9, 11 or 13mm Nagler?

Guest · Posted: Fri Feb 29, 2008 12:53 am Post subject: 9, 11 or 13mm Nagler?

I can only afford to buy one Nagler eyepiece. My telescope is a f/6 (fl=655) good quality ED. I have a 2X and a 2.5X barlow. The 9mm would give me 73X, 146X and about 180X. The 11mm would be roughly 60X, 120X and 150X. The 13mm would be 50X, 100X, and 125X.

Is there a compelling reason to pick one as definitely better than the other 2 in terms of preferable magnification ranges for viewing? As I understand it, Naglers are best for DSOs rather than planetary viewing, though I would want to use it that way too. If you could choose just one, which one would it be? Which would be the most versatile? Or is it just not that critical and all 3 would work well?

[I will add that I have a number of lesser quality eyepieces that cover most of the usable viewing spectrum so there in no other consideration other than which Nagler I will choose. ] Thanks.

Jne_K · Site Admin Joined: 24 Sep 2003 Posts: 5022

Hi

You also have to factor in telescope size and observing conditions when making decisions on magnification and there is also a matter of how mcuh image quality, or lack of it, you can live with as you crank the magnification up.

Assuming you have at least an 80mm scope and it is ED, as you said, it will be a matter of what you are trying to see. If you are strictly doing DSOs, the lower range of magnifications will do nicely - you will seldom need 180x, though 150x might prove handy when resoling globulars. If you are also doing planets, though, that's another matter. 180x is certainly appropriate for planets, even for a small 80mm ED scope and average conditions. I have used a touch more than this for Saturn, even under our very light polluted skies on an exceptional night with such a scope. Just a matter of how much image quality you want, though.

By the wway, just because Naglers are the darling of us deep-sky nuts does not mean they are slouches when it comes to planets.
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Guest · Posted: Fri Feb 29, 2008 9:22 am Post subject:

Thanks Joanie. My telescope is a ED refractor at 110mm.

Jne_K · Site Admin Joined: 24 Sep 2003 Posts: 5022

Yu are very welcome.

A 110ED should be able to eat 180x for lunch, assuming you have any skies at all.
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Guest · Posted: Fri Feb 29, 2008 10:32 am Post subject:

Last question. I have always been more confused about the LOWER end of magnification. I certainly understand that higher magnifications are good for planetary and lunar observing as long as you don't exceed the capability of your telescope (40X-60X per inch). But I see many people value lower magnification, especially for DSOs. Is there advantages to have 50X versus 60X versus 73X as your lower level? Naglers have very wide fields and I have a fast scope, so I should be able to see reasonable swaths of sky given that combination. Is 50X more or less useful (just generally) than 73X as the lowest starting point? I guess I am leaning towards a 11mm simply because it is between and I am not sure. I like the idea of the 9mm for its power, but just wonder if the 73X will reduce its usefulness at the lower end? Again, I can only afford ONE, and I would like to get the one that would be most versatile.

Thanks very much Joanie.

Jne_K · Site Admin Joined: 24 Sep 2003 Posts: 5022

Hi

Good question. On the lower end, there is a point of diminishing returns as far as image brightness. Once you hit your maximum exit pupil size (varies with your age and observing conditions), dropping to a lower magnification doesn't buy you any more image brightness. It may, of course, get you a wider field of view. Either way, there is no penalty for using too low a magnification, other than a possible loss of contrast.

Keep in mind, though, that different DSOs do better with different magnifications and that can change, nightly, or even by the hour as conditions change and it's also a matter of what you want to see when you find one. With DSOs, there is no magic formula as to which magnification to use, but then, trial and error is half the fun. I can tell you that, in astronomy, a difference of 10x or 20x is absolutely insignificant. Don't cut it too fine. Just cover your self with a basic low, mid and high magnification range and all your bases will be covered.
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