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

480sparky · Sep 14, 2013

The other day, during a brief moment when my brain is actually making contact with the rest of my body, I had an idea.

What if?...............

What if.......... I took a close-up filter, and installed it on a lens? Backwards.

Yes, put in on with the 'wrong' side facing the subject.

Would the lens then have the ability to focus beyond infinity? If so, could I scale the idea up and use a telescope thus outfitted and see beyond the edge of the known universe? Could I see back further in time than any other astronomer ever has? Should I contact NASA and sell them the idea? Have I finally entered the realm of the Great Thinkers? Am I pondering things beyond the scope of mere mortal comprehension?

WHOA! Let's not get ahead of myself, I thought. First things first.... I gotta try it. Since my body decided to make contact with my brain a few minutes ago, I decided to check out my "Divide by zero" experiment. I tossed some oddball stuff on the table, threw on the 105 Micro, and took this:

I then spun on a +4 lens the 'right' way onto the lens, and moved it closer (not changing the focus setting), and got this:

Now for the moment of truth: put the +4 onto a 52/52 reversing ring and install it 'backwards onto the 105. I didn't change anything else... not even the focus point.

(Drumroll, please!) Net result:

What the!?!?!? There's no difference! The close-up lens works the same both ways! Instead of making up some far-fetched conspiracy theory about the Illuminati or NSA or Elvis being involved, I thought I post my results here and ask for a bit o' edyoukayshun: Why does the CU filter work the same both ways?

Gavjenks · Sep 14, 2013

Because a close up lens is usually a simple convex lens in a ring. It is symmetrical, so it works both ways. (sometimes they may be a bit more complex, like achromats, but even still, the net effect is a basic convergent lens equivalent)

Try taking a pair of reading glasses and holding them in front of any random photography lens, and you will be able to focus on things closer than before.

Flipping things around only has different effects for multiple element, more complex designs that tend not to be symmetrical.

480sparky · Sep 14, 2013

Gavjenks said:
Because a close up lens is usually a simple convex lens in a ring............

Nope. Try again.

Gavjenks · Sep 14, 2013

I have one in my hand right now that is clearly a simple convex lens in a ring. At most it might be a cemented achromat convergent double, but the coloration and curvature look the same on both sides, so i don't think so. Even if it is a cemented achromat, it would have equal magnifying properties reversed (although different spherical aberration qualities etc.)

I also just now double checked and verified that a lens sitting on my work shelf for homemade lenses, which is 100% absolutely a simple convex lens, held up in front of my 70-300mm Canon lens, reduces the minimum focus distance from 5 feet down to about 4 inches, with reasonable image quality considering I was just holding it in the air.

480sparky · Sep 14, 2013

Gavjenks said:
I have one in my hand right now that is clearly a simple convex lens in a ring. At most it might be a cemented achromat convergent double, but the coloration and curvature look the same on both sides, so i don't think so. Even if it is a cemented achromat, it would have equal magnifying properties reversed (although different spherical aberration qualities etc.)

I also just now double checked and verified that a lens sitting on my work shelf for homemade lenses, which is 100% absolutely a simple convex lens, held up in front of my 70-300mm Canon lens, reduces the minimum focus distance from 5 feet down to about 4 inches, with reasonable image quality considering I was just holding it in the air.

Well, obviously you're not looking at the lenses I have.

Gavjenks · Sep 14, 2013

Also focusing beyond infinity is already possible with plenty of mediocrely made commercial lenses without adding anything at all. Just slide the focusing ring to "infinity" on a lens poorly calibrated in the right direction. All it means is that your lens isn't quite powerful enough to focus parallel incoming rays down to a single point by the time it gets to your sensor. If you were to move the sensor back slightly on such a lens (e.g. with an extension tube of correct length), you would once again be able to focus at infinity

Well, obviously you're not looking at the lenses I have.

Okay, describe what appears to be the element layout, and it will help in figuring out why reversing has no effect. It might just be two convergent lenses, which will also act almost exactly the same forward or backward.

manicmike · Sep 14, 2013

Magic?

Joeywhat · Sep 14, 2013

Yes it is possible, but you need a Mr Fusion, or a good source of plutonium.

pixmedic · Sep 14, 2013

it would have worked if you had used the camera with the flux capacitor.

480sparky · Sep 14, 2013

astroNikon · Sep 14, 2013

480sparky said:
.... some far-fetched conspiracy theory about the Illuminati or NSA or Elvis being involved,

Actually it was Elvis. I saw him at the park, I tried taking a picture of him but he was hiding behind a tree with a bag full of lenses and flux capacitors. He then jumped in his DeLorean and disappeared.