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You can equip the standard 2" Clicklock star diagonal with a M68-thread using Baader M55/M68 (Zeiss) Adapter for 2" CL-Stardiagonal # 2956110 (https://www.baader-planetarium.com/en/baader-m55m68-(zeiss)-adapter-for-2%22-cl-stardiagonal.html), but then you still have a 2"-star diagonal basically.

The M68-star-diagonal hasn't got this simple option for reconfiguration to 2"-SC-thread. But you can use

- Baader M68 Conversion Ring # 2458195 to change the male M68-thread of the star diagonal to a female thread (https://www.baader-planetarium.com/en/baader-m68-conversion-ring.html)
- M68 to 2" UNFi Conversion Ring # 2458232 to change the female M68 to female SC-thread (https://www.baader-planetarium.com/en/m68-to-2%22-unfi-conversion-ring.html)
- Baader 2" NexStar locking ring. # 2458270 as a counter nut to set the orientation of the star diagonal at the telescope (otherwise it would stop wherever the thread ends). https://www.baader-planetarium.com/en/baader-2%22-nexstar-locking-ring..html

Of, course, this isn't a cheap solution as one more adapter is required, but I'd recommend the NexStar Locking ring whenever you want to screw a star diagonal onto a Schmidt-Cassegrain.

The backfokus tolerance is +/-1mm.

I'm not sure if I understand your problem correctly - in M48-configuration, the MPCC needs 2mm *more* of back focus. So, if your setup has got 55mm of backfocus, you are too close to the MPCC, at a distance of 52.5mm. By adding 1.5-2mm, you get into the specified distance. You can bridge this gap e.g. with our M48 spacer rings https://www.baader-planetarium.com/en/m48-fine-adjustment-rings-(03--05--1-mm)---aluminium.html in 0.3, 0.5 and 1mm thickness. But more than about .5mm does not work - and this is only possible if the thread of your camera adapter is not recessed. Depending on how well the threads fit to each other, it might be a good idea to secure the camera with the camera strap at the telescope, so that it can't fall down.

On the other hand, if you have a camera adapter with S52-ring-dovetail, you can try the Baader M48 Spacer Ring for MPCC III / Protective EOS T-Ring # 2458405 - often, you can remove the T-2-thread and access a ring-dovetail.

But as the Nikon-F-bajonet has got a diameter of only 44mm, which is smaller than the lens of the MPCC and smaller than the sensor of the 8300, you can also use T-2 instead of M48.

To make full use of the larger diameter of M48 - e.g. for an Off-Axis-Guider or if you have a large camera bajonet - take a look at the RCC I, Rowe Coma Corrector # 2956800 which provides a much larger back focus and is designed to allow for an off-axis-guider between camera and coma corrector.

You find the drawings of the filter wheels on http://flicamera.com/cfw/index.html when you click on "Colour wheel specification" and then on the little pdf logo "Download Drawing"

If you can use the eyepiece with barlow for visual use, there is usually also no problem with attaching a camera. This is mostly a problem with refractor spotting scopes, where you often can't focus to infinity with the Barlow lens.

Please note that you will achieve a very high magnification and a low f-stop with the Barlow; you can find the formulas for calculating the effective magnifications in this PDF: https://www.baader-planetarium.com/en/downloads/dl/file/id/444/product/3117/digiscoping_camera_adaptations_for_afocal_photography_and_eyepiece_projection.pdf

The 2"-nosepiece has got the S52-dovetail and fits into our Wide-T-Rings, you just have to remove the T-thread from the Wide-T-ring with an Allen key.

The UV/IR-Cut-Filter #2459210A fits into the 2"-filter-thread of any standard 2"-nosepiece, including the one of this adapter.