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Binocular Magnification?

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#1 Joad

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Posted 02 July 2005 - 08:06 PM

I have some hunches about the answer to this question, but I'd like an expert's point of view (not "opinion" because I know the answer will be simple and objective without any need for subjectivity) on it, and I know there are a number of folks here who can offer just that. My question is why very large binoculars (let's say 100mm, or even 150mm) have such a limitation on magnification, even with the interchangeable EP binoscopes like the Oberwerk 100mm binoscope. Since refracters seem to be able to take a proportionately high magnification per inch of aperture (I see posts on the Refracter forum here about 80mm refracters going to 200X w/o image breakdown), I wonder why binoculars, which are refracting instruments, seem to max out at 100X (tops), with seasoned viewers finding 40-62X about the real upper limit. I know that the Fuji 150s only go to 40X, and I once saw a Russian behemoth (180mm) that only had a 30X. I know there's an easy explanation here. Any takers? Thanks.

#2 Glassthrower

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Posted 02 July 2005 - 08:22 PM

That's a darn good question that I would be very interested in hearing an answer to as well. We all know the basic fundamentals of focal length of objective/focal length of eyepiece, but it does appear that binocs "top out" at the low end of the magnification spectrum....why?

I have heard (arbitrarily) that the upper-limits of useable magnification is approx. 50x per inch of apeture. Given that my 100mm binocs have the equiv. of 4 inches of apeture, I would expect the maximum magnification should be around 200x. What gives? Why hasn't a manufacturer made a pair of fixed power giant binocs with a magnification of say 75x or 100x??????? Or would that be considered a bino-spotting-scope??

MikeG

Sorry, I know that didn't answer the question!

#3 AJTony

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Posted 02 July 2005 - 09:05 PM

If your binos were 3 to 4 feet long, you could up your power, because magnification is determined by dividing the focal length of the objective by the focal length of the eyepiece. So, a normal 100mm bino would have an objective focal length of about 600mm. Therefore, 10mm eyepiece would give you 60 power. If your binos were about three feet long, 900mm focal length, the 10mm eyepiece now gives you 90 power.

Well, that's my little input. There are much more knowledgable people on this forum who will be able to really help clear up this question much more than I can.

AJ

#4 Pinewood

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Posted 02 July 2005 - 09:13 PM

Perhaps the limiting factor is difficulty to collimate high magnification. Or perhaps tiny exit pupils limit the stereo effect.

Clear skies,
Arthur

#5 MaritimeSky

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Posted 02 July 2005 - 11:03 PM

It's probably due mostly to the dual barrels. While a single barrel telescope will provide fantastic images at high magnification, binoculars need both barrels to be VERY precisely aligned and rigid to support the two-eyed view we all love so much. If it were easy, I'm sure nobody would own a single barrel telescope. Collimating binoculars at near planetary observing magnifications would be a severe exercise in frustration, I believe.

#6 Rich N

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Posted 02 July 2005 - 11:04 PM

Most of these binoculars are designed for the purpose of giving relatively wide fields of view and bright images. This is why they are relatively low power for the objective size.

To get high quality images at 200x you need much better optics than you find in most binoculars. People sometimes make binoscopes by fitting to telescopes together.

Rich

#7 BillC

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Posted 02 July 2005 - 11:31 PM

Why don’t army tanks have leather interiors, air bags, and 6-CD changers?

‘Cause that is not what they were designed to have.

1) Binoculars were designed to provide wide fields of view in a hand-held format. And, you can’t have wide fields and high magnifications at the same time.

2) Collimation in high powered binoculars is pretty much out. First, there are not enough people on the planet with the patience and skill to keep even 200 of these things going.

3) Manufacturers are not going to spend the money to come up with systems that are adjustable enough and rigid enough to make the effort worth while.

4) If they did, they would cost about three times as much as the current Fujinon 25x150, which are already WAY too expensive for most of us.

5) Finally, if you had a system in which collimation could be attained and maintained, the chromatic aberration of a 6-inch, f/5 doublet at high-power would render an image so full of lateral color, it would look like a George Harrison nightmare.

So much for my 2-cents worth.

Kindest Regards,

Bill

#8 DJB

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Posted 03 July 2005 - 01:21 AM

Hi Pinewood and all,

I haven't read all the posts, but I will commit to the real probability that, getting, or even keeping, such binos in collimation would be a real and expensive bear.

Observe the posts on the CELESTRON 25x100mm binos with collimation problems. I had that problem with an ORION 25x100mm, but 'they' made it right. Bought the OBERWERK, and it was dead nuts on.

I would suggest that opto-electrical systems could do the trick for about 30k to 45k, or more, such as can be found in military devices of all sorts. Just a thought.

Regards,

Dave.

