Bird-Jones mirrors

[jjjnettie]

Bird-Jones This is a modified Newtonian with a spherical primary mirror. Before the light strikes the flat after being reflected, it passes through a Barlow-like achromatic lens that corrects the spherical aberration of the primary mirror. The system is also corrected for coma

This is the only information that I've been able to find on this style of reflector. Has anyone here had any experience with them? Would you reccomend them? :help3:

Thanks in advance,
Jeanette

[Roger Davis]

Hey J,
You wanting to make one or buy one?
First there is the JOnes Focal corrector spot diagrammes on axis and off-axis are quite a lot larger than the Airy disc. Improvement was made with the Brixner focal corrector where the spot diagrammes are great for red and blue light, but the green suffers bad aberration at 20mm off axis.
When the Jones-Bird came along, it is air spaced doublet, the spot diagrammes were reduced to within the Airy disc for on-axis, but spread out to 20 times the size only 10mm off axis. Axial colour on the J-B is good, but suffers from astigmatism and field curvature.
You could use this telescope quite well for planetary views and some stellar views, after all the eye can accommodate some aberration.
A combination of Erfle eyepieces and the J-B telescope works well as the eyepiece corrects some fo the aberrations present (see Telescope Optics by Harry Rutten & Martin van Venrooij).

[avandonk]

Sounds like a Newtonian version of the Tal 200k design. Be difficult to align and or collimate.

Bert

[Roger Davis]

'tis, 'tis. The spot diagrammes show an incredible spread once you get only 2-3 mm off-axis.

[dhumpie]

I think I have seen some commercial ones on a chinese dealers web site. Wonder how good the views are...

Darren

[jjjnettie]

I've been asked if I want to buy one or if I knew of anyone that would be interested in it.
It was originally bought for about $2000 but he wants to sell it for $1000.
I'd rather buy an Argo Navis for the dob though at that price.
I thought that collimation would be a bit hairy with this sort of setup. I've not looked through it to be able to say how it compares with a straight newt.
Thanks for the info.

[dhumpie]

Argo Navis sounds better since you have a dob ;)

Darren