35mm eyepiece

[mrdusty]

I'm getting a nexstarn130slt. I've a bunch of 1.25 mm eyepieces, but it will also use a 2" eyepiece. My question is should I get the 2" 35mm eyepiece or stay with 1.25"?

[newtyng5]

Hi mrdusty

If you are new to astronomy, perhaps give the 1.25" eyepieces a whirl for a while. You can always try 2" later.

Personally I have all 2" eyepieces now, but it's down to many factors which you prefer, one of which is often cost.

[cloudsweeper]

If you want to optimise your field of vision, use 2" EPs - especially in the 35-42mm range.

HTH,

Doug.

[mrdusty]

Thank you both for your advice. I should have said that I only have the Orion Skyseeker 100 and a Meade ETX 70AT (gifted) with a bunch of 1.25 eyepieces including one zoom StarGuider 7-21mm. Should be getting the Celestron nexstar 130slt soon and now I believe that I'll go for a 2" in the 32-40mm range. Should be an interesting change.

[michael.h.f.wilkinson]

Note the Nexstar 130SLT is F/5, and a 35mm EP will result in a rather large exit pupil (7mm). This might not be best under even slight light pollution, yielding rather washed-out views. Besides, if your own pupil doesn't dilate to 7mm (e.g. due to age) you will be losing light.  In an F/5 scope a 25mm EP yields a more reasonable exit pupil (5mm), but note that a fast scope also requires quite well-corrected (i.e. quite expensive) EPs. A good choice might be the Meade, ES, or MaxVision 24mm 68 deg super-wide angle, which gives the biggest possible FOV in 1.25" fit. 2" alternatives are the 24mm 82 deg ultra-wide angle EPs of the same brands (much more expensive), or the excellent TV Nagler T5 26mm. These latter EPs might be rather heavy for the SLT mount, and cause balance issues. 

[John]

I was just going to make the point that Michael has regarding the implications of the F/5 focal ratio of the Nexstar 130 SLT. I agree with his viewpoint that an 25mm - 30mm focal length eyepiece would be more suitable.

[Geoff Lister]

I've got a 2" 56mm Plossl that I bought to give wider views with my Skyliner 10" Dob. It's big, heavy, needs a short extension tube to reach focus; and as soon as I want more magnification, I have to remove the EP, remove the extension tube, remove the 2" EP holder, and fit the 1.25" EP holder; before using any of my other EPs. I normally stick with my 1.25" 32mm 52 deg. FOV Plossl for the wider views.

Geoff

[cloudsweeper]

29 minutes ago, John said:

I was just going to make the point that Michael has regarding the implications of the F/5 focal ratio of the Nexstar 130 SLT. I agree with his viewpoint that an 25mm - 30mm focal length eyepiece would be more suitable.

I also agree John - I'd overlooked the low f-ratio in this case.  Ordinarily, I'd suggest a long FL would still be useful for finding your way round (despite the washed-out view), but of course this is less of a benefit with a GoTo 'scope!

Doug.