Click here if you are having trouble logging into the forums
Privacy Policy |
Please read our Terms
of Service | Signup and
Troubleshooting FAQ | Problems? PM a Red or a Green Gu.... uh, User
jkevn
sage
Reged: 03/02/06
Posts: 211
Loc: Tucson, Arizona
|
|
How bad does astigmatism need to be for it to really make a difference using eyeglasses or not, when using binoculars for astronomy?
I have mild astigmatism, .25 diopters in one eye, .5 in the other, and I can get away without using eyeglasses in general. But to get maximum sharpness, I think that it probably makes a difference. I think that it also might make a difference in seeing the faintest possible magnitude stellar object.
Is there a problem with scratching glasses extensively using them with binoculars? It would seem like the rubber eyecups would eventually scratch the lenses from particles on the rubber. I don't want to try this and find out...!
My current binoculars are Nikon 8x42 Monarchs and Nikon AE 10x50. With the Nikon 8x42 I can see the full FOV with glasses, with the eyecups pressed against my eyeglass lenses. With the Nikon AE 10x50, with glasses, not quite. Without glasses, I can see the whole sharp FOV without glasses, with the eyecups all the way out with the 8x42, and one click out with 10x50 AE. My facial features with deep set eyes require a lot of eye relief.
Kevin
|
Tony Flanders
Post Laureate
Reged: 05/18/06
Posts: 3468
Loc: Cambridge, MA, USA
|
|
Quote:
How bad does astigmatism need to be for it to really make a difference using eyeglasses or not, when using binoculars for astronomy?
I have mild astigmatism, .25 diopters in one eye, .5 in the other, and I can get away without using eyeglasses in general.
Stars are *the* most demanding tests of eyesight that exist -- period, bar none. So if your astigmatism is bad enough to need glasses at all, your views of stars through binoculars will be significantly degraded without glasses.
I always wear glasses when using binoculars, and of the numerous things that scratch my eyeglasses, I don't think binocular eyecups are a significant one. Obviously, the desire to use glasses seriously limits which binoculars I can use. But I really don't have much choice; I'm myopic enough so that I need glasses to *point* the binoculars in the first place. And with 1.0 and 1.5 diopters astigmatism, my binocular views are *seriously* degraded without glasses.
--------------------
Tony Flanders
First and foremost observing love: naked eye.
Second, binoculars.
Last but not least, telescopes.
And I sometimes dabble with cameras.
|
EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14731
Loc: Cumberland, R I , USA42N71.4W
|
|
Quote:
Is there a problem with scratching glasses extensively using them with binoculars? It would seem like the rubber eyecups would eventually scratch the lenses from particles on the rubber. I don't want to try this and find out...!
Well, I have destroyed a pair of glasses once, but not from the rubber. It's not the rubber that you need to worry about!
I refer you to my Small Binocular Series reports. In each of the four articles I address the issues under the section of eye relief. I've said this many times but it's worth repeating.
For eyeglass wearers:
Increased usable eye relief , at the expense of depth to the eye lens or protection from the eye lens metal ring, is just as detrimental to the design of the binocular as any aberrations or deficiencies anywhere else in the binocular system.
Usable eye relief is important, but so is protection from damaging contact.
If the eye lens is only 2mm recessed below the surface of the eyecups, you eyeglasses are going to come in contact with the eye lens. Eventually, eyeglasses and binocular eye lenses are going to scratch. Binocular eye lenses should be a minimum of 3mm deeper than the eye cup to prevent contact with eye glasses.
If the eye lens is 3-4mm below the eyecup, BUT the metal retaining ring that houses the eyelens is close to or at the surface of the eyecup, then the metal ring may come in contact with your eyeglasses.
These two conditions represent design that can be detrimental to eyeglass wearers and you should be cognizant of this issue when choosing binoculars. It is far better to lose 5% of the field of view and be protected by a full cover rubber eyeguard than to have 2mm extra eye relief, see the entire fov, but be exposed to potential damaging surface contact with glass or metal. This is an issue I've addressed in every review I writen in the last few years.
I like my GO22x85, but take a look at the eyepiece design. There's plenty of depth to the eyelens, BUT the metal ring is flush with the rubber eyecup. That is a poor design. You'll note in my review of the 22x85, I suggested cutting stick on felt and covering that metal.
Take a look at the Fujinon 10x50 or the Nikon SE 10x42. The rubber eyecup completely covers the metal rim. At the expense of a slight loss of fov edge when wearing glasses, there is no possible chance of coming in contact with the metal.
edz
--------------------
Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
|
Mark9473
Post Laureate
Reged: 07/21/05
Posts: 3209
Loc: 51°N 4°E
|
|
EdZ, your rule of thumb about needing at minimum a 3 mm recess of the binocular eye lens, is that only for convex lenses?
--------------------
Mark
Leica 8x20; Vixen 8x42; Swift 8.5x44, 10x50 and 20x80; TS 7x50; Orion 15x63; Docter 15x60
WO Megrez II 80 FD + Baader 90° T2 Amici
|
EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14731
Loc: Cumberland, R I , USA42N71.4W
|
|
Quote:
EdZ, your rule of thumb about needing at minimum a 3 mm recess of the binocular eye lens, is that only for convex lenses?
Well, I've seen flat eyeglasses, but they are not common. if you have flat eyeglass, you are not going to have a problem hitting eye lenses. You might still have a problem if the metal rim is flush.
edz
--------------------
Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
|
KennyJ
Reged: 04/27/03
Posts: 12895
Loc: Lancashire UK
|
|
I presume most prescription glasses are designed to provide the client with something akin to what we in the UK used to call 20 / 20 vision ( the distance is always indicated in METRES now here , instead of feet , so has become 6/6 ).
