· Get a Cloudy Nights T-Shirt · Submit a Review / Article 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 You are not logged in. [Login] Entrance · Main Index · Search · New user · Who's Online FAQ · Calendar Equipment Discussions >> Binoviewers Previous   Index   Next   Threaded   Pages: 1 ErikB super member Reged: 02/05/06 Loc: Central Arizona Merging questions: eye centering, ep focal lengths       #5342698 - 07/30/12 01:29 AM Edit   Reply   Quote Quick Reply   I have developed an itch to try a bino. Deep down this itch comes from deteriorating eyesight and "wanting to see what I can see before it is too late". Maybe because of imperfect vision, I have never been a very much for looking through an eyepiece for more than a few moments. Now I imagine that I am missing something, and perhaps a bino would give me access to it... Or at least get rid of the strain that comes from keeping one eye closed. Actually my vision is not bad by common measures. I easily pass the test to drive without glasses. It is just that, when I look through a telescope producing a substantial exit pupil (more than 1 or 2 millimeters) I see double, and I need to move my eye to place that light beam to an optimal position on the cornea. If I look at the moon with one naked eye, I see two images, one overlapping the other, offset by about 1/4 moon diameter, or 8 minutes of arc or so. To read a newspaper I squint a bit to reduce the effective pupil. The same technique works on the moon. When using a scope with large exit pupil I move the eye off axis so that only part of the exit pupil enters the eye pupil. With high magnifications (shorter ep's) the double vision is rarely seen, but it still helps to move the thin beam of light to hit a good part of the cornea. The only explanation I have come up with is that my cornea is segmented and functions as multiple lens fragments imperfectly assembled together. Anyway, I have questions about bino's. I read about how it may sometimes be difficult to merge the images. Will that be even harder if I have to move each eye off axis? Both eyes behave similarly, so I may get away with, let's say, moving both eyes upwards a bit from being centered on the ep's. Aside from the expected vignetting, do bino users commonly lose the image merge if they do that? I have also read that people are having trouble merging the images if the ep focal length is shorter than 10 mm or so. A 10 mm ep should give good magnification and a not-too-big exit pupil in an 8" sct, allowing me to binoview planet detail. But in my ED80 that eyepiece would only produce 60x. For planetary viewing I often use a 3.5 N6, producing 171x. Will I have to give up planetary viewing if I use a bino with the ED80? Thanks in advance for any thoughts. Oh, and btw, does anyone have a similar vision problem? Post Extras:       GlennLeDrew Postmaster Reged: 06/18/08 Loc: Ottawa, Ontario, Canada Re: Merging questions: eye centering, ep focal lengths [Re: ErikB]       #5343535 - 07/30/12 02:29 PM Edit   Reply   Quote Quick Reply   Have you had an opthamologist examine your eyes, and give this condition a name? By the way, you described the effects, and an interpretation of the cause, very clearly, as a scientifically minded observer would. If the binoviewer delivers reasonably collimated images, the fact that the emerging light from both eyepieces is parallel ensures that individual eye misplacement *by itself* will not cause the images to 'un-merge.' Now, with your 'fractured' views causing a separation of images, there is a potential fly in the ointment. It might well require to ensure that the 'non-opposing' offset images be the ones which contribute to what you see. And so you may have to work more at steadying your head/eyes and maintaining careful positioning. You could perhaps assess this beforehand, by placing very close before each eye a piece of card stock (or other material) having a hole of diameter equalling the exit pupil diameter you wish to test for. Make each piece of card large enough so that they can be held together with some kind of clamp (Bulldog clips are good.) You can then move the cards with respect to each other, knowing that you're positioning the 'exit pupils' closer together or farther apart, and at the same time moving one or both up and down, exploring all possibilities of differential placement. This 1X treatment is as valid as doing the same under magnification, due to the condition of parallelism of the light coming from the object. You must ensure that your pupils are at least nearly fully dilated. This will happen quite quickly once you step outside at night. If no stars or Moon ate visible, you can use a distant streetlight The 'admonition' against the use of short focal length eyepieces on BVs is only because they more strongly amplify any mis-collimation. If you are lucky enough to get away with it, then nothing stops you from going shorter. But you can install a Barlow ahead of the BV if yet more exit pupil reduction is desired, thus obviating collimation concerns when very short f.l. eyepieces are employed. Post Extras:       ErikB super member Reged: 02/05/06 Loc: Central Arizona Re: Merging questions: eye centering, ep focal lengths [Re: GlennLeDrew]       #5344559 - 07/31/12 01:14 AM Edit   Reply   Quote Quick Reply   Glenn, thanks for your thoughtful response. I have seen two good ophtalmologists about the problem, and neither had a name or identification for the condition. "Here are some eyedrops, and don't rub your eyes". Your suggested method of testing is definitely of interest. It is amazing how some relevant external input can stimulate the thought process. In this case a sequence of thoughts led me to a new explanation for the condition. First, when I envisioned the steps involved with the determination of best simultaneous exit pupil locations, my mind went to the simplifications I had made in the original