More to Close-Focus (1 Viewer)

[WJC]

Close Focus:

It’s amazing that a group of people who are so driven to achieve the non-extent “perfection” in binoculars consistently bemoan instruments that won’t focus just inches away.

Part of the problem relates to the very definition of binoculars:

“Binoculars are versatile tools that provide enlarged images of distant objects ....”

Note that it says that they were designed for “distant objects,” not for people demanding their right to make a silk purse out of a sow’s ear. Since Birdforum is about bird watching, my amazement rests with the fact that many to most of those touting the close-focus on their binocular rarely, if ever, consider what they are giving up in distance focusing (where most birds are) while bathing the wonderfulness of their close-focusing instrument. It’s reminiscent of the person who has to have a super-wide field, even if the outer half of that field is far less than the adequate. Of course, the problem can be attenuated by throwing money at it, but only the VERY wealthy, those willing to deal with the added weight, or pay for exotic glass types and curvatures can reduce it to the “perfection” observers like to talk about.

The problem does diminish with every hundred dollars thrown at it. But remember the saying from optical engineering: “It takes 90% more money to achieve a 10% improvement in performance.” And since the AVERAGE observer obviously doesn't notice the difference ... why bother? The manufacturers are not going down this non-productive rat hole. So, we are left with ATTENUATION and NOT ELIMINATION.

You’ll probably NOT find your answer in sales literature or in the profusion of “binocular forums,” since many writers and “experts” don’t know or care. Someone once asked me to explain. When I did, I was told, “I can’t understand all that.”

Well, I am only responsible for what I say ... not for what someone else understands. So many people come to bino forums to get an in-depth understanding of binoculars, but if the answer requires more than an elementary education or “thinkology,” they would rather live in optical ignorance than chip a nail doing a little research reading competent, peer-reviewed material.

This time, I won’t break a sweat covering the material that others, with a minimum command of the English language, can read for themselves. Actually, there are tens of thousands of files on this Big Mac and I can’t remember how I labeled the article; it’s an old guy thing!

Holger would be your goto-guy for better answers.

“Bah, humbug,”

Curmudgeon, out.

 

[MFoortjes]

Not to forget that people criticize companies who decide to decrease close focus capability of certain popular models. And that although the new focussing wheel is more precise than before. Personally I would call this step a wise decision. But I'm already a pretty old guy too. ;-)

 

[Brink]

Since Birdforum is about bird watching, my amazement rests with the fact that many to most of those touting the close-focus on their binocular rarely, if ever, consider what they are giving up in distance focusing (where most birds are) while bathing the wonderfulness of their close-focusing instrument.

I didn't know they were giving up anything. What is the detriment to long distance focusing in these instruments?

 

[WJC]

I didn't know they were giving up anything. What is the detriment to long distance focusing in these instruments?

Not a thing from MY perspective. You may note that I addressed the non-existent "perfection" in my very first sentence. But, how many time does that non-existent "perfection" post do we see here each year? I also stated the more money is thrown at the issue, the less of an issue it becomes.

Overall, most aberrations are corrected for one distance. At shorter or longer focal lengths those aberrations creep back in, in various magnitudes. To me, It's stacking BBs. Yet, some people make a career of that.

Cheers

 

[Ted Y.]

Overall, most aberrations are corrected for one distance.

This is news for me, but when I think about, it is not a surprise. I imagine if a binocular have "acceptable" CA, this CA will stay "acceptable" at all distances; different but "acceptable". Correct?

Binoculars reviews does not mention the distance used during the evaluation, nor this behavior. It is not so relevant or just no one is interested?

 

[WJC]

This is news for me, but when I think about, it is not a surprise. I imagine if a binocular have "acceptable" CA, this CA will stay "acceptable" at all distances; different but "acceptable". Correct?

Binoculars reviews does not mention the distance used during the evaluation, nor this behavior. It is not so relevant or just no one is interested?

Depending on your accommodation for that anomaly.

