How do I photograph water without catching glare from sun?

Question

For fun, I have been trying to photograph a small, fast-moving creek near my house, and I cannot figure out how to take a picture of the creek in good lighting without it reflecting the sun and causing glare. All of the water droplets are flying around and causing a ton of problems like chromatic aberration and reflections. How do I eliminate this stuff?

Asked by J. Walker

Answer

"Good lighting" for outside pictures is pretty much dusk or dawn. If you're getting a harsh reflection of the sun at this point, you should be able to easily rotate a bit and get the sun out of your frame. In fact, some of the best light is just before the sun rises and just after it sets. There's still plenty of light to shoot with - especially for landscapes - and you'll not have to worry about these reflections and glare.

Overall, I suspect you're just shooting too much in the middle of the day.

For any lighting questions, especially those revolving around the angles and glare and such - Light: Science and Magic is a great, great resource.

Answered by rfusca

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What causes longitudinal chromatic aberration on Nikon 50mm f/1.4D?

Question

I have looked on my new 50mm lens photo (I have Nikon D90) and I see blue contour, blue highlight around the unfocused objects (longitudinal chromatic aberration). What's is going on? Is it common for this lens (Nikon 50mm f/1.4D) or I did something wrong?

Asked by garik

Answer

What you're seeing is longitudinal chromatic aberration (otherwise known as axial colour), whereby the light at the edge of the bokeh disc undergoes a colour shift depending on whether it is in front of or behind plane of focus. The reason for this is that light of different wavelengths focus at different distances along the axis of the lens.

This is very common of ultrafast lenses like your 50 f/1.4 and is exacerbated by strong contrasts such as shooting against the open sky. Unlike Lateral Chromatic Aberration (where colours are shifted outward regardless of depth) which can be fixed easily in software, occurrence of Longitudinal Chromatic aberration depends on depth information, which is absent from the image. As such it is more difficult to correct automatically (though some software such as Capture NX2 and DXO offer this feature). It does however reduce rapidly on stopping down.

In a nutshell there's nothing wrong with the lens, it's just this type of subject/shooting environment is not ideal for f/1.4 lenses.

Answered by Matt Grum

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Longitudinal chromatic aberration on Nikon 50mm f/1.4D

Question

I have looked on my new 50mm lens photo (I have Nikon D90) and I see blue contour, blue highlight around the unfocused objects. What's is going on. Is it common for this lens (Nikon 50mm f/1.4D