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Eyepiece advice sought

Matthew.Blake

By Matthew.Blake
in Discussions - Eyepieces

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Matthew.Blake

Matthew.Blake

Posted
Posted

I'm looking at buying one of the Skywatcher Aero eyepieces and their 2" ED barlow. I shall probably get the 40mm eyepiece. The scope they are going in is the an 8" F/5 refractor. Once my wallet has recovered I intend to get either the 7mm Nirvana or WO equivalent for my high power eyepiece. These will complement my 6.3mm, 15mm and 26mm plossl lenses.

Can you pass comment on these goals please. In particular:

Will a 40mm eyepiece give too low a magnification in my scope, would I be better off with the 35mm (the large exit pupil does not bother me)

Is the WO for £10 more than the Nirvana just £10 more for the same quality?

Would I be better off with the 4mm lens as my high power lens or, since I couldn't really use the barlow with it as 2mm would just be silly, would 4mm be a waste?

Kirk or Picard?

Would you recommend anything in the middle or, with the barlow do you think I have it covered?

Ta muchly.

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rawhead

rawhead

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Assuming that's 1000ml (my maths are ****)

40mm EP will give you a mag of X25 (35mm = X28.5)

I understand the WO and the Nirvana are the same (an SGL review should be coming soon)

4mm = X250 That sounds about right for high mag obs :)

(I assume you mean 8'' reflector?)

Make it so!

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Matthew.Blake

Matthew.Blake

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Assuming that's 1000ml (my maths are ****)

40mm EP will give you a mag of X25 (35mm = X28.5)

I understand the WO and the Nirvana are the same (an SGL review should be coming soon)

4mm = X250 That sounds about right for high mag obs :)

(I assume you mean 8'' reflector?)

Make it so!

No no, it's a refractor.... ok, maybe I made a small typo.

Are those magnifications sensible though? Is there a lowest useful magnification much like there is a highest useful magnification or is the only reason people might shy away from the 40mm eyepiece the size of the exit pupil (since my pupils do yoga I'm not worried)?

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DaveS

DaveS

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Exit pupil should be about 7 mm if you're under about 35-40 ish, for us oldies, more like 5 mm. Really young observers under dark skies could get 8-9mm (Goes green with envy :)).

So just divide your 200 mm aperture by the exit pupil you have, hence lowest usable magnification.

Dave

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Matthew.Blake

Matthew.Blake

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Exit pupil should be about 7 mm if you're under about 35-40 ish, for us oldies, more like 5 mm. Really young observers under dark skies could get 8-9mm (Goes green with envy :)).

So just divide your 200 mm aperture by the exit pupil you have, hence lowest usable magnification.

Dave

Does the FOV make a difference e.g. 15mm plossl vs 15mm nagler, would the exit pupil be the same?

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Rob

Rob

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Why do you say that?

Its all about exit pupil, kidney beaning & black outs. Its also about size of image. If you google and research it should answer all of this. The 30mm is about the max size you should look at, more so in a f5 scope. The image will be small, but even smaller in a 40mm.

Just some thoughts before you part with the cash and end up selling at a loss!!.

Think hard and google the above effects. The 30mm will be a fantastic EP. I have a 30mm UWA MoonFish and use that in my 8" f6 Newt with great effect... almost space walking accross the milkyway

Hope that helps

Rob

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Andrew*

Andrew*

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I admit to being young, and hence probably having larger fully-dilated pupils, but I have used the 40mm Aero in my f/4.5 Lightbridge (8.9mm EP!!), and had brilliant views. Yes, there was some central darkening (minor, especially when you put your eye right in), but it was the only eyepiece which revealed nebulosity in the Pleiades from my LM 5 skies. My eyes would not have been fully dilated for this either due to some local light. I also saw just as good detail in M31 as with more "sensible" exit pupils on the same night and scope.

It only got better in my 8" f/5 scope. For me, for now, the "max exit pupil" idea is meaningless.

I will get a 40mm eyepiece for my scopes, even if only for viewing nebulosity in the pleiades and other very wide views.

Be warned though - this is only one (young) man's experience. Also remember that eyepiece choices are very personal. I may be particularly tolerable of secondary shadow while you may hate it. I just wanted to level the playing field a bit.

Andrew

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Matthew.Blake

Matthew.Blake

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I admit to being young, and hence probably having larger fully-dilated pupils, but I have used the 40mm Aero in my f/4.5 Lightbridge (8.9mm EP!!), and had brilliant views. Yes, there was some central darkening (minor, especially when you put your eye right in), but it was the only eyepiece which revealed nebulosity in the Pleiades from my LM 5 skies. My eyes would not have been fully dilated for this either due to some local light. I also saw just as good detail in M31 as with more "sensible" exit pupils on the same night and scope.

It only got better in my 8" f/5 scope. For me, for now, the "max exit pupil" idea is meaningless.

I will get a 40mm eyepiece for my scopes, even if only for viewing nebulosity in the pleiades and other very wide views.

Be warned though - this is only one (young) man's experience. Also remember that eyepiece choices are very personal. I may be particularly tolerable of secondary shadow while you may hate it. I just wanted to level the playing field a bit.

Andrew

I might compromise and go for the 35mm then (t'will save me a whole £5 as well!)

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mdstuart

mdstuart

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I have a 30mm 2 inch moonfish clone eyepiece and I find it is fab but I get lots of coma near the edges. This is the issue you face. I would try BEFORE you buy somehow. You may decide you actually had a better view with a plossl even thought the FOV was slightly less....

Mark

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