Newt refurb - protostar secondary holder owners?

[coatesg]

Hi,

I'm starting the process of refurbishing my newtonian prior to mounting it in the observatory which is pretty much finished now.

The secondary is too small to get a decent sized 100% illuminated area - I have a new 3.5" mirror on order but need a replacement secondary holder. The current one is a Protostar 2.6" - are there any protostar owners who know whether the holders are interchangeable without having to get a whole new spider as well? (The main thread is the same, but don't know if there's a difference in eg locations of the collimation screws, the clutch plate, etc.

Thanks

Graeme

[coatesg]

(Or another idea: If there's anyone with a 3.5" protostar secondary mount, would you mind taking some measurements?)

[starman345]

I can't help with any measurements but I do have a Protostar 3.1" mirror, holder and spider, I'm assuming you are using the shroud? I just siliconed my 3.1 to the holder, wouldn't that be a cheaper route for you to take? Even with the smaller 2.6" holder I don't think that would be any problem, maybe 1/4" or so of the mirror would be protruding beyond the holder.

[coatesg]

That's the way I'm starting to look at this (esp given the extra cost and the lead time)- it'll have a bit more overhang than 1/4" with a 3.5" mirror- more like 1/2" on the minor axis and almost 3/4" on the major but I'm not sure that should cause too much issue. (unless anyone can say otherwise).

[starman345]

Right you are, I was comparing my 3.1 rather than your 3.5", still, I think your holder would suffice, maybe someone with a similar setup will chime in.