Me no understand...'slain this to me.

[480sparky42 41]

Yeah this is SO a Helen question.

Someone break out the Helen signal.

Is that like the BatSignal? :scratch:

 

[astroNikon]

Helen will make this all right.
she is three shades of awesomesauce.

awesome sauce ?

 

[manaheim]

Yeah this is SO a Helen question.

Someone break out the Helen signal.

Is that like the BatSignal? :scratch:

While you were doing that, I was doing this...

 

[manaheim]

And yes that really is Helen's head on that.

 

[Murray Bloom]

What makes it a close-up lens is that it's thicker in the center, making it the equivalent of a magnifying glass. It's curved overall to help deliver a sharper image to the flat focal plane. Reversing the close-up lens still has it thickest at the center, which, at most, will change the magnification factor. I can do the same thing with my reading glasses.

 

[pgriz]

Sparky, I think you have telescope gear. Check out your Barlow lens. It extends the focal point further out (increasing the effective focal length). As for the magnifying lens, it doesn't have to be symmetric to give the effect - only that the center is "thicker" than the perimeter, causing the light wave to bend inwards. As Murray already pointed out.

Now as for the looking past the edge of the universe, be careful what you wish for. This was already done, and for her efforts to explain, she was burned at the stake. Years later, her explanations scribbled onto the walls of her cell were finally decoded, and the fellow who replicated her results was declared insane and was lobotomized "for his own good". Now his notes were found and the last person trying to demonstrate was declared a terrorist and vaporized with a Hellfire missile. That track record is beginning to discourage the truth-seekers, at least those with families and mortgages. So... don't fool around with the what's behind the edge of infinity. And if that doesn't deter you, because nowadays, you might be run over by a Google car mapping out the aformentioned corners of the universe. :mrgreen:

 

[480sparky42 41]

Sparky, I think you have telescope gear. Check out your Barlow lens. It extends the focal point further out (increasing the effective focal length). As for the magnifying lens, it doesn't have to be symmetric to give the effect - only that the center is "thicker" than the perimeter, causing the light wave to bend inwards. As Murray already pointed out.

Now as for the looking past the edge of the universe, be careful what you wish for. This was already done, and for her efforts to explain, she was burned at the stake. Years later, her explanations scribbled onto the walls of her cell were finally decoded, and the fellow who replicated her results was declared insane and was lobotomized "for his own good". Now his notes were found and the last person trying to demonstrate was declared a terrorist and vaporized with a Hellfire missile. That track record is beginning to discourage the truth-seekers, at least those with families and mortgages. So... don't fool around with the what's behind the edge of infinity. And if that doesn't deter you, because nowadays, you might be run over by a Google car mapping out the aformentioned corners of the universe. :mrgreen:

A barlow isn't intended to change anything other than to invert the image so the 'scope can be used for terrestrial views right-side-up. Besides, a barlow is not in the same place in the optical path as a Close-Up lens.

As for my CUL being thicker in the middle, I have to way to measure it... it just feels like it is.

 

[Gavjenks]

So it's just that one positive meniscus lens, 480?

A positive meniscus lens is still positive (convergent) no matter which way it is facing. What makes it a convergent lens is not whether the front surface is convex or concave. What makes it convergent is that the middle of the lens is thicker than the edges.

No matter which way you flip it, the middle is still thicker than the edges, so it will still converge rays, and thus have the exact same magnifying properties.

It will NOT have the same affects on distortions, however. Flipping it one way (I think with the convex pointing out, but could have mixed that up) will create less spherical aberration usually than flipping it the other way. Or it interacts in certain ways with other types of shapes to minimize aberrations, or something. I used to know this, but have forgotten the specifics on that, but I one of the main reasons people manufacture positive meniscus lenses is to somehow or other use them to control aberrations. As opposed to just always manufacturing biconvex lenses.

Well, also, a second reason is that you can fit lots of meniscus lenses inside of each other, and thus cram a lot more glass into a smaller space, which consumers like, because then your lens isn't bulky.

I can't say for sure what their motivation was here for using a meniscus shape (probably the aberrations). But in any case, the close-up effect depends on the optical strength which depends on the middle versus edge thickness, not the meniscus shape, and thus should be virtually identical either way, because the difference in thickness is symmetrical, even if the literal shape of the lens isn't.





If you take your close up lens and walk outside on a sunny day, you should be able to use it to fry ants pointing in either direction, by itself, from about the same distance above the ground. I.e. the individual element's focal length / optical power does not change by direction.

 

[Gavjenks]

What makes it a close-up lens is that it's thicker in the center, making it the equivalent of a magnifying glass. It's curved overall to help deliver a sharper image to the flat focal plane. Reversing the close-up lens still has it thickest at the center, which, at most, will change the magnification factor. I can do the same thing with my reading glasses.

Aw, apparently you sniped me on the thicker in the middle thing.

However, I sniped you on mentioning reading glasses in this thread. So we can call it even *narrows eyes and backs away slowly*

 

[snowbear118 49]

Magic?

No; bacon. It's always bacon.