Eye Piece advice/opinions requested

[MinnDon]

So far, all I have for my C11 is the 40mm 1.25" eyepiece that came with it, and I'm getting an itch to see some things with greater magnification.

My present dilemna is in deciding whether to go right away to 2" eyepieces, as a fellow from Celestron suggested when we were researching our scope before we bought it. My level of ignorance will show with this next statement, but this is the Beginner's forum, right? It is true (or not?) that a 2" EP of the same focal length as a 1.25" gives the same magnification, but a wider field of view that could make dimmer objects more visible due to the fact that there would be more black space around them?

Also, what would be a practical set of ranges of focal lengths to try to acquire for a C11 (for some one who is in their first year of owning a somewhat "serious" scope)?

Celestron has a set of of 3 eyepieces (2") with filters, barlow, star diagonal and case that's about $70 cheaper than buying the components separately, but the EP's are 40mm (already got a 1.25"), 32mm and 26mm. If I did my math right, those EP's give magnifications of 72X, 90X, and 110X, respectively (for a 2800mm scope). Is that kind of a narrow range, or is 110X the max that I should consider at this time? Is this set something I should consider, or would it be wiser to get aditional pieces separately?

Lastly, if I do go on to buy separate pieces, the various brands and designs of eye pieces compound my problem, too. Are there certain EP's that I shouldn't waste my money on (due to inferior optics), but at the same time not waste money on high end pieces that would, in football terminology, "out punt the coverage" of my C11?

We don't mind spending a couple hundred bucks (or maybe a few hundred) on this stuff, but like most folks, we'd like to get stuff we'll be happy with "down the road".

Thanks in advance for any and all opinions, advice, and comments.

Don (and Anne)

P.S. I should make a mention that Anne and I really enjoyed the presentation on "Cass A" (?) at last Thursday's MAS meeting. Took us both back to our college days (in a good way!). Could some one refresh our memories as to the gentleman's name that gave the talk?

[Dick Jacobson]

You are correct, the magnification does not depend on the diameter of the eyepiece, only on the focal length. Divide the focal length of the telescope by the focal length of the eyepiece to get the magnification. The purpose of the 2" barrel is to allow a wider field of view. I would definitely recommend investing in some 2" eyepieces for the longer focal lengths. One of these should be a low-power eyepiece that gives the widest possible field of view. I assume your scope's focal ratio is f/10 with a 2800 mm focal length. A 50 mm eyepiece would be a good choice for wide-field viewing. For high-power viewing of the Moon and planets, I would recommend about 10 mm. This gives 280x or about 25x per inch of aperture which I have found is ideal for high-quality images. If my budget was limited to two eyepieces, these are the focal lengths I would choose.

I agree with your opinion that 40, 32, 26 mm is too narrow a range. You shouldn't waste your money on such a limited magnification range. For deep-space viewing of star clusters, nebulae, and galaxies, I usually use a low-power eyepiece to find the object, then a variety of high powers to examine it further. Medium powers are relatively useless. High powers are also best for the Moon and planets. To expand beyond the 10 mm and 50 mm eyepieces, I'd recommend a 14-16 mm and a 2x Barlow lens. This gives a nice range of 5, 7-8, 10, 14-16 for a good selection of high powers depending on the object and the atmospheric conditions. In addition, a 2" diameter eyepiece in the 25-35 mm range would be a good gap filler, though if your experience is like mine you will probably end up not using it a lot.

Premium eyepieces like TeleVue and Pentax are expensive but well worth the investment in my view. They last many years. I have some cheaper eyepieces but never use them any more; high quality eyepieces make viewing so much more enjoyable.

Finally, though it may be beyond your budget, there's the question of binoviewers. I bought a Denkmeier II last year and enjoy it so much that I hardly ever use my single eyepieces any more. Of course, this also doubles your eyepiece expenses!

In response to your PS, the presenter was Larry Rudnick. I thought it was a wonderful presentation, kind of a "CSI Cassiopeia", examining the debris from the explosion and trying to deduce what happened. We've had some really marvelous talks over the last year by U of M faculty; those who don't attend the meetings have really missed a lot! My thanks to Lauren Nelson who has been instrumental in arranging these talks.

[rcobian]

Hello,
I'll give your questions a shot here.

2" eyepieces have the ability to give wider fields of view than 1.25" eyepieces. However, that is not always the case. The true field of view (TFOV) depends on the apparent field of view (AFOV) and the magnification (M)

TFOV = AFOV/M

So, if you have a 26mm eyepiece with a 50 deg AFOV it would give you a magnification of ~108 and a TFOV of 0.46 deg.

Which eyepiece is best depends on what you are interested in seeing and what your individual preferences are. For deepsky observing I tend to like wider fields of view. For observing the planets you probably don't need a large FOV. In addition, eyepieces with wider AFOV tend to be much more complicated designs that have more lenses and consequently lower light throughput. This means that on the planets, simpler (and cheaper) designs such as plossls and Orthoscopics may actually provide sharper images with more contrast than the more expensive wide field designs.

On the other hand, the views through wide field eyepieces can be quite addicting. The wide AFOV can make you feel like you are really there as opposed to just looking at it thru a telescope. This is what they refer to as a "spacewalk" experience.

As for eyepiece quality, there are probably many opinions out there. Eyepiece quality becomes more important as the focal ratio of the telescope decreases. At f/10 your scope should be much more forgiving of eyepiece quality than my dob at f/4.8. So, the lowest quality eyepieces that would still provide good images would be different for you and me. However, if you are looking for top of the line eyepieces then you'll want to look at televue.

Also, notice the thread at the top of the beginners forum that has a nice spreadsheet for comparing eyepieces.

[MinnDon]

Thanks for Mr. Rudnick's name, Dick. His presentation at our first MAS meeting has certainly given us lots of enthusiasm for attending future meetings. And yes, Kudos to Lauren Nelson, too.

Thanks to you both for your 'takes on eye pieces. This helps zeroing in on the next addition greatly - more good info to weigh into the decision making process before reading a credit card # over the phone!

[Kirk]

If you haven't done so, check out this spreadsheet.


http://jjmaden.tripod.com/meadeds2130ate/id7.html

You type in the info for your scope and the eyepieces you are considering and it gives you all kinds of good info. It really helps to compare eyepieces before you buy them. It also helps you think about what size eyepieces will fill out your collection nicely.

I have found it very helpful.

~Kirk

[MinnDon]

Thanks for the advice Kirk. In fact, we did use this spread sheet to look over some options. In spite of the use of this fine tool, we ended up buying that 2" kit from Celestron,... couldn't resist the price. After using it for a couple months I can offer a rank newbie's impression: the only thing that has proven useless in this kit has been the 32mm EP. Not because of its quality, but because if we want to get closer than the 40, we always go to the 26, and then the barlow. At first, I thought the barlow was junk, but am beginning to think that nights with seeing good enough for its use with the 26 are kind of rare - we have had a couple fleeting episodes where views through the 26 and barlow actually yeilded fairly sharp images.

In fact, over the A-day weekend I was able to compare the view through our C11 with the 26 EP and the view through two of the big white refractors out at Onan during Io's transit. When the air settled down for a few seconds I swear that Io's shadow on Jupiter was as distinct in my C11 as it was in the refractors. Maybe it would not have appeared that way to more "veteran" eyes, but that was my impression. I was pretty pleased with the comparison.

Will probably "grow out of" these EP's in the future, but the wish list is long (CCD camera, better mount, etc, etc) - at least we've got some mag options (for cheap) in the mean time.

Thx to all for the advice.