I'm coming at this as a casual birder and lazy binocular astronomer who appreciates good optics. I just want to see more of everything - better than I can see it now in 10x bins. I live in semi-rural Idaho with pretty dark skies in my yard (Bortle 4-5). I also enjoy camping in the Owyhees which are DARK. A big dob would be super fun here. Yet, the small refractors are wooing me with their grab-n-go-ness and their robust portability. I fear dragging a dob out of the garage, collimating it, then letting it cool for 30-60min would be a deterrent (I am lazy and always have other things I should be doing). I also fear trying to take a 8" dob camping would be a bulky, dusty hassle and possibly damage the scope. ("Camping" = miles of washboard followed by miles of off-roading.)
Thus the appeal of the sleek little refractor...
A few thought's/experiences:
- You do not have to wait any time at all for a Dob to cool down. If you want it's best possible views of the planets at high magnifications, it's best. But for viewing the deep sky, it's unnecessary.
- As others have said, an 8 inch Dob would show you far more than an 85 mm refractor, it's really a different world. Globular clusters like M13 show a myriad of tiny stars instead of being a fuzzy blob. Galaxies begin to show some detail, planetary nebula come alive.. The larger scope captures 5 times as much light and has more than twice the resolving power.
- If you do decide to go with a small refractor and a small refractor is certainly a viable option, I have several I frequently use, I would look at more possibilities than just TeleVue.
I have a TeleVue NP-101 which is a unique scope and a fine scope for deep sky as well as all around observing. It's a 4 element dual ED modified Petzval, it has excellent color correction as well as flat field, stars at the edge of a wide field view and stars at the center of the field are in focus simultaneously. That is not the case with doublets like the TV-76 and 85 nor it is true with triplets. The NP-101 is about $4000. The competition is from Takahashi, it costs $6400..
If I were looking for another small high quality ED/apo refractor, the TeleVue 76 and 85 would not be on the list. They are very nice scopes but there are scopes as good, scopes that are better, that are less expensive. A TeleVue 76 is $1700, an 85 is almost $2200. Mention has been make of an ST-80. This is the other end, I have an ST-80 fitted with a 2 inch focuser because it's capable of views my more expensive apo/ed refractors cannot provide.
But more importantly, there is a lot of middle ground, the $400 Astro-Tech AT-80 ED will provide views that are nearly as good as the TeleVue scopes. Spending some more, $900 buys the 80mm EDL with the same or better color correction than the TeleVue scopes, a guaranteed Strehl ratio of 0.95, very nice mechanicals, the focusers are excellent.
And I would also be looking at scopes larger than 85mm. a 4 inch refractor is a handy size, a little bigger than the 80mm class refractors but still very portable and handy while taking the performance level up a notch. The Astro-Tech 102ED is $600, the 102EDL is $1100. It has the same quality optics as the 80mm AT-80 EDL.
I am using the Astro-Tech scopes because I know them but there are other vendors, that offer similar scopes at similar values. TS optics in Germany is one. And too Astro-Tech is the house brand for Astronomics, the people who pay all the bills to support Cloudy Nights.
https://www.astronom...anufacturer=360
And don't forget a diagonal, a mount and some quality eyepieces. I look at a scope like my William Optics 80mm F/7 FD.. I've had it for fifteen years plus, I bought it used but new it was around $700 at the time. It has very good optics, I would say they rival the TeleVue pair. It seems like a very nice scope for a $700 investment. But then I step back and look at the total investment that is providing those views. I have a 2 inch TeleVue Everbrite diagonal.. If I bought it today, that would be $400. An Astro-Tech diagonal would be $120. And the mount, a Vixen Portamount is a good mount for an 80mm, that's $300.
And then there's the eyepieces. TeleVue is known primarily for it's eyepieces, not for it's telescopes. How much have you budgeted for eyepieces? When I look at that $700 80mm refractor, it is being supported buy several thousand dollars worth of TeleVue eyepieces.. It's not just a $700 investment.
Back to the 8 inch Dob for a minute, the Dob does not need a diagonal, it has a mount, and it might be $600 for a scope that that will outperform any of these refractors on any object that fits in the field of view..
If you do decide to go with a refractor, there are many, many good one's out there.
Jon