If you could only have one eyepiece for your telescope...

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If you could only have one eyepiece for your telescope...

Postby joe-khalaf » Tue Sep 01, 2015 7:03 pm

Which one would it be?
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Re: If you could only have one eyepiece for your telescope..

Postby steve-fung » Tue Sep 01, 2015 10:38 pm

Hi Joe, I'm sure you're going to get a lot of heated answers, but the Baader Hyperion 8-24 mm Clickstop Zoom Mark III is my primary all-purpose eyepiece that I use most often.

http://www.alpineastro.com/Eyepieces_Accessories/Eyepieces_Accessories.htm#Zoom

It's a well-built heavy-duty seven-element 2"/1.25"-convertable zoom eyepiece with multi-coated optics that produces fairly good sharpness, contrast, color, and transmission throughout its zoom range. Zoom action is smooth and precise, producing continuously variable focal lengths with sharp click stops at 8, 12, 16, 20, and 24 mm focal lengths. While not perfectly parfocal, focus remains pretty close throughout all focal lengths. FOV is moderately wide 68-deg at 8 mm and 50-deg at 24 mm. It has relatively long eye relief of 12-15 mm, which is good because I wear corrective lenses. I love its modular design, allowing me to thread 2" and 1.25" filters, and the rubber eyecup can be removed to reveal a M43 thread for attachment of a M43/T-2 adapter ring (I use a T-2 quick change system) for afocal eyepiece projection astrophotography, which is what I generally use for imaging the sun, moon, and planets. Additionally, I recommend getting the Baader Hyperion Zoom 2.25x Barlow, which is specifically designed to work with the Mark III, converting the the eyepiece into a 3.5-10.5 mm zoom. Therefore, with this setup (Mark III +/- Hyperion Barlow), you get almost 7x zoom range of 3.5-24 mm focal lengths. While not cheap (about $290 for Mark III alone and $390 for Mark III + Hyperion Barlow), I think it is reasonably priced for its optical quality, build, and versatility. I give it high recommendations, as with most other reviewers if you check.
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Re: If you could only have one eyepiece for your telescope..

Postby steve-munsey » Wed Sep 02, 2015 9:22 am

Hey Steve,
Someone (sorry I am so bad with names) had one at the Urban [email protected] Bush Park the other Day.
I was pretty impressed but what I would like to see are a few pics through this thing. You got any?


So far my one eyepiece I find myself using the most is my 20mm UMA Meade 5000 85 AFOV. It's a big chunk of glass!!!
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Re: If you could only have one eyepiece for your telescope..

Postby joe-khalaf » Wed Sep 02, 2015 4:45 pm

Yeah, I have a Meade 40mm Super Wide Angle (4000 Series) and it is a beast. It does give nice images, but I've never had any of the "super fancy" eyepieces to compare it to. Some of the reviews I've read online have been so-so.

I may ask my wife for a 21mm 2" 100° field Ethos eyepiece. I'm sure she'll say it's not necessary, but there's nothing wrong with starting high and negotiating down to somewhere in the middle.
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Re: If you could only have one eyepiece for your telescope..

Postby clamison » Mon Oct 05, 2015 1:02 pm

Steve-M, In response to your post referring I believe to the Hyperion Zoom and George Bush park it may have been our mutual observation of the Double-Double in Lyra with my Orion 4" Mak-Cass and the Hyperion set to 8 mm. If so, at the time I also noted I had discovered during solar observation (and I believe you may have confirmed), that there was a bit of dust in the internals. I am happy to say that Baader had me send it to Alpine Astro for repair and they replaced the eyepiece with a new one at no cost. (It hadn't yet gotten back to me for last week's George Bush session where, to give you credit, you recognized me first.)

To respond to Steve-Fung's post I also use the Hyperion 8-24 mm Click Stop Zoom more than any other eyepiece and use it both on the Mak-Cass and a Coronado PST. (That said my other eyepieces are all standard accessory ones that came with the telescopes and probably added together would not cost as much as the single Baader.)

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Re: If you could only have one eyepiece for your telescope..

Postby edward-fraini » Tue Oct 06, 2015 12:41 pm

I also have a 40mm which gives me about 50 X. This is the first eyepiece I use on most all targets. The view is super and it is easy to find objects if they are close to the FOV. Generally I go to an Ethos 13 to really observe and If I had to use just one I would use the Ethos which gives me 152X. I can still find objects pretty easy with it and you definitely have plenty of detail to note with it.

