I have posted several descriptions of the on-going mods I started about 9 years ago using a Lunt DSII module as they evolved over the years. I started to look at options to get a larger solar scope but no PST to use for a donor etalon. I did have a Lunt DSII internal DS module for my LS80T solar scope, so the first mod was to have an adapter made up to fit it to the rear of my Celestron C102 (f10) OTA with a front mounted Lunt 100mm ERF. The second scope used as a mod was a Celestron CR-150 OTA (f8), using an internal mounted 110mm Baader D-ERF.
Both of these mods worked well, but I was wanting to get a narrower band-pass and was having issues with the Daystar Quantum and Quark reaching the correct temps in the winter (yes as most know I'm out at -10C to -20C on a regular basis and the most annoying issue is the delay in reaching proper operating temperature when trying to image off the center Ha band. The Pressure tuned Lunts are quick an deficient in this regard. So my attempt to get a DS system with the Lunts was a shot in the dark. The commercial line of their scopes offer an easy add on of a second pressure tuned etalon fitted on the rear of the OTA, but the individual DSII units were never intended to be stacked...but I figured it was worth a shot and ordered a second DSII.
Once I received the unit I found the first mod needed was an adapter to allow the two etalons to join together...since the cavity at the focuser end is not deep enough to fit the protruding assembly that fit the internal primary etalon...that was planned for. Os, I had a local machine ship make up a short collar to allow them to fit together. The CR-150 was the first scope to have the mod attached and it worked. I have many pics posted through this past winter and spring taken with the modded setup. Most would leave it alone at this point.
I have made a decision to de-commission one of the 3 observatories in my back yard and have fought with options to consolidate solar and wide-field deep sky into one system that can be easily converted form solar to night use. The CR-150 is an achromat, so not the best choice for deep sky work and it is a heavy OTA that was taxing the mount. So my plan evolved to getting a slightly smaller APO scope to meet the deep sky needs and make it solar friendly. I found a used Orion EON 130ED OTA online from a fellow in Winnipeg Canada and had it in hand about the time the spring rush started at work. So I used the Quantum filter for Ha as it did not need any mods to work, and now that I have a little more of my life back I started have the required adapters made up to fit the mods to the Orion.
Below are a few pics of the scope...one thing to note is that I did not get a pic is the internal 2" Astronomic 12nm Ha filter that I have mounted ahead of the first optical element of the first DSII...I need to make some changes to the filter holder in order to mount it in the new adapter.
So, first is the Orion 130 and Lunt LS80T/LS75HA , showing the ERF cell on the 130 as well as the front mounted Lunt LS75FHa etalon used the DS the 80mm Lunt scope. The original Orion focuser was installed when this was taken and has the Lunt Solar Wedge mounted in the focuser: I replaced the original Orion focuser with a 2.5" Moonlite focuser that I had (not begin used), so I got a flange form Moonlite that threaded into the rear of the OTA and provides a large male flange that mates the focuser to the scope. This will work fine for WL/Cak where a standard 2" nosepiece fits the filter to the scope. Below is the a pic of the motorized focuser, and the WL/CaK filters: The ends of the Moonlite focuser tube in M68 threads which allows multiple options to fit different devices to it. In the pic I have a standard 2" eyepiece holder, but for deep sky imaging I can either attached a camera with a 2" nosepiece or remove the 2" adapter and thread the focal reducer onto the M68 thread. Below is a pic of the focuser, reducer and ASI294MC cooled camera: Now for the mod
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The first images were posted yesterday and I hope to get many more in years ahead.
One other mod I have to pull together is the home built pressure control for one of the DSII units...I have the Lunt remote unit but didn't want to spend the money for a second one...more come on that topic.
One last thought on the mods...I used no math/optical design software/etc to put these evolving mods together. My measurement was to find the focus of the scope on a target like the moon, and focus the DSII on the LS80T scope like it was designed for and had the adapter made to place the DSII focus in the same position. The DSII does not add any significant change in the optical path...on the Lunt scope there is a spacer to remove when the DSII in installed so it made it much easier to mod. Another benefit of the f7 optic in the Orion scope is that it matches the f7 that the LS80T objective has, and as a result has the largest sweet spot' of the 3 mods I've made using these etalons which provides a larger FOV on the chip. I was having to use a smaller than full frame ROI, which I expect will have a big benefit for the large scale features that should appear as we move into the solar maximum.
Oh, one second last though...I did not post any measurements as they will be unique to this setup but if anyone wants measurement I can try to provide them in a PM.
Brian