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Old Saturday 14th October 2017, 09:40   #26
Troubador
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[quote=wdc;3629718

For example, the notion that a wider field confers a 'big' advantage at close range seems entirely rational until one starts to look at the numbers a bit.

Binocular 'A' has a 372' FOV at 3000'
Binocular 'B' has a 430' FOV at 3000'

That's a 58' difference..... at 3000' It looks BIG on paper until you realize that difference only exists over a half mile away.

Bill[/QUOTE]

Hi Bill

Work out the area of the circle of view of each of these binos using the pi multiplied by radius squared, the radius being half of your linear fov measurement. Divide the smallest into the biggest to work out how many percents bigger the biggest fov is. Lets say its 20% bigger. It will be 20% bigger at every distance from the observer so it will be 20% bigger at 10 feet and 20% bigger at half a mile. And what can look like a modest number of feet difference can be very significant when calculated as an area of the circle of view.

However you cut it this means a 20% better chance of getting your binos on that warbler flying between trees to catch flies then hiding behind leaves or a 20% better chance of getting your binos on a dragonfly hunting next to a pond and changing direction so fast and so frequently that it makes your eyes hurt.

Lee

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Old Saturday 14th October 2017, 12:59   #27
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As a happy amateur, I don't pretend to understand the physics of some of these posts but, as with art, I know what I like. Having spent years with a Kowa 8.5x44 (fov 122m at 1000m), I have changed to a Nikon (fov 145m at 1000m), and am convinced it is less of a strain on the eyes during prolonged searching, makes it easier to follow birds through foliage, and FOR ME makes birding more pleasurable. Light transmission? I'll leave the experts to debate.
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Old Saturday 14th October 2017, 13:19   #28
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Originally Posted by Egrets Ivadafew View Post
As a happy amateur, I don't pretend to understand the physics of some of these posts but, as with art, I know what I like. Having spent years with a Kowa 8.5x44 (fov 122m at 1000m), I have changed to a Nikon (fov 145m at 1000m), and am convinced it is less of a strain on the eyes during prolonged searching, makes it easier to follow birds through foliage, and FOR ME makes birding more pleasurable. Light transmission? I'll leave the experts to debate.
Egrets

I think of it this way. Every time I look through SF 8x42 (148m) I see a bigger slice of the world so I feel that with every minute of viewing I am getting value for money. I am sure you feel the same way about your MHG.

Lee
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Old Saturday 14th October 2017, 16:34   #29
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Since the human retina/brain system does not have a linear response to stimuli, I would question its ability to see a 2-3% change.

But that's just me.
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Old Saturday 14th October 2017, 18:49   #30
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The relationship between light levels and perceived brightness is a tricky one. It is non-linear for a start. If you were to stare at steadily lit scene, then a sudden 3% drop in light level would only appear to drop by only 1%. That may well be detectable if you are sufficiently alert, but blink and you would miss it entirely. However you also have to factor in that your pupil diameter is constantly changing. Even when the light entering the eye is constant the light level at the retina will continually fluctuate up to 30% as much as twice second, and respond to changes in light level in a fraction of a second. If you were to look down for long enough to pick up another binocular all bets are off. At least the few friends and family I've used as guineapigs can't spot a 10% change.

It's often suggested that higher transmission extends the usage time at dusk. At least on the evening I sat outside with a light meter, the levels dropped about 50 fold in 10 minutes of roughly 3% every 18 seconds.

I'm not denying that binoculars can appear to differ in brightness in low light levels. One 8x42 I had for review looked distinctly brighter than one I own well after sunset. It was likely that the peak tranmission of that one was just a few percent better than mine, but when I blocked 10% of the objective it still looked brighter. That's a totally different can of worms.

David

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Old Monday 16th October 2017, 15:52   #31
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Linet Imperial made by Hiyoshi Kogaku (c. 1980). Quite a beautiful binocular.

Ed
i would really like to have a look through those - I'll admit your description tempted me to run a couple of ebay searches (to no result, perhaps fortunately). There are few things more enjoyable in using binoculars than looking through a pair with a really wide yet well corrected view, and drinking in that wide swath of landscape. Are those Hiyoshi binoculars single coated or multi-coated, and how do you find their image in terms of distortion, aberration etc? Holger Merlitz in his educative discussion of wide angle binoculars believes that the eyepieces of the day were "overstretched when applied to angles beyond 70 degs".