post. In fact, the offsets between the images is not constant, and there are usually more than 2 images, often 3 in a clover leaf pattern. I briefly went outside, and right now the moon image to the right side is especially prominent, while the offset between the upper and lower images is much smaller than what I stated. So, given that the pattern is not constant, how meaningful is it to determine optimal corneal areas? More importantly, if imperfections in the cornea are the cause, how can the condition change so rapidly? The answer, as I see it now, is that the multiple images must be caused by the lensing action of floaters. (I have developed very substantial floaters over the last few years.) I guess that the floaters are not essentially the dark bodies that I sometimes see somewhat clearly, but larger lumps of transparent material, with a refractive index that differs from that of the surrounding liquid. If this is so, and given that big floaters are common in older people, I would venture to speculate that my condition is not unusual, despite the fact that nobody on the forum has acknowledged similar problems. It seems that if I get a binoviewer I will need to adjust my head position and the distance between eyepieces for each observing session, rather than find some shortcut approach. On the topic of adjustment, it seems that bino's easily lose their collimation. If I understand you correctly, you are saying that the use of a Barlow does not aggravate the effects of mis-collimation as shorter FL eyepieces would. I think someone in another thread expressed the opposite opinion. In any case, wouldn't it make sense for the bino's to have external collimation adjustments? Maybe you even have that already on your homemade binoculars? (Interesting projects, but I haven't had time to look at the details.) Post Extras:       GlennLeDrew Postmaster Reged: 06/18/08 Loc: Ottawa, Ontario, Canada Re: Merging questions: eye centering, ep focal lengths [Re: ErikB]       #5344587 - 07/31/12 02:01 AM Edit   Reply   Quote Quick Reply   If floaters are a problem, they being in suspension, see what happens after a short spell of rapidly flicking your eyes so as to 'stir up' the vitreous humour. Your description of multiple (more than two) images reminds me of a similar problem on somewhat older friend went through a few years ago. She was developing lens problems and had them replaced with artificial lenses. I've only ever encountered the advice that a Barlow (in lieu of or in addition to the usual OCS) does not ever cause a collimation problem. In any event, that's most certainly true. Miscollimation can only occur *after* the light has transited the beam splitter. Indeed, with all the binos I've built, externally accessible adjustments for collimation are de rigeur. Post Extras:       tomcody professor emeritus Reged: 07/06/08 Loc: Titusville, Florida Re: Merging questions: eye centering, ep focal lengths [Re: ErikB]       #5345470 - 07/31/12 02:49 PM Edit   Reply   Quote Quick Reply   Here is a site that speaks about possible causes of this condition. http://www.allaboutvision.com/conditions/double-vision.htm Any of them look like what you are experiencing? Rex Post Extras:       ErikB super member Reged: 02/05/06 Loc: Central Arizona Re: Merging questions: eye centering, ep focal lengths [Re: tomcody]       #5345545 - 07/31/12 03:36 PM Edit   Reply   Quote Quick Reply   Rex, thanks for the link. I will look more at that page, but I still suspect the floaters. The extra images are certainly not nearly as intense as the main image to the unaided eye. When I look at the computer screen right now from 3 ft away, with relaxed eyelids, I see only the main image. If I force the eyelids more open, as in astonishment, I see a light gray double of each text row, located just below the solid black main text image. So, it is nowhere as bad as the baby image example at that website. The phenomenon is much more noticeable when viewing a bright object against a dark background, as in astronomy. I haven't tried to view the moon through a neutral density filter, but I would expect that to make the extra images rather faint. When I look through binoculars with large exit pupil in the daytime, the extra image can appear as bright as the main image. Some time ago I was looking at an orange hanging on a tree 70 ft away in my back yard. If I centered the eye on the eyepiece, I saw two equally bright oranges, overlapping like olympic rings. By moving the eye up or down I could shut off one or the other image. In the middle, besides the double orange, I saw an overall blurring of everything. Post Extras:       tomcody professor emeritus Reged: 07/06/08 Loc: Titusville, Florida Re: Merging questions: eye centering, ep focal lengths [Re: ErikB]       #5346241 - 07/31/12 11:57 PM Edit   Reply   Quote Quick Reply   Have you considered consulting an eye surgeon? I have found them to be much better at diagonosing conditions. Rex Post Extras:       ErikB super member Reged: 02/05/06 Loc: Central Arizona Re: Merging questions: eye centering, ep focal lengths [Re: tomcody]       #5347079 - 08/01/12 02:14 PM Edit   Reply   Quote Quick Reply   Rex, thanks for the suggestion, I will consider doing that. Post Extras:       tomcody professor emeritus Reged: 07/06/08 Loc: Titusville, Florida Re: Merging questions: eye centering, ep focal lengths [Re: ErikB]       #5347164 - 08/01/12 03:17 PM Edit   Reply   Quote Quick Reply   Don't want to worry you, but a family member started having double vision problems and it turned out to be a tumor pressing on his optic muscles and nerves behind one eye. This is probably NOT your problem, but maybe its better to get it diagonosed. Rex Post Extras:       Pages: 1 Previous   Index   Next   Threaded   Extra information 3 registered and 8 anonymous users are browsing this forum. 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