When I look through the peephole in my door, everything’s blurry. When I lower my glasses and look through the peephole without having my glasses intervene, everything is in perfect focus. I am near-sighted. I have received confirmation from another person that they find the view through the peephole to be blurry, but they are not near-sighted.
Is there something wrong with the peephole? Why is it able to make the image from the other side of the door absolutely perfect when I don’t look through my glasses? Just coincidence that the lens in the hole is the right power to be basically the same as my glasses? Is there perhaps another part to the peephole that’s missing that corrects the image, like an eyepiece in a telescope? It’s really freaky that I can see outside with 100% clarity through the hole if I lower my glasses, but if I look through my glasses it’s as if I’m not wearing them when viewing the distant scene. I’m tall enough to see above the window above the door and don’t use the peephole when there are people outside, so I don’t know if the view of much closer objects is better or not, but judging from the uniform blurriness, it seems unlikely.
That’s just the way optics work. If you are nearsighted due to being myopic (like me) then narrowing the field of view also narrows the blur area on the retina, making things come more into focus. The same thing will happen if you look through any sort of pinhole. There’s no lens required. You can make a fist and don’t quite close your fingers all the way, then look through the hole and you should experience the same thing. Poke a small hole in a piece of paper and look through it and again it will be the same.
This picture gives you a nice diagram of what is happening:
Seems like the peephole is in fact set to be suitable for use by a short sighted person.
This could be because the wrong size peephole was adjusted to fit the door ???
My “significant other” (long-time, live-in, own-a-house-with girlfriend is just to much to say most of the time) learned this little trick several years ago. Making an “OK” sign with her hand with the smallest possible opening and holding it right up to her eye lets her read things like text messages, menus, ingredients on packages and things like that. In a pinch? Fine. Out to dinner or in the grocery store? Not so much. Often times she does this with reading glasses within arms reach or even on the top of her head. Once at the CVS a staff member, apparently thinking she was more than just visually challenged, came over and gently asked her if she needed any help with her shopping. I cringe when we go out to eat and she starts doing this. Oh, well.
This is the way those “pinhole glasses” work. Restricting the aperture very significantly allows you to get sharp images, at the expense of having less light. For a long time, pinhole glasses used to be the only option for people with severe lens deformations (there are now others).
The use of pinhole glasses has been verified for use in Asia several centuries ago, and I have argued elsewhere that pinhole “monocles” and “lorgnettes” could wll have been used in the ancient world.
Yes, I’m well aware of using a restricted field of vision to improve the clarity of an image as a near-sighted person. It may well explain why I am capable of seeing things clearly through the peephole without my glasses. But it doesn’t explain why it makes things blurry for myself with my glasses, and for the other person who has looked through the peephole. It seems to completely invalidate the intended purpose of the peephole, as anyone who looks normally through it can’t make out much of anything. How is it that it makes things blurry for those with normal vision, but when used as vision correction for someone that’s near-sighted be nearly perfect?
I’m near sighted and made a quick experiment. I made a pinhole with my fingers and looked at a distant object without my glasses. The pinhole gave me a relatively sharp image. I did this again, but this time looking through the pinhole and through my glasses, no change in sharpness. Based on that there needs to be something else or more behind this effect than the peephole being similar to a pinhole, which after all it really isn’t, you have lenses at both ends working to increase the field of view over that you’d seen through such a small opening.
Have your non-near-sighted friend look at something with your glasses on. If what they see has similar blurriness to the peephole then your theory about the peephole ‘prescription’ accidentally matching that of your glasses is probably correct.
Sounds like the peephole isn’t focused correctly. Most likely the eyepiece is slightly too close to the objective lens. This will cause the light rays to be divergent, just like the rays after they pass through the concave lens of your eyeglasses.
I doubt there is a focus adjustment on a peephole. I’d guess it got damaged somehow, and the lens knocked out of proper placement. Or, as Isilder suggested, someone may have modified it to fit, not realizing that it would affect the focus. I doubt it’s a missing lens - one missing lens would make the peephole completely non-functional.
I suspect you are either overcorrected or over the age of 45.
Your symptoms are those of presbyopia. Physiologically, assuming you are corrected for distance with your glasses, when viewing at near, the ciliary muscles surrounding your your natural lens contract and cause the natural lens to take a rounder more convex shape. The increased convexity of the lens makes light rays focus on the retina for a sharp image. If your glasses are too strong for what you truly require, these ciliary muscles are working (for the wrong purpose) full time to keep images in focus. They will be overwhelmed if they are required to focus at near (like the peephole) and you will be blurred. If you are over 45 these muscles naturally weaken and again will be overwhelmed for viewing at near.
Because you are “near sighted,” removing your glasses will take the ciliary muscle activity out of the equation and you will see clearly through the peephole.
I believe that the peephole was an after-market addition, added by someone who may not have known anything about how they work, and that it stands to reason that such due to such inexpert installation, the distance between the two lenses is not correct to restore the image for those who have normal sight, but diverges the images just enough to be reasonably close to the prescription on my glasses.
FWIW, I have the same situation with the peephole in my front door. I can see clearly out of it without my glasses, but not with my glasses.
It seems unlikely to be a bad installation in both cases. I would expect it to be more a matter of where you actually have to focus, which is very close, as opposed to your perceived focus, which is far away.
The peepholes I’ve installed over the years have fixed lenses on the inside of the door. The rest of the unit is a threaded tube that slides through the hole from the outside and the lens unit screws into. No real way to misalign the lenses and unlikely to be damaged.
One variant of the legend of Peeping Tom (guy who peeped on Lady Godiva’s ride) claims that he was struck blind when he did that. It must have been an optical effect of his peephole?
I have noticed the exact same thing. I am also nearsighted without my glasses.
However… I have only noticed this when looking out the peephole *without *anyone standing in front of the door. That is, when the nearest thing to look at is across the street. Perhaps, just maybe, if there were someone standing ten or twelve inches from the peephole, the reverse would be true? I haven’t done this experiment yet, but it might make a difference.
