Orquid "Phoenix"

Orquid "Phoenix"

by ceinmart

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A couple of months ago I was playing with my camera and a magnifying glass and I noticed that this glass produced a very soft chromatic aberration. Here's an example:

(Here is the full size, 18mp image)

Altough the effect was pretty cool, I couldn't focus too far from the lens. Here's another example, but with an object to a few meters farther.

dog

Maybe at this resolution the dog seems to be focused, but in the full picture you can notice that it isn't. Also the CA effect isn't that pronounced as in the first picture. (For pixel peepers, here's the full size image)

So, is there an easy way to produce chromatic aberration? I know that there are some lensbaby optics that can do that, but I'm looking for something like DIY.


ADDENDUM

Just a random thought: Could I emulate it by shifting the color layers of the image? I mean, the image is composed by three diferent layers of color, if i offset them a few pixels, will that produce some CA?

I'm pretty sure that the colors of the photo will go nuts, but maybe there's a related solution.


ADDENDUM ADDENDUM

I'm offering 300 sexy points of my own reputation for a cool, nice and DIY solution for this. Go go go!


LASTUM ADDENDUM ADDENDUM

Well, this wasn't easy. Coneslayer gave me the best answer, but Autopulated gave me the most easy, direct and (not-so) DIY solution. So:

1) I've accepted Coneslayer answer

2) I've gave the 300 sexy points to Autopulated

Thanks for your help, you both are awesome!

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If you like this effect and similar, I highly recommend getting some of the Lensbaby lenses. It's a small company with a niche product, so prices are a bit high, but they're well done and the people there are a pleasure to work with — as are the products. –  mattdm Apr 25 '11 at 15:02
    
As I said in the bottom of my question, I'm looking for a DIY solution. I've considered Lensbaby, but they are a little pricey for me. (I live in Argentina and the S&H is about 50% the price of the product) –  Andres Apr 25 '11 at 15:27
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In response to your addendum: I was thinking about this. You could deliberately mis-apply the CA correction in your software (e.g. Lightroom), which would do a credible job in the plane of focus. But I don't think it would look like real CA in the out-of-focus regions. Can't hurt to try it and see if you like it. –  coneslayer Apr 26 '11 at 16:17
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Oh man, I sure wish I had a better grounding in optics, 'cause getting sexy points sounds double-awesome! Thanks, that made me laugh... :-) –  Jay Lance Photography Apr 29 '11 at 3:55
1  
XD Thanks for the sexy points! –  James May 1 '11 at 12:42
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6 Answers

up vote 11 down vote accepted

I think the dog is in focus, but it's not sharp. And it's not sharp because a magnifying glass isn't corrected for any aberrations, chromatic or otherwise. In other words, it's a technically poor lens (though you're still welcome to have some fun with it, of course).

Lenses focus light by slowing it down as it passes through the glass, which bends the rays ("refraction"). But glass slows down blue light more than red light, bending the blue light more strongly, so the different colors come to a different focus. We say the refractive index for blue light is greater than for red light, and the fact that they're different is called dispersion, and the difference can be expressed as a dispersion index.

While all types of glass are dispersive, some are more dispersive than others. If you combine two lens elements made with different types of glass in the right way, one with a high dispersive index and the other with a low dispersive index, you produce an achromat, which reduces the chromatic aberration by bringing red light and blue light to the same focus. Pretty much any camera lens provides at least this level of correction; your magnifying glass does not. An achromat still has some residual chromatic aberration; for example, green light may come to a different focus than red and blue. Further correction produces an apochromatic lens.

If you swapped the glass type for the two elements of an achromat, it seems like you would end up with a system that exaggerates chromatic aberration. You might be able to source the required elements from an educational supplier like Edmund Scientific. Or you could just try to find a convex singlet (like your magnifying glass) made from a high-dispersion glass, which may be called "flint glass."

There are lots of other lens aberrations besides chromatic aberration: These include spherical aberration, which degrades sharpness. Your magnifying glass is, again, uncorrected for spherical aberration, which contributes to the lack of sharpness. In a real camera lens, spherical aberration is corrected through the use of multiple lens elements and/or aspherical lens elements, which are more difficult to produce than spherical elements (whose surface conforms to the surface of a sphere).

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Does anyone know how "flint glass" translates to spanish? Google doesn't give me a coherent response. Or, where is it used usually? Maybe it's used in some kind of device that I could cannibalize and extract that kind of glass. –  Andres Apr 27 '11 at 1:26
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@Andres: I went to Wikipedia hoping they would have Spanish-language articles on "Flint glass" or "Achromatic doublet," but they do not. However, in both French and Italian, it looks like the English terms are used: "verre crown"/"verre flint", "vetro Crown"/"vetro Flint". Perhaps the same applies to Spanish. –  coneslayer Apr 27 '11 at 11:17
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I think the search phrase you're looking for is "DIY toy lens".

This will lead you to a number of interesting projects, including this one made from toy magnifying glasses like the one you were playing with. The basic construction is quite simple: an extension tube is used to mount a tube of cardboard to the camera, and the lenses mounted within that tube. That's pretty simple, and flexible enough that you could adapt the idea with lots of different possible improvements.

Other projects, like the fisheye tin-can lens use peephole lenses designed for looking out one's front door. That gives a different effect, but may also appeal to you since the results will be decidedly lo-fi.