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Old Wednesday 18th October 2017, 19:41   #32
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i would really like to have a look through those - I'll admit your description tempted me to run a couple of ebay searches (to no result, perhaps fortunately). There are few things more enjoyable in using binoculars than looking through a pair with a really wide yet well corrected view, and drinking in that wide swath of landscape. Are those Hiyoshi binoculars single coated or multi-coated, and how do you find their image in terms of distortion, aberration etc? Holger Merlitz in his educative discussion of wide angle binoculars believes that the eyepieces of the day were "overstretched when applied to angles beyond 70 degs".

Best regards
patudo
Hi Patudo,

Sorry to miss your post. The only other person I knew who owned a Linet was Fan Tau, who specialized in wide-angle binoculars. By the time I contacted him some years ago he had already sold his 7x?. But he was very complimentary about it from a WA perspective.

My specimen is fully (single) coated, and therefore not as bright as a multicoated instrument. Considering the wide angle, however, it displays remarkably little lateral color fringing, and very little distortion. The center is very sharp. The one serious limitation is eye relief, and when I use it without glasses it allows for very little eye rotation without producing a kidney bean effect. This means that in use, redirection must be done primarily with the head and not the eyes.

I don't know what criteria Holger uses to define "overstretched," but I do agree from a human engineering perspective that a 63-70 deg. AFOV is probably optimal for general purpose use for two reasons: (a) reasonable eye relief can be achieved (15-19 mm), and (b) it corresponds more or less with the natural overlap region of the eyes. Anything beyond that necessarily includes large monocular regions and a different manner of instrument use. For astronomy it's probably advantageous if one can cope with the eye relief issue.

Ed
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Old Thursday 19th October 2017, 11:11   #33
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Thanks elkcub! Based on a number of ebay/web searchers (I just had to, honest!) you seem to be in possession of a rare bird indeed. I have used a Swift Holiday 7x35, the 572ft/1000 yard field of view version (writeup in progress), and the field of view through that was impressive enough, but the same image quality/correction etc. in an 8x with well over 600 feet would be amazing. Nothing captures flocking birds better than one of these extra wides.
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Old Friday 20th October 2017, 11:32   #34
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Zeiss HT is the absolute benchmark (at the moment, until someone does better) for light transmission among modern roof prism binos and if you are often viewing during the 1st half hour or last half hour of light in the day then you would struggle to better it with another roof prism bino. Of course there are many other aspects of importance to a bino's performance but we are discussing light transmission here. Personally I wouldn't put extreme light transmission such as the HT's as the most important priority, but HT has a very nice transparancy of view and handles really well too.

Lee
Lee.

The 95% quote is correct, but as you should know, it is at a certain nm reading. it is not always 95% across a wide range. Other binoculars achieve over 91-92% across a wider spectrum so at a certain nm figure could be said to have a higher transmission reading than those which have a high figure at a specific point. Some optical guys (who are really in the know) state that 5% variation is noticeable, but not less. I also think in some instances the "badge" makes all the difference to individuals perception of light transmission?

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Old Friday 20th October 2017, 17:46   #35
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Mak, post 34,
Intensity (transmission) differences lower than 3% can not be observed as I have outlined on page 24 of my literature study of "Color vision, brightness, resolution and contrast in binocular images" which is published on the WEB-site of House of Outdoor. It is in English, so not a problem for many readers of BF.
Transmission differences of 5% clearly show up as differences in brightness certainly for trained observers.
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Old Saturday 21st October 2017, 00:40   #36
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What percentage change (difference) is 0.1 magnitude?

Trained AAVSO observers regularly report such differences by means of reference stars.

(unless they are all using photometry today)
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Old Saturday 21st October 2017, 08:56   #37
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The ability to discriminate between levels of brightness (luminance) obviously depends on how bright it is to start with and the size of the areas compared. For instance using big bold paterns at high light levels on a professional 10-bit computer monitor it's apparently possible to detect differences as small as 0.1%. Of course simultaneous comparisons within a field of view are not what we are talking about here. We are asking whether it is possible to spot a 3% difference in transmission between binoculars.

