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Interesting Takahashi .965" Prism Diagonal w/Odd Scale

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#1 Tom Duncan

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Posted 18 June 2019 - 08:42 PM

What looks to be a Takahashi made 90 degree .965" prism diagonal with some sort of lockable rotating dial on the EP side with markings for 360 degrees, like a setting circle. What would be the purpose for this?

 

I'm assuming this to be Takahashi because of the collet type EP retainment and its identical in design (except for the scale and the size) to the 1.25" Tak prism diagonal that I use with all my refractors. The diagonal is unmarked as to maker or country of origin.

 

Tom

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Edited by Tom Duncan, 19 June 2019 - 03:30 PM.

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#2 Brett Waller

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Posted 18 June 2019 - 09:16 PM

I don't know what it was made for, but it would be very handy for determining position angles for binary or multiple stars. Paired with an eyepiece with a reticle and it would be a useful tool.

 

Brett  



#3 Astrojensen

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Posted 19 June 2019 - 03:06 PM

I don't know what it was made for, but it would be very handy for determining position angles for binary or multiple stars. Paired with an eyepiece with a reticle and it would be a useful tool.

 

Brett  

It's too coarse for anything else than a rough estimation. I've been unable to find it in the Takahashi catalogues I have access to online. Never seen one of these before. 

 

My first thought was that it was a camera rotator (for better framing of objects) but the narrow 1.25" aperture makes that idea questionable. 

 

 

Clear skies!
Thomas, Denmark



#4 Tom Duncan

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Posted 19 June 2019 - 03:12 PM

I failed to mention in the description that this diagonal is .965", since edited into the original post. 

 

Tom 


Edited by Tom Duncan, 19 June 2019 - 03:30 PM.


#5 Astrojensen

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Posted 19 June 2019 - 03:42 PM

That just makes it even more unlikely that it's a camera rotator. 

 

 

Clear skies!
Thomas, Denmark



#6 Esso2112

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Posted 20 June 2019 - 09:51 AM

I have the same diagonal. The ring rotates, but the eyepiece doesn’t. Mine came with a reticle eyepiece. It may have been for measuring angles, but I honestly don’t know. There is little info on it out there. Very good prism diagonal though.

#7 Tom Duncan

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Posted 20 June 2019 - 06:00 PM

Agreed, a very good prism, significantly reduces CA in achromats. I got two of the standard .965" TAK prisms in this lot and they are now permanent members of my .965" kit. I'm a Gemini so two of everything is normal for me. 

 

Tom 


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#8 junomike

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Posted 22 June 2019 - 09:56 AM

I recall seeing something like this before.

EDIT:  Here and near the bottom Here.



#9 Tom Duncan

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Posted 22 June 2019 - 11:04 AM

Excellent Mike, those two links brings us much closer to understanding my diagonal.

 

So this is designed to tell one what the angle is of double stars. 

 

So how does one actually use it? Estimate what point on the circle the EP reticle crosshair is pointing at?

 

Tom



#10 Astrojensen

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Posted 22 June 2019 - 02:38 PM

The problem is that the scale on the Tak diagonal is WAY too coarse to be useful for measuring the position angle of double stars.

 

 

Clear skies!
Thomas, Denmark



#11 TxStars

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Posted 04 July 2019 - 11:58 PM

The diagonal is used in conjunction with an Astrometric Eyepiece to help determine a position angle.

 

 

https://wsaag.org/im...inary_stars.pdf



#12 Astrojensen

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Posted 05 July 2019 - 09:55 AM

The diagonal is used in conjunction with an Astrometric Eyepiece to help determine a position angle.

 

 

https://wsaag.org/im...inary_stars.pdf

No, this can't be the case. I've already pointed out that the scale is WAY too small and too coarse to be useful for that. And there's only two astrometric eyepieces ever produced that I'm aware of and both are 1.25" (Meade and Celestron/Baader Planetarium). 

 

 

Clear skies!
Thomas, Denmark




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