Mystery Tasco Scope!

[Rick Parrott]

I'm hoping that one of you good people can assist with this telescope that a colleague at work asked if I could take a look to see about the fuzzy image.
It's a little Tasco Catadioptric which at first glance looks like a normal reflector, but it has the glass at the top as well as a mystery little gizmo that seems to flick out a small mirror into the tube.


Details: Tasco 13T, D=4.5", F=1000mm, f / 8.7
It is quite solidly built, all metal (even the dust cap!), I think it has an equatorial mount.

Can I collimate this like a normal reflector?
What the heck is the gizmo on the side for?
Any other thoughts/comments?

[julianh72 (Julian)]

It looks like you've got a Tasco / Tanzutsu / Nocom / Towa / Insert-Brand-Name-Here "Catadipotric Newtonian":
http://www.cloudynights.com/topic/18...have-i-bought/

It seems the front glass is just a flat "window" (not a corrector), which mounts the secondary without a spider, and also acts as a permanent dust cover. There is a built-in Barlow in the focuser, and the flip-out mirror is the built-in viewfinder - flip the mirror into the tube to use the finder, flip it clear to use the main focuser.

Optical reviews are - well, let's just say they're not great!

[julianh72 (Julian)]

A bit more googling suggests it is technically called a Jones-Bird Newtonian:
https://en.wikipedia.org/wiki/Newton...ope#Jones-Bird

A Jones-Bird Newtonian telescope (sometimes called a Bird-Jones) is a mirror-lens (catadioptric) variation on the traditional design sold in the amateur telescope market. The design uses a spherical primary mirror in place of a parabolic one, with spherical aberrations corrected by sub-aperture corrector lens[20] usually mounted inside the focusser tube or in front of the secondary mirror. This design reduces the size and cost of the telescope with a shorter overall telescope tube length (with the corrector extending the focal length in a "telephoto" type layout) combined with a less costly spherical mirror. Commercially produced versions of this design have been noted to be optically compromised due to the difficulty of producing a correctly shaped sub-aperture corrector in a telescope targeted at the inexpensive end of the telescope market.

[Rick Parrott]

Julian, that was amazingly quick response, thank you!
I will give it a clean and check it with some of my eyepieces (it only has a Huygens 20mm with it), and perhaps collimate if possible.