T from old Coronado) with my Quark.

It clearly boosted contrast significantly. Not as much as a Lunt scope double stacked nor as much as the Lunt DSII paired with the Quark, but enough to make a difference.

Didn't work so well when placed before the Quark, but for this experiment I was using a 92mm f/5.5 scope. It was after the Quark that contrast improved.

It was very dim, but I don't know how much that is just low transmission of the prom filter. I really don't feel like trying to dissemble the prom filter's optical assembly. Not sure if the layers of glass are cemented and if they need to be rotated correctly.

I also need to double check for polarization. Rotating the prom filter might help.

But the bottom line is that even a wide filter, when paired with a narrow single-cavity filter, can produce a substantial improvement, presumably due to reducing light from the tails.

George