• Welcome to BirdForum, the internet's largest birding community with thousands of members from all over the world. The forums are dedicated to wild birds, birding, binoculars and equipment and all that goes with it.

    Please register for an account to take part in the discussions in the forum, post your pictures in the gallery and more.
ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

Compact (8x20) Binocular Focus (1 Viewer)

D

dalethorn

Well-known member
Something I discovered trying for critical focus adjustments with the 8x20 Ultravid:

Initially I tried focusing in the daytime at a local park with trees and seating facilities etc., not able to get what I thought was a perfect (or nearly so) focus and diopter adjustment.

Then this morning at dawn when it was still somewhat dark, while I was musing on the subject of Twilight Factor, I had the idea to try the 8x20 on some parked cars and buildings around 75 yards distant. What I discovered surprised me, in that I could focus much more easily and accurately under this dim light.

I get the notion that the combination of high resolution with this binocular, plus the lack of unneeded distractions competing for my attention (less light and simpler objects to focus on), made such an important difference for me in achieving critical focus.
 
Dale

While simpler subject to focus on may have helped (registration plates can be good) the dim light works against you because as your pupils get bigger, your eye's ability to perceive small details reduces. If you are a photographer you may be familiar with the fact that lenses at f2.8 do not usually reproduce details as well as at f8.0 and its similar with eyes too.

Lee
 
Troubador said:
Dale

While simpler subject to focus on may have helped (registration plates can be good) the dim light works against you because as your pupils get bigger, your eye's ability to perceive small details reduces. If you are a photographer you may be familiar with the fact that lenses at f2.8 do not usually reproduce details as well as at f8.0 and its similar with eyes too.
Lee
Click to expand...

That was certainly my instinct before doing this experiment, but when I saw the dramatic difference, my secondary instinct kicked in for the explanation, which seems quite obvious at this point:

How much light do I need, and would too much light increase the difficulty?

Can I get better focus on irregular objects such as trees and leaves - details of which are very small at distance? Or do better with items that are engineered with straight lines, sharp edges, familiar details?

My eyes go with "just enough" light, good contrast, and familiar sharp/regular objects. And it's not even close.
 
Since focus is so critical in low light, maybe it makes it easier for you to find the correct setting. Perhaps the low light also helps your eyes relax and let the binocular and diopter do the focusing. With higher light levels, there is more to see, and more can be brought into focus through accommodation and pupil contraction, but maybe your eyes aren't up to those tasks anymore so they do better to relax and let the bins do the work. Also, in low light, the details you see may be dominated more by visual processing/imagination, so you "see" the simple edges clearly and are not getting enough signal to be confronted with the limitations of your vision.

The above aside, it is tricky to set the diopter on 8x20 bins. You must take _great care_ to keep the proper IPD and keep the exit pupils properly aligned with your pupils. Maybe the low light also helps you to do that.

--AP
 
Alexis Powell said:
Since focus is so critical in low light, maybe it makes it easier for you to find the correct setting. Perhaps the low light also helps your eyes relax and let the binocular and diopter do the focusing. With higher light levels, there is more to see, and more can be brought into focus through accommodation and pupil contraction, but maybe your eyes aren't up to those tasks anymore so they do better to relax and let the bins do the work. Also, in low light, the details you see may be dominated more by visual processing/imagination, so you "see" the simple edges clearly and are not getting enough signal to be confronted with the limitations of your vision.
The above aside, it is tricky to set the diopter on 8x20 bins. You must take _great care_ to keep the proper IPD and keep the exit pupils properly aligned with your pupils. Maybe the low light also helps you to do that.
--AP
Click to expand...

My night vision is excellent when driving, so I think rather than a normal situation with tired eyes, it's something else. But anyway, my purpose in making this post wasn't to speculate on my vision anomalies, but rather to offer what might be an unexpected tip to those who have excellent optics, but are struggling to focus as I was.
 
Last edited:
dalethorn said:
My night vision is excellent when driving, so I think rather than a normal situation with tired eyes, it's something else. But anyway, my purpose in making this post wasn't to speculate on my vision anomalies, but rather to offer what might be an unexpected tip to those who have excellent optics, but are struggling to focus as I was.
Click to expand...

