A little follow-up to post #15....
Three-plus years ago, when I got my ES 102CF refractor, I also eventually got five ES eyepieces for it, including the 68° 40mm... only to discover that, as my only 2" eyepiece, using it was more trouble than it was worth. Along with having to remove-or-reinsert the 2"/1.25" adapter, it also involved having to drastically re-balance the scope, before and after each use. Consequently, I only ended up using it about three times.
Once I started using the ES refractor for AP though, I de-forked my trusty C8, put it on an un-motorized Orion SkyView Pro EQ, and began using it for visual while my ES was busy taking photos. But the eyepieces I'd been using for the past forty-three years with the C8 are all as old as it is... so once I'd started using the more wide-field 1.25" ES eyepieces with it, I quickly got spoiled (the two original Celestron Kellners have AFOVs of only 34.4° for the 40mm and 43.0° for the 25mm), and started wondering about the possibility of putting a 2" visual back on it.
Reading Jon Isaacs' post #15 is what convinced me to seriously consider the 2" visual-back project though... because of his mention of the relative light weight of his TeleVue 32mm Wide Field. It also got me thinking that if I had two 2" eyepieces, I'd be more likely to use them... especially with the C8's much shorter moment-arm (hopefully) creating less need for drastic re-balancing. Amazingly, just a day or so later, I found (and bought) a TV 32 WF in excellent condition on eBay... and for a great price!
Of course, attaching a 2" visual-back to the '77 C8 turned out to be every bit as problematic as I'd anticipated (there aren't any currently-commercially-made ones that have the same threading)... but thanks to input from C-N member "B l a k S t a r", I was able to accomplish it.
Back to the long-focal-length wide-field eyepieces... it turns out that the ES 40mm 68° and the ES 30mm 82° are almost identical in size and weight. Here's a relative-size comparison, between the three:
ES 40mm 68° -- Length: 130mm, Width: 80mm, Weight: 35.2 oz
ES 30mm 82° -- Length: 131mm, Width: 82mm, Weight: 35.5 oz
TV 30mm 65° -- Length: 100mm, Width: 55mm, Weight: 17.6 oz (Half the weight of the other two)
... and here's what the ES 40mm and the TV 32mm look like, side-by-side:
Best of all, the clouds and rain actually held off here for a couple of days, so last night I was finally able to put my efforts to the test... and it was a resounding success! As I'd hoped, the whole balance/re-balance/re-re-balance issue disappeared, due to the C8's shorter tube. I was able to switch back-and-forth from using the heavy 2" eyepieces to the lighter 1.25" ones without having to re-position the counterweights at all!
But aside from the balance issue... the biggest question in my mind had been whether or not I'd end up having unacceptable vignetting with the 2" eyepieces, due to the older C8's rear opening not having been designed for use with them. Much to my surprise and delight, there was none!
And the wide-field views through the C8 with the 40mm (68° AFOV) and the 32mm (65° AFOV) are so much more immersive. Absolutely wonderful.
So THANKS for the tip on the TV 32mm WF and its "Big Easy View", Jon!