Mark V Großfeld (Giant)-Binocular with Storage Case

In this case, you will need an additional 2" nose-piece with the product number: 2458130 2" Nosepiece to T-2/M48a – with Safety-Kerf - English

We always recommend a T-2 star diagonal as this gives you the shortest possible adaptation, so that you can use a GPC with a lower factor and use lower magnifications, too. Chances are good that you can use the 1.25x gpc with a T-2 prism diagonal and achieve lower magnifications, without having a disadvantage at higher magnifications. If you don't mind the disadvantages of a GPC with higher magnification, you can use a 2" star diagonal on a refractor.

On a Schmidt-Cassegrain, you can reach focus with almost all accessories, and don't need a GPC to reach focus. But: As you are moving the main mirror, you are increasing the focal length, while you are at the same time loosing aperture, because the main mirror moves closer to the secondary and can’t fully illuminate. Image quality also doesn’t improve when you change the distance between the optical elements so drastically and observe at f/13 or worse.

We developed the T-2 star diagonals not only so that you can achieve focus with shorter GPCs, but also so that SCs and similar telescopes can be used closer to the focal point for which they were designed.

That’s why we do not recommend using a bino-viewer behind a 2“ star diagonal even if you can reach focus with a Schmidt-Cassegrain: You’ll probably be disappointed by the image and think that it is a problem oft he bino-viewer, although it is caused by the drastically changed optical configuration inside oft he telescope itself.

Even on a SC with T-2-star diagonal, we recommend at least the 1.25x gpc, too, at least for higher magnifications. At f/10, it is not strictly necessary – but it still shortens the necessary back focus, so that optical aberrations induced by the mirror distances are less.

You would be right if the optical design of our glass path corrections were based on a telecentric system and not on a Barlow lens design (you can find information about the differences here https://www.baader-planetarium.com/en/blog/the-benefits-of-telecentric-systems/ )
Every Barlow lens widens the beam path, so you won't see any vignetting in our bino with a glass path corrector. All customers who have bought Mark V Binoviewers with these correctors over the last 25 years can confirm this.

25mm is tricky, as even the Newton GPC only saves ca. 80mm and the binoviewer requires ca. 110mm.

There is however one option: You can use a SunDancer Telecentric System:

# 1363070 - Baader SunDancer II Telecentric System TZ-3S

# 1363080 - Baader SunDancer II Telecentric System TZ-4S

They give you 3x or 4x magnification and do not correct the coma, but the do not change the focus position too much. If I compare it with a 1.25" eyepiece and the 2"/1.25" Pushfix reducer #2408151, I need to extend my focuser to the following positions:

1.25" eyepiece plus Pushfix Reducer: 3.3cm

1.25" eyepiece plus Pushfix Reducer plus TZ plus binoviewer: 1.5cm (TZ-3S) or 1.6cm (TZ-4S)

1.25" eyepiece plus TZ (in 2" clamp) plus binoviewer: 3.7cm (TZ-3S) or 3.8cm (TZ-4S)

So, there is almost no change in the position if you switch from a 1.25" eyepiece with 2" adapter to the TZ-3 in the 2" eyepiece clamp. The downside is of course the additional 3x magnification. We do not have a 2x Telecentric System, as they were mainly made for H-alpha-filters at f/15-telescopes (these filters need f/30), and these telescopes have become rare. However, we are working on a new version or production run of the # 2456300 2" Glasspathcorrector 1,7x for Newtons, but it needs at least 30mm of back focus at the moment.