Circle T prism diagonal

[nightfisher]

I see there is a circle T 1.25 90 degree prism diagonal on ABS, are these any good so would it be worth getting this as apposed to a newer mirror diagonal, i have to keep "borrowing " the diagonal from my Tal for the TS 80, so would like one to leave on it 

[Saganite]

Hi Jules,

I recall that Dave F15 RULES did a fine report  for this forum on these, but when and where it is I cannot say.

[Saganite]

Sorry Jules, just remembered it was a Takahashi prism 

[Chris]

I've read that prism diagonals are really good for long focal length scope, but can exagorate CA in shorter focal length scope. I've only ever used my Tak Prism in an f/17 scope so I can't say from experience.

I guess you could use the Circle T diagonal in your Tal, and the Tal diagonal in the 80mm if you still wanted to get it?

[nightfisher]

Maybe for the time being i will keep to "loaning" the Tal one, i do have a rather nice 2" dialectric that works well in the Tal

[dweller25]

I use the same circle T prism diagonal and a Meade prism diagonal in my F/8 refractors and F/15 Mak - both are superb - very sharp and very low scatter.

 

 

[F15Rules]

Hi Jules,

The Circle T prism is nice. It's well made and solid. The only thing I don't like about them is that they use the old fashioned single set screw (that's just what they did in those days), and the screw is quite small. So, a) it can make small marks on your eyepiece barrel and b), probably more importantly, you might not want to hand any heavy, large 1.25" eps on it (I'm thinking for example of an ES 24mm 68 or Meade UWA 14mm) - although your little orthos would be absolutely fine.

Steve (Saganite) mentioned the Tak prism, and it is superb, I know Roy, Derek (DRT), and Chris Lock to name but a few have them. I used to have one and was very impressed with it. Again, for smaller eps, the rotating locking mechanism on the Tak is excellent.

Another superb prism is the Baader T2 32mm. I should declare I am selling one of the two I have, over on UKABS, but if funds permit you at some point they are superbly built, and can use both 2" and 1.25" nosepieces (the prism has a full 32mm aperture) and have a focusing helical eyepiece holder on the eyepiece side, which gives you 5mm of very fine focus, ideal for high power use.

I use one on my Vixen ED103s which is F7.7. I have heard that the prisms can induce a little CA at less than F7, but I've certainly not seen any at F7.7 :-).

Hope that helps Jules,

Dave

[nightfisher]

Thanks for the replies, like i said i think i will keep with the Tal one for time being, but you have me thinking about the Baader unit now

[AndyH]

A good quality prism is a fine item to have in the kit box. Scatter is reduced, I've noticed it when comparing diagonals. Plus they 'use up' less of the available focus. Rather handy for those with scopes that are a bit ticht for infocus.

There's a certain someone we both know selling a Baader prism(32mm c/a) with T2 fittings. I think it has the rather clever 1.25" low profile helical micro focuser/ep cup. Would in effect give your Tal single speed focuser a fine focus option. Obviously not as cheap as the circle T, but with T2 threads has various nose and cup options.

Lolol. That certain someone has just replied to this thread.

 

Andy.

[AndyH]

That helical fine focuser is something I've long been considering for my scopes, none of which have a 2 speed focuser. A shed loads cheaper than changing focusers, as all mine are rather decent as is, but this item intrigues me, as I can screw it onto my big Tak prism.

I do like clever little bits of kit

[nightfisher]

I have caved in and bought the Circle T, the price got reduced a few times to a point where it was silly not to buy it

[F15Rules]

An utter, silly, crazy bargain Jules!:-)

Dave

[nightfisher]

6 hours ago, F15Rules said:

An utter, silly, crazy bargain Jules!:-)

Dave

Yes, it just had to be worth a punt at that price, it will live in the TS 80 f7.5....happy days just need some good skies, hoping to go camping at Usha gap in Easter so this will be the big field trial for this scope under super dark skies

[nightfisher]

A little update, i rather liked this circle t diagonal prism, but i accidentally left it with a scope i sold on, the CR4 oops, but i found a replacement on astroboot so have ordered it for my little 102 Maksutov that is getting a few upgrades