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Old Tuesday 20th February 2018, 23:25   #76
typo
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I've been busy and haven't had time to go through all the recent posts, but I think it's worth picking up on this point from #68.

"It's not that the faint stars brighten with magnification, but they become detectable because sky background becomes dimmer and the contrast between a faint star and the sky background is better."

Contrast is the ratio of signal to noise. In this case star to night sky. Increasing the magnification and reducing the exit pupil dims the whole view, both signal and noise so the ratio would be unchanged. That is, until the instrument, or the eye, becomes diffraction limited and the point source spreads when the signal to noise, or contrast would decrease. It doesn't seem to explain why increased magnification making stars more visible.

I need some sleep. I'll have a look at the rest tomorrow.

David
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Old Tuesday 20th February 2018, 23:46   #77
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I've been busy and haven't had time to go through all the recent posts, but I think it's worth picking up on this point from #68.

"It's not that the faint stars brighten with magnification, but they become detectable because sky background becomes dimmer and the contrast between a faint star and the sky background is better."

Contrast is the ratio of signal to noise. In this case star to night sky. Increasing the magnification and reducing the exit pupil dims the whole view, both signal and noise so the ratio would be unchanged. That is, until the instrument, or the eye, becomes diffraction limited and the point source spreads when the signal to noise, or contrast would decrease. It doesn't seem to explain why increased magnification making stars more visible.

I need some sleep. I'll have a look at the rest tomorrow.

David
Hi, David:

You probably shouldn't talk too much about defraction because if the "A" type personalities knew just how bad even the "Alpha" binos were, they would probably just say to heck with it and take up ... needlepoint!

Bill
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Old Wednesday 21st February 2018, 05:35   #78
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Bill,

I'm not going to defend the optical industry on that one. I think the ISO14133 standards used by the industry, including the big three, are woefully inadequate. Fortunately, most of the time for terrestrial use the instrument resolution value is pretty much irrelevant. By accident, if not design there are binoculars about that will deliver 116/D when it matters. They are worth looking out for.

I really don't need to remind you that terrestrial observation is quite different to astro viewing. Even the most exotic astro refractor on the planet would have a practical magnification limit of about 12x per inch for some users. My eyesight isn't that good. It's about 14x for me.

David
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Old Wednesday 21st February 2018, 06:00   #79
typo
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..............

Two things occur to me here. Firstly that the amount light being transmitted through the bino might be different from the brightness as perceived by the viewer and secondly that the significant factor might be the area of the retina being stimulated by the EP rather than the density of photons in the EP.

Lee
Lee,

I'll answer those two components separately.

"the amount light being transmitted through the bino might be different from the brightness as perceived by the viewer ".

I think there is a strong case to be made that perception is critical to this story. As I mentioed above, reducing the EP and dimming the view wouldn't increase real contrast, but perceived contrast is quite different. That's dependant on the biochemisty and physiology of the eye and the neuronal processing of the electrical signals from the receptors. I've no more than the sketchiest knowledge of what happens there, but I'm sure it's the key to answering some of these questions.

".... the significant factor might be the area of the retina being stimulated by the EP rather than the density of photons in the EP"

The area covered by the projected image of the star? Almost certainly. Not the angle of view passing through exit pupil and projected on the retina.

David

Last edited by typo : Wednesday 21st February 2018 at 06:05.
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Old Wednesday 21st February 2018, 14:52   #80
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Bill,

I'm not going to defend the optical industry on that one. I think the ISO14133 standards used by the industry, including the big three, are woefully inadequate. Fortunately, most of the time for terrestrial use the instrument resolution value is pretty much irrelevant. By accident, if not design there are binoculars about that will deliver 116/D when it matters. They are worth looking out for.

I really don't need to remind you that terrestrial observation is quite different to astro viewing. Even the most exotic astro refractor on the planet would have a practical magnification limit of about 12x per inch for some users. My eyesight isn't that good. It's about 14x for me.

David

Ah, but just think how often "... is pretty much irrelevant" could be used concerning so many things observers sweat about.

B
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Old Thursday 22nd February 2018, 23:26   #81
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I have used the 7x42 Dialyt, P version, a fair amount. It has more field of view than any of my other binoculars with comparable eye relief, but in most scenarios all that the extra 10m or so did was let the pigeon being hunted come into view a second or so earlier. When I did get to see flocks under attack in the open sky, the large field of view did let me see more of the flock, but I found the falcon might go off so high and/or far away before attacking that it was very difficult to follow with 7x. The 7x42 has some great qualities - I love the way it comes so easily to my eyes and is so steady compared to 10x (and even 8x) which together make for a really enjoyable fatigue free view - and is great for closer observation but (as of right now anyway) I prefer the size of image 8x or 10x gives me at most of the distances I'm observing at.

Last edited by Patudo : Thursday 22nd February 2018 at 23:39.
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Old Thursday 22nd February 2018, 23:40   #82
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I have used the 7x42 Dialyt, P version, a fair amount. It has more field of view than any of my other binoculars with comparable eye relief, but in most scenarios all that the extra 10m or so did was let the pigeon being hunted come into view a second or earlier. When I did get to see flocks under attack in the open sky, the large field of view did let me see more of the flock, but I found the falcon might go off so high and/or far away before attacking that it was very difficult to follow with 7x. The 7x42 has some great qualities - I love the way it comes so easily to my eyes and is so steady compared to 10x (and even 8x) which together make for a really enjoyable fatigue free view - and is great for closer observation but (as of right now anyway) I prefer the size of image 8x or 10x gives me at most of the distances I'm observing at.
Hello Patudo,

All very good points, except that the older Dialyt 7x42 does not have a very close focus. In wooded areas, I see no great advantage in an 8x glass. 10x glasses provide too narrow an FOV for following flying birds and in my hands are too shaky for targets much above the horizon. Certainly the glass has to meet the needs of a user.

Happy bird watching,
Arthur
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Last edited by Pinewood : Friday 23rd February 2018 at 16:19.
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Old Friday 23rd February 2018, 16:17   #83
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...the older Dialyt 7x42 do not have a very close focus...
Mine get down to 12 feet, which is competitive with most full sized bins, including several top-end current models. In their day, 12 feet was probably considered excellent. Many old bins have a hard time under 20-25 feet.

I find the Zeiss 7x42 BGATP not good for butterflies, but fine for most birding.

--AP
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Old Sunday 4th March 2018, 12:32   #84
simonineaston
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How many here like the 7X42 format...
A.W.
Just about to find out! There's a pair of ancient Habicht 7x42s in the post to me. I've been using mid '70s Trinovid 8x40 up 'till now but thought I should try slightly less magnification in case it improves the over-all expereince. Am expecting that I'll benefit from deeper depth of field and an image that's slightly easier to keep still. Will let you know :-)
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