Should I get a new diagonal?

[Don Pensack]

You might also find this interesting:

https://www.cloudynights.com/topic/860739-adjusting-collimation-on-a-cheap-mirror-diagonal/?p=12448264

[badhex]

On 31/07/2023 at 21:50, John said:

This group test by Bill Paolini is quite often posted but it is relevant so here it is again if you have not seen it:

Mirror vs. Dielectric vs. Prism Diagonal Comparison - Articles - Articles - Articles - Cloudy Nights

It also highlights the importance of effective baffling / blackening within the diagonal body. 

 

Finally got round to reading this; one of the 2" diagonals reviewed is an Astro-Tech dialectric, same as the WO, Skywatcher and various others. The below paragraph confirms what we concluded in the thread I posted above with diagonal measurements, and as @Mr Spock also mentioned regarding this specific design of diagonal. Since the maximum clear aperture of these diagonals is only 41.5mm the below results are not surprising. 

"Regardless of the diagonal used, the lateral color generated by the eyepiece remained consistent.  However, during the lateral color tests another issue became apparent.  With the Takahashi 2" Aluminum Mirror and the Astro-Tech 2" Dielectric diagonals there was significant light falloff near the field stop when a 2" eyepiece was used with a maximum field stop.  As example, when the 40mm XW was used in either of these two diagonals (approximate 46.5mm field stop size), dimming near the field stop was apparent."

[Louis D]

On 05/08/2023 at 06:19, badhex said:

Finally got round to reading this; one of the 2" diagonals reviewed is an Astro-Tech dialectric, same as the WO, Skywatcher and various others. The below paragraph confirms what we concluded in the thread I posted above with diagonal measurements, and as @Mr Spock also mentioned regarding this specific design of diagonal. Since the maximum clear aperture of these diagonals is only 41.5mm the below results are not surprising. 

"Regardless of the diagonal used, the lateral color generated by the eyepiece remained consistent.  However, during the lateral color tests another issue became apparent.  With the Takahashi 2" Aluminum Mirror and the Astro-Tech 2" Dielectric diagonals there was significant light falloff near the field stop when a 2" eyepiece was used with a maximum field stop.  As example, when the 40mm XW was used in either of these two diagonals (approximate 46.5mm field stop size), dimming near the field stop was apparent."

I stick with the GSO dialectrics (three at last count, one being a quartz) and haven't had any issues with any of them with regards to vignetting.

[badhex]

16 hours ago, Louis D said:

I stick with the GSO dialectrics (three at last count, one being a quartz) and haven't had any issues with any of them with regards to vignetting.

Indeed, the input from you and @Mr Spock on the original thread was what convinced me to invest in the GSO. I did eventually buy a Baader primarily for the clicklock, but the GSO is an excellent option—especially since it is a third of the price. 

Edited August 7, 2023 by badhex

[Mr Spock]

The Baader is really nice. However, I've yet to detect any difference between that, the Revelation (GSO) and the Takahashi prism. The prism is 1.25" and for use on the planets with the TOEs - which, other than Venus, I've not actually seen with the FC-100 yet.

[badhex]

13 minutes ago, Mr Spock said:

The Baader is really nice. However, I've yet to detect any difference between that, the Revelation (GSO) and the Takahashi prism. The prism is 1.25" and for use on the planets with the TOEs - which, other than Venus, I've not actually seen with the FC-100 yet.

I also can't see any real, dramatic visual difference between the Baader and the GSO. I recall that there might be some light path difference so one might be better than the other for some who have focus issues with a specific EP combo, but mostly it's just about the clicklock.

I know there are other twist-lock style fittings on the market, such as the one on the Starfield as stock, but the clicklock is by far the best that I've encountered and I rapidly upgraded my Starfield (well, TS102) to a clicklock fitting once I'd bought the diagonal. I also knew I wouldn't have much money for quite a while due to moving countries so I took the opportunity whilst I could still afford it! 😂

Edited August 7, 2023 by badhex

[Mr Spock]

Once you use a clicklock there's no going back. I've converted as much as I can.

The twist lock on the Tak prism is nasty! As it has a short light path I considered using a short extension tube permanently fitted to it so I don't have the stress of trying to get eyepieces out of it by force!

[Ratlet]

Cheers for the feedback.  I've got some time to consider things.  Current plan is to get a Starsense 80mm, primarily for the unit but also to try out a longer focal length refractor prior to picking up the 102 later in the year.