my fav from that thread (and i propose to make this a copy pasta):
My entire gripe around these scopes is the instruments being offered today, the sub-aperture lens arrangement is not doing any corrections. The lens is a straight up Barlow, nothing more.
If you look at the Bird-Jones design, the design is very specific in the design of both the primary & correcting lens. This means that both elements need to be not only matched but also well manufactured in order to work as designed. When you then look at the few true Bird-Jones instruments that were manufactured, such as the Tasco 8V (which was manufactured by Vixen), the Celestron G8-N and one other (escapes my mind right now but I’ll add it when I remember), these scopes were not cheap but pushing flagship status for these brands & supplied with swish mounts. And none of these scopes can be readily collimated by the end user as the alignment of the optics is so precise it is done in-factory. The 8V alone still maintains almost cult status.
The Bird-Jones design is not without its own shortcomings. It is not perfect without aberration. It is important to remember the ideas behind its design, to provide a short tube OTA option with what was able to be readily manufactured at the time, that being good spherical mirrors.
What is made today is a far cry from what a Bird-Jones offers performance wise. Made cheap with a poor spherical primary & that they are totally collimateable by the end user shows these are not a precision scope. Add to this that not a single Bird-Jones instrument is to be found anywhere else besides these cheap things. Doesn’t this say something?
These cheap instruments, really all cheap instruments are a double edge sword. They make astro more accessible, yes, but their poor quality ends up killing off more people’s enthusiasm for astro than firing it up. Add to this that for many novices if the mount is not a complicated equatorial one then it isn’t an astronomical instrument, & the difficult manner of using a wobble-tron mount & tripod with the mental gymnastics required just too much for most people who buy these and just give up way too soon.
Yes, there will be a few people who will be able to make these scopes work, being all they can afford, and all power to them. I will support such persons. But these are very few compared to the overwhelming number of people who just give up after the poor experience they get from these instruments. Too them astro is just all too hard, and mainly because of a poor instrument.
Call these cheap instruments what they are, a barlowed Newtonian.
dogsnest