Pentax scope is coming back

[E621Keith]

One vital question is if they will source a 2" adaptor as part of the package as the standard back does not support 2" and the threads are P1. If not the Baader 4-in-1 is going to be like gold dust!

Actually you need the Baader M84-M68 adapter. The 4-in-1 doesn't support Pentax, at least the current one doesn't. (The current 4-in-1 adapter supports Vixen M60, Zeiss M68, Astro-Physics 2.7" and Skywatcher M56)

However, you made a good point, I waited weeks for my Baader M84-2" adapter. My 125SDP came with the old 0.965" back so I couldn't even use it for visual until the Baader arrived. The Pentax back is a straight through visual back anyway, so a Baader adapter will be needed if you want to use the scope for visual with a diagonal. Even then some eyepieces still don't have enough inwards travel and I have to use a T2 prism.

Hopefully Vixen will include a low profile M84-2" adapter as standard. The SDP is a excellent visual scope as well as astrograph.

btw, M42P1 is M42 mount, it was the old universal screw mount once used by Zeiss, Pentax, Zenit and a few other cameras. A Borg 7856 will convert the M42 mount to T-mount (M42P0.75). M68P1 is Zeiss/Baader's format and it is part of the Baader adapter, so you can't blame Pentax for that 1mm pitch. Borg helical uses proprietary M68.8p0.75, so I don't think it will fit even if Zeiss pitch was 0.75.

Slightly off topic:

If you need helical focuser, consider 1. Baader 2458204 Pentax M84 - Zeiss M68 -> 2. Baader 2957103 Zeiss M68 - Vixen M60 -> 3. Borg 7901 Vixen M60 - Borg M57 -> 4. Borg 7860 M57 DX LII helical focuser. (The 7860 has the widest internal diameter of all Borg M57 helical. It's 5mm narrower than the larger 7835 found in Borg series 80 refractor, but it is still wide enough for a 2" nose piece to fit inside. However, be quick on the 7860, it is being discontinued and will be replaced by the 7861 which has a smaller ID of 49mm. The new focuser will be too narrow for 2" accessories)

[NickK]

I got the PX and the 4-in-1 as a single unit with the SDP, hence regarding it as one thing - but you're right they're two separate parts as you've indicated. The PX adaptor has an inner lip that stops the focuser's inward travel - so even if the pitch worked it still has a problem.

The reason I went for the M68 sized borg M7835 was to maximise rigidity. Your point about the "Borg helical uses proprietary M68.8p0.75, so I don't think it will fit even if Zeiss pitch was 0.75." is very interesting and I'll ensure that I'll pass is onto the engineer to check as I'd initially said M68!

[E621Keith]

Definitely check it. Hutech's website, Borg 2011 English parts catalogue and Borg's Japanese website all states M68.8p0.75

http://www.sciencecenter.net/hutech/prices/borgparts/html/7835.htm

http://sciencecenter.net/hutech/catalog/catalog-2010.pdf

http://www.tomytec.co.jp/borg/products/partsDetail/arguments/37

[NickK]

The engineer has now got all the measurements etc so some time in the future I should have the Pentax and Borg attached