Annoyed at my choice failing.

[Chaz2b]

I ‘ve just purchased a Tele-Vue 85 and a TV 55mm plossl 2”, using the supplied 2” everbrite diagonal I don’t have enough back focus! I had to pull the eyepiece back another 15mm ish to get it to focus….terrestrially! My TV  40and 32 plossls are 1.25” and focus is fine, what am I missing? Apart from a few grey cells!

 

chaz

[John]

The field stop of the 55mm TV plossl is close to the end of the chrome barrel to avoid vignetting. It therefore needs a lot more outward focus travel than most other eyepieces.

On terrestrial targets even more outward focuser movement is required to reach focus so that compounds the problem. A focuser extension tube or an eyepiece barrel extender (a better option) will sort the issue out.

The Tele Vue instructions explain this:

https://www.televue.com/pdf/literature/55mm Plossl and 41mm Panoptic.pdf

 

 

Edited May 16, 2021 by John

[Chaz2b]

Thanks for the link John, now I need to source a barrel extender.

chaz

Edited May 17, 2021 by Chaz2b

[Mr Spock]

There's one here https://www.firstlightoptics.com/adapters/tele-vue-2-eyepiece-barrel-extender.html

[Captain Scarlet]

On 16/05/2021 at 21:13, Chaz2b said:

I ‘ve just purchased a Tele-Vue 85 and a TV 55mm plossl 2”, using the supplied 2” everbrite diagonal I don’t have enough back focus! I had to pull the eyepiece back another 15mm ish to get it to focus….terrestrially! My TV  40and 32 plossls are 1.25” and focus is fine, what am I missing? Apart from a few grey cells!

chaz

I never used the 55 I think so was unable to warn you of the problem, hopefully a barrel extender sorts it out!

M

[Louis D]

Better than finding out you don't have enough in-focus to reach focus.  That situation requires finding a diagonal with a shorter optical path length or simply going without a diagonal.

[Chaz2b]

On 17/05/2021 at 08:30, Mr Spock said:

There's one here https://www.firstlightoptics.com/adapters/tele-vue-2-eyepiece-barrel-extender.html

Ha, it should have been “ logical” to have searched there first! Now purchased….Kirk out.

Well it’s arrived, a day earlier than RM said they would deliver! Something wrong there…wow!

chaz

Edited May 19, 2021 by Chaz2b