Sorry it's another diagonal thread

[Chris H]

I've purchased my first refractor and I need to buy a diagonal. I will be using my dual skirt Nagler 12T4 and Ethos 8mm ep's can I use these two ep's in a 2" diagonal or will I find the 1.25" barrel hits the mirror?

[Moonshane]

I am sure the Johns (jahmanson / johninderby) must use theirs in 2" diagonals OK but they will confirm I am sure.

[John]

Yep, I use my Ethe (including the 8mm) in a 2" diagonal and they clear the mirror easily. I've not used a 12T4 but I'd imagine it would be the same. Be aware the the 8mm and 6mm Ethe need quite a lot of outward focuser travel to reach focus when used in 2" mode. I tend to use a 2"-1.25" "high hat" adapter with them so that their focus point is closer to my other eyepieces.

[Chris H]

Thanks, I know very little about refractors and their components but I did think that Al Nagler would not have made such a fundamental error.

[John]

Thanks, I know very little about refractors and their components but I did think that Al Nagler would not have made such a fundamental error.

It's worth asking the question - damaging a nice diagonal mirror would be very annoying.

Just for reference, I have a William Optics 2" diagonal and a 2" Tele Vue Everbright so there is no problem with those. I guess it's possible that it may be an issue with a diagonal that had a particularly low profile eyepiece tube.

[Chris H]

All but two of my ep's are Televue is the Televue diagonal best suited to the ep's? Or is the William optics 2" model just the same mechanically?

[johninderby]

The Televue diagonal has better fit, finish and build quality than the WO.

John

[Moonshane]

blimey - it must be good then as the WO is very good too.

[pwalsh61]

If you're concerned about the EP hitting the mirror/prism, how about using a parfocal ring Such as here? I found to my horror that my 6mm EP doesn't have a "shoulder" on it so when I first popped it into my 1.25" - 2" adapter it dropped straight through and hit the prism of my WO 2" diagonal. Fortunately the mark it made appears to be outside the FOV so I consider myself rather lucky.

Parfocal rings are useful if you're doing some webcam astrophotography as, with a bit of trial and error, you can use them so that when you've focused on an object with the EP and then replace the EP with webcam the object should be perfectly in focus.

Well worth having, considering how comparatively little they cost!

[John]

blimey - it must be good then as the WO is very good too.

The TV Everbrights body, eyepiece tube and barrel are machined entirely from a single block of metal so there is no chance of anything unscrewing when you have a really heavy load on board.

I agree about the WO though, thats a nice unit as well

[Rossco72]

The 12mmT4 works just fine in a 2" diagonal.

However if you are going to use a filter you may have an issue. I use 2" filters exclusively and just filter the diagonal if I need to but I suspect a 1.25" filter on the end of my 6mm Ethos or 12mm Nag might hit the mirror.

Cheers

[John]

.... I suspect a 1.25" filter on the end of my 6mm Ethos or 12mm Nag might hit the mirror....

Good point Stuart

I use 2" filters screwed onto the end of the diagonal as well but a 1.25" on the end of the Ethos might just be enough to contact the mirror.

[astro_al]

As previously mentioned a parfocal ring could be used if there is any doubt. The only thing is the set screw for the ring will mark the eyepiece barrel. I have to use one with my Nagler Zoom when using either of my prism diagonals. I unscrewed the tops of both my diagonals then put the eyepiece in to see just how far the barrel stuck out of the bottom. The ring means that the safety undercut isn't used but this doesn't matter to me as I use a compression fitting so it actually works better.

AL

[Moonshane]

for 1.25" ep's I use a baader fine tuning ring on the 2-1.25" adapter.

http://stargazerslounge.com/diy-astronomer/122780-novel-use-baader-fine-tuning-rings.html

[Chris H]

Televue 2" diagonal ordered.