[scratchpaddy]

This morning, I woke up with an idea in my head: how about making a single-element lens, a lens that is literally just one lens? It should work. Every converging lens has a focal point; just put the lens at the right distance from the sensor, and you have a camera! Who needs all those other elements, anyway?

I have an old fungus-infected JCPenney zoom that came in a lot from eBay. It was 8 lenses, including a Kiron 70-210 f/4, which is a fine lens. It must have gotten overlooked, because I was the only bidder at $10.

Lucky for me, the crappy JCPenney was the only one with fungus. I didn't mind taking it apart for this little experiment.

I got to it as soon as I got home from work. It's not like there's much else to do when it's 110° outside.

To keep most of the light from getting to the sensor from around the lens, I needed a tube. I used two toilet paper tubes, since they were available. I had to crimp one down a bit so it would fit inside the other. I could use the sliding action between the two for a focus mechanism. I used scotch tape to get the lens onto the tube, and it was done! The TP Special: a real piece of precision optical engineering.



There was still some room for stray light to get into the mirror box, but whatever. This is just a prototype.

It's a shame I got the lens from a telephoto. It's a little clumsy to work with something so long. I think the focal length of this lens is about 200mm, but I don't have anything laying around to measure it with. And I call myself an engineer. This is unacceptable!

This was the first shot I got. Only the overexposed background was in focus, but it had lots of pretty colors.




Maybe they put all those elements in lenses to get some detail in places other than the exact center of the photo?




I showed it to my dog, but she was unimpressed.




Sharpness is obviously not this lens's strong suit. Horses for courses, I say. Use it to capture all that optical mess you never see with all those other elements correcting for it.




This is my favorite so far. You can see the whole spectrum on the edges of the leaves with the brightest backlight.




Not bad for toilet paper, eh?

[Johnyb3000]

This may be the coolest use of a toilet paper roll ever! Did you just happen to have an empty one laying around or did you have to empty it in the name of science?

[scratchpaddy]

This may be the coolest use of a toilet paper roll ever! Did you just happen to have an empty one laying around or did you have to empty it in the name of science?

I just happened to finish a roll of toilet paper and paper towels in the same day. It was a fortunate coincidence. I'd hate to be wasteful, but I'd do most anything in the name of science!

It's too bad Skippy doesn't appreciate it as much as you do. Dogs just don't have much interest in science, it seems... or maybe she's just tired of having lenses tested on her?

[Tako Kichi]

Ya know if you got some caulking you could use it to seal up those gaps between the tube and the camera. Might make swapping lenses a tad difficult though.

[panoguy]

Nice!
I think Tamron made a TP-PK Adaptall mount... didn't they?

[bdery]

This is pretty cool, in a back-to-basics kind of way. Contrats on the funny narrative!

[lytrytyr]

PRIC will be miffed to hear that their 07 Mount Shield lens is no longer the worst.

[TropicalMonkey]

Yeah! the dog does look dreamy!!

Edit: Hey I like that radio behind the camera :-)

[scratchpaddy]

Ya know if you got some caulking you could use it to seal up those gaps between the tube and the camera. Might make swapping lenses a tad difficult though.

You know, I thought about cannibalizing the K-mount from another worthless lens, and then using some sort of rubber tube to connect it to the lens, but somebody already did that, and they called it a Lensbaby.

I might try just gutting all those superfluous elements from the JCPenney, but that wouldn't have that same special "kludge" quality.

Nice!
I think Tamron made a TP-PK Adaptall mount... didn't they?

Maybe so, but I'm afraid it might involve epoxy, like Larry said.

This is pretty cool, in a back-to-basics kind of way. Contrats on the funny narrative!

Thanks! There's no logical reason to do this, but that "back-to-basics" feel gives me the warm and fuzzies. It's a learning experience, too. Science!

PRIC will be miffed to hear that their 07 Mount Shield lens is no longer the worst.

Shhhhh! You'll hurt its feelings.

Yeah! the dog does look dreamy!!

Edit: Hey I like that radio behind the camera :-)

That's the "are you done, yet?" look.

I like that radio, too. That's my favorite thrift store find, ever!

[VisualDarkness]

Hey Paddy!
What about going for a TP photowalk? Too bad we are so far apart.
https://www.pentaxforums.com/forums/pentax-q/226445-ugliest-macro-setup-around-q.html

[scratchpaddy]

Hey Paddy!
What about going for a TP photowalk? Too bad we are so far apart.
https://www.pentaxforums.com/forums/pentax-q/226445-ugliest-macro-setup-around-q.html

We should start a TP Club! Cardboard tubes unite!

I've been meaning to do something like this ever since I saw that awesome setup of yours, and TropicalMonkey's question about single element lenses gave me the push I needed. Thanks for the inspiration.

I would love for this lens to get out more, but I worry about dust... and gravity.

[c.a.m]

Do you have plans to produce a WR version?

[sam-joseph]

Bit of a crappy job, isn't it? Normally this kind of lens would be used with an open aperture....Do you notice any purple fringing with this one, or is it a different colour?...
I bet the wide-angle version is big, but....
Ok, I'll stop now.

Regards

[scratchpaddy]

Do you have plans to produce a WR version?

What, this isn't resistant enough for you? It resists the weather for a short while before... melting.

Then you make a new one!

Bit of a crappy job, isn't it? Normally this kind of lens would be used with an open aperture....Do you notice any purple fringing with this one, or is it a different colour?...
I bet the wide-angle version is big, but....
Ok, I'll stop now.

Speaking of apertures, this one's got quite an unusual shape. It makes the highlights a bit wonky.



Considering fringing, was there a particular color you had in mind? We've got red, green, yellow, blue, purple... any color you like! Actually, if you wanted something besides fringing, you're flat outta luck.



I'm afraid there won't be a wide-angle version. Without a retrofocal group, I can't get any wider than the K-mount's FFD, which is 45mm.

[Jean Poitiers]

The dog "capture" is the best ... J