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Uhmmmm interesting approach the one with extension tube and magnifying glass! –  Andres Apr 27 '11 at 16:34
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If you split your image into red, green and blue channels, and then:

  1. Leave the green channel alone.
  2. Scale the red channel up slightly, around the centre of the image
  3. Blur (slightly) the outside of the red channel: you could use a radial followed by rotational blur to do this.
  4. Scale the blue channel down more than you scaled the red channel up, still about the centre of the image.
  5. Blur (slightly more) the outside of the blue channel.
  6. Recombine your red green and blue channels.
  7. crop off the edges of your image (where you scaled the blue channel down).

This will reasonably accurately re-create some chromatic aberration.

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I've got some awesome results following your steps: i.imgur.com/d7lHX.jpg (may be a little exaggerated) –  Andres Apr 30 '11 at 14:49
    
@Andres Cool! Maybe some more blurring around the edges would make it less obvious... –  James Apr 30 '11 at 15:38
    
I think the best part is in the center of the image, where the CA is subtle but visible. I will try with other images later. Thanks @Autopulated! –  Andres Apr 30 '11 at 15:43
    
@Andres: This would even more closely replicate the CA that a lens produces if you leave out the scale changes. Just apply a varying amount of blur to the red, green, and blue channels. The scale changes would reproduce a chromatic magnification error, which is basically non-existent in any lens made in the last century :) –  Colin K May 16 '11 at 16:27
    
@Colin There was definitely definitely a magnification error in my old 18-55 kit lens! –  James May 16 '11 at 17:50
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You'll have more CA by using fast glass, i.e. where the ratio of focal length to diameter is smaller; for more chromatic aberrations, you'll want to avoid achromatic lenses. Along with CA, faster lens will also make image more misty (spheric aberrations); you can reduce that by stopping the lens down using an aperture disc (I cut mine out of a plastic binder). My first DIY lens was based on a 110mm f/1.8 magnifying glass bought from local market, CA was quite prominent.

I ordered glass for my second DIY lens (64mm f/1.7 achromatic, US $7 + $5 int'l shipping) from Surplus Shed - they have quite wide selection of lenses at affordable prices.

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True, my 50mm f/1.8 creates a lot of CA. It shifts to blue when the focus is too far and to orange when is too close. I will try this lens and the magnifying glass. –  Andres Apr 28 '11 at 14:50
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You are correct that you could simulate this in an editor by shifting the layers a bit, however since the amount of fringing grows as things are farther away you end up needing to slice and dice the image and shift different parts of the image different amounts. Also the corners of the lens tend to shift more than the center, so you would need to shift more out there as well. And also... since CA isn't side to side, it's radial inside to outside, you would need to shift different pixels in different directions based on where they are in the image.

Personally, if I were going to try to fake it in PS, I'd use a bit of motion blur instead of shifting pixels. Split it into color plates like you suggested, take the blue to the outside and the red to the inside. Probably copy the layers, apply the radial motion blur to the key items in the image, based on how close they are, then apply a bit more to the background, and finally apply a layer mask that hides most of the effect in the middle of the shot and none of it in the corners. You aren't likely to get an exact technical replication of what CA is going to looklike, but if you're looking for the artistic effect it presents, you'll get close.

OR just go buy a cheap plastic lens. :)

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Definitely going to try the motion blur in the color layers, nice workaround cabbey! Also, besides lensbaby, are there any plastic lenses for reflex cameras? (Canon mount if possible!) –  Andres Apr 27 '11 at 16:36
    
lens baby isn't plastic afaik, it's very good glass. I'd suggest calling one of the big camera stores and saying "I want a cheap plastic lens with lots of chromatic aberration, got any? or any recommendations of stuff you refused to carry because it was junk?" I bet a few of the places in NY will be FULL of suggestions for that. :) –  cabbey Apr 27 '11 at 16:42
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Lensbaby has interchangeable optics, one of the options is plastic lens. Looking at samples in Lensbaby gallery, it seems to add glow, not chromatic aberrations. –  Imre Apr 27 '11 at 19:55
    
@cabbey -- shipping a package from NY to Argentina is about $50. –  mattdm Apr 27 '11 at 20:14
    
@mattdm, true, so Andres probably doesn't want to BUY one there, but the phone call should be cheaper, and should impart some useful info. –  cabbey Apr 27 '11 at 21:50
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I think what you are looking for is similar to the effect you can get with a Lensbaby lens.

However, the simplest way to get this effect, and I think the most flexibile, because you can do this AFTER the image is taken, is to do this is Photoshop ( or even GIMP). This way, you can determine where you wish to put the focal point, and what range you wish the CA to cover.

Rather than outline the technique here, I suggest you Google: photoshop lensbaby effect.

A few interesting links:

http://photocreative365.com/day-30-lens-baby-effect-in-photoshop/

http://www.adorama.com/alc/article/A-Faux-Lensbaby-Effect

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While it's true the LB does introduce a little bit of CA, the majority of it's effect is a shifted focal plane, which is what both of those tute focus on. While the OP's sample images show a bit of that, they specifically asked about CA, neither of those appear to even attempt to address it. (I didn't watch the first one fully, but the sample it produced doesn't have any.) –  cabbey Apr 27 '11 at 16:19
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I agree with cabbey, the technique that you mention here recreates the blur effect more than the CA effect. –  Andres Apr 27 '11 at 16:38
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