2" diagonal on a 127 Mak?

[JamesF]

When I purchased my 127 Mak it already had a converter and a 2" diagonal fitted. I had the scope apart the other day though and I'm wondering if there's really any advantage to it. A good half of the length of the OTA is taken up by the baffle tube and that can't be much more than 1.25" in diameter, if that (I've now just measured it at the back of the tube as being between 26mm and 27mm internal diameter). This must presumably lead to some degree of vignetting?

If there's not likely to be a discernable benefit then I'd be tempted to convert it back to a 1.25" diagonal as there'd be less weight on the mount and when using the scope for imaging I'd even have the possibility of removing the diagonal completely and replacing it with a straight extension tube. I have what I believe to be the original visual back, though I would have to work out how to remove the SCT converter that's already in place.

James

[Dunkster]

I did a bit of reading/asking about this recently as I was thinking about the suitability of my 6SE for visual DSO if the day comes when I can et to darker skies...

6SE has the same focal length and baffle diameter, so I wonder if there are similar limitations? Anyhow, one thread elsewhere showed a little experimentation and found 32mm ep with 70 deg fov to be about the limit, with no report of vignetting with a full 1.3 deg view (unless I misunderstood). I'd link if I was more sure of policies/spirits.

So I guess it depends on how wide you want to go

[SiriusB]

Hi James,

On paper, not much point having a 2" diag, in practice i can get pleasing 1.3deg tfov with a 2" ep & no readily discernable vignetting (though it must be there by rights)~ @1.5 deg vignetting is very apparent.

Like you say it adds a fair bit of weight to the tail end of the mak, i find the 2" diag preferable for visual as with a 1.25" the finder always seemed to get in the way of my head.

....The sct adapter should just unscrew should you so wish.