17 replies to this topic

[Andrea Salati]

Assuming the two diagonals in the first picture are the same, with the nosepiece/thread adapter being the only factor differentiating them, does anyone know the length of their light path?
I need to know the distance A-B and, more important, A-C.

Thank you in advance.

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[davidgmd]

From Agena at https://agenaastro.c...r-diagonal.html
 

 

Optical path length (as measured by Agena) = 105mm in 2" mode, 113mm with included 1.25" eyepiece adapter

[Andrea Salati]

From Agena at https://agenaastro.c...r-diagonal.html
 

This is embarrassing. Another senior moment, I guess. I was convinced I had read and re-read carefully their page.

Thank you!

[edit] I actually did but I focused on the one currently available and I do not see it there. But maybe I am having another moment! =)

Edited by Andrea Salati, 24 June 2023 - 04:54 PM.

[davidgmd]

No worries, we’ve all done it. Just ask my wife.  I’m hoping for a long history of senior moments.

[25585]

They are useful if you want to use a TSFlat2 visual flattener with a refractor.

[Andrea Salati]

That is indeed the reason why I was searching for that piece of information.

[davidgmd]

They are useful if you want to use a TSFlat2 visual flattener with a refractor.

 

 

That is indeed the reason why I was searching for that piece of information.

  
I just went through the same exercise. Diagonal optical path lengths do not include the nosepiece which inserts into the focuser.

 
If the nosepiece is not removable and the TSFLAT2 screws onto the end of the nosepiece rather than directly onto the diagonal body, add the length of the nosepiece to the diagonal optical path when calculating the distance from the M48 thread to the corrector (or eyepiece in my case).

[Andrea Salati]

I know and I am set with the OTA I bought the field flattener for but I am on the market for a diagonal for a new purchase and, even if I do not think the field flattener will be beneficial with that telescope, I want to keep the door open to trying.

[davidgmd]

I know and I am set with the OTA I bought the field flattener for but I am on the market for a diagonal for a new purchase and, even if I do not think the field flattener will be beneficial with that telescope, I want to keep the door open to trying.

  
 
 

The Baader diagonals are versatile that way. What I ended up with to optimize the flattener.

[Andrea Salati]

Currently the TSflat2 lives attached to a Baader diagonal, with a spacer to fine tune the setup. I love (certain, not all of them) Baader products. You are preaching to the choir.
"Sadly", the manufacturer's specs and the impressions of at least one fellow observer here who has done exactly what I plan to do, i.e. test the flattener on a telescope way out of the flattener's optimized range of focal lenghts, tell me I should keep the door open to the possibility but not base everything on that.
It is more of an experiment than anything else.
But, as luck would have it, a friend reached out and offered a used diagonal for the test, so I may be able to do things in steps. We will see.

[davidgmd]

Looking forward to your impressions Andrea. Real world experience is a most valuable addition to published specs.

[Andrea Salati]

Agreed but impressions are also very subjective so I recommend you always take mine with a grain of salt!

[thecelloronin]

Why is this mirror so much shorter than the typical 112mm you see for mirrors? Or does that 112 figure typically include the 1.25” adapter?

[Oldfracguy]

Why is this mirror so much shorter than the typical 112mm you see for mirrors? Or does that 112 figure typically include the 1.25” adapter?

Yes, it does include the 1.25" adaptor.  If you have a simple 1.25" eyepiece like a Plossl where its Field Stop is at the shoulder where the barrel rests atop the 1.25" eyepiece adaptor, the current 2" WO Dura-Bright will have an optical path length of 112 mm.  In 2" mode with a 2" eyepiece its optical path length will be about 105 mm.

Edited by Oldfracguy, 07 May 2024 - 09:31 PM.

[RichA]

Assuming the two diagonals in the first picture are the same, with the nosepiece/thread adapter being the only factor differentiating them, does anyone know the length of their light path?
I need to know the distance A-B and, more important, A-C.

Thank you in advance.

Only diagonal apart from a Lumicon silver coated unit that I've seen the coating deteriorate.

[Oldfracguy]

Only diagonal apart from a Lumicon silver coated unit that I've seen the coating deteriorate.

 

   Was that the older WO diagonal, or one of these newer dielectric mirror diagonals?

Edited by Oldfracguy, 09 May 2024 - 08:59 AM.

[Oldfracguy]

I needed to clean the mirror on my 2" William-Optics Dura-Bright 99% Reflectivity Carbon Fiber Dielectric Mirror Diagonal,

 

 

 

and that gave me the chance to get inside and measure the actual Clear Aperture.  Here is the best of several pictures I tried to take:

 

 

 

Without having to hold up the diagonal, ruler and camera at the same time, I measured a Clear Aperture of 43 mm.

 

 

 

 

 

 

 

 

[Procyon]

Assuming the two diagonals in the first picture are the same, with the nosepiece/thread adapter being the only factor differentiating them, does anyone know the length of their light path?
I need to know the distance A-B and, more important, A-C.

Thank you in advance.

 

PS> I noticed an 17mm ES 92 which has it's field stop right on the flange or shoulder therefore adding 0mm to the optical length. That leaves me with 6mm of infocus left on my 100mm/f6 refractor when using a 2" Baader Clicklock that has an optical length path of 112mm.. I'm trying to get a 25mm ES 100 to come to focus, it needs 10.2mm of infocus. Am I correct to assume a 2" WO Diagonal with 105mm optical length will allow the ES 25mm 100 to come to focus? 

 

6mm (remaining infocus) + 7mm (Optical Length reduction from the WO vs the Baader) = 13mm of new infocus? Am I calculating all this stuff correctly?

 

Any help would be appreciated, thanks. 

Edited by Procyon, 29 April 2025 - 08:47 AM.