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dentheman
newbie
Reged: 10/12/09
Posts: 2
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I have 2 porro prism bins and 2 roof prism, all are different brands, one is new, one is 3 years old, one 5 years old, and one is 25 years old . When the porros are focused, the diopter mark is toward (-). When the roof prisms are focused, it's toward the (+). Is this the way it should be, or do I have 2 sets of the same style that are improperly marked (highly unlikely, I would say).
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Erik D
Post Laureate
Reged: 04/28/03
Posts: 3196
Loc: Central New Jersey, USA
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I have 20/20 left eye and -4.0 right eye. About two dozen binoculars. I never pay attention to the right diopter marking on any of my binoculars. They are all over the place...
Just checked four pairs. A late model Celestron Regal 10X42 roof is set for -3.5. The 4 year old Leupold 12X50 roof is -2.0. A pair of Minolta 10X50 porro is ~ -5.0. A pair of 25 year old Celstron Nova 7X50s show scale from +2 to -2 only. But set for my -4.0 right eye I estimate the mark would be close to -6.0.
About 8 out 10 pairs I try have sufficient RDA range for the four diopter difference between my left and right. Some of the lower cost Chinse 80 and 100 mm giants do not. No problem with my Japanese 20X80 or 25X100s. Some models just make it at the limit of RDA range. IIRC, a pair of Swarovski 10X42 EL only seem to reach -3.0. Insufficient for me. The 15X56 SLC I tried on the same day was fine.
I only care if the RDA range is sufficient for my eyes. Do not care if the marking is spot on or not. More often than not they are not. I have my eyes checked once a year. They have not changed for the last five.
ERik D
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DJB
Carpal Tunnel
Reged: 02/23/05
Posts: 1589
Loc: Lisle NY
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Hi there,
As in my case(s), sometimes the actual ring which holds the diopter inscribes can shift off axis, if you will.
Generally, this happens because of a lot of heavy use of the ring by the user.
And keep in mind that this ring is usually retained in place by three or four set screws. More than likely, two or more of these set screws have loosened. This causes slipage of the ring.
What I would do is this. Set them to the mfg. configuration if you can, or, as I like, set them to zero to accommodate your (my) eye requirements.
Of course, keep in mind that the actual NUMBER would probably be useless for other folks who might use your binocular. If no other person does, then, so be it. Good luck. Besides, the number is ONLY a reset reference.
Best regards,
Dave.
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dentheman
newbie
Reged: 10/12/09
Posts: 2
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I have another porro on order that should get here tomorrow or the next day. It will interesting to see the adjustment! I guess what I really wanted to ask was: Is there an inherint difference between porro and roof prisms that would cause one design to be set toward - and the other toward +?
Edited by dentheman (10/30/09 01:19 AM)
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Rich V.
Pooh-Bah
Reged: 01/02/05
Posts: 1393
Loc: Carson Valley, Nevada, USA
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Den, I don't see how there's any correlation between prism design and the accuracy of the diopter scales. Depending upon the quality control of the mfg. the diopter calibration of a new binocular can be all over the place.
It's really quite arbitrary where the marks line up as long as you can reach focus personally. It becomes a real deal breaker if the inaccuracy is such that it prevents you from reaching perfect focus, though. Say you need a -4 diopter setting for your right eye. Your binocular has an 8 diopter adjustment range but it isn't balanced equally ± 4 D either way. Instead it's +6/-2; you're out of luck!
In my experience, higher quality binoculars tend to have more accurate diopter reference marks. It shows that more care was put into the assembly and calibration of the optics; all the optical elements are accurately placed where they were designed to be.
While anyone's eyes can vary in a minor way from hour to hour, I know my eyes are equally corrected so theoretically the diopter of any binocular I've focused should read very near "0". I consider myself fortunate that my particular Nikon and Pentax CF binoculars are all real very close to "0" for my eyes; right where they ought to be. Certainly within ± 1/2 D.
It's not always the case, though. I've used a couple inexpensive 15x70s that needed the diopter turned nearly all the way one direction or the other (± 4+!) to reach my personal "0" point. The one Nikon AE model I've tried needed nearly 2 D correction according to it's scale. In these cases, I know it's the binocular, not me! No big deal as long as I can reach focus though, but a bit disappointing as far as the QC goes.
