Dielectric Diagonal

[vagk]

Is it worth upgrading the factory Sky-Watcher 2" dielectric diagonal to William Optics 2" dielectric diagonal dura bright, for SW 80ED? They are the same ?

 https://www.firstlightoptics.com/diagonals/william-optics-2-dielectric-diagonal.html

Edited November 6, 2022 by vagk

[StarryEyed]

Their so similar in performance it's possibly not worth the cost. Depending on your eyepieces you might find better views by investing there. 

Have you tried viewing stright through without the diagonal this is a clear indication of how good/bad a diagonal can be. 

 

Edited November 6, 2022 by StarryEyed

[Louis D]

Check to see if your SW diagonal has a restrictor ring at the bottom of the eyepiece holder tube.  If it does, I'd make sure any replacement does not have one.  I know the GSO made 2" dielectrics do not have this issue.

[badhex]

We did a bit of collaborative investigating a while ago on the thread below - as far as anyone can tell the WO is the same as the skywatcher (and the skywatcher deluxe model) only with carbon fibre panels - which add nothing optically. 

They are not bad diagonals except for the quite restrictive barrel stop lip on the inside of the EP side, which can cause vignetting with very low power EPs (anything with a field stop larger than 41.5mm).

As Louis said, the GSO diagonals have no such restriction and are well priced. The only other option I'm aware of with the same clear aperture are the Baader clicklock BBHS diagonals, which are fantastic but 3x the price of the GSO. 

 

 

[bosun21]

As far as I know they are optically identical and only differ in their housing. With the Skywatcher the hard stop only becomes relevant when using very low power wide field eyepieces. For everything 1.25” it isn’t relevant. I have a 2” Skywatcher deluxe dielectric and recently upgraded to the 2” Baader clicklock diagonal and the Takahashi 1.25” prism diagonal for everything 1.25”

[vagk]

15 hours ago, Louis D said:

Check to see if your SW diagonal has a restrictor ring at the bottom of the eyepiece holder tube.  If it does, I'd make sure any replacement does not have one.  I know the GSO made 2" dielectrics do not have this issue.

But isn't this ring necessary to keep the eyepiece barrel from hitting the mirror?

[Louis D]

2 hours ago, vagk said:

But isn't this ring necessary to keep the eyepiece barrel from hitting the mirror?

It need not be any thicker than the eyepiece barrel thickness which is at most 1mm.  Kept at that width/thickness, it would not contribute to vignetting.  The SW/WO diagonals go with at least a 3mm lip, which is completely unnecessary.  I have a 1.25" WO diagonal with just as thick a lip, and the vignetting in a 32mm Plossl is quite noticeable.