# Anybody ever tried a homemade fresnel lens?



## Gavjenks (Jun 30, 2013)

I am considering either trying a plastic DSLR fresnel lens like in the back of rear projection TVs, or one of the ones they use for studio lighting, that doesn't have the stipling on the back of it to make it soft.

I'm well aware that this will have all kinds of terrible aberrations.  What I'm wondering is just if anybody has tried this at all compared to homemade normal lenses, using for example lenses from surplusshed.com ? 

The goal is to attempt to make a hilarious ~1000mm, f/0.8 lens that can maybe resolve enough to vaguely actually identify things in photos (i.e. "there mayyyy be a building in this photo" levels of resolution, if lucky). Or if not that, then just regular types of lenses.

However, if somebody has tried this and fresnel lenses are vastly worse than uncoated surplus crown glass lenses of equivalent power (to the point of not being able to make out anything, even with a reasonable FL at f/8 or something), then I may not bother.


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## Dikkie (Jun 30, 2013)

Isn't there any McGuyver thread available for this?


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## Gavjenks (Jul 16, 2013)

Hey, so I went ahead and actually did this!

I got some $2-3 each giant plastic fresnel lenses about 300mm focal length, made for reading books more easily.  Chopped a circle out of the middle of one, and put it on a PVC tube, lined with painter's tape for a little bit of contrast help instead of a white interior.  I already had a universal PVC 2" Tube -> Canon EOS adapter and push/pull focuser I made a long time ago.

Total build time like 10-15 minutes.  Product was this:
Amazon.com: 5 Fresnel Lens -- Solar Oven + DIY Projection TV: Office Products

Lens:



Sample photos (LOTS of RAW editing to make these not hazy pieces of junk, but for a $3 plastic lens weighing half an ounce, these are pretty great I think!) A little chromatic aberration, almost no coma or astigmatism, decent amount of spherical aberration:


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## amolitor (Jul 16, 2013)

That's awesome, dude! It's like a telephoto lensbaby. I dig what it does to specular highlights.

I wonder what portraits would look like?

You could *totally* rock a Pictorialist gum bichromate look with this thing.


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## vintagesnaps (Jul 16, 2013)

Did you think about the interior of the lens being black instead? Wondering if that would make much difference, anything I have, even pinhole cameras, have a black interior. 

Somewhat similar looking effects to what people get with some plastic or homemade or pinhole cameras. I think it can be interesting depending on the subject, I like this best with the floral shots I think, although I sort of like it with the motorcycle, gives almost a bit of an illusion of movement. 

Now you need to put some black stripes on that lens so it goes with your camera body.

edit - I can't say though that it has the look of photos I've taken with one of my Lensbabies, doesn't have the look you get when you turn and angle the lens.


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## amolitor (Jul 16, 2013)

Yeah, the lensbaby definitely modulates its effects across the frame, which this thing does not. I find this to be pretty much the single most irritating thing about the lensbaby, though. If a lens is soft, even extremely soft, I can see how to work with it. A lens with multiple personality disorder just does not produce results that make any visual sense to me.

I probably should have said "lomographic" rather than "lensbaby" or something.


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## Gavjenks (Jul 16, 2013)

> lensbaby



Yeah it's actually fairly different from a lensbaby.  Lensbabies work by having a huge amount of uncontrolled astigmatism and coma, both of which create more streaking and directional blur away from the center of the plan of focus.  As you tilt, then, the center moves by Sheimpflug principle, moving the "sweet spot."

In fact, this lens is almost exactly the opposite of a lensbaby. It has coma and astigmatism seemingly very well under control, but spherical aberration and polish (general softness issues) are both poor, whereas lensbabies make a priority of controlling for those so that the middle is nice and sharp.

If you were to tilt this lens, it would actually look much more like a traditional tilt shift lens, with a fairly uniform line of focus from a nice evenly moved plane, and less of the circular effect.



