Focus position BCO vs Televue Plossl

[Moonshane]

Anyone have any idea whether BCOs focus further in or out vs a TV plossl and if so by how much?

Cheers

Shane

[jetstream]

 Shane,I'll go check now at a distant treeline- I''ll do the 25mm TV plossl and the 10mm,18mm BCO... back in a bit.

[Moonshane]

Brilliant thanks Jerry

You can probably guess why lol

 

 

[jetstream]

I set the 90mm up with the Baader prism diag for testing.

On the focuser the 25mm TV plossl gave 5.5cm, the 18BCO gave 5.2cm and the 10BCO 5.05cm.

So the 18mm BCO needs 3mm more infocus toward the objective than the 25mm TV plossl and the 10mm BCO needs 4.5mm more infocus than the 25 TV. I think the BCO's are supposed to be parfocal...

One thing- on my binos I can adjust the holders for the different focus positions between eyepieces- ie the 25mm TV plossls need slight adjustment to bring both barrels in perfect focus together. Doing this really enhances the views..... no matter the method to do it.

Eagerly waiting your reports Shane

[Moonshane]

Cheers Jerry.  I was hoping for a bit more of a difference

With my pst mod I cannot focus with my 18mm bcos and 1.7x gpc but can with the 2.6x but at 145x mag which is a bit high.

Not had a proper go yet though. Might eventually have an adapter made to fit my pst eyepiece holder to t2 as I can then use a baader t2 prism which should do it as I think I would shave off 25mm+