Rich V
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Binoculars:
33/50/75/150x100 Saturn III, 16x70 FMT-SX, 10x50 PCF-V, 10x43 DCF-SP, 10x35 E2, 7x35 E, 8x30 E2, 7x26 Custom, 8x23AS Diplomat, 8x23 Travelite
Scopes:
C9.25, 6" f8 reflector, SV80S
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mooreorless
Just worried
Reged: 07/05/05
Posts: 1824
Loc: Cornpropst Mills,Huntingdon,Pa
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Hi, I have -2.0 diopter in my left eye.I have an older Swarovski 7x30 SLC and have set it at 2.0 diopters and all the Nikon SE,LX and even the EDG I tried were set at 2.0 diopters. I have some "other" binoculars that are set at this or that.:-)
Hi Erik, I bet it helps reading up close with -4.0, I know it helped me put off getting bifocals with -2.0 in left eye. :-)
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Regards,Steve M
Edited by mooreorless (10/30/09 05:06 AM)
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14728
Loc: Cumberland, R I , USA42N71.4W
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Quote:
It's really quite arbitrary where the marks line up as long as you can reach focus personally. It becomes a real deal breaker if the inaccuracy is such that it prevents you from reaching perfect focus, though. Say you need a -4 diopter setting for your right eye. Your binocular has an 8 diopter adjustment range but it isn't balanced equally ± 4 D either way. Instead it's +6/-2; you're out of luck!
While no one can argue with the comments above that a persons eye perscription will cause the diopter to be off zero when set to best focus. it is also true that a person with eyeglasses with presumably eyes corrected to 20/20 vision should find that at best focus the diopter falls right on the zero mark.
In some instance the reason it does not fall on zero is because the objective lenses are set within the barrel housing at slightly different depth. In order for the diopter to fall right on the zero mark for 20/20 corrected eyes, the objective lenses in both barrles must be exactly the same distance from the focuser. If they are not, it will cause the diopter to be offset from zero at best matched focus. A difference of 2-3mm in objective recess will cause a difference of 2-3mm in eyepiece focus distance to match. Since most dipoters have a plus/minus range that results in a depth change of the eyepiece of about 6mm, that could result in the dipoter being fully one half it's total range from where it should be expected to focus.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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KennyJ
Reged: 04/27/03
Posts: 12889
Loc: Lancashire UK
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In my experience , on a size for size basis , accuracy in terms of closeness to zero marks runs more or less directly proportional to the price of the binoculars !
Kenny
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If everyone is thinking the same thing , no-one is thinking - General George S.Patton
Zeiss 7 x 42 BGAT
Captain's Helmsman 7 x 50
Nikon 10 x 42 Superior E
Swift Audubon Kestrel 10 x 50
Helios 15 x 70 Observation
Strathspey 20 x 90
Televue 76 APO
Zeiss 85 Diascope
Helios 102 f5 refractor
Various eyepieces barlows tripods mounts etc.
Panasonic Lumix DMC - TZ5 digital camera
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jkevn
sage
Reged: 03/02/06
Posts: 211
Loc: Tucson, Arizona
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In addition to possible errors that EdZ pointed out, it is my understanding that the typical person's ability to notice a difference in perfect infinity focus is about a quarter diopter. So that could result in an apparent half diopter difference between two eyepieces, even with everything else being perfect.
I guess the realistic bottom line is, can you get both eyes in focus at the same time, without worrying about what the tic marks read? I admit I have a problem with wanting the tic mark readings to be perfect...but I remind myself that typical binoculars' diopter scales are NOT intended to be used for testing for eyeglasses prescriptions...
From a practical standpoint, if several people will be using your binoculars, it would be good if the range is kind of near the middle, so focus will accomodate the most people. More expensive binoculars do tend to be more accurate in this regard.
Kevin
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Erik D
Post Laureate
Reged: 04/28/03
Posts: 3196
Loc: Central New Jersey, USA
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Quote:
Hi Erik, I bet it helps reading up close with -4.0, I know it helped me put off getting bifocals with -2.0 in left eye. :-)
Hi Steve,
Yes, it helps quite a bit. In fact I have never needed glasses for reading a book. My -4.0 right eye sees every little detail from about 8-12 inches. My 20/20 left eye takes care of distance vision.
I have had lopsided vision since my early teens. IIRC my first pair of glasses were -1.25 right eye but I didn't wear them much. Then it got worse over the years, - 2.0. -3.0 finally settled at -4.0 about 5 or 6 years ago. My near vision is as sharp as ever.
I finally needed to wear corrective lens when I reached my late 40s. Only for middle distance when I am in front of a desk top computer. I came back from a week long business trip to Asia then a cruise to Bermuda. Discoverd that I could no longer focus on the computer screen after 2.5 week away. ~ 24 inches. I still don't wear glasses for anything else except rifle shooting. Don't need glasses with a laptop computer either. I just get close as If I am reading a book.
I tried progressives and bi-focals. They don't work for me. I see double vision when I try to read with them. I guess my vision defect turned into an asset later in life. The eye doctor who examed my eyes for progressive lens shook his head in amazement. He couldn't believe I was walking around with -4.0 right eye and no glasses, but I could read the smallest letter on the chart with my left. ;-))
My brother and sisters wore contacts for most their life. All of them had laser surgery. I am very thankful I do not need glasses with most of the binoculars to this day.
ERik D
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DJB
Carpal Tunnel
Reged: 02/23/05
Posts: 1589
Loc: Lisle NY
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Hi Kenny,
You are correct, actually. Precision is proportional to cost. It works out every time, my friend.
Best regards,
Dave.
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