> black inside tube


Yes, that absolutely makes a difference.  I've made multiple homemade lenses before, and typically what I do is to flock the inside of the tube with thin, fine black felt, which just sucks up light like it's nobody's business.  As good or better than the interior of Canon lenses, probably.

The painter's tape is because I'm a lazy bastard and made this in 10 minutes.

It also has no lens hood, which makes a huge difference.  A few dollars on a 2" to 3" PVC coupler and a foot or so of 3 inch pipe also lined with felt would massively help contrast as well.

However, even with both of those improvements, which normally would make even a terrible glass lens super contrasty, it still wouldn't help entirely with the fresnel lens. Part of the fogginess is due to light hitting the flat sides of each fresnel lens, which can't be helped fully ever, no matter what.  If I could choose my material and use coated glass with very little reflection but lots of refraction, then it would help (like Canon does in their diffractive optics fresnel lenses), because than light hitting the straight parts would just go straight through and bounce off of felt 10 times and not be an issue.  The relfecting off of the straight parts on my uncoated plastic, though, kills contrast like it's its job.



> specular highlights


This is partially due to the lens, but also due to the fogginess / very low contrast, which is making me get like 3 stops of dynamic range in each shot.  RAW helps tremendously by giving me the data to stretch that back out in converting to a jpeg. The extra 4 bits of data mean I essentially have 4 additional stops of dynamic range on top of that, which makes it workable.


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## Derrel (Jul 16, 2013)

It rivals many of Canon's telephoto zoom lenses! Nice work man! I'd consider painting the barrel solid black, then painting a nice, thin red stripe around it.


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## cgipson1 (Jul 16, 2013)

Derrel said:


> It rivals many of Canon's telephoto zoom lenses! Nice work man!



Really? I thought it looked more like Sony, myself!


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## Derrel (Jul 16, 2013)

cgipson1 said:


> Derrel said:
> 
> 
> > It rivals many of Canon's telephoto zoom lenses! Nice work man!
> ...




Ehhhh, not quite, and I say that because Sony lenses usually have lower levels of contrast than this eccentric beauty Gavjenks hath wrought, but I get whatcha' mean Charlie---it does have something of a *Sony-esque* look to its drawing style...


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## weepete (Jul 16, 2013)

Nice one mate! This kind of stuff is right up my street, I love making stuff like this. Plus you can totally get that authentic 60's oof look should you wish, sweet!


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## Gavjenks (Jul 16, 2013)

Note that this is not actually a telephoto lens, as that implies a telephoto group that makes the lens physically shorter than its FL by having a positive element then a negative element.  It's just a long lens.

However, I did also buy a plano-CONCAVE fresnel lens online, which is marketed to put on the back of your car's rear windshield to see the area around better and not run into kids and trees and stuff. It is more expensive though, so I'm biding my time on deciding what to do with it.  A telephoto (or retrofocus) lens is possible.  Or maybe some other things.

Also, the original fresnel positive sheets are like... the size of an A4 piece of paper, they're HUGE.  They cast a HUGE image rectangle, enough to maybe even cover an 8x10 large format piece of film. Certainly 4x5, at like potentially f/1.4.  I only cut out a 2" piece here, and it's at f/6.

The softness is only going to get more out of control at larger apertures, but I still feel like it is my civic duty to go get a piece of like 6" pipe and step it down to make an f/2 lens or so out of one of these, and possibly a wacky large format cardboard camera out of another one.



Another fun thing to do with a positive fresnel sheet:   Draw a little area of black on a piece of computer paper with a sharpie (to absorb more light), and line up one of these with it in a beam of sunlight, and it will burst into flames in approximately 1 second.  =P  Amusingly, they do not warn you about that on the packaging.

One possible thing to do with the negative fresnel element of roughly the same but opposite FL is to make a collimated beam of high intensity light by placing it near the focal point but not quite at it.  Assuming it doesn't melt my plastic lens, that would = a no-focus-required, ranged death ray


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## Gavjenks (Jul 16, 2013)

Actually, come to think of it, if I put 3 in a row in a 6" piece of pipe, I could make an f/0.65, 100mm lens!

