As the title implies, it's impossible to do any test on the optics, so what I'm trying to do is some other tests:
1. Cheapy-ERF: it's just too big. My Cheapy-ERF has 6.5" clear aperture and when used with the C5, it's not too large. However, when I placed it in front of the dew cap of that 100ED, it's obviously too big. I shall look for something else.
The lens cell has 108mm thread, it would be great if I can find a red filter with 108mm thread.
2. When fully assembled, i.e. dew cap and lens cell attached, my tripod bag is obviously too short for this purpose. There is 12" uncovered. When the lens cell is removed, the dew cap can be "retracted", I mean the OTA can be placed inside the dew cap and there're only a few inches outside. It seems like I shall take it out disassembled for better portability.
3. When properly balance, the Unistar Light can take it with ease. When I said ease, I have even used a 5x Powermate with a 13mm Nagler Type 6 to scan around, vibration is there, but it's useable definitely. I didn't calculate immediately, wow~ it's around 350x! Light weight OTA has a good advantage, long is not an issue here and it's even better, I found it better to use this long OTA than with a short C5 OTA.
4. The LXD55 carries it well as expected. This test is more on indoor purpose. The objective is way outside the window and it looks dangerous. You know, I even tried to shake the dew cap to see if it's secure or not. I spent some more time with this setup with different eyepieces, refractor view is definitely superior to the eyes!!! Super sharp and contrasty! f/9 is definitely great for visual observation! Okay, back to my test. I have made the OTA more "outside" and I found that the mount can handle this imbalance, since the OTA is light anyway, however, it does not help much to clear the view, I mean it will not provide me with more access to the outside sky. In short, I have yet to see if this OTA can replace my C5 for indoor purpose. Yes, the C5 cannot be used to reach the outside world, too. I just want to see how they compare. Maybe I will end up with another altazmount? My primary purpose is indoor solar imaging now. Maybe time to sell my LXD55? No quick decision requires, more testing first.
A short summary:
1. This OTA is definitely nice for visual observation, better than my C5. Frankly, I don't find my C5 anything too good for visual purpose. It's compact and convenient, and it works great on planets and solar imaging, but that's about it.
2. I will need to hunt for a suitable ERF for this new member, to try it out on the sun, especially about how it works in an indoor setting when compared with my C5.
3. This OTA really finds values to my eyepieces!!! My beloved Pentax SMC XL 40mm survives again!
Follow up actions:
1. Find suitable ERF for the 100ED
2. Try out the 100ED with a herschel wedge!
3. Use my TG-SP II more from an indoor setting, if it could be done, sell my LXD55! And buy a replacement altazmount for better indoor imaging
Further Test on focuser travel:
1. A SCT reducer will not work without special adapter, I'm using a 2"->SCT thread adapter (JMI) and then a 2" SCT visual back, but it won't reach focus. Anyway, I ain't interested in using this scope for deep sky work, so a reducer is not going to be very much useful.
2. PST etalon: it won't focus, not enough in-travel without special adapters. Right now I used the original 2" visual back, and then the original 1.25" adapter, plus the PST etalon, BF10 afterward. I have tried to remove that 2" visual back and the original 1.25" adapter, also remove that 1.25" nosepiece from the PST etalon, and to hand held the etalon to the focuser draw tube directly, it will focus, and still have less than 1cm left. Therefore, I imagine if I made an adapter to connect the PST etalon directly to the focuser draw tube, it will work. Sad thing.
On adding a 2.5x binoviewer corrector in the nosepiece of the PST etalon, it will work. Alternatively, I can use that 2.5x corrector in the nosepiece of the BF10, it will also work! I really need the sun to really try out, since I didn't really conduct the above experiment with a BF10 for its too dark to use except on the sun, instead I just use a Tele Vue 1.25" mirror diagonal to simulate the result. I shall see how it works first with the corrector. If it goes well, I will consider making an adapter for it.
Finally, I have successfully mounted that cheapy-ERF on the 100ED!