Wide Field eyepiece.

[Guest]

I have just one more eyepiece to complete my collection.At the moment I have a TV 5mm Radian,8.5 & 12mm Pentax XF,19mm TV Panoptic.Also 9mm & 25mm Circle T orthoscopics.

I have a NATO military eyepiece which has a two inch barrel diameter.It has served me well over the years,being appros 32mm focal length and a huge field of view.One thing about thid wide field eyepiece is the bluish sky background.Is the bluish sky a feature with all wide field eyepieces regardless of quality?

I would be looking to buy a two inch barrel with between 25mm to 30mm focal length.With of course a black velvet appearence of the sky.

[AlexB67]

One thing about thid wide field eyepiece is the bluish sky background.Is the bluish sky a feature with all wide field eyepieces regardless of quality?

I would be looking to buy a two inch barrel with between 25mm to 30mm focal length.With of course a black velvet appearence of the sky.

For different quality eyepieces the sky background may appear darker than another in the same focal length, depending on number of elements, coatings and construction.  It is worth bearing in mind though that the main factor is that sky background brightness depends on exit pupil and there is nothing you can do about that in that it grows with increasing eyepiece focal length. Just to point out not to expect wonders no matter what you spend.

As for FOV, a 32mm focal length eyepiece with  FOV of a 100 or 60 will appear to have an equally dark sky background everything else being equal.

The other way to look at it.  An eyepiece with shorter focal length and wider FOV that bags the same amount of sky compared to a longer focal lengthand narrower FOV, in that case the first option will yield the higher mag and smaller exit pupil, therefore the sky background will be darker. 

[Mr Spock]

You don't say what scope you are using.

If it's a short focus Newt, then yes, sky brightening will be a problem with all 30mm-ish focal lengths.

[Guest]

I have a 10 inch f 4.7 dobsonian and a 150mm Skywatcher Star travel.I think that eyepiece focal length  for an  exit pupil of 5mm would be around 25mm fl.

[Mr Spock]

I used to have a 10" Skywatcher. I never went above 22mm and more often than not stuck to 13mm. My 42mm was completely useless in that scope. The 32mm Plössl was only of use as a finder, the background was too bright for anything else.

[RikM]

I have a Skywatcher 10" and use an ES 28mm 68° as my widefield EP. Before that I had a Vixen LV 30mm 60°. Both very nice eyepieces but I prefer the ES. The slightly shorter focal length darkens the sky background a little and its focus position is closer to my other EP's. It was a toss-up between the ES and a 27mm Panoptic for me. If I had less light pollution to contend with, I would have gone for an ES 30mm 82°.

[Moonshane]

for me there are three main contenders here:

24mm Panoptic

26mm Nagler

27mm Panoptic

I went for the middle one.

as above the main issue is a bigger exit pupil = brighter sky unless you have no LP and even then.......