 

[Ted Y.]

Depending on your accommodation for that anomaly.

I understand if I have a generous accommodation, I do not need to buy $2K binoculars (with better, let say, CA correction).
Sure, the accommodation can be less generous for another kind of anomaly, therefore try before buying!

 

[Tringa45]

I didn't know they were giving up anything. What is the detriment to long distance focusing in these instruments?

Just as a camera objective focuses an image on film or sensor, the binocular objective places a virtual image at or near the focal plane of the eyepiece, according to the eyesight of the observer.
As the distance between objectives and eyepieces on most modern roof prism binoculars is fixed (no focussing bridge as on many Porros), focus is achieved by internal focussing lenses, which alter the focal length of the objectives.
If the designer wants to increase the close focus capability and maintain focus overtravel for the near-sighted, then the travel (mechanical complexity) or power of the focussing lenses or both must be increased.
Either of these solutions will compromise chromatic and spherical aberration at some settings. It's a bit like using a macro lens for distant photography or a standard lens withh bellows for macro photography.
I don't know if these compromises will be apparent to the observer, but there's something to be said in favour of simplicity and, if one wants to observe insects, a low magnification monocular or Pentax Papilio might be a better and cheaper solution.

John

 

[Troubador]

Close focus binoculars? What decadent rubbish. And why this obsession with magnification? Any sailor knows that more than 7x is a waste of time, and as for12x and 15x: madness! I don't know what bino manufacturers are smoking but for decades they have been pushing wide fields of view down our throats. Why? If a porthole is good enough for a sailor, a porthole view through binoculars should be good enough for anybody.
Whatever gimmicks will they come up with next? Wide straps to make the binos more comfy? If a bootlace strap was OK for my granddad carrying his 6lb porros why can't folks today be satisfied? Next news they will be glorifying 'adjustable eyecups'.

What is the world coming to?

Lee
(Its ironic)

 

[Troubador]

Seriously Bill, on Bird Forum we might think the binocular world revolves around those who obsess about only birds, but out there in the real world, binocular manfacturers want their instruments to appeal to those birders, and others, who have a wider interest in the world than birds at infinity. You state that binoculars are to bring objects in the far distance closer. Guess what? They still do that. And they also allow the study of nature at close distances too. In case you haven't noticed, some birders are interested in more than just birds. As for the 'cost' of this, you hint that we are losing something by having this close-focusing capability. Well, I use binoculars from wide range of price-points: modestly priced models such as Opticron's Traveller 32mms, mid-priced models such as Leica's Trinovid HD 8x32m Kowa's Genesis 8x33, Zeiss's Conquest HD 8x32, and pricier models such as Zeiss's SF 8x32 and guess what? Despite their close-focus capability they all deliver excellent and enjoyable and informative images from near to far.

Lee

 

[Binastro]

Binoculars can be designed to focus close and far.
This has to be the basis for the design.

Macro lenses can also be designed to focus at 1 to 1 and infinity. They perform well close and far.
They are usually slow and simple 4 or 5 element designs, such as the Vivitar 90mm and 100mm lenses.

The very best professional lenses are computed for the normal distance at which they are likely to be used.
However, and strangely, they are tested by the makers at infinity for quality control.
The difference in image quality at the finite working distance and infinity is small.
Each lens has to pass certain test results at infinity, usually by projection.

There are other lenses designed for large format, 5x4 and 10x8 inches.
These are used stopped down to f/32 or smaller.
The cameras have tilt and shift and the lenses cover a wider area than normal.
The detail shown is extraordinary.

Modern large format high pixel count digital cameras and lenses are also extraordinary.

There are other classic lenses such as the Deep Field Panchro that have special characteristics.

With normal fast prime lenses used for close up, I use them with a reverse adapter stopped down or back to front mounted in front of a short telephoto.

Regards,
B.

 

[Ted Y.]

I don't know if these compromises will be apparent to the observer, but there's something to be said in favour of simplicity and, if one wants to observe insects, a low magnification monocular or Pentax Papilio might be a better and cheaper solution.

