Fieldstop Skymax 127

[Miguel1983]

Hi,

this weekend i bought 3 Baader Hyperion EP's (13/17/21) and the 14/28mm fine adjustment rings, when i was in the shop i also told the vendor i was thinking of buying an 2" diagonal since the Hyperions can be used as a 2" EP (21mm becomes 32 @ 2").

So those 3 Hyperions essentially can replace my whole Celestron Plössl case an then some.

The vendor said that a 2" diagonal on a 5" Mak wouldn't be a good thing because the fieldstop of the telescope woud be in most cases smaller than the fieldstop of many 2" EP's.

Does anyone know what the fieldstop of a SW 5" Mak is and does anyone have some experience using 2" diagonal and EP's on a similar scope ?

Thanks

[Mr niall]

You can’t go over about 1.3 degrees tfov I think 

[Miguel1983]

7 hours ago, Mr niall said:

You can’t go over about 1.3 degrees tfov I think 

Thanks for the reply, but i what the vendor in the store meant was that putting a 2" diagonal and low power EP with a field-stop matching the EP diameter i would get black edges in my view.

Could someone elaborate on that ?

Thanks

[Louis D]

I've got the Celestron 127mm Mak and have adapted it to use 2" eyepieces on occasion.  There is some slight vignetting with max field 2" eyepieces, but it's hard to see with your eye.  The only real issue for me is when a bright object casts an odd, distorted oval reflection on the opposite side of the field of view when the object passes the 27mm field stop limit of the baffle.  I don't know if your version has SCT threads already so you can attach a 2" visual back, or if you'll need a step up adapter ring first.  IIRC, the latest Celestron 127mm Maks come with a 2" visual back (or at least SCT threads to attach one).

[Miguel1983]

The skymax 127 is pretty much the same, the inner tube is 27mm but the threads on the back are 45mm, i've already found an adaptor to adjust this to accepts 2".

What's the lowest power EP you use in this scope ?

So the rule is if the field stop of the EP is bigger than that 27mm, you get vignetting ?

Just measured my Baader Hyperion 21mm in 2"-mode the field-stop is 30mm, guess there wil be some fading on the edges

 

[Louis D]

I used a 40mm Meade SWA 5000 with a 46mm field stop with imperceptible vignetting.  The human eye is not very good at detecting vignetting of a dark background.  You have to look for stars at the limit of perception that start disappearing as they move to the edge.  It would probably be more noticeable if you used it while looking at a clear blue sky.  The "Wow" factor, though, is tremendous when you suddenly open up the otherwise narrow field of view.