7 replies to this topic

[Tom Duncan]

Got these two matching oddball 45 degree prism diagonals a while back, can't seem to find any info on them via an internet search. I posted about these here on CN some time back but can't seem to find it now.

 

The designations on them are what look to be an image of a Kiwi (as in the New Zealand bird) and "ATM". 

 

The 'oddball' part is the image through a common achromat refractor is correct left/right but upside down. Every 45 degree diagonal prism I've run across is correct left/right and right side up. What would be the application for this design?

Anyone know anything about these? 

 

Tom Duncan 

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[Jon Isaacs]

I wonder if they were designed to use with a Newtonian...

 

Jon

[Rich V.]

Instead of the standard Schmidt roof prism, these appear to be half-penta prisms which create a 45° deviation in the light path but without the image inversion of the Schmidt prism.

 

You can see the different prism designs here:

 

https://www.edmundop...optical-prisms/

 

Rich

[Tom Duncan]

Instead of the standard Schmidt roof prism, these appear to be half-penta prisms which create a 45° deviation in the light path but without the image inversion of the Schmidt prism.

 

You can see the different prism designs here:

 

https://www.edmundop...optical-prisms/

 

Rich

Why would this be a wanted aspect? The Edmund page says the single application is "Pechan Erector Assemblies", an internet search of which left me confused. 

 

Tom 

[jimr2]

Tom,

 

Well, if you do live in CA--i.e., the Northern hemisphere--and if these were made in New Zealand (the kiwi logo), then of course the image is upside-down, as as everyone knows, everything is upside down down there in the southern hemisphere from what it is up here in the north (ha ha)!!

 

-jim-

[Rich V.]

Why would this be a wanted aspect? The Edmund page says the single application is "Pechan Erector Assemblies", an internet search of which left me confused. 

 

Tom 

Tom, that type of prism is most commonly used as half of a Schmidt-Pechan prism assy used in most roof prism binoculars, so I understand the application in a two prism "Pechan erector assy", but I see no practical use for one by itself with a telescope.  

 

Rich

[Tom Duncan]

Tom, that type of prism is most commonly used as half of a Schmidt-Pechan prism assy used in most roof prism binoculars, so I understand the application in a two prism "Pechan erector assy", but I see no practical use for one by itself with a telescope.  

 

Rich

I'm of the same opinion Rich, I can't imagine why I'd want to use such a prism for astronomical use. However  as they are 1.25" and .965" they clearly were aimed for that. That's why I posted this thread...hoping someone can enlighten us. 

 

Tom 

Edited by Tom Duncan, 05 July 2022 - 08:36 PM.

[Rich V.]

It  did enter my mind that forks used to the inverted Japanese style straight-through viewing w/o diagonal could "cheat" for the sake of their sore necks by using one of those diagonals.  I know my neck would want the relief.  

 

Rich