Prism diagonal

[wookie1965]

I have just bought one of these, https://www.firstlightoptics.com/diagonals/celestron-90-prism-diagonal.html?_gl=1*ghbf8m*_up*MQ..*_ga*OTA5MjI1OTE4LjE3MTI5MTI1MDU.*_ga_F6VGWQ0MW9*MTcxMjkxMjUwNC4xLjEuMTcxMjkxMjUxMC4wLjAuMA..&gclid=CjwKCAjwt-OwBhBnEiwAgwzrUiuYxdFUAt2dmCpCht4Daqu6B6i3Zy-ERji0hSlwXiWDEo-3z1o-jhoCh1UQAvD_BwE

The reason is I have been told that the light path is shorter so I will gain 10-12mm extra in-focus on my Vixen 102M. 

Has anyone used one or has one can tell me the difference in views are please. 

Paul 

[Mr Spock]

I don't have one of these but I do have an older Celestron 45° erect image prism. It is surprisingly good.

[John]

What diagonal have you been using up to now Paul ?

The 10-12mm of in focus gain that I mentioned was compared with an Altair 1.25 mirror diagonal, like this:

 

Edited April 12 by John

[wookie1965]

16 minutes ago, John said:

What diagonal have you been using up to now Paul ?

The 10-12mm of in focus gain that I mentioned was compared with an Altair 1.25 mirror diagonal, like this:

 

Hi John it's this one not got a name on it but it's a mirror diagonal. 

Paul 

[John]

The prism should compare similarly to your mirror diagonal as it does with mine.

I really hope so anyway 🤞

Have you any idea how many mm of inwards focuser travel you need to gain to get the 3-8 Svbony zoom to focus ?

 

Edited April 12 by John

[wookie1965]

1 hour ago, John said:

The prism should compare similarly to your mirror diagonal as it does with mine.

I really hope so anyway 🤞

Have you any idea how many mm of inwards focuser travel you need to gain to get the 3-8 Svbony zoom to focus ?

 

Probably about 2/3mm 5mm at most hopefully. 

[Naughty Neal]

21 hours ago, wookie1965 said:

Hi John it's this one not got a name on it but it's a mirror diagonal. 

Paul 

Looks pretty much like a generic diagonal seen for sale in various places  , the side panel fluting looks the same as a Skywatcher or Stellamira. 

[John]

On 12/04/2024 at 19:29, wookie1965 said:

Probably about 2/3mm 5mm at most hopefully. 

I've been doing some measuring for you Paul.

I'm using my Tak FC100 so the focuser position at focus is not the same as your Vixen but the difference between using the 2 diagonal types should be the same. 

1st photo shows the 1.25 mirror diagonal (similar to your current one) with the Svbony 3-8 zoom at 3mm which is the setting that needs the most inwards focus. The eyepiece is at sharp focus on a star in Leo.

2nd photo shows the exactly same as above but using the Celestron 1.25 prism diagonal. You can see the additional in-focus gain that the prism gives which I measured at 15mm.

Hope that helps reassure you 🙂

Edited April 13 by John