Binocular faults: correct terminology? (1 Viewer)

[Cluster]

I have had and returned a few problem binoculars recently. when trying to describe the problem, I wonder if I could have used better terminology to describe the problem.

These faults have included alignment, focus area differences (sweet-spot), mechanical problems in the focus and two kinds of dioptre problems. It's one of the dioptre problems that have caused me some problem in trying to describe (although when returned to a proper binocular dealer/distributor, they should get my meaning perhaps).

The first, mainly only seen on cheap bins, is where the dioptre requires re-adjustment for near focus (~3m) and far (>30m). I guess that this is self explanatory.

The second is more of a problem and is present on several of my binoculars. This is where, after setting up the dioptre, I notice that when re-focussing on the same object the dioptre adjustment is off again. Careful investigation reveals that any dioptre adjustment is only good for when the focus is reached from a particular direction, say from near to far or from far to near. I guess that, in these cases there is some drag or stiffness within the focussing mechanics for one barrel, so that one always lags the other..................The only way to use a binocular with this fault is to get used to arriving at the final focus from the same direction each time, more difficult than you might imagine.

....Is there a commonly accepted/known short description for this "coming or going" focus fault?

Dave.

 

[John S.]

I suspect the cause of the latter diopter problem is slop and drag in the main focus causing the diopter to shift position. I would describe it as such. An otherwise excellent pair of 8x30 russian bins had the same two problems you describe. I didn't have the patience of others who kept returning them until the random good pair was delivered.

 

[John Russell]

Swarovski use spring loading of the focussing elements to ensure synchroous movement. This results in a difference in torque between clockwise and anticlockwise movement of the focussing wheel. They have taken a lot of stick for this but I think it's a small price to pay for maintaining the diopter setting.

This difference in torque, cw/acw is also just noticeable in my 8x33 Kowa Genesis.

John

 

[Kammerdiner]

...

The second is more of a problem and is present on several of my binoculars. This is where, after setting up the dioptre, I notice that when re-focussing on the same object the dioptre adjustment is off again. Careful investigation reveals that any dioptre adjustment is only good for when the focus is reached from a particular direction, say from near to far or from far to near. I guess that, in these cases there is some drag or stiffness within the focussing mechanics for one barrel, so that one always lags the other..................The only way to use a binocular with this fault is to get used to arriving at the final focus from the same direction each time, more difficult than you might imagine.

....Is there a commonly accepted/known short description for this "coming or going" focus fault?

Dave.

I once called this "barrel slop," but I've never seen a technical term for it. It's caused when one barrel has more freeplay/slop in the focus mechanism than the other side. As a result good focus only happens arriving from one direction because one barrel lags behind going the other way. You can use the diopter to change the direction in which good focus occurs, or if it's not too bad split the difference and hope your eyes can accomodate, but you can't focus well from both directions no matter what you do. I agree it is annoying. I suspect when folks say they have to "hunt" for perfect focus, or that it doesn't "snap" into focus they might in fact be experiencing barrel slop (or whatever you might choose to call it).

I think if you explain what's happening, the repair technicians should easily see it too.

A Zeiss wouldn't be involved would it? Holger mentioned seeing two samples of the new 8x32 Conquest HD that had this problem.

Mark

 

[Cluster]

It's helpful, for me, to understand what's happening. As you have pointed out, it can look like they are just incredibly fussy to focus and become really frustrating. Understanding the problem can at least provide a means to work round it, it's just not ideal.
No Zeiss involved, but I am surprised to hear that they can suffer!......

 

[kabsetz]

Cluster,

I think your explanation is good and clear. As far as I know, there is no proper term for this. Obviously, from the point of view of binocular manufacturers, this should not happen in the first place so why would they have a term for it? We could maybe come up with a term, such as lack of focus synchronicity, or asynchronous focus, but any new term would need an explanation about as long as yours.

The same problem is pretty common in cheaper CF porroprism binoculars, where the eyepiece bridge moves in and out while focusing. The bridge can rock left to right and cause rather pronounced diopter imbalance depending on how you lean it against your face, and one or the other eyepiece tube typically has more friction than the other so lags behind when focusing.

John,

I'm with you on this. It is much better to have uneven focus resistance than to risk asynchronous focus or barrel slop. It is not only Swarovski that uses this spring loading technique, though. The new Zeiss Victory HT's have it too, but since their focus wheel is bigger people don't seem to notice it as with a larger wheel diameter your finger exerts more torque when focusing.

Kimmo

 

[John Dracon]

Dave - a non-scientific word yet useful word to decribe having the optical elements moving so that the desired focal points are repeatable is the word "timing."
The current binocular designs have to be able to move the optical elements back and forth with accuracy and repeatability, if they are to be useful.

To accommodate the difference between eyes in resolving power (there are of course other eye issues which cannot be resolved by adjustments , e.g. astigmatism), the diopter adjustment (normally on the right barrel) also comes into play. Some binoculars, normally the more expensive, incorporate the diopiter mechanism internally, but this reguires very sophisticated mechanisms and mechanical relationships. Most internal focusing designs enhance waterproofness.

The classic way of dealing with it is found in CF binoculars with oculars which move back and forth, and the right ocular can be adjusted still further. This requires close tolerances as the ocular casings have to slide in a sleeve, and minute bits of whatever can be drawn into the mechanism causing galling and other problems. The excellent B&L Zephyr binoculars and many other external focusing CF binoculars have this problem. If one side hangs up, then a timing problem in focus is created.

