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Help needed to repair BL discoverer 7x24 diopter (1 Viewer)

Hi all. This is my first post on this forum, although I've been a long time lurker who found a lot of informations about bins here.
I just bought a pair of Bausch&Lomb 7 x 24 discoverer on Ebay Uk, for a reasonable price ( 25 £). I immediately fell in love with this ugly bulky little thing. There's no collimation problem, and the image is bright and quite sharp from edge to edge. But .... ebaying always means taking a risk.

The problem is that I have to turn the diopter adjustment on the right ocular all the way up in order to bring both images in focus, and even that way, there's still a little difference. One image is not perfectly sharp. My eyes are not faulty, as on my other bins I usually let the diopter around O.


I don't want to send them to Bushnell repair service for this would mean sending them from France, with a high probability to have them returned with a " sorry, bins are too old" message. I'd rather save to buy me a brand new 7x26 Elite Custom instead. So I'd like to try to fix it myself.

I've been scratching my head for a few days and here are my conclusions.
Such a difference in diopter adjustment between the two barrels means the optical distance between ocular and objective lenses are different : one is longer than the other. When looking through the objectives, I noticed that one lens was a bit closer to the border than the other, so the distance from the objective lens to the prism is certainly different. Could this be the cause of my problem?

Another solution would be to change the distance between the ocular and the prism. In some bins there are hidden screws around the diopter ocular, enabling to re-set the diopter adjstment. I couldn't see these screws on my Discoverer bins. If I unscrew the whole eyepiece, will I find a way to modify its distance from the prism, i.e. its height ?

I know there are bin repair gurus around here, and any advice will be welcome in order to help me bring this little gem to life again. Thanks in advance.
 
Hi all. This is my first post on this forum, although I've been a long time lurker who found a lot of informations about bins here.
I just bought a pair of Bausch&Lomb 7 x 24 discoverer on Ebay Uk, for a reasonable price ( 25 £). I immediately fell in love with this ugly bulky little thing. There's no collimation problem, and the image is bright and quite sharp from edge to edge. But .... ebaying always means taking a risk.

The problem is that I have to turn the diopter adjustment on the right ocular all the way up in order to bring both images in focus, and even that way, there's still a little difference. One image is not perfectly sharp. My eyes are not faulty, as on my other bins I usually let the diopter around O.


I don't want to send them to Bushnell repair service for this would mean sending them from France, with a high probability to have them returned with a " sorry, bins are too old" message. I'd rather save to buy me a brand new 7x26 Elite Custom instead. So I'd like to try to fix it myself.

I've been scratching my head for a few days and here are my conclusions.
Such a difference in diopter adjustment between the two barrels means the optical distance between ocular and objective lenses are different : one is longer than the other. When looking through the objectives, I noticed that one lens was a bit closer to the border than the other, so the distance from the objective lens to the prism is certainly different. Could this be the cause of my problem?

Another solution would be to change the distance between the ocular and the prism. In some bins there are hidden screws around the diopter ocular, enabling to re-set the diopter adjstment. I couldn't see these screws on my Discoverer bins. If I unscrew the whole eyepiece, will I find a way to modify its distance from the prism, i.e. its height ?

I know there are bin repair gurus around here, and any advice will be welcome in order to help me bring this little gem to life again. Thanks in advance.

Welcome to BF:

You may be focusing the right side first. Not all, but most binos are focused LEFT side first. Then while looking at the same target, focus the right side; just STARE and let the bino do the work.

If that doesn't work, you will will need to recess the offending objective a millimeter or so.

Bill
 
Thanks for your imput, WJC. I have tried all methods for focusing, starting by the regular one : left eye only using the general focusing knob, then right eye only using the diopter. There's no way to have both images on focus. So I'm thinking as you stated about modifying the position of the faulty objective. I've already dismounted some porro bins so I think I can deal with unscrewing the rings that maintain the protective lens and the objective lens in place.
But which one is the faulty one ? Is the right ( diopter side) objective too close to the prism, or is the left one ( steady side ) to far to the prism ??? Gives me headaches....
 
It sounds like a mechanical problem. The focusing lenses of the two barrels are not moving exactly the same when the focus knob is turning this way and the other. This may be caused by poor lubrication of the focusing lens mechanism or play in the moving parts. I am afraid it is difficult to be repaired outside the factory.
 
Thanks for your imput, WJC. I have tried all methods for focusing, starting by the regular one : left eye only using the general focusing knob, then right eye only using the diopter. There's no way to have both images on focus. So I'm thinking as you stated about modifying the position of the faulty objective. I've already dismounted some porro bins so I think I can deal with unscrewing the rings that maintain the protective lens and the objective lens in place.
But which one is the faulty one ? Is the right ( diopter side) objective too close to the prism, or is the left one ( steady side ) to far to the prism ??? Gives me headaches....