I am using such a combination: a binocular 6x and one 10x. But this means 2 binoculars to transport and use in the field. Less convenient for some people.

And:
-who can say what is the difference at long rage between two binoculars, one with close focus and one without? "Same" optical quality for both, sure. If one knows, please suggest two binoculars one can buy to compare. Not from eBay, if possible.
-how about the price? For almost same price, maybe people prefer to buy the one with close focus, because "more capable". Or maybe the preferred brand produces just close focusing binoculars.
-it is not easy to be sure what one needs in long term.
-if the binocular is to be sold, must be what "all" people want. Like cars, at least in my region: buy a gray car, it will be easy to resell.

It’s amazing that a group of people who are so driven to achieve the non-extent “perfection” in binoculars consistently bemoan instruments that won’t focus just inches away.

I interpret this as a friendly call to know and understand what we need.

 

[Tringa45]

And they also allow the study of nature at close distances too.

Lee,

You probably wear varifocals, but if you wore bifocals as I do you would see that the optician had had the reading lenses made about 5 mm closer together than your IPD. That's because when you read at close distances you squint.
No-one here on the forum is more aware than Bill that the optical axes of binoculars should be parallel at all settings. Most 32 mm roof prism binoculars have an objective spacing that corresponds to the IPD but from 42 mm onwards the objective spacing is usually larger.
I also have an 8x33 Kowa Genesis. Its FoV of 140 m @ 1000 m corresponds to 21 cm at its close focus of 1,5 m.
Try inscribing two 21 cm circles on a sheet of paper with their centres spaced 6,5 cm (an average IPD) apart and see what's left in the middle. Of course, you can ameliorate this a little by reducing the IPD of the binocular, but it's still a dirty compromise.
Horses for courses. For such applications a small reverse Porro or monocular (like your 6x18 Zeiss) is better suited.

John

 

[tenex]

“Binoculars are versatile tools that provide enlarged images of distant objects ....”

I don't understand the argument of this post at all. This definition is a dinosaur from the era of Porro prisms, and if you find internal focusing somehow impure you can keep using those. Relative to small objects like butterflies, moths, or spiders, 6ft/2m is rather distant, and 10ft/3m is very far away. Stepping back to focus (if you can) loses much of the magnification, and possibly also the target. If you think one should need to carry around a Papilio too for this instead, I'll ask you to carry a flip phone, calculator, GPS, PDA, etc instead of a smartphone. All the optical corrections one could notice or worry about are surely optimized for long distances, so any difficulty is at the near end and that's just the way I'd want it too. Close focus is one of many features I like in my UV32.

 

[Maljunulo]

I have noticed that some seem to spend more time berating a binocular because it isn’t what it isn’t, rather than enjoying the fact that it is what it is.

 

[Conndomat]

I don't understand the argument of this post at all. This definition is a dinosaur from the era of Porro prisms, and if you find internal focusing somehow impure you can keep using those. Relative to small objects like butterflies, moths, or spiders, 6ft/2m is rather distant, and 10ft/3m is very far away. Stepping back to focus (if you can) loses much of the magnification, and possibly also the target. If you think one should need to carry around a Papilio too for this instead, I'll ask you to carry a flip phone, calculator, GPS, PDA, etc instead of a smartphone. All the optical corrections one could notice or worry about are surely optimized for long distances, so any difficulty is at the near end and that's just the way I'd want it too. Close focus is one of many features I like in my UV32.

The question is whether all alpha models need these extreme close ranges?

It is often not only optical compromises that you make, such as sharpness and loss of contrast, but also mechanical ones! The focus has to be more filigree, which reduces stability, and it often happens that the focusing lenses are no longer perfectly synchronous.

Or I use more glass to minimize the optical loss, but more glass also means loss, heavier weight and more costs.
The optical calculation is simply complicated, if I still want to have a good picture in the close-up range at 1.5 m, I have to crop it in the far range.

