100x EP with 82 FOV vs. 83x EP with 60 FOV

[thomasr]

I am trying to understand what kinds of EPs will work best with my Nexstar 6se. I have the Luminos 15mm on order, which by my math would give me 82 degree AFOV and 0.82 degree TFOV. It seems this might be a little tight for some DSOs and I might want something with a wider field. Problem is, the Luminos range maxes out at 15mm (unless I want to invest in a new diagonal) so as an alternative I was considering the X-CEL LX 18mm, which by my math would give me 0.72 degree TFOV.

Doesn't seem like a great deal to me: lower power and less view of the sky. What am I missing here?

[NGC 1502]

Lots to consider with that, but one advantage of a higher power (within reason) combined with a very large apparent field, is a darker sky background, this increases the contrast between object and sky. 

Al Nagler calls it "majesty factor".

Regards, Ed.

[Roy Challen]

Well, obviously there is quite a bit of difference between 82 and 60 degree fields of view, and not that much difference between 15 and 18mm so you will need to consider EPs with 82 or more afov and/or a different make of EP.

[thomasr]

My takeaway (so far) from the responses is that so long as the brightness, contrast, edge sharpness, etc. are good with a higher-magnification wide field EP, that will always be preferred to a lower-magnification narrow field EP.

I figured somebody would jump into this thread and start talking about exit pupils, magic pixie dust, or some combination of factors that would make the X-CEL LX the preferred EP in certain situations. I suppose that the f/10 ratio of my scope makes it more forgiving of these kinds of things?

[Stu]

If you are looking for maximum fov in a 1.25" eyepiece then the choices are basically a 24mm 68 degree afov such as the Televue Panoptic/Maxvision, or a 32mm Plossl with a 50 degree afov.

In both cases this will give you just over 1 degree of sky, which as I say will be the max until you move to 2" eyepieces.

The 32mm will give you an exit pupil of 3.2mm, the 24mm will give an exit pupil of 2.4mm. Basically the more expensive wider field eyepiece will give you the same area of sky but with a darker sky background because of the smaller exit pupil.

The long focal ratio of the scope only affects things like off-axis performance, the fundamentals of exit pupil and field of view remain the same.

Oh, and something about magic pixie dust

[rwilkey]

I reckon the Luminos 15mm will surprisingly fulfil your needs in this middle range, so I would wait and try it, as others have said, you won't see much more sky amd the Luminos should show a dark and contrasty sky.