This is good advice from Alexis, the IPD is tricky on these small binoculars, and so very important with satisfaction of view.

I have the same binocular, and would advise when getting the diopter where you want it, under the lighting conditions you mentioned, to just leave it alone
when you get there.

Small binoculars are fiddly, not as easy or user friendly as larger sizes, compromises are real with the very small size.

Jerry
 
NDhunter said:
This is good advice from Alexis, the IPD is tricky on these small binoculars, and so very important with satisfaction of view.
I have the same binocular, and would advise when getting the diopter where you want it, under the lighting conditions you mentioned, to just leave it alone
when you get there.
Small binoculars are fiddly, not as easy or user friendly as larger sizes, compromises are real with the very small size.
Jerry
Click to expand...

Yes, agreed. Once I set that diopter this morning, all focusing since then has been OK. Maybe not ideal given my prescription (can't focus without the glasses), but resting the binoc on a stable surface, I can run the knob from out-of-focus one direction through good focus to out-of-focus the other direction. Items at a real distance, more than, say, 150 yards, tend to focus at the very end of the focus wheel's turning.
 
dalethorn said:
Yes, agreed. Once I set that diopter this morning, all focusing since then has been OK. Maybe not ideal given my prescription (can't focus without the glasses), but resting the binoc on a stable surface, I can run the knob from out-of-focus one direction through good focus to out-of-focus the other direction. Items at a real distance, more than, say, 150 yards, tend to focus at the very end of the focus wheel's turning.
Click to expand...

4. DIOPTRIC ACCOMMODATION

This is an anomaly of your own physiology, something that affects almost every observer, and is something you control.

Frequently, an observer will focus on a target quickly and expect the instrument to remain focused—at least at the given distance. However, let’s say you have a dioptric accommodation range of 4 diopters and stop focusing the instant you have an adequate image. As time goes on, observing may become problematic because your natural (relaxed at that distance) focus setting should be -1.5 diopters. That means being in a hurry has placed your focus at an accommodatable, but strained, setting.

Then, as fatigue sets in, you may fiddle unnecessarily with the focus or suppose there’s something wrong with your eyes or the binocular when neither is true. In addition, as this “fiddling” takes place, the observer will more than likely repeat the hurried technique that got him into trouble in the first place, leaving him or her once again with an imprecise focus. Perhaps your mother taught you never to stare. Nevertheless, if you want a crisp image, you had better forget that advice.

Dioptric accommodation (the ability to focus at a range of distances) is achieved through the eye’s ciliary muscles, which stretch and compress the eyelenses in order to achieve a sharp focus.

A 10-year old may have as much as 14 diopters of accommodation. But as we age dioptric flexibility drops off fairly quickly. By age 20, it has dropped to 8 to 10 diopters with the average binocular user—40 to 50 years of age—having only a 4-diopter accommodation. Thus, with each year that passes—up to about 60—the focus mechanism, becomes ever more critical.

Learning to stare comes easily for some people but takes a great deal of practice for others. But learning to stare, letting the binocular’s focus come to you, is worth the effort and is absolutely essential to attaining the sharpest image, most trouble-free focus, and the sharpest views of the nature around you. :cat:

Bill
 
Bill I guess we are close in age, well you are a little younger.;) Oh Ok I see now , July so you are older. I do feel the age sometimes.;)
 
Last edited:
mooreorless said:
Bill I guess we are close in age, well you are a little younger.;) Oh Ok I see now , July so you are older. I do feel the age sometimes.;)
Click to expand...