The binoculars are therefore more complex and expensive overall, for people who do not need an extreme close-up point an expensive cherry with no taste.

Andreas

 

[Troubador]

Lee,

You probably wear varifocals, but if you wore bifocals as I do you would see that the optician had had the reading lenses made about 5 mm closer together than your IPD. That's because when you read at close distances you squint.
No-one here on the forum is more aware than Bill that the optical axes of binoculars should be parallel at all settings. Most 32 mm roof prism binoculars have an objective spacing that corresponds to the IPD but from 42 mm onwards the objective spacing is usually larger.
I also have an 8x33 Kowa Genesis. Its FoV of 140 m @ 1000 m corresponds to 21 cm at its close focus of 1,5 m.
Try inscribing two 21 cm circles on a sheet of paper with their centres spaced 6,5 cm (an average IPD) apart and see what's left in the middle. Of course, you can ameliorate this a little by reducing the IPD of the binocular, but it's still a dirty compromise.
Horses for courses. For such applications a small reverse Porro or monocular (like your 6x18 Zeiss) is better suited.

John

Hi John

Yes I do wear varifocals and I understand what you are saying. However, I have been using close focusing binoculars for years (and so has Troubadoris) and have no problems or difficulties to report. When the distance to the subject gets down to a matter of cms (for example when laying face-down looking into a rock pool by the sea at inter-tidal marine life) then I do indeed resort to my trusty old Zeiss 6x18. If we plan to do a lot of close-focus work then we both use Leica Trinovid HD 8x32s as our two units focus down to about 1.0m.

For anyone who finds it too strange to look through a binocular at close distances such as 1.0-1.5m I suggest this: focus down to the close distance and look at your subject through one tube only by covering the other. There is a nice close view of your subject. Now cover the tube you have just looked through and view through the other. Another nice close view of your subject. Tell yourself that if you have seen two perfectly nice views through both tubes separately, looking through both tubes together will be even better. Now look through both tubes and only look at your subject. Don't be tempted to look at the perimeter of the view. We did this a few times and very quickly we became comfortable with the view at close distances and this has allowed us to study and enjoy so much of the natural world.

BTW John, in the part of England where I live, to 'squint' is to half close your eyes due to the brightness of light. What you are referring to as squinting we would call 'going cross-eyed'.

Lee

 

[Maljunulo]

BTW John, in the part of England where I live, to 'squint' is to half close your eyes due to the brightness of light. What you are referring to as squinting we would call 'going cross-eyed'.

Lee

The first definition is the only one I have ever heard in the US, and the first time I encountered the second usage I was completely mystified, and had to look it up.

 

[tenex]

The question is whether all alpha models need these extreme close ranges?

This reminds me very much of the question whether they all need to make obvious sacrifices (FOV, deep eyecups etc) to fully accommodate eyeglasses, except the suggestion that they don't seems unpopular here, and Swarovski didn't reduce the eye-relief of legacy models, although I myself would find that aesthetically and ergonomically more appealing.

...Perhaps it's experience with cameras that makes close focus seem a no-brainer. True macro lenses are indeed a specialty, but those focus to inches/cm. Camera lenses are designed to higher optical standards than binoculars, yet most focus (internally these days) under 1m, and even telephotos to 2m or so. No one argues about who does that how often, or calls it unnecessary complexity or expense.

 

[Pinewood]

Hello,

I suspect that to have close focus without additional chromatic aberration, a floating element in the internal focussing would do the trick. It would just complicate the mechanics and drive up the cost.
I note that some manufacturers decrease the cost of their lower price lines by removing the integrated dioptre setting device for focussing; replacing it with a setting ring on one of the eyepieces. It would seem to me that is no great disadvantage. Focussing no closer than three metres seems to be another cost saving.
N.B. As a myope, I can take my glasses off and focus a little closer, which is why close focussing is not high on my list of optical necessities.

Stay safe,
Arthur Pinewood