And then never point it at the sun... because it might actually be able to burn my shutter leaves.

Lol.


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## Tony S (Jul 16, 2013)

Your shutter has leaves on it?  Do they blow around in the wind?  

  The aperture blades are in the lens usually, you might burn the sensor when the mirror flips up though.  Or melt the back side of your viewfinder.


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## Gavjenks (Jul 16, 2013)

Tony S said:


> Your shutter has leaves on it?  Do they blow around in the wind?
> 
> The aperture blades are in the lens usually, you might burn the sensor when the mirror flips up though.  Or melt the back side of your viewfinder.


I said shutter, not aperture diaphragm.  The thing that is right in front of your sensor that stops it from being exposed and that is being referred to by "shutter speed."

It consists of two curtains, each of which is made out of a bunch of tiny thin little overlapping leaf/blade thingies, almost like venetian blinds.  Video:





This is the thing that is most exposed to the sun's image at the focal point of the lens while not exposing.  The sensor is very unlikely to receive damage even if you took a picture, because with that much light, it would always be at 1/4000th of a second which isn't enough to cause damage, unless I set it to manual and forced it higher or whatever like a chump.

I think they're made out of metal, though, so they probably wouldn't actually be damaged.





Also, after more research, I discovered that the size of the mount versus the flange to focal distance makes it only possible to go down to like f/0.8 or something on Canon. So I may have to settle for that, or more like f/1.0 ish.


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## Derrel (Jul 16, 2013)

Not sure what you mean the shutter is being subjected to light when not exposing...the reflex mirror is sending the light up through the pentaprism, and right out the back of the camera...the shutter is exposed to light for a few milliseconds before it begins the exposure....and then the mirror comes back down...

Burning a hole in a focal plane shutter dates from the rangefinder era with rubberized silk shutters, not modern, titanium-alloy or high-tech composite shutters with a honking reflex mirror in front of them...


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## Gavjenks (Jul 16, 2013)

[Accidental double post]


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## Gavjenks (Jul 16, 2013)

Well right, I guess a given section of the shutter is exposed for approximately 1/25th of a second before it starts sliding and exposing a new spot.

And the ground glass isn't in any danger.  Your eyes might be though.... it's not focusing on them, but just looking at something that bright even if it's diffusing for a short distance, etc. might still really hurt.


Dunno.  f/0.9 lenses and such are commercially available, but they're never 100mm+ which could make a big difference. At that FL it could be I think 4x more overall light on the ground glass and thus flooding into your retina than a 0.9 50mm lens?  Not all in one spot though, which may be the saving grace.


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## Gavjenks (Jul 17, 2013)

New lens I made just now.  It's that kind of day =P  Was a tad bit more careful with this one.

It's an approx. *180mm* single achromat (two elements cemented together to cut down on spherical and chromatic aberration) from surplusshack for like $4 or something.  This one was slightly smaller than my 2" PVC tube standard, so I wrapped a piece of electrical wire around the inside diameter, duct taped it in place (which doubles as reflection prevention, black tape, still glossy though), and then seated the lens.

Being a proper glass lens AND an achromat, the results are substantially better.  This lens has a fixed aperture of *f/2.2*. It is designed as a portrait lens, though I don't have any portrait subjects and don't feel like lining myself up right at the moment.

Instead, here is a typewriter and a snail lady sculpture in my hallway:



Compare to a hasty snapshot that i zoomed to make the composition the same on my Canon 70-300 IS USM (it's a tiny bit motion blurred, but I think that's only fair as a showcase of the homemade lens' 2 1/3 faster stop aperture hehe). The Canon was at its widest aperture of 5.0:



The lens looks exactly like the other one, except shorter, from the outside.  Not gonna bother juggling smartphone photos.

The Canon is obviously better in technical control of aberrations, however not by much. It's a little difficult to directly compare, due to the inability to test both at the same aperture (without building a diaphragm for my lens) And regardless, I think the homemade one is actually much more attractive anyway, and especially would be for portraits (I'll update with one as soon as I have it). It has a very intentional-seeming "this is slightly imperfect and dreamy, but by absolutely no means a fuzzy wreck" look to it.

