Simplified eyepiece selection

This month's question wandered in via email from member George Feliz, who is curious about choosing eyepieces for mooning.

Complicated question, as he was also curious about mounts, floaters, and whether I agreed with a planetary/lunar eyepiece review at cloudynights.com. So let's dive in.

First a ground rule: I'm only going to talk about lunar viewing. That's what we're here for.

And for that reason, the above URL is not particularly useful.1 But: it is instructive to consider why, even if the discussion breaks my first ground rule.

Why? Because there is not a great deal of overlap between planetary and lunar observation, and they try to cover both in one article.

The object of most planetary observation is the distinction of fine shades of color (often similar colors!) with soft edges. This can be seen especially when you consider the two "tough" planets, Jupiter and Mars.

Really seeing what's going on requires an extremely fine revelation of contrast and color.

Enough of planets.

On the Moon, most demands for contrast nearly disappear. There is no atmosphere to "smudge" the light. There are no clouds. There is almost no color and it seldom comes into play.

It's basically a problem of seeing medium gray contrasted against a really hard black, with some whitish elements thrown in. The range of contrast from the lighter portions of the Moon to the incredible black of a lunar shadow is about as sharp as it gets short of stellar observation (I love double stars!)

Another point: we get a Lot of light from the Moon. It's very bright.

Blah blah. What does it mean?

It means we're ready to mention another point: eyepieces don't look at the Moon without a telescope.

If you have an 80mm refractor or a 4.5-inch newt,2 eyepieces are not going to be overly important. You won't be able to get much above 180x or so, and that will usually be fairly steady. The image will be somewhat dim, so there won't be a lot of detail to distinguish. This will also go for the 5" catadioptrics.3

If you have a 4-inch refractor or a six inch newt or Mak, you're in the "medium" ballpark where you can get into the 225x range fairly well, and maybe push 300x at times (though you're again getting a dim, uncontrasty image).

Over that, you're in Fat City and you'll need some fairly good eyepieces to get the very best out of your scope.

More blah blah. Now what does it mean?

It means yet another problem: focal length. The longer the focal length and the longer the f/ratio, the better. Just take my word for it.

Long focal length, though, means you're not going to worry much about eye relief. Even standard plossls will deliver just fine.

Enough blah blah. What's the bottom line?

Based on experience, you want a 7mm Nagler.

Really.

It's the eyepiece I use the most, was once popular with Rich Neuschafer, and is still almost the exclusive favorite of Craig Wandke. All of us have something of a reputation as lunar observers, so.

Now ask any of us, and we'll tell you it won't give you the very finest contrast. It might have internal reflections under some conditions. It might have a bit of a soft image compared to the very best eyepieces.

So why do we like it? It's close in all categories, has reasonable eye relief, and has a wonderful wide field of view, which gives you "context" and "an attractive field."

Does it give you the best "data?" Nope.

So, in your next incarnation as a computer, stay away from Naglers. In this life, take a look through one and see what you think.

Wait, Dave. You threw out all this technical crap and then said something like that? Are you nuts?

Maybe. On the other hand, the idea here is to look at the Moon and have some fun. Enjoy.

For a lot of folks, trading obtuse theories is the fun of astronomy. For others, it's playing with hardware. For others, it's looking at stuff. For most of us, it's some combination of those things.

I have noticed, however, that the folks that enjoy looking at stuff often break with acknowledged theory, even when they agree with it.

Some examples:

Jay Freeman claims aperture wins, flat out (I agree mostly) and proceeds to observe with smaller instruments.

Rich agrees a good newt of greater aperture will deliver more data than a smaller refractor, and proceeds to enjoy the wonderful views through his refractor almost exclusively.

See a pattern?

In my case, I know the best views of the Moon and planets have come through my 12.5-inch newt with Takahashi eyepieces, so most of the time I look at it through a five-inch refractor and a Nagler.

Why?

Partly because most nights, the seeing isn't that great. With average to poor seeing, that combo is comfortable, fun, and shows most of what I'm going to see.

If I spot something, I'll change to a better eyepiece. If the sky turns out great, it's easy enough to drag out more horsepower.

So, what do I think are better eyepieces?

First, make sure you have the 180x 225x 300x power points covered with some eyepiece or other. Those are going to be the workhorse spots.

The very best eyepieces I've seen are the Zeiss Abbe orthos, and they are what sucked Rich away from his Nagler. They're incredible, but they're also impossible to get and cost a fortune. Oh well.

I like the Takahashi LE and Standard eyepieces a lot - they're what I use for the very best views. I like most plossls I've seen, and consider them the equal of most orthos. I get reasonable views through Naglers and panoptics both, but they do give up some detail and contrast.

I have an outstanding 6mm Vixen Lanthanum. Your mileage may vary; some VLs I've seen are not very good, and some are excellent. They will sometimes have a touch of false color, which is not important on the moon.

I like Brandons, which is a controversial view. I don't own any.

What do I tote around? For the Moon, depending on scope and conditions, I have 2.8 and 4mm Takahashi orthos, 5 and 7.5 Takahashi LEs, 6mm Vixen Lanthanum, 7mm Nagler, 9mm Vixen Lanthanum, 13mm Televue Plossl and a 19 Panoptic for "full disk" views.

I do not necessarily think my selections are the best for anyone else. I definitely do not like Televue Radians, for example, and they have been quite popular. I consider them soft, twitchy and full of reflections.

I don't like the cheapo orthos I've seen, though they do get good reviews from other folks.

I do like a lot of eye relief, especially in the winter when the mist from my warm eye can fog the eyepiece.

But here's the real point: there's so much contrast on the Moon that any decent-quality eyepiece will do. This is not true on planets, but I'm not writing a planet column, so there.

Reflections are a drag when they happen, but the most common form is a pupillary reflection off your eye, and that is sometimes just a function of where you stick your head.

Now that's not really very specific advice, is it?

Nope.

But it's probably as good as you can get. Because the real trick is to go out and try other people's eyepieces in your scope, preferably at a Moon party (they happen fairly often at Houge Park) and draw your own conclusions. Theory aside, it's your scope and your eyepieces.

If you've got a 7 Nagler, fill in the gaps however else you want.

George was curious about floaters, which will be a problem on the Moon because magnification is the point.

Get a binoviewer. Only solution I know about. Then you can get two of each eyepiece, too!

However, I'm not an expert on this since I'm not really much afflicted by floaters (yet).

Oh, one other thing George asked about: mounts. Dob or equatorial?

That one's easy: equatorial. Especially if you want to sketch or shoot the odd photo.

The problem is, my very best scope is a 12.5-inch dob, and I don't have an equatorial platform (which you should get, if you insist on using a dob all the time).

And that's another reason I often use the 7mm Nagler - that wide field can help with nudge-nudge disease.

On the other hand, I've used the 4mm Tak ortho on that scope because the settle time is effectively zero and the touch is good enough to allow that kind of high-power view (that's almost 400x, and it operates at 600 just fine when the sky allows).

It's just that I'd rather not fuss with the scope that much unless the sky is really, really good, in which case all bets are off and I'll be trying to borrow a Zeiss from Rich...