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Thread: Possibly adding to my 2" EP collection - hoping to hear thoughts on a few EPs

  1. #21
    j.gardavsky's Avatar
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    Default Re: Possibly adding to my 2" EP collection - hoping to hear thoughts on a few EPs



    Thanks n_F_A.

    The ratings of the binoculars in the link are very interesting, surprizingly the Vixen (Japan) falls in the 2nd tier
    (2nd rang in German), even if their 80mm binoculars are pretty expensive.

    There are basically 3 checks when looking for the binoculars suitable for astronomy.

    1. Fully multicoated is necessary, but broad-band fully multicoated is important, as even the fully multicoated binoculars from the Far East may suffer from a transmissivity drop at the short wavelength of light, like the H-Beta emission line in the nebulae. The not broad-band fully multicoated binoculars fail also on the deep red carbon stars, due to the transmissivity lost at deep red colors.

    2. The Porro Prisms. The BAK4 is not BaK4. The BaK4 prisms add an increasing transversal CA towards the edge of the field of view. The BAK4 phosphate glass prisms (China design), thanks to the lower dispersion of light, don't add as much CA, but they loose at least 2% of the transmission of light. The BaK4 Porro prisms used to be a problem in the made in Japan early copies of the Zeiss (and Hensoldt) binoculars around 1980, and then up to nearly 1990. Hence the designers in Japan have switched to the low dispersion BK7 prisms, especially on the wide field binoculars.

    3. The cheap Porro prisms assemblies are mass produced in one type of design, and you can find them in all budget binoculars from 7x50 up to 15x70 or even bigger. Quality big binoculars match the size of the Porro prisms to the front lens size, and to the requirement of the unobstructed view through the often larger EPs. There are also technical reasons to make the Porro prisms for the bigger binoculars bigger.

    There are 4+1 manufacturers of the top notch binoculars with the highest contrast, brightest views, and hardly any visible aberrations: Leica, KOWA Genesis)*, Swarovski, Zeiss (alphabetically), plus some high grade (HG) binoculars found at Minox and Nikon, where the difference to the first 4 is not much pronounced, even if I can see it. Minox HG looks closer to the (discontinued) Leica Ultravid line, the Nikon HG is a sort of outlier design regarding its overengineered eyepieces, I have discussed elsewhere
    All of them are using the phase coated roof prisms, which are much more expensive to manufacture than the Porro prisms, but which allow for a compact and more comfortably hand-held operation.

    )* I am thrilled of their optics design and performance Kowa Genesis XD44 8.5x DCF Binocular
    for 1/2 price of the Swarovski EL Swarovision.

    Best,

    JG
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  3. #22
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    Default Re: Possibly adding to my 2" EP collection - hoping to hear thoughts on a few EPs

    Thanks for the above advice. Now i'm curious to see what my exit pupil is using the hex key method mentioned by not_Fritz. It looks like my target EP will be an ES82° 30mm which covers my TFoV desires, doesn't create a shadow from the secondary mirror, and most likely is aligned with my maximum exit pupil. I'll keep my eyes peeled on the secondary market.

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    Default Re: Possibly adding to my 2" EP collection - hoping to hear thoughts on a few EPs

    Quote Originally Posted by Reddog1972 View Post
    Thanks for everyone's sage advice and input. I'll definitely look into the suggestions provided, but at the end of the day you're probably right to wait and invest in the better ES series of EPs.
    You should also consider used. I've had good experiences with that route.
    Don

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    Default

    +1 on the buying used suggestion. That's how I picked up my Naglers and LVWs, along with several others along the way. You can often make worthwhile savings that way, and people tend to look after their eyepieces (especially expensive ones) .

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    Default Re: Possibly adding to my 2" EP collection - hoping to hear thoughts on a few EPs

    The ES82 30mm is definitely a good choice. Mine certainly isn't going anywhere!
    Celestron Powerseeker 114az "Little Tyke", CPC 1100 GPS “Big Daddy 2.0”
    ES82 30mm, 6.7mm, 4.7mm; Tele Vue Delos 17.3mm, 12mm; Tele Vue DeLite 9mm; Meade UWA 14mm; Assorted Budget EPs
    ES 2" 99% Dielectric Diagonal

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    Default Re: Possibly adding to my 2" EP collection - hoping to hear thoughts on a few EPs

    I agree with nFA. I find the ES 82 24mm is as long in focal length as I wish to go with my f/4.5 to f/5 dobs, which gives me an exit pupil of around 5mm. That is exactly where I prefer to hold the line for myself.

    As far as one's pupil dilation goes, one thing to consider is that due to light pollution brightening the sky and and general surroundings, plus the impact of ambient ground lighting nearby, most of us are never going to achieve full dark adaptation nor full potential pupil dilation. So an excessive exit pupil with be even more noticeable under such conditions.

    Though I am late to this party I do have direct experience with one Q70, the 32mm. I used to have one years ago and in a Zhumell Z12 I had at the time, at f/4.9 it was messy. A good portion of the outer part of the field was full of smeared stars mostly due to astigmatism of the eyepiece design more than coma inherent with faster mirrored optical systems. Almost any eyepiece is good in the center and its when you start moving away from the center of the field of view that you will start seeing such issues. When I sold that scope I gladly gave it to the new owner to be rid of it. They are somewhat of a modified Erfle design, similar to a lot of the 2 inch 30mm eyepieces that are included with many of the mass produced dobs. As Andrey said, the Agena SWAs are the same eyepiece with their house brand label on it. They can be very good in slower optical designs, but in faster systems they struggle. So if you want to go with an 82° AFOV eyepiece, I would personally go with the 24mm based on my experience.

    I too have had good success with the used market for various things. Though I will say, my run of ES 82s were all bought new during their sales. But there are always plenty of good eyepieces in the used market to be had.
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    Default Re: Possibly adding to my 2" EP collection - hoping to hear thoughts on a few EPs

    I have used the 30mm Olivion (available under many brand names RPD1, Moonfish, OWL, and unbranded directly from China on ebay for about $75 currently as a UW80) and it is fine as a "sweeper-finder" in all but the fastest sub f4 scopes. The other suggestions for 80 degree or greater fields will progressively improve the edge performance at increasingly exponential increases in price. If you want clean wide views to the edges, the TeleVues and ES's justify their cost, but remember that the acute field of human vision is a cone of less than 5% diameter of your total field of vision. If you can't stand the esthetics of a soft or distorted perimeter as you view extended objects, the expensive eyepieces are the only solution, but if you don't mind bumping your target back to the center every few seconds, you can save yourself a lot of money while still enjoying the benefit of not losing your target due to limited field size. The older narrower field and longer focal length designs above 40mm like the above mentioned Russells, will be cleaner further to the edges, but the equivalent field will still be smaller and have noticeable brightening of the sky due to their lower magnification. There will also be a greater risk of excessive exit pupil size or secondary mirror shadow, especially if you will eventually get a larger Dob, so I don't find them as useful overall as the 80 degree 30 or 31 mm eyepieces.
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