" . . . But which one is the faulty one ?"

I know nothing of your knowledge of binoculars, so PLEASE don't be offended with the following:

If you can't tell which is the faulty one, you don't seem to be having a dioptric issue, but rather a collimation issue. In working with the public for years, I've come to see some people see a double image and will call the problem a problem of focus when, in reality, focus has nothing to do with it.

Are you sure your problem is dioptric?

Bill
 
A couple of quick collimation checks. First focus on a power line as best as you can. Then move your eyes back away from the lenses. Doers the power line remain as a solid line, or does it separate into an upper and a lower line? Does a distant star stay as a single image or does it appear to split into two stars?

Has the diopter ring slipped? Look for a small set screw or as many as three around the edge of the diopter ring. Maybe these have loosened (if they are even there in the first place) and the ring has slipped. If that is the case you can experiment with realigning the ring.
 
A couple of quick collimation checks. First focus on a power line as best as you can. Then move your eyes back away from the lenses. Doers the power line remain as a solid line, or does it separate into an upper and a lower line? Does a distant star stay as a single image or does it appear to split into two stars?

Has the diopter ring slipped? Look for a small set screw or as many as three around the edge of the diopter ring. Maybe these have loosened (if they are even there in the first place) and the ring has slipped. If that is the case you can experiment with realigning the ring.

And, if it IS a collimation issue, let us know and I will send you something to read before you start turning screws willy-nilley, as so many armchair opticians might encourage you to do.

A Conditional Alignment is well within the grasp of all. However, while that can make an instrument perform fine at one IPD, it can take the instrument away from true Three-axis Collimation, and might cause the instrument to be frustrating to unusable for others.

Bill
 
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Thanks for your replies.
WJS, I'm not offended at all, I just have a basic knowledge in bins and have already dismounted an old porro. OTOH, I work everyday with microscopes and binocular magnifying lenses so over time I've experienced the most common optical problems such as chromatic aberration, double image, etc. ...
I do not think my bins have a collimation problem, for when I do the test Steve C suggested, I only see one power line. When closing one eye then the other, the image does'nt jump at all, one is just sharper than the other, but both are at the same place.

I had already checked for the three screws on the diopter ocular, there are none....

Aklstang, these are reverse porro type bins. When focusing, its the objectives themselves that move. In fact there are two inner tubes one inside the other, and both are moving. The outer of the two bears the objective lens set by a threaded ring. The whole lot is protected by the aluminium casing and closed by a flat protecting lens, probably applied on a toric joint. I don't think there's a focusing lens in addition, like in a roof prism design.

In fact my problem sounds stupidly simple : the diopter doesn't go up enough to make the right image as sharp as the left one. Something like one-eighth of a turn is missing.
I checked the focusing distances of both barrels. The left ( steady ) one focuses from 1,7 m to infinity, reaching infinity exactly at the end of the course of the focusing wheel. I don't like the fact that's there no margin there, in case the infinity suddenly decides to go further away, you never know....
The right ( diopter ) one with the diopter all the way up focuses from 1,9 m to infinity and beyond. With the diopter all the way down ( 5 mm and 3/4 turn ) it focuses from 3m to way beyond infinity.

In the same time, looking at the objective lenses, the right one is more recessed into the body ( farther from the edge ) than the left one, by a few millimeters.

This is why it makes sense to me that I have to turn the diopter all the way up in order to try to achieve the same optical distance between ocular and objective in both barrels.

Need an Alka-Seltzer at the moment ...
 
Hi. I am a new member and found this thread while searching an issue I have had with 2 pairs of Bushnell Binoculars in the last year. Both pairs worked fine with sharp focus initially when the diopter was set in the middle of its range, and both pairs slowly changed over 4 months until the diopter ring would not turn far enough to allow me to focus the right barrel when the left barrel was in clear focus. Perhaps this is related to the problem discussed in this thread. The first pair were new Bushnell Nature View 8x42's that I had read good reviews about and was very pleased with. After they would not focus anymore, I sent them in to Bushnell with the required $10 for inspection and warranty repair. I received an email back that they were faulty and would be replaced. Problem was they were on backorder, so months later just before leaving on a trip to Alaska I was able to arrange to get a new pair of Bushnell Excursion HD 10x42's. I really liked these binoculars for birding and took great care of them, but gradually over 4 months the same thing happened ...slowly at first but quickly during the last week. The diopter ring, which started out almost at the "0" mark in the center needed to be moved farther and farther to one side until they could no longer be brought into proper focus. Again I spoke to Bushnell customer service and was told to send them back in with my check for $10. I am presently awaiting Bushnell's response. During this whole time, my two pairs of marine binoculars work just fine, so it's not my eyes. Not only that, both pair crapped out with or without my prescription glasses on. I am guessing that in spite of gentle handling, something in both pairs (2 different models, but likely the same Chinese manufacturer) was not securely glued or fastened. Have other users run into this problem, and could someone familiar with the optics please explain? Thanks
 