I carry 9 to 10 eyepieces around with me and I often wonder why bother, two is plenty and you sure could get through the night with just one if you had to.

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Re: If you could only have one eyepiece for your telescope..

Postby john-haynes » Wed Oct 07, 2015 5:12 pm

I have a celestron ultima 30, one of the old ultima series. it's my go-to eyepiece most of the time.

I actually have two of them now... just need a bino viewer....
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Re: If you could only have one eyepiece for your telescope..

Postby kdrake » Sun Oct 11, 2015 12:00 pm

That is a tough question. For most of my setups, I would need a 10mm eyepiece. I would stress high quality. Although I'm not sure it would even work in my scopes (10"f/5.6, 13.1"f/4.5, and 24"f/5.6 - all Dob light buckets), something like the TAK10-UW. At $945, I'm not even willing to give it a try unless someone dares to loan me one. Art, are you listening? I might have to settle for a Nagler 9mm or 11mm T1. They are both awesome widefield eyepieces but the 11 T1 is a collectors item. So you ask, why 10mm..... It's all about working a scope at the best power but yet a wide enough field to get a bunch of dim stuff in the field of view. That turns out to be ~13 power per inch of glass - Cains' Magic Number. That's the point where the scope presents enough usable magnification for the average eye. I would consider a Televue Ethos 10mm to be my perfect carry anytime ocular. It's $350 less than the Tak. The only negative might be its weight if used in a small, light scope. All of mine are over-constructed heavy Dobs.
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Re: If you could only have one eyepiece for your telescope..

Postby edward-fraini » Tue Oct 20, 2015 7:05 pm

very interesting note, Cains' magic number indeed. So that is helpful. I have a 20" f3.9 and that calculates out to be an 8mm eyepiece. I debated between an 8mm and a 6mm ethos when a had some pocket money from the sale of some equipment and for reasons unremembered I selected the 6mm. It has never been much use to me as it seemed there was just a dim view. Going to it never resulted in a positive improvement in observations. So it sits in my eyepiece case. The last post helps me understand why it has been unsatisfactory. Guess I will have to put the 8 on the Xmas list. Maybe the kids can collect their quarters up and buy it for me as a group gift :D

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Re: If you could only have one eyepiece for your telescope..

Postby steve-fung » Sat Oct 24, 2015 5:06 pm

I too was intrigued by the mention of Cains’ magic number but could not find an online reference to the eponymous magic number. However, I remember reading somewhere that although the dynamic range of exit pupil is ~1-7 mm, an exit pupil of 2-3 mm is considered optimal for maximizing resolving power. Since

exit pupil (mm) = aperture (mm)/magnification, and

PPI (power/inch) = magnification/aperture (inch) = 25.4 x magnification/aperture (mm) = 25.4/exit pupil (mm),

substituting an exit pupil of 2-3 mm, we find that the optimal PPI is 8.5-12.7 power/inch, which the upper limit is close to Cains’ magic number of ~13, probably where the number comes from.

I find the following websites helpful in determining useful ranges of PPI for visual observing:
http://www.chuckhawks.com/ocular_starter_set.htm
http://www.cloudynights.com/page/articles/cat/articles/how-to/useful-magnification-ranges-for-visual-observimg-r535

These are summarized below:
  • Low magnification: 3.7-9.9 power/inch (David Knisely), 5-8 power/inch (Chuck Hawks)
  • Medium magnification: 10-18.9 power/inch (David Knisely), ~10 power/inch (Chuck Hawks)
  • Medium-high magnification: 15-20 power/inch (Chuck Hawks)
  • High magnification: 19-31.9 power/inch (David Knisely), ~30 power/inch (Chuck Hawks)
  • Very high magnification: 32-46.9 power/inch (David Knisely)
  • Extreme magnification: 47-75 power/inch (David Knisely), although most people would argue that magnification >50 power/inch is empty magnification.

Therefore, Cains’ magic number of ~13 power/inch would fall within Medium Magnification range. From my own experience, I generally prefer PPI of ~10 power/inch, which is more in line with Chuck Hawks’ recommendation. To determine which eyepiece to use for given exit pupil or PPI and f-ratio,

eyepiece (mm) = exit pupil (mm) x f-ratio = 25.4 x f-ratio / PPI

Hope this helps with finding your optimal eyepiece for your telescope.
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