Telescope Reviews: Kasai pentaprism diagonal

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mercedes_sl1970
professor emeritus

Reged: 12/02/05

Loc: Canberra, Oz

Kasai pentaprism diagonal
#5244785 - 05/28/12 10:21 PM

Hi - I posted this query on another site but have not had any responses.

I was wondering if anyone has had any experience with this pentaprism diagonal from Kasai Trading: Kasai pentaprism

Here's a "better" explanation/translation: Widescreen - Kasai pentaprism

It is stated to have 97% reflectivity which seems rather good for such an arrangement, and with all the benefits of a correct view. However, it only seems to come in 1.25" and has a longish light path (around a 2" mirror diagonal, but that's ok), and is not cheap! Sounds interesting, though.

Andrew

Post Extras:

GlennLeDrew
Postmaster

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada

Re: Kasai pentaprism diagonal new

[Re: mercedes_sl1970]
#5245052 - 05/29/12 02:09 AM

Interesting that BaK-4 substrate is used. Because of the steep angle at which light strikes the two reflective surfaces, no glass would offer total internal reflectance even on axis, let alone from any off-axis angles. Hence the necessity for high-reflectance coatings on these teo surfaces. Therefore I should think your basic BK-7 substrate would be perfectly useable. It looks like a case of having to address the needless ignorance in the community, where across the board non BaK-4 prisms are seen as inferior.

Nonetheless, reading the description leads me to think this is a very nice diagonal!

Post Extras:

Mark9473
Postmaster

Reged: 07/21/05

Loc: 51°N 4°E

Re: Kasai pentaprism diagonal new

[Re: GlennLeDrew]
#5245115 - 05/29/12 05:15 AM

It looks very interesting Andrew; please give it a try and let us know how it does.
I would be particularly interested if both the nosepiece and the eyepiece holder thread off and a T2 thread happens to lie underneath.

Post Extras:

mercedes_sl1970
professor emeritus

Reged: 12/02/05

Loc: Canberra, Oz

Re: Kasai pentaprism diagonal new

[Re: Mark9473]
#5245282 - 05/29/12 09:27 AM

Thanks for the comments. Will have to mull this over, and ask the standard and somewhat redundant question of whether I "really need" another diagonal... Sigh.

Andrew

Post Extras:

Mark9473
Postmaster

Reged: 07/21/05

Loc: 51°N 4°E

Re: Kasai pentaprism diagonal new

[Re: mercedes_sl1970]
#5245752 - 05/29/12 02:25 PM

Yes you do!

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Astrojensen
Post Laureate

Reged: 10/05/08

Loc: Bornholm, Denmark

Re: Kasai pentaprism diagonal new

[Re: Mark9473]
#5245853 - 05/29/12 03:36 PM

It doesn't appear wide enough to have a T2 thread underneath.

We have to persuade Baader that they'll have to make such a prism. With T2 threads, of course.

Clear skies!
Thomas, Denmark

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Mystral
member

Reged: 02/06/09

Re: Kasai pentaprism diagonal new

[Re: mercedes_sl1970]
#5245923 - 05/29/12 04:16 PM

Quote:

... with all the benefits of a correct view.

I have it. It's not a correct view.
Up and down are inverted, and left and right too.
It's like to look through a Newtonian telescope!

Perhaps useful for star-hopping at the eyepiece.
I never use it.
IMHO it's only a rare and esotic accessory.
Perhaps I can use it in my dob and have a correct view

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brianb11213
Postmaster

Reged: 02/25/09

Loc: 55.215N 6.554W

Re: Kasai pentaprism diagonal new

[Re: Mystral]
#5246749 - 05/30/12 03:01 AM

Quote:

It's not a correct view.
Up and down are inverted, and left and right too.
It's like to look through a Newtonian telescope!

Well at least it's not half inverted ... that makes star charts hard to use & is very confusing to beginners. Totally inverted is easy to understand (just hold the chart upside down).

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mercedes_sl1970
professor emeritus

Reged: 12/02/05

Loc: Canberra, Oz

Re: Kasai pentaprism diagonal new

[Re: Mystral]
#5246796 - 05/30/12 05:25 AM

Quote:

Quote:

... with all the benefits of a correct view.

I have it. It's not a correct view.
Up and down are inverted, and left and right too.
It's like to look through a Newtonian telescope!

Perhaps useful for star-hopping at the eyepiece.
I never use it.
IMHO it's only a rare and esotic accessory.
Perhaps I can use it in my dob and have a correct view .

Oops. Helps if I read the description properly!

Andrew

Post Extras:

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