Hi. I am a new member and found this thread while searching an issue I have had with 2 pairs of Bushnell Binoculars in the last year. Both pairs worked fine with sharp focus initially when the diopter was set in the middle of its range, and both pairs slowly changed over 4 months until the diopter ring would not turn far enough to allow me to focus the right barrel when the left barrel was in clear focus. Perhaps this is related to the problem discussed in this thread. The first pair were new Bushnell Nature View 8x42's that I had read good reviews about and was very pleased with. After they would not focus anymore, I sent them in to Bushnell with the required $10 for inspection and warranty repair. I received an email back that they were faulty and would be replaced. Problem was they were on backorder, so months later just before leaving on a trip to Alaska I was able to arrange to get a new pair of Bushnell Excursion HD 10x42's. I really liked these binoculars for birding and took great care of them, but gradually over 4 months the same thing happened ...slowly at first but quickly during the last week. The diopter ring, which started out almost at the "0" mark in the center needed to be moved farther and farther to one side until they could no longer be brought into proper focus. Again I spoke to Bushnell customer service and was told to send them back in with my check for $10. I am presently awaiting Bushnell's response. During this whole time, my two pairs of marine binoculars work just fine, so it's not my eyes. Not only that, both pair crapped out with or without my prescription glasses on. I am guessing that in spite of gentle handling, something in both pairs (2 different models, but likely the same Chinese manufacturer) was not securely glued or fastened. Have other users run into this problem, and could someone familiar with the optics please explain? Thanks

Welcome sandstone:

Your marine binos are likely individual focus. Thus, there is no balancing act. Another problem that you MAY have intimated, is that you're expecting the bino to be in focus at "0" diopters. This is rarely true. In addition, it changes all the time, as the distance to your target changes.

1) Focus the appropriate side, first--usually the left--though not always. It must be focused in the order it was designed to be focused.

2) JUST STARE! The brain wants to see things in focus quickly. To that end, it will compress and elongate the eyeball via the cilary muscles to get the job done. This creates a strained focus that is hard to maintain and won't last long.

3) Then when focused and comfortable there, focus the right eye, the same way on the SAME target.

After that, the center focus wheel should get you where you want to be over the long haul. I don't know how much you know about binos. But, some people start by focusing the wrong side, first. Those people will NEVER achieve focus.

Hope this helps.

Bill
 
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Sandstone, thanks for your interesting input. It seems we've had the same problem with our bins, with a difference : you saw it happen gradually, when in my case the problem was already there when I bought them second hand. Thet's interesting because it eliminates a bump or a fall on the ground as the cause. What's more, I read another thread on another forum, where the poster (an experimented bins user ) reports having tried a pair of Bushnell and he had to set the diopter all the way up in order to achieve good focusing. He was wondering wether this was a deliberate choice from Bushnell or a defective one.
It seems there's something wrong in the construction of these bins, that appears only some time after the purchase. In your case it was worth sending them to Bushnell, in my case I guess it would have been useless.
The strange thing is your bins were chineese made, maybe by the same factory, mine are japan made, some 20 years ago ....
WJC, your advices for a good focusing methods are precious, but in my case it's obviously the bins that are faulty, not the guy ( or to a lesser extend !).
 
...an issue I have had with 2 pairs of Bushnell Binoculars in the last year. Both pairs worked fine with sharp focus initially when the diopter was set in the middle of its range, and both pairs slowly changed over 4 months until the diopter ring would not turn far enough to allow me to focus the right barrel when the left barrel was in clear focus. ....

This is a problem that I've seen in several units of the Bushnell 8x42 Legend Ultra HD (as mentioned in the detailed thread on that bin http://www.birdforum.net/showthread.php?t=213464 ). The problem is that the focus drive slips a little bit on one side of the bin from time to time (I found that it happened at one of the limits of focus, I can't remember if the far or near, I think near), such that the diopter has to be used to compensate. This is a problem that I've seen in other cheap Chinese roofs. In fact, one of the first tests I conduct when evaluating a new bin is to run it back and forth, fairly hard, between its focus limits 20 or 30 times and then check that left-right focus synchrony (and diopter setting) is maintained. If not, I consider the bin faulty. The only high-end bins that I've tested with a similar problem were two units of early production Swarovski 8.5x42 EL (the original version, ~13 years ago).

