William Optics 1.25 Erecting Prism Diagonal

[astro mick]

Hi.

If anyone uses the above William Optics Diagonal with a refractor scope,do you find you get a bright spike either side of a bright Star.

I am finding this on a new diagonal,and wondered if it was the norm.

Cheers.

Mick.

[Louis D]

Yes, I have heard that this is the norm due to the roof edge in the Amici erecting prism causing a diffraction spike.  It's also my understanding that a porro prism or pentaprism would not cause a diffraction spike.

[Chris]

Hi Mick, I've not long sent one of those diagonals back as it showed stars as a bright vertical line with a red dot either side, kind of like a division sign turned 90 degrees. This was with my Tak fs60 f/5.9. Great built and helical focuser but terrible image quality I found with my example at least.

[Peter Drew]

To be fair, these diagonals are meant for terrestrial viewing where the roof prism diffraction spike won't show.

[astro mick]

9 hours ago, Peter Drew said:

To be fair, these diagonals are meant for terrestrial viewing where the roof prism diffraction spike won't show.

You are proberbly right Peter,but the description does.nt really make this clear, which if designed for daytime viewing it should say so.

Mines going back.

Mick.

 

Thanks for the comments guys.

Mick.

[Peter Drew]

12 hours ago, Louis D said:

Yes, I have heard that this is the norm due to the roof edge in the Amici erecting prism causing a diffraction spike.  It's also my understanding that a porro prism or pentaprism would not cause a diffraction spike.

A Porro prism is a "spike free" arrangement but won't give you the angled benefit of a diagonal, where are they now?, they used to be a poular item years ago. A Pentaprism is a constant deviation prism, it will give an angled viewing position as per a PST which employs one, however it doesn't alter the input orientation so in use it maintains the original astronomical orientation.

[Louis D]

6 hours ago, Peter Drew said:

A Porro prism is a "spike free" arrangement but won't give you the angled benefit of a diagonal, where are they now?, they used to be a poular item years ago. A Pentaprism is a constant deviation prism, it will give an angled viewing position as per a PST which employs one, however it doesn't alter the input orientation so in use it maintains the original astronomical orientation.

What about about two diagonals at 90 degrees to each other?  The first would flip left for right while the second would flip top for bottom, or am I missing something?  Would that yield the 180 degree rotation needed for a refractor image to correctly orient it?

[LukeSkywatcher]

19 hours ago, Peter Drew said:

To be fair, these diagonals are meant for terrestrial viewing where the roof prism diffraction spike won't show.

Good to know. I was just thinking of buying one. 

[25585]

Got one last week. Must try it out, but it was meant for spotting purposes as I have an astro diagonal as well.

[Alan64]

For those who wish for their maps and charts to match what they're seeing through an ocular, at night, then yes, a penta-prism seems to be the new ideal...

https://www.amazon.co.uk/Orion-52055-1-25-Pentaprism-Diagonal/dp/B07C85Z8V4

I saw that one, the only one I believe on the market at present, and just the other day... https://www.youtube.com/watch?v=mJEl6Rba_VU

Would that the presenter had had a wee screwdriver handy, then to take out the prism and exhibit it.

It's likely made by either GSO, or Synta; the former I'd wager.  The port, where an ocular would be inserted, its stop looks to be narrowed, and similar to that of this 90° GSO Amici that I have...

 ...with its Amici-line visible, and as the camera revealed.  The line wasn't visible to the eye at the time.

The clear aperture of my GSO is 20mm; that of the penta-prism: 29mm, and most generous for an erect-image diagonal.  Still, the presenter didn't tilt it quite far enough to see its full aperture, there where an ocular would be inserted, and either unwittingly or intentionally as the case may have been.  It may be narrower on that end.  Perhaps they'll drop the price a bit in future...

 

 

[Peter Drew]

I think this will give a corrected image only when used in conjunction with the Orion Premium binoviewer. With just an eyepiece the orientation will still be upside down and back to front. 

[FLO]

On 29/06/2018 at 23:16, Peter Drew said:

To be fair, these diagonals are meant for terrestrial viewing where the roof prism diffraction spike won't show.

 

On 30/06/2018 at 08:35, astro mick said:

You are proberbly right Peter,but the description does.nt really make this clear, which if designed for daytime viewing it should say so.

Sorry to hear you were disappointed. Our product description has been updated ?

William Optics 1.25" 90 degree Erecting Prism

[Stub Mandrel]

The one that came with my Celestron C90 doesn't do this, at least not that I have noticed.

[25585]

23 hours ago, Peter Drew said:

I think this will give a corrected image only when used in conjunction with the Orion Premium binoviewer. With just an eyepiece the orientation will still be upside down and back to front. 

That is correct. The YT videos I linked to in my thread on the Orion and TS bino viewers, explains that.  

[Paz]

I've one of these and the line across small bright objects is normal. I use this diagonal the majority of the time as I prefer the correct image orientation. If I want the best view I switch to a mirror diagonal or a Tak prism diagonal but then I have the confusion of a flipped image.

The WO diagonal is a good one, the line is not a quality issue.

On the moon and on fainter stars I don't notice it, it is only noticeable on planets and brighter stars.

[markse68]

Does anyone know or mind measuring the clear aperture of this prism for me?

Thanks,

Mark