What I discovered when experimenting with some astigmatism -correcting lenses once kindly sent to me , was that even if astigmatism is only officially recorded as being .25 , using lenses to correct for .50 or .75 , increasingly sharpens the appearance of stars to finer points of light .
The astigmatism in my worst eye ( left ) was only recorded as being .75 in my last eye test , but even then , for example a half moon viewed without glasses appears to have an ( indefinite shaped ) area approximately 30% larger when viewed without correstive glasses than the almost perfect semi - circular area seen WITH .
I've mentioned this several times before ( with no recollected volunteers or respondees ) but if anyone reading this wears prescription eyeglasses to correct for astigmatism , and happens to have TWO pairs , just TRY wearing BOTH pairs at the same time , when viewing stars .
I'll be surprised if you don't notice how much smaller , sharper and crisper they appear !
Kenny
|
Mark9473
Post Laureate
Reged: 07/21/05
Posts: 3209
Loc: 51°N 4°E
|
|
Quote:
Quote:
EdZ, your rule of thumb about needing at minimum a 3 mm recess of the binocular eye lens, is that only for convex lenses?
Well, I've seen flat eyeglasses, but they are not common. if you have flat eyeglass, you are not going to have a problem hitting eye lenses. You might still have a problem if the metal rim is flush.
edz
I asked because the other day, while cleaning the binocular eye lenses on my Nobilem 15x60, I noticed they are noticeably concave.
--------------------
Mark
Leica 8x20; Vixen 8x42; Swift 8.5x44, 10x50 and 20x80; TS 7x50; Orion 15x63; Docter 15x60
WO Megrez II 80 FD + Baader 90° T2 Amici
|
KennyJ
Reged: 04/27/03
Posts: 12895
Loc: Lancashire UK
|
|
Sets of rubber ( or neoprene ) "O" rings can be purchased , that could easily be fitted to the inside rims of any ocular to raise the profile sufficiently to negate the possibility of contact with metallic or glass surfaces around the eyepieces .
Kenny
|
EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14731
Loc: Cumberland, R I , USA42N71.4W
|
|
Quote:
Quote:
Quote:
EdZ, your rule of thumb about needing at minimum a 3 mm recess of the binocular eye lens, is that only for convex lenses?
Well, I've seen flat eyeglasses, but they are not common. if you have flat eyeglass, you are not going to have a problem hitting eye lenses. You might still have a problem if the metal rim is flush.
edz
I asked because the other day, while cleaning the binocular eye lenses on my Nobilem 15x60, I noticed they are noticeably concave.
Oh, you meant the binocular lens. Well that doesn't matter, as the 2-3mm is measured to the surface of the binocular eye lens from the plane of the eyecup. 2mm is 2mm, whether your eyeglass lens hits a concave or convex surface.
edz
--------------------
Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
|
Mark9473
Post Laureate
Reged: 07/21/05
Posts: 3209
Loc: 51°N 4°E
|
|
I then suppose you mean to say you do that measurement at the lens center?
It would be much more intuitive, to me at least, to measure the thickness of the rim at the edge of the lens. But possibly that's because I don't wear glasses.
--------------------
Mark
Leica 8x20; Vixen 8x42; Swift 8.5x44, 10x50 and 20x80; TS 7x50; Orion 15x63; Docter 15x60
WO Megrez II 80 FD + Baader 90° T2 Amici
|
EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14731
Loc: Cumberland, R I , USA42N71.4W
|
|
Quote:
I then suppose you mean to say you do that measurement at the lens center?
It would be much more intuitive, to me at least, to measure the thickness of the rim at the edge of the lens. But possibly that's because I don't wear glasses.
Correct ,measured at the center.
Measuring the thinkness of the rim doesn't tell you anything. It would not account for the shape of the eye lens. Also, if glasses are going to come in contact with eye lens, since they are almost always convex, it will occur at the center of the binocular eye lens.
edz
--------------------
Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
|
KennyJ
Reged: 04/27/03
Posts: 12895
Loc: Lancashire UK
|
|
Expanding upon my earlier post and going back to the question asked in the very first sentence of this thread , I was just thinking about 20 / 20 vision , which I believe , rightly or wrongly , cannot be achieved without some form of correction , be it glasses , contacts or lazer surgery , by anyone suffering from astigmatism , regardless of whether or not they are also either short or long sighted .
Apparantly the oft - quoted " 20 / 20 vision " reference came about because it was discovered that certain sized letters or symbols could be definitively resolved by people with " normal " eyesight , from a distance of 20 feet .
Hence , anyone with 20 / 10 vision would be able to resolve from 20 feet , what a person with " normal " vision would need to stand as close as 10 feet away to be able to resolve .
That is simple enough to follow , but now I have a few questions !
1. How does anyone know how NORMAL -- "normal" really is ?
2. If in this context " normal " is just another way of saying " average " , then how do we know if " average " is not as good / efficient as human vision actually COULD or SHOULD be ? -- or indeed if it's not " better " than could be expected ?
3. If 20 / 10 is " better " than 20 / 20 , then surely 20 / 5 is even better -- so why aren't efforts made to " improve " our acuity , by any possible technological means to a level of 20 / 5 ?
4. Would or could providing such artificially sharp vision be harmful in any way , and if so , why ?
5. Finally , if we DID have 20 / 5 vision , would it necessarily make stars appear more pinpoint than if we had 20 / 20 vision , and if so , why ?
Kenny
|
|
13 registered and 13 anonymous users are browsing this forum.
Moderator: EdZ
Print Thread
|
Forum Permissions
You cannot start new topics
You cannot reply to topics
HTML is disabled
UBBCode is enabled
|
Thread views: 257
|
|
|
|
|
|
|
Previous
Index
Next
Threaded
Edit
Reply
Quote
[Re: 