the thing that attaches to your glasses to help you see..wazzit?

Diopter. Merit Corp. sells one that's adjustable. http://www.meritcorporation.com/ . Actually it is an adjustable aperture, not a diopter. I believe the diopter is a lense for vision correction or to help focus on the front sight.

is it called the "Optigrab"? or will that just make you nearsighted?

Bifocals?

Yes, it would work with bifocals and yes people will pay $65 for it. The reason is for certain types of shooting it works.

In photography we call it a pinhole lens which has no glass elements, merely a small hole in something. I used to use it to win bets that I could take your picture with a piece of aluminum foil.

In Nuclear Medicine we use the same princaple to obtain the highest spatial resoulution (sharpness) from our gamma cameras. Typicaly used to image thyroid glands.

NukemJim

It's late but I will try to explain the principle. By reducing the amount of light (like closing the aperture on a camera) you extend the focal point. A cheap way to demonsrate this is to simply cut a small piece of electrical tape and put a hole through it with a needle. Stick it to your shooting glasses with the hole where you normally sight. Look through the hole. Now line up your iron sights. Presto, you can see the back sight. you can see the front sight. You can see the target. It's like a time machine that lets you see with 20 year old eyes again.

More correctly, a pinhole has an infinte (or close to it) depth of focus and depth of field. (The two are different.) This is why the wazzit thingie works.

I used to mount an extension tube with a piece of bronze sheet with a properly-cut pinhole in it to achieve extreme depth of focus in some "pattern shots," like a row of fenceposts, and for some macro-photography.

Pinhole cameras are interesting things. There is a whole technology surrounding them. A proper pinhole aperture has to have sharp edges, so you first drill the hole, then cut a taper into it so the actual hole has sharp edges.

There's a compromise involved, though. With smaller and smaller pinholes, you soon run into diffraction effects, which tend to drop the resolution. There are formulae to calculate the optimum pinhole diameter for a particular use. The iimage also gets dimmer with a smaller pinhole.



This is a pure fun "pinhole" thing to do which illustrates a lot about pinholes and the way the wazzit works:

One thing that impressed the heck out of my kids when they were younger was to close off a window (using cardboard, aluminum foil, whatever) in a room with a white wall opposite the window. With about a 1/2" hole in the cardboard (or whatever), you could see an upside-down full color image on the wall of everything happening outside when the lights are turned off. Cars moving by, people picking their noses, etc. The bigger the hole, the brighter the image, but also the more blurry.

It is quite a dramatic effect, especially to kids --has the flavor of a "miracle," sort of.

You will note that no matter how far away the object (car, nose-picker) is, it will be in focus (depth of field). And no matter how far away the wall is, it will still be in focus (depth of focus).

It's called a Camera Obscura in case you want to look it up.

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BTW, the "diopter power" of a lens is 1 meter divided by the focal length in meters. That is, a lens with a focal length of 1/2 a meter is a 2 diopter lens.

The beauty of using diopters is that the combined power of two (or more) lenses is simply the sum of the diopters. A 2-diopter lens plus a 3-diopter lens will be the equivalent of a 5-diopter lens.

(But when you go to the drugstore for a pair of inexpensive reading glasses, they usually drop the decimals. A " + 275 " strength pair of glasses are actually 2.75 diopters focal length.)

23ORN: Astronomers often use this method to examen eclipses of the sun without damaging their eyes (or for just examining the sun in general). Easiest way to do it is to create a pinhole using the crook of your index finger and project the image onto a white piece of paper or index card.

I remember reading one article where an astronomer had shown this to an old couple whose farm he was observing this on. They thought he was using witch craft, and abruptly asked him to leave their property.

I use an aperture when I shoot milsurps with open sights. The difference in the clarity of the sights is almost spooky. I paid a bit less than $65 for the ones I currently use, though. I have an old hole punch from my dad's toolbox that has several very small sizes, and a roll of tape.

With the aperture, I can shoot 1-2" groups out of my Swede Mauser off the bench, without it I'm doing well to keep them in 5".

Jubjub, Careful how you use that "spooky" word.

Jubjub, what's your experience with the diameter of the aperture?

What size is best for you for what kind of lighting and what kind of shooting? (Is it different for handgun at more or less arm's length versus milsurp rifle, where the rear sight is closer?)

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Nukemjim, what's the wavelength put out by your apparatus (near gamma?), and what's the diameter of your "pinhole?" (Is it actually a pinhole in a sheet of metal? Lead?)

I only use it with open sighted rifles. I can see handgun sights well enough, but those little black rifle sights just dissolve into a blur for me.

The punch I have is like one of those leather punches with the different sizes on a wheel on one jaw, but is smaller and lighter built, like a paper punch. Couldn't say what its intended use is. The size I use looks to be somewhere around 1/32nd. I haven't tried any other sizes.

Electrical tape works fine, though not after it's been in a hot car. Then it leaves sticky goo behind on the glasses.

Depth of field, yeah that's it. I barely remember some of that stuff from a photgraphy class I took in the '70's. I use the tape trick when I shoot .22s with my son. It helps a lot.

I've been using a Merit Disc for years, and it definitely works. Well worth the price if your eyes are getting weaker.

When I was shooting well, a guy a couple of lanes down came over to congratulate me on my targets. When he saw the disc, he said, "oh, so that's how you do it."

No, the disc just helps me see. It doesn't shoot for me.

I've shown the disc to several other shooters, and they were very impressed.

My god, what kind of person is paying $65 for these things...

Click to expand...

That man isn't paid $50,000 for placing an X with a piece of chalk, but for knowing where the X belongs.

its called a lens...