#9 edwincjones

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Posted 03 July 2005 - 06:39 AM

Binoculars and telescopes are two different beasts-binoculars look at the forest, telescopes look at the trees.
We blur the boundries with binoviewers for telescopes and interchangeable eps for binoculars. The two groups that may succeed most are the binoscopes with two refractors and JMIs reverse binoculars-both expensive.

If I am racing across Iraq in a tank, I would like to have leather seats, good music on the stereo CD, a frig full of cold beer, and my binoculars mounted on the top; but that will not happen soon. In the meantime, I will use binoculars and telescopes as complimentary tools side by side.

Ed Jones

#10 edwincjones

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Posted 03 July 2005 - 06:58 AM

To be accurate, I do have 37x eps for my 20x100, but rarely use them because the 20x are more enjoyable; and I usually use binoviewers with telescopes because I can see better with two eyes.

Ed

#11 Joe Ogiba

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Posted 03 July 2005 - 09:06 AM

I have a 80mm fluorite triplet APO that can do 600x in the right conditions but when I want to use 200x with both eyes I use my binoviewer with my C9.25 or 10" Dob. I think a binoviewer/telescope setup is the only way to go for high power since a JMI Telescope RB-16 Reverse Binoculars are $10,000 and a 20" Starmaster with Zambuto mirror for $7,495 plus a binoviewer might be a better setup.

#12 Pinewood

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Posted 03 July 2005 - 10:13 AM

Do we have a consensus that 25x is the practical limit for binoculars?

Clear skies,
Arthur

#13 EdZ

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Posted 03 July 2005 - 10:58 AM

Do we have a consensus that 25x is the practical limit for binoculars?


Well, No, I don't think so.

I've been using my BT100s at 24x, 31x, 37x and most often recently at 44x. My two favorites are 31x and 44x.

But I do agree that one of the most important limiting factors is the difficulty of collimating precisely at high magnifications.

The fast focal ratios pretty much dictate lower magnifications than what you might think of using for scopes. Most small binoculars are near f/4. The Celestron 25x100 is near f/5. The Oberwerk BT100 is f/6.2.

Maximum powers of 50x-60x per inch can be achieved in some scopes. My TV85 can get near 70x/in. My Stellervue AT1010 maxes out at about 45x-50x/in. My 6" f/5 reflector is best used at 30x-40x/in. or less. But optimum exit pupils are often thought of as in a range near 2mm, some very large scope owners even say 2.5 to 3mm. For any optic, a 2mm exit pupil is 12x per inch. That would be 48x for the BT100.

Binoculars are optimized, not for high powered viewing, but for lower power, wider field, brighter image viewing.

edz

#14 Joad

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Posted 03 July 2005 - 12:16 PM

Thanks, all. My hunch was that collimation was a major factor in the equation.

On a related note, last night I tried to see if a cheap 20X50 binocular that I got as a loss leader for $25 some years ago would work as a spotting instrument, especially for Tempel 1. Well, the thing works well in the daytime but it is completely useless at night not only because (as I know) 20X is far too much for a hand held binocular but also because I couldn't get both oculars to focus on any sky object. Collimation must be out by about as far out as that can go. No matter, I got the thing for a song.

I also think that the best combination is a giant binocular (the Oberwerk design in the triplet 100s is especially conducive to solid collimation--mine have always seemed to be well collimated) to see the forest, and a telescope to see the trees. I am seriously considering a bino-viewer for the scope though. I guess I'll go to the bino-viewer forum for guidance. Thanks.

#15 grbrown

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Posted 10 July 2005 - 05:10 AM

My wife and I have joined the "International Kunming Century Binocular Association", having just bought a pair of 45 degree 100mm binoculars.

[For UK readers the same Chinese made bins that are sold in the US as Oberwerk are marketted here by at least 3 companies, under different brand names: Kay Optical, Monk Optics, Cyber Services - study each carefully before buying, as prices vary greatly!].

Our choice has been greatly helped by studying Cloudy Nights and other US websites, so thanks to you all!

The reason for this post is that we both wear spectacles and the standard 40x eyepieces are not spectacle friendly, with only around 8mm eye relief. So we are looking at buying more suitable ones, which prompts us to also consider a different focal length to get the best out of our new toy. I should say that whereas we will use them for astronomy we are especially thinking of bird watching!

So this string has been very interesting, especially EdZ's comments. If it does not cause astronomers mortal offence, any further suggestions for daytime use would be appreciated, but we now have a very useful steer!

Best wishes,

Graham. :bigshock:

#16 Rich N

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Posted 10 July 2005 - 08:24 AM

At 40x aren't those binoculars showing quite a bit of CA in the bright daylight?

Rich

#17 Guest_**DONOTDELETE**_*

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Posted 10 July 2005 - 08:30 AM

Welcome to CN Graham! And to the big bino community. A question. Which binocular do you have exactly? I am a bit confused about your statement of "standard 40x EPs".

