Good points Jon. That 10" was a random sample. I'm curious as to how he likes it as he just got the base for it.
Well, I just came inside after using the XT8Plus and the "XT7Plus" ( ). There was one surprise, which I'll mention a little later, but no surprises really.
The sky was clear and quite calm early on, which allowed for good star testing, which was done at 240X with a Clave 10mm and an older Celestron/Vixen Silver top 2X barlow. Collimation was "spot on", pun intended. I spent a lot of time on Aldebaran, some on Betelguese. At the full aperture the turned edge was obvious in the inner/outer focus diffraction patterns being quite dissimilar. Inside of focus the rings were washed out to a large extent, with the outside of focus patterns very distinct. In focus, however, showed what some would say was a nice airy disk with a couple of uniform diffraction rings around it but some scattered junk too. "Classic" turned edge behavior IME.
At the 7" aperture, the inside/outside of focus rings were much more similar in appearance. But not identical. I could detect the outer zone on the inside of focus close to focus and the outside of focus pattern was a little more distinct. But each side "behaved well", even if they appeared a little different than each other, with the close-in patterns falling evenly into focus and then back out the other side. There was a nice "clean" airy disk at focus with one faint-ish ring, and notably less scatter/junk than at full aperture. I spent some time on M42 and, especially the trap. Here, aperture ruled for the most part, except at moderate to higher powers the trap, with the E&F stars visible, seemed "tighter", "cleaner" and to stand out from the nebula a bit better even though the view was a little dimmer at 7" than at full aperture. Ditto with the finer, delicate structures and filaments at moderate power (~120x). I've seen exactly this contrast thing before, once comparing one of my older pre-ED AP triplets to a very good C8. The 6" gave the "crisper" image showing a wealth of fine structure that was just easier to see than in the C8, despite the C8's brighter view. Ditto here but the extra light grasp of the 8" aperture was noticeable and also appreciated too.
I started the star testing with the 7" stop, waiting until I got a nice airy disk and decent in/outside of focus ring patterns before really looking carefully. Then I removed the stop and OMG what a complete mess the patterns were with flaring and no distinct rings inside of focus and a fuzz ball at focus. The 7" mask was doing exactly what my aperture masks are suppose to do with my big refractors during cooling, masking the over/under correction from the rapidly cooling outer edge. This allows high power use during cooling but with reduced aperture. Except it was way more obvious with this newt. I had to wait a good while for the primary to stabilize more. So, folks, even with a perfect mirror, it may make sense to make an aperture stop for you newt with conventional glass too, allowing it to operate well at higher powers earlier than normal during the cooling process.
At either full or 7" aperture, I saw no on-axis coma (good collimation!) or astigmatism, even at high power.
Now the surprise. I also had a trash rescued Meade Polaris, 114mm F8 newt out on my Vixen SP mount. I had cleaned the mirrors up, collimated it (actually a well put together OTA) and put it in DPAC. It showed "jail bar" straight lines and served up just wonderful views tonight with a very nice star test. at 180X. A complete surprise, though I have found several of these cheap, rescued from the dump, scopes lately that are really quite good.
Edited by Jeff B, 30 January 2021 - 07:41 AM.