I've mentioned before the little experiments I've done on myself and others masking objectives to reduce transmission. When conducted in a way to represent the way most people compare binoculars, no one I've tried could spot a 10% difference. Here's an even simpler test for those with a light meter and a dimmable room light. Get someone else to edge the brightness up or down while you look away (as you would while comparing binoculars), checks the meter reading, and note any difference you think you might see. Some might find the results surprising.
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Old Saturday 21st October 2017, 10:42   #38
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And then there is the role of the eyepiece, which is supposed to keep stray/ environmental light out, but never succeds at that for the full 100%. If I add to this the logic of perceived brightness and the role background colors such, as illustrated in the image in post 7, comparing brightness of binoculars becomes somewhat less exact than one might hope...
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Old Saturday 21st October 2017, 19:13   #39
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Hi Maljunulo, post 36.

A difference of 0.1 magnitude is 10% (9.65%).
There are different magnitudes. Visual, photographic and others.
The comparison stars and main star have to be the same colour, otherwise errors occur.

With say Betelgeuse or Mars it is difficult to judge because of the warm colour.
Also the comparison stars need to be at the same elevation to avoid atmospheric extinction. In a good sky compensation can be made.

The comparison stars must be non variable. But different catalogues may give different values.
There are many things to consider to get it right.

The main binocular star may be 2/5ths brighter than A and 3/5ths fainter than B. The resulting magnitude might be mag 7.63, which is rounded to mag 7.6.
One must be careful to centre the stars or have them equidistant around the centre field.
Telescopes are used for faint stars, down to mag 15 visually and considerably fainter with cameras.

I haven't made estimates for a while, but could estimate to mag 0.1 values. Many people cannot make star estimates.

Comet and extended objects are more difficult, but are given to 0.1 mag, but probably only accurate to mag 0.2 maybe worse. There are different methods and one must state the method used.

Several observers use ancient Japanese 10x50 Porros. They have made 100,000 or many more estimates over decades.

This is all a bit different than saying how bright the white columns are in binoculars 120m away from me in the daytime or twilight.

P.S.
Visual estimates are still commonly made.
Photometry can be more accurate, say to 0.01 magnitude, but only if one sets up the equipment to an exact standard.
Photometry can also give a light curve with very short time intervals or for extended periods.

Last edited by Binastro : Saturday 21st October 2017 at 19:21.
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Old Saturday 21st October 2017, 19:22   #40
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Hi Maljunulo, post 36.

A difference of 0.1 magnitude is 10% (9.65%).
Thank you.

I was pretty much aware of all the factors, but just concerned with the visual magnitude. I always assumed that the comparison stars were chosen with color (spectral type) as a consideration.

I tried estimating quite a long while ago, and immediately decided that it was not something I would ever be good at, so I moved on to other things I was not good at.
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Old Saturday 21st October 2017, 23:54   #41
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The ability to discriminate between levels of brightness (luminance) obviously depends on how bright it is to start with and the size of the areas compared. For instance using big bold paterns at high light levels on a professional 10-bit computer monitor it's apparently possible to detect differences as small as 0.1%. Of course simultaneous comparisons within a field of view are not what we are talking about here. We are asking whether it is possible to spot a 3% difference in transmission between binoculars.

I've mentioned before the little experiments I've done on myself and others masking objectives to reduce transmission. When conducted in a way to represent the way most people compare binoculars, no one I've tried could spot a 10% difference. Here's an even simpler test for those with a light meter and a dimmable room light. Get someone else to edge the brightness up or down while you look away (as you would while comparing binoculars), checks the meter reading, and note any difference you think you might see. Some might find the results surprising.
David,

I've done the same and concluded that I must be an absolutely terrible judge of brightness.

Ed
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Old Sunday 22nd October 2017, 20:55   #42
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Estimating the brightness of extended objects is difficult.
The following is for night observations, not daytime.

For estimating the brightness of comets visually one needs to list the following.

Method of estimating, there are three or four.
The type of telescope of which there are several.
The aperture of telescope or binocular or E for unaided eyes.
The magnification.
The focal ratio of the telescope, but not of binoculars.

The results are given to 0.1 magnitude although the typical spread is 1 to 2 magnitudes with different size optics. (2.5x to 6x).
The reason is primarily that the larger the telescope, the fainter the magnitude or total brightness the coma or head appears to be.
An empirical formula can be used to correct for aperture, but the raw results are usually given.

Frequently a magnitude 7.0 comet in binoculars, say 20x80, will be readily seen in a dark sky by unaided eyes as magnitude 5.5 or 5.7.
All manner of binoculars are used down to 2x opera glasses.
The observers are usually very experienced.

Last edited by Binastro : Sunday 22nd October 2017 at 20:58.
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