Explore Scientific ED127 FCD100: First Light
Some changes have come to my gear lineup. While I am happy with the results of the work put into the Orion 10" I have decided a few things...
1. I don't want to deal with 2 Newtonian scopes. I had originally planned to run the Orion and ONTC as a pair and eventually send the ONTC to an out of state dark site. This would have made the Orion my primary home telescope.
2. While both Newts have been pretty solid after some work, I don't feel confident in having one so far away. I'd be paranoid it would randomly decide to lose collimation or someone bumps it throwing it out of alignment.
3. I want automated rotation on the remote rig and the only solid way to achieve that with a Newtonian is to purchase an extremely expensive focuser such as the Moonlite Nightcrawler. As awesome as that thing looks I'm not willing to shell out that kind of money just for rotation capability.
All these factors lead to my purchase of an Explore Scientific ED127 FCD100 F/7.5 Triplet Refractor. For not much more than the price of a Night Crawler I've got a scope that I can send it to a dark site with much more peace of mind that it's going to work correctly night after night since there is no collimation involved. Adding robotic can be done much easier and cheaper. And the smaller body means less work for the mount. It helps that I already own a compatible rotator, focus motor, and field flattener. Also, when you consider the secondary obstruction of a 10" Newtonian, the 127mm aperture isnt much smaller than that of the Orion and ONTC. There is still a good amount of light gathering power.
Image Train:
30mm M48 Spacer w/ ring stop (1.5mm thick)
10mm M48 spacer
Pegasus Astro Falcon Rotator (M54 to M48 Female adapter, telescope side. M54 to M48 Male adapter, camera side)
Hotech SCA 2" Field Flattener (compression ring removed)
ZWO OAG-L
ZWO 7x2" Filter Wheel
ZWO ASI2600mm Astronomy Camera
Accessories:
ZWO 30mm F/4 Mini Guidescope
ZWO ASI120mm Mini Guidecamera
iOptron GEM45 Mount
Pegasus Astro Powerbox Adv
The FCD 100 version of the ED127 comes with a 2.5" rack and pinion focuser with an M63 male thread at the end of it. The scope also comes with a threaded compression ring adapter and 2x 37mm (1.45") M63 spacers. ES also sells threaded adapter that threads to the end of the focuser as well. The focuser has 40mm of outward travel. When imaging with a field flattener the focal plane is approx. 216mm(8.5") behind the focuser collar with the focuser racked in.
Depending on your exact configuration you may need one or both of the M63 spacers. I only needed to use one. It threads onto the focusers M63 thread and then the compression ring (or threaded adapter) screws onto the spacer. I like that the focuser spacers thread at the back of the focuser instead of in front of it the way Moonlite and Feather Touch do.
Next comes the rotator. The falcon comes with M54 female threads on both sides of the device so there are many possible ways to connect it to anything. Since I are using the compression ring that means I needed a nosepiece on the telescope side of the rotator to slide into the focuser tube.
On the telescope side of the rotator I placed; an M54 to M48 female thread adapter (2mm thick), a 30mm M48 spacer with a ring stop placed on the thread to make it sit flush witht the focuser collar, and a 10mm M48 spacer threaded onto the 30mm and then onto the rotator. The 30mm spacer acts as a nose piece but gives an M48 Male thread for whatever spacers may be needed to achieve focus with room to move the focuser in and out.
On the camera side of the rotator there is an M54 to M48 male threaded adapter (2mm thick). The 2" self centering nosepiece of the Hotech flattener unscrews so I removed it and threaded it to the rotator. The camera side of the flattener provides an M42 male thread so I used a ring adapter to make it an M48 thread.
To that flattener male thread attaches the OAG, FW, and camera (which are all bolted together). Convientiely when bolted together this ZWO configuration makes exactly 55mm of back focus which is what the Hotech flattener calls for.
All said and done my image train achieves focus with the focuser racked out about 18mm, so about halfway through its travel. while maintaining the required distance between the field flattener and camera sensor. I like to configure my image trains so that they only rack out as far as necessary to help prevent tilt in the drawtube.
Results
I was only able to get about an hour of data for first light before clouds rolled in but that hour tells a very encouraging story.
The stars are sharp
The field is flat
There are no signs of pinched optics.
I am very impressed at the amount of signal I was able to get in just 1 hour of 30s subs. The site I was shooting from is normally around magnitude 20.2 but this night was quite humid so I'm sure it was a little under 20.
Eventually I will probably replace the compression ring with the threaded adapter but to be honest this compression ring is the best I've ever used. Much better than what I've experienced on my Moonlite and Feather Touch focusers. It is still better to have a completely threaded image train. I will also eventually replace the FocusCude2 with a Sesto Senso2 motor because when on the GT81 the grubs screws that attached the motor shaft to the focuser shaft would come loose over time rendering the motor useless unless you go out and re-tighten them. This is what prompted the switch to the Sesto on the dual GT81 rig. Its fine while I'm using the scope locally but I definitely won't be sending the scope out of state with an inconsistent motor.
Lastly, you're probably wondering why I have an OAG but am not using it. Thats because my LRGB and narrowband filters are of 2 different brands and the thickness between the 2 different enough to prevent the OAG from being in good enough focus to guide no matter which filter is in use. Even if I focus in-between the 2 sets the stars are just too out of focus to work. I left the OAG attached though because its an easy and solid way to make the required 55mm back focus. I just covered it with a few layers of tin foil to prevent light leaks.