As for the OP's bin, I did see a similar problem with a B&L 7x26 Custom. The focus operation of that bin was stable, but it was manufactured with a slightly longer barrel for one ocular than the other, such that the diopter had to be set at its limit for a person with perfect vision. I brought the bin to the Bushnell repair facility in Lenexa, KS where the fellow I talked to made an adjustment to the spacing of one of the objectives to compensate. Also, at my request, he set the focus limit to allow maximal close focus (minimal drive past infinity) to optimize the unit for butterfly watching. All repairs, including perfecting the alignment, were done free of charge. But that was maybe 10 years ago, so I'm not sure if doing the same is possible today. That bin is still in perfect working order.

--AP
 
Sandstone, thanks for your interesting input. It seems we've had the same problem with our bins, with a difference : you saw it happen gradually, when in my case the problem was already there when I bought them second hand. Thet's interesting because it eliminates a bump or a fall on the ground as the cause. What's more, I read another thread on another forum, where the poster (an experimented bins user ) reports having tried a pair of Bushnell and he had to set the diopter all the way up in order to achieve good focusing. He was wondering wether this was a deliberate choice from Bushnell or a defective one.
It seems there's something wrong in the construction of these bins, that appears only some time after the purchase. In your case it was worth sending them to Bushnell, in my case I guess it would have been useless.
The strange thing is your bins were chineese made, maybe by the same factory, mine are japan made, some 20 years ago ....
WJC, your advices for a good focusing methods are precious, but in my case it's obviously the bins that are faulty, not the guy ( or to a lesser extend !).

Are you discussing a Insta-Focus/Zip Focus/Quick Focus bino?

Bill
 
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No, just standard manual focus bins that require the user to first focus the left eye with the center focus knob; then focus the right eye on the same object with the diopter ring on the left eyepiece. I think Alexis has the problem diagnosed with his statement, "The problem is that the focus drive slips a little bit on one side of the bin from time to time...". I don't know how the mechanicals work inside these things, but obviously the center focus must move both barrels the same and allow the user to focus on both near and far objects. The diopter should change the distance between the lenses in one (the right) barrel to allow the user to customize the optics to allow two eyes with differing vision to both be in focus. Problem was that somehow this relationship did not maintain over use and time on two pairs of these Bushnell bins. It must be a faulty design in the internal "gearing" that lets one side slip until the diopter no longer has adequate range to adjust.
 
Well, I think A. Powell has described and diagnosed the problem quite accurately. It seems impossible to repair unless i send them to Bushnell, and I won't put more money, let alone burn kerosen, on theese. They'll now live in my glove box. BTW I didn't know it was possible to have the minimum focusing distance reduced by a qualified tech without sacrifying the infinty focus ability. A pair of 7x26 custom with 1,5 m close focus would be my dream bins.....
Thanks all for your help. WJC, i'm interested in your method for collimation issues ...
 
...BTW I didn't know it was possible to have the minimum focusing distance reduced by a qualified tech without sacrifying the infinty focus ability.

Bins are always manufactured to focus beyond infinity to allow myopic users to focus at infinity without wearing corrective lenses. I always wear my glasses, so I chose to have that travel used for closer focus, leaving little adjustment beyond infinity (i.e. sacrificing infinity focus ability if a myopic user were not wearing corrective lenses). Back in the 1980s, I heard that Zeiss would make this same adjustment at the user's request, so I thought to ask for it.

...A pair of 7x26 custom with 1,5 m close focus would be my dream bins...
If you want to pursue the matter further, you might try to find the B&L 7x26 Custom (model 61-7261) that preceded the version that added the bulky plastic shell (model 61-0726). In my experience, close focus varies among individual units of these bins, but it is usually something like 5 feet in the old version (which gained it a good reputation with bug watchers), but is more like 8 feet in subsequent versions.

--AP
 
Well, I think A. Powell has described and diagnosed the problem quite accurately. It seems impossible to repair unless i send them to Bushnell, and I won't put more money, let alone burn kerosen, on theese. They'll now live in my glove box. BTW I didn't know it was possible to have the minimum focusing distance reduced by a qualified tech without sacrifying the infinty focus ability. A pair of 7x26 custom with 1,5 m close focus would be my dream bins.....
Thanks all for your help. WJC, i'm interested in your method for collimation issues ...

Send me your REAL email address and I will send you the SPIE paper. It's not MY method, but rather the one that was devised by USC for the Navy at Mare Island--I just tweaked it, a little. You can get from New York to Los Angeles via Atlanta, but it would be a huge waste of gas and time. If you don't take the axle/hinge into consideration, the most you will get--in most situations--is Conditional Alignment. And, of course, the "you just tweak these screws" crowd doesn't know you have to take the hinge into consideration. Some people read too fast; some people don't believe; some people don't care.

My address is wjc 1111 (at sign) hot mail dot com

Bill
 
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