Let's not go there ... it's embarrassing. Besides, who are you? I don't recall giving you this number! See what I mean? In high school and college, I had a MENSA IQ. Today, I don't even have a MENS IQ. :eek!:

Bill
 
WJC said:
4. DIOPTRIC ACCOMMODATION This is an anomaly of your own physiology, something that affects almost every observer, and is something you control. Frequently, an observer will focus on a target quickly and expect the instrument to remain focused—at least at the given distance. However, let’s say you have a dioptric accommodation range of 4 diopters and stop focusing the instant you have an adequate image. As time goes on, observing may become problematic because your natural (relaxed at that distance) focus setting should be -1.5 diopters. That means being in a hurry has placed your focus at an accommodatable, but strained, setting. Then, as fatigue sets in, you may fiddle unnecessarily with the focus or suppose there’s something wrong with your eyes or the binocular when neither is true. In addition, as this “fiddling” takes place, the observer will more than likely repeat the hurried technique that got him into trouble in the first place, leaving him or her once again with an imprecise focus. Perhaps your mother taught you never to stare. Nevertheless, if you want a crisp image, you had better forget that advice. Dioptric accommodation (the ability to focus at a range of distances) is achieved through the eye’s ciliary muscles, which stretch and compress the eyelenses in order to achieve a sharp focus. A 10-year old may have as much as 14 diopters of accommodation. But as we age dioptric flexibility drops off fairly quickly. By age 20, it has dropped to 8 to 10 diopters with the average binocular user—40 to 50 years of age—having only a 4-diopter accommodation. Thus, with each year that passes—up to about 60—the focus mechanism, becomes ever more critical. Learning to stare comes easily for some people but takes a great deal of practice for others. But learning to stare, letting the binocular’s focus come to you, is worth the effort and is absolutely essential to attaining the sharpest image, most trouble-free focus, and the sharpest views of the nature around you. :cat: Bill
Click to expand...

I appreciate the information and advice, especially about all the variables involved. In engineering, we learnt about things like iteration and interpolation, which makes it easier to understand what you're saying, and get it into practice.
 
Last edited:
Bill: really nice explanation of dioptric accommodation.

Bill & Steve: got you both beat. I'm 69 and still breathing, most days.

Lee
 
WJC said:
Perhaps your mother taught you never to stare. Nevertheless, if you want a crisp image, you had better forget that advice.
Click to expand...


Bill, would you mind please expanding a bit on stare, i.e. why it's important, and how to do it right (other than the obvious)? thanks!

Does moving past the focus point, and then approaching it as the midpoint between where it goes out of focus on either side, help to avoid focus accommodation?
 
cdmackay said:
Bill, would you mind please expanding a bit on stare, i.e. why it's important, and how to do it right (other than the obvious)? thanks!

Does moving past the focus point, and then approaching it as the midpoint between where it goes out of focus on either side, help to avoid focus accommodation?
Click to expand...

Staring is important because if you can’t/won’t do it, you may never get an at-rest focus, which causes you to keep fiddling with the focus and making the same mistake over and over again.

Focus at infinity; the blue sky will be adequate. Then move the bino in place trying NOT to focus at first. You should still be concentrating on infinity. Then, still concentrating on infinity, NOTICE the bino’s focus at a given target. BUT, just notice, don’t concentrate. When the image starts getting sharp, then pay attention. Over time, you will learn the ropes.

When I first got into binocular astronomy, I had a hard time finding that faint fuzzball, the Andromeda galaxy. Today, I can just put the bino to my face and there it is. It just takes practice. :cat:

Bill
 
Warning! This thread is more than 5 years ago old.
It's likely that no further discussion is required, in which case we recommend starting a new thread. If however you feel your response is required you can still do so.

Similar threads

dorubird
Leica Ultravid 8x20 dissection (The beauty)
4 5 6
Replies
115
Views
12K
dorubird
dorubird
dorubird
Trinovid 8x20 BCA vs Ultravid 8x20 BR
2
Replies
30
Views
5K
ReinierB
R
I
best pocket/compact binoculars for opera & shows?
2
Replies
20
Views
2K
Trinovid
T
J
My First Experience Purchasing Birding Binoculars. Part 2 first anniversary
Replies
2
Views
654
Scott98
S
has530
SVBONY SA205 Review
Replies
3
Views
653
has530
has530

Users who are viewing this thread

Total: 2 (members: 0, guests: 2)
Back
Top