Also, the PVC lens is almost exactly the same size as the Canon fully retracted, almost 2 inches SHORTER than the Canon at equal focal lengths, and about 1/5th the weight of the Canon.



When was the last time you saw a 6 ounce, 180mm lens that was perfectly useably sharp at f/2.2 for $5 ?


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## Gavjenks (Jul 17, 2013)

Okay, got bored and did a portrait of myself with the achromat lens. DOF is like an inch on this thing (maybe it's actually wider than 2.2...? Or it's slightly soft already, making DOF narrower in general), making it virtually impossible to take self portraits that show off the quality of the lens optimally, but whatever.  

I took like 30 shots trying to get my eye in focus and gave up. You can see how sharp it CAN be though right at the point of focus, by looking at the stubble on my chin and the chevron patterns on my left collar. Plenty able to resolve impressively in a narrow narrow range. But it's almost buttery smooth blur on the cloth right behind that same collar! Craziness. It's acting like a f/1.2 or something, but metering at 2.2.

This particular shot is orthochromatic (I removed the red channel) to increase sharpness a bit, since red was actually aberrating noticeably softer than the other channels.

Anyway, totally a successful lens for this! Could take some awesome portraits if I could see what was happening before hitting the button.


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## amolitor (Jul 17, 2013)

That's really nice. To my inexpert eye, it has some of the same qualities as an olde skoole portrait lens. Possibly it's because we're seeing (I think..) multiple images cast by what are really multiple partial lenses, with varying degrees of sharpness and defects.

Compare with the Cooke PS945 which is.. more expensive.


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## grafxman (Jul 17, 2013)

You can stop the lens down and achieve some depth of field by using a disk of black construction paper over the front of the tube. You can cut disks with different size holes in them to change aperture size. I've done that with a couple of lenses. One is a Vivitar 800mm mirror lens and the other one is a Bower 650-1300mm zoom. A lot of light will be needed though.


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## Gavjenks (Jul 17, 2013)

Yeah I did try stopping it down, but then it loses all its character and look like a boring normal lens, so I might as well use a modern autofocus, etc., you know?


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## cynicaster (Jul 17, 2013)

Gavjenks said:


> View attachment 50197



It's Dexter Morgan!

Cool DIY.


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## grafxman (Jul 17, 2013)

cynicaster said:


> Gavjenks said:
> 
> 
> > View attachment 50197
> ...



:lmao::lmao::lmao::lmao::lmao::lmao::lmao::lmao::lmao::lmao::lmao::lmao::lmao:


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## Gavjenks (Jul 17, 2013)

I had the idea of putting the lens onto a macro bellows today, and using that to focus instead of pushing pieces of plastic together clumsily.  Makes a huge difference, and this is now much more of a joy to use.


Also the huge range of the bellows means basically any lens I put on it is a true macro lens.  The 180mm goes from infinity to 1:1, without me even having tried to design it like that! (You do have to extend the module forward a bit to get to 1:1. it's about 0.8x with bellows movement only) A 50mm for instance would go from infinity to extreeeme macro, 3:1 or so.

Snapshot from today with the above setup


next steps are:
1) A 2x 4" fresnel module with 150mm or higher focal length and about f/1.4
2) Aperture added to modular system
3) Eventually tilt movements added to modular system, maybe shift.


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## Tony S (Jul 18, 2013)

All I can say is I had a brain fart.....  lol


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## grafxman (Jul 18, 2013)

Say Gavjenks, since you're clearly a bright, inventive guy how about inventing an antigravity device. Consider this. We control all the natural forces such as light, RF energy, electricity, etc. but no one knows how to control gravity. So get with it Gavjenks. If you invent a way to control gravity, anti-gravity shouldn't be too hard. Then we can cruise around the solar system with just solar power and storage batteries.


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