"This new learning amazes me!" - King Arthur to Sir Bedevere from Monty Python and the Holy Grail
Got myself a pair of 12.5mm Morphei to go with the Maxbright II and the GPC 1.25 hoping for 200X magnification to duplicate the normal magnification that I use for planetary observation in cyclops mode with the 10mm Ethos. First time out with that I spent a lot of time looking at Saturn and Jupiter thinking to myself that wow things do look bigger in a binoviewer, the illusion of those objects appearing bigger than what I was used to in cyclops mode no doubt created by the binocular summation. Little disappointed that the view was slightly muddy relative to cyclops mode but that's OK because in total the view was easier to take in and study using both eyes. The view reminded be of when I try and go past 200X in cyclops mode with my skies that rarely allow much more that that.
Then it all came into "focus" and I remembered my research into SCTs and binoviewing the concept of operating focal length. Somehow I thought that that only happened to other people why would I have to worry about such things? Certainly my SCT wouldn't annoy me with such considerations because we have known each other for so long and have I have always treated it so well. Once the reality of me not having considered the operating focal length of my SCT with the binoviewer sunk in, the unexpectedly larger slightly muddy view of Saturn and Jupiter in evidence, I obviously needed to rethink planetary eyepiece power. After even more research into this matter it was apparent that the first step was to calculate the operating focal length of my SCT with the binoviewer. There are star drift methods whereby one measures the time it takes for a star to traverse the field of view but that seemed complicated as there are too many moving parts like choosing just the right star at the celestial equator for the math to work out. Then I found what was for me an easier, done in the daytime with no moving parts, method to determine effective focal length based on this article written by Professor Edz:
I started with my Televue 85 which has a focal length on 600mm, which I have verified that mine actually is, to get the baseline measurement. I propped up a measuring tape against a telephone pole down the street extending up from the ground against the pole about 8 feet. I had to use duct tape to attach the measuring tape about 6 feet off the ground so it would not curl and bend down in the slight breeze. My neighbor watched me attach it to the pole next to her mailbox probably wondering what was going on but did not ask. From my yard 100+ yards away the 12.5mm Morpheus showed 79.5 inches of the measuring tape through it at its maximum field of view top to bottom with 48X magnification.
Armed with that information I then did the same thing with the 8" Edge SCT. The 12.5mm Morpheus in my usual 2" Baader BBHS prism diagonal showed 22 inches of the measuring tape and in the binoviewer showed 17.125 inches. Using the 48X magnification provided by the Televue 85 and its 79.5 inch starting point I determined that the actual magnification at the Baader diagonal was 173X and at the Maxbright binoviewer 223X. From that I figured that at the diagonal the system operates at focal length 2163mm (f10.8), and at the binoviewer 2788mm (f13.9). There is a magnification factor increase of 1.08X at the diagonal and 1.39X at the binoviewer. Feel free to correct my math but I checked it several times.
So anyone newly getting into binoviewing, like me who wants to utilize the binoviewer on an SCT, really needs to do this one time calculation of the extra magnification factor provided by the binoviewer on their own telescope by one method or another. My understanding is that that is not necessary on other types of telescopes perhaps someone can add more information here as it might relate to that.
For me, my next course of action is to hopefully be able to exchange the 12.5mm Morphei for 14mm Morphei which should provide 199X, about the original power I had been looking for. I will bet things will look a little smaller but sharper and less, and hopefully not at all, muddy.