Wow, thanks for the advice you guys. I didn't say so in the opening post so as not to bias the advice one way or the other, but I have been leaning toward the GT81 for all the reasons you all have indicated.
I've mostly been a little worried about the AVX mount. It just doesn't seem to track real super smoothly and I was worried that it's lack of performance would be evident with the added focal length. But every time I go to the WO website, I see that Z103 for the exact same price and I just keep hearing "Bigger is better! Bigger is better!" pounding away in my head like the latest Armin Van Buuren dance music track.
I'm going to definitely be buying the GT81. If I want more focal length I can add a barlow or something.
So I have one last question for those of you in the know about optics...
APO refractors come in doublets, triplets and quads. I've heard that a quad APO is just the same thing as a triplet but with the field flattener built in. My question is whether that is actually true or not?
Bigger is better is a visual thing. It can be true for an imager well down the road, learning will go better if you start small. If your ultimate goal is to image small galaxies with a big scope, you'll get there faster/better/cheaper if you start small.
Quads could be built for a variety of purposes, but getting the field flat is usual. I don't know of a quad that doesn't do that. It's a nice feature, I have a Stellarvue SV100Q. More than a little above your budget.
I've looked at that scope. I can't figure out how they're getting the extra speed out of it. They're using Schott/Ohara ED glass which I've had a hard time getting any detailed information about but I can't imagine that it out performs FPL53 to that extent.
As for their price, it isn't really any more expensive because theirs comes with a field flattener and a canon t-adaptor and some other things that the WO doesn't include in thier base price. When you add all that up, it's actually cheaper and I think its the glass that accounts for it. I only wish I could get a good explanation for their claimed f/5 ratio.
Speed is a matter of design. Faster is harder to build well, and if not done well, you wind up with various optical aberrations. The Esprit has a good reputation.
Get the specs somewhere near where you want them. Short, light, and fast are good, in that order. Set a budget, research, choose a scope. But...
If saving some money on the scope will get you a better mount sooner, that's a serious consideration. AVXs have a very mixed reputation, and there can be disputes. People who got a good one can't fathom why people who got a bad one dislike the mount so much. I have no idea of the relative proportions, there are significant numbers of both.
This is another visual deal. Visual people getting into imaging have a hard time wrapping their brain around the fact that the mount is more important than the mount, deserves more of their budget. Putting a $1650 Esprit on an $800 AVX is a strange idea, you're unlikely to get the value out of the scope. On the other hand, experienced imagers will put a $1000 scope on a $5000+ mount, and it's not a silly thing to do.
It's just not intuitive. Your gut will lead you badly astray on this one. <smile>
The above is all solid information. This is an opinion. Get the cheapest scope you're comfortable with, it will do fine for learning on. This would be a good choice. $469.
Know this. If you were buying everything new I'd recommend one of the $1200 mounts and that 72, over an Esprit on an AVX.
Scroll down to the picture of this very experienced author of this book. That's a $500 refractor (70mm doublet, no longer made) on a $1200 Sirius. He did not make a mistake, using that as an example of a good beginner setup.
Edited by bobzeq25, 20 February 2019 - 09:50 AM.