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Ken_stargazer

Effects of Reducer/Corrector, and 2" v 1.25" eyepieces?

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Hello.  I'm a new user of my telescope, a Celestron NexStar 8SE, and unfamiliar with the effects of accessories.  So I'm asking this in order to best select a set of eyepieces (my telescope came with only one 1.25", 25mm eyepiece).

My first question involves a Reducer/Corrector:  I've heard of the benefits of using Celestron's accessory, a 0.7X "Reducer/Corrector (#94175) to brighten dim objects (f10 to f6.3).  However, I also understand that it widens the field of view, so I'm wondering how it would affect apparent magnification.  For example, if I like the view of a hypothetical object (i.e, how much it fills the field) using a 15mm eyepiece, how might that change when I use this Reducer/Corrector?  Would I then, using the Reducer, want to use a shorter focal length eyepiece (e.g., a 10 or 12 mm) instead.

My second question involves going to 2" eyepieces (this telescope came with a 1.25" eyepiece), noting that if I do go to 2" eyepieces, I'll also include buying a fully 2" diagonal as well rather than an adapter to a 1.25" diagonal.  I have been led to believe that 2" eyepieces have a wider field of view, so I wonder how that compares to the 1.25" eyepieces.  For example, hypothetically assuming that I want to retain a certain magnification that I get from my 1.25" diameter/25mm f.l. eyepiece, am I right to believe that I would want to go to a shorter focal length in a 2" eyepiece?

I really appreciate any help and advice you can offer.  Thank You, in advance.

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Hi Ken, and welcome to SGL.

Magnification is simply  Effective Focal Length of Scope/Eyepiece Focal Length.

Field of View is Apparent Field of View of eyepiece/Magnification.

So adding the Reducer will reduce the magnification of a given eyepiece by 0.63 and increase the FOV by the same amount.

The maximum FOV of a 1.25" eyepiece is limited by the barrel diameter.

In your scope this could be achieved with a 32mm 50 degree 1.25" eyepiece giving about 0.8 degrees at F/10 and about 1.3 degrees with the Reducer.

If you want a wider FOV you need to use a 2" eyepiece.

For example a 32mm 82 degree 2" eyepiece will give about 1.3 degrees native FOV or 2 degrees with the Reducer.

Note that both these 32 mm eyepieces have the same Magnification since this depends on focal length not barrel diameter.

If you click on Resources/Astronomy Tools/FOV at the top of this page you can choose a target (maybe M45 Pleiades) and experiment with various eyepieces.

Enjoy your scope.

Edited by lenscap

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The focal reducer/flattener works well with 1.25" eyepieces to widen the view without having to jump to 2" eyepieces.  It will cause vignetting with widest field of view 2" eyepieces like the 41mm Panoptic.  Ultimately, it is the rear port of the SCT which tends to limit the widest field of view possible.

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