Even my Zeiss alphas such as the 7x42 BGTA and 15x60 BGTA are subject to timing issues. The only design that I have used that seems to avoid this without extraordinary costs is the IF binocular. The Zeiss 8x30 Safari model illustrates this easily.
All the optical elements save the oculars are fixed internally. The oculars movements are snug and creates water and dust proof interiors. This designs allows also collimation to be unaffected when the oculars are moved in and out. But of course the IF binocular is hardly a handy birding binocular.

When comparing the least expensive Zeiss, the Terra to the most expensive model, the HT, Zeiss incorporated the effective and time tested diopter adjustment, the external friction system. Undoubtedly less expensive to do than the system in the HT.
IMO many of the simpler designs minimize timing problems.

John

 

[pshute]

The first, mainly only seen on cheap bins, is where the dioptre requires re-adjustment for near focus (~3m) and far (>30m). I guess that this is self explanatory.

I've got a cheap pair of 8x21s that do that. OK for any use where the subject is usually the same distance away (horse racing?), but very frustrating for birding.

I'd like to know if this one has a technical term, and it would be good if it was mentioned in specs so it could be avoided.

The second is more of a problem and is present on several of my binoculars. This is where, after setting up the dioptre, I notice that when re-focussing on the same object the dioptre adjustment is off again. Careful investigation reveals that any dioptre adjustment is only good for when the focus is reached from a particular direction, say from near to far or from far to near. I guess that, in these cases there is some drag or stiffness within the focussing mechanics for one barrel, so that one always lags the other..................The only way to use a binocular with this fault is to get used to arriving at the final focus from the same direction each time, more difficult than you might imagine.

I haven't noticed that in my Nikon Monarchs (roof), but it happened with my Bushnell Legends (porro), especially in the cold. I used to just rock the bridge a few times to fix it, or overshoot the focus and come back from the other direction.

I used to fiddle with the dioptre on the Bushnells all the time, thought my eyes were varying. I haven't touched it on the Monarchs since I got them.

 

[walternewton]

Is there a commonly accepted/known short description for this "coming or going" focus fault?

Backlash?

 

[brocknroller]

Cluster wrote: The first, mainly only seen on cheap bins, is where the dioptre requires re-adjustment for near focus (~3m) and far (>30m). I guess that this is self explanatory.

I'm curious to find out which binoculars had this problem?

I found this issue with my Nikon 8x32 and 10x42 HGs. It was worse with my first sample 8x32 HG, which required resetting the diopter at close, medium and far distances. The focus wheel had some backlash and had almost no resistance, but since the diopter is on the EP, I don't think there was an mechanical connection.

My second sample 8x32's HG focuser was more precise, but I still had to focus the diopter at near and far distances. Ditto for both 10x42 versions I had (HG and HGL).

I think the problem was not with the diopters but with the incompatibility of a fast focuser with my bad focus accommodation.

The 8x42 model, which I also tried, had better depth of field even though it had the same focus speed as the 10x42 model, so I could pretty much "set and forget" the diopter. I would have preferred the 8x42 over the 8x32 for its better ergonomics, sharper image, relatively slower focuser (1 turn vs. 1/2 turn), better ergonomics, and better depth perception, but the full sized models have very little pincushion, which created distracting "rolling ball."

Sometimes the fault lies not in the diopters but in our eyes.

<B>

 

[typo]

The second is more of a problem and is present on several of my binoculars. This is where, after setting up the dioptre, I notice that when re-focussing on the same object the dioptre adjustment is off again. Careful investigation reveals that any dioptre adjustment is only good for when the focus is reached from a particular direction, say from near to far or from far to near. I guess that, in these cases there is some drag or stiffness within the focussing mechanics for one barrel, so that one always lags the other..................The only way to use a binocular with this fault is to get used to arriving at the final focus from the same direction each time, more difficult than you might imagine.

....Is there a commonly accepted/known short description for this "coming or going" focus fault?

Dave.

Dave,

I'm not an engineer but I believe this is commonly called whiplash, backlash or occasionally hysteresis. The Swarovski sprung mechanism preventing this in turn would be an anti-whiplash device. Focus slop would also be covered by the same terms.

David

 

[hinnark]

Dave,

I think the correct technical term you are looking for is called 'focusing difference (between telescopes of binocular systems)'. Unfortunately there are many binoculars out there suffering from this more or less. Recently I've got the impression that at Kamakura they have some special problems with this. It is possible to measure the amount of the focusing difference. All service departments of binocular manufacturers should be able to do this.

Steve

 

[Cluster]

Thanks for your input.
I guess the long description will do. Slop or backlash sounds right, but this is how I would describe the slack in the focus control anyway, the portion of the focus knob that turns without moving anything within.
The near and far diopter adjustment was a feature of an early (and not new) Barska Benchmark, plus more than one of my more recent purchases. It's something that I check for immediately.
I've sent binoculars back, having only tried them for minutes. The last was a "used", "as new" Excursion 8x36 that had other issues, so may have been a real bad sample (my Excursion EX 7x36 is pretty good in this respect).

Dave

 

[pete_gamby]

If someone complained of backlash in the focus system of a binocular, we'd expect to be checking for a lack of movement in the entire focusing system when changing the direction of the focus wheel.

There's a pretty good Wiki entry on the term:

http://en.wikipedia.org/wiki/Backlash_(engineering)

I'd tend to describe what I think you are seeing as differential focusing which could be caused in part by excessive backlash in one side of the focus system.

HTH

Cheers, Pete

Cheers, Pete