#18 Joad

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Posted 10 July 2005 - 10:36 AM

Welcome to CN grbrown (I like using our "code names"). I've got the same Kunming setup you have (the Oberwerk 40X100 45° binocular) and, even without eyeglasses, I have experienced that scant 8mm eye relief problem. (Night Watch, Monk Optics, as well as Oberwerk, still offers the 40X100 45° binocular with fixed proprietary oculars as an "upgrade' to the 25X100mm 45° binocular--this is different from the new fork-mounted 45° binocular with interchangeable EPs.) My experience is that the eye relief problem is trickier by day than at night (though I do not notice any significant CA by day). That is, the field of view is more noticeably restricted in daytime viewing, but the viewing is still very nice. The 45° ocular angle is not as important for daytime viewing near or below the horizon, which gives you more choice if you are looking to switch binos. And if you are thinking in terms of birding, you might want to consider a lighter setup. I realize that even the lighter binos (Miyauchis, for example) are not something you can hang around your neck, but the Kunming bino is VERY heavy, as you well know. It's built like a tank, which has the advantage (in the single solid unit) of holding collimation very well. Good luck on your search for the bino that's best for you.

#19 Guest_**DONOTDELETE**_*

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Posted 10 July 2005 - 12:14 PM

Oh ok. Thanks for the clarification Joad. There are a few varieties of the BT100 out there. I get them mixed up sometimes.

#20 grbrown

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Posted 11 July 2005 - 04:01 PM

Hi 'night watch',

If you care to go to:

http://www.binocularschina.com/

you will discover the Chinese manufacturer of Oberwerk binoculars and that Oberwerk have secured the sole rights to the USA. Here in the UK there are at least 3 importers, all using their own brand names, 'Strathspey' being the ones we selected. Oberwerk, Strathspey and the others each chose to include as part of their standard package a different mix of the various accessories the makers offer.

So our 'Strathspeys' are the 45 degree model, in a cool champagne paint and came with both 25x and 40x eyepieces (62x are also available from the makers, though Strathspey don't import them). We also got the finder scope included in the price.

Unfortunately, despite being built like a tank, ours got knocked out of colimation in transit, so have gone back to be reset. For anyone who has not come across these bins, they come in an intimidatingly large and heavy box! It is difficult to think of such a heavy object being 'fragile', but our seller reckons about 1 in 20 suffer this problem.

But back to eyepieces, the 25x are OK, but we are already considering buying an alternative brand of spectacles-friendly eyepieces to replace the 45x. Any suggestions will be greatly appreciated! I gather the latest Meade 5000 series are Chinese-made, and also attractive because they appear to have movable eyecups rather like our Leica Trinovids.

Has anyone found some really great alternatives? Look forward to hearing from you,

Graham. :watching:

#21 grbrown

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Posted 11 July 2005 - 04:04 PM

I should have added that our Oberwerk/Strathspey have 1.25 inch interchangeable eyepieces.

#22 EdZ

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Posted 12 July 2005 - 08:59 AM

Go to the Binocular MiniReviews and follow the link to the thread on Eyepieces for the BT100. Post any questions on interchangable eyepieces to that thread which at this point probably includes discussions on about 12-15 different eyepieces for this binocular.

edz

#23 KennyJ

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Posted 12 July 2005 - 11:25 AM

< Unfortunately, despite being built like a tank, ours got knocked out of colimation in transit, so have gone back to be reset. For anyone who has not come across these bins, they come in an intimidatingly large and heavy box! It is difficult to think of such a heavy object being 'fragile', but our seller reckons about 1 in 20 suffer this problem.>

Graham ,

A belated welcome to Cloudy Nights !

With regard to your statement which I've cut and pasted above , are you SURE these 1 in 20 specimens are properly collimated BEFORE they leave the factory ?

To me , 5% sounds like an unlikely high figure for such robust bits of kit to be damaged in the way your supplier is trying to make you believe.

Regards , Kenny

#24 EdZ

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Posted 12 July 2005 - 11:31 AM

I agree Kenny. In fact, I commented on this post, but I posted the comment in another thread where the discussion was about all binoculars losing collimation in shipping, which I also consider rubbish.

This binocular has one of the most robust prism shelf adjustments you are likely to come across. This binocular would have had to incure some serious abuse, not standard shipping/handling, in order to be knocked out of collimtion during shipping. Either it was out before it was shipped or somebody is literally throwing boxes around.

edz

#25 grbrown

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Posted 12 July 2005 - 01:46 PM

Thanks for the various greetings and comments. On the robustness of these binoculars I can only repeat what our dealer said, which is that they were checked for collimation before shipping to us! Compared with their trip from China to the UK they did not have to travel far from him to us. When they return we will see if they survive this time.

I am still finding my way around here, so am off to the minireviews to see what more I can learn about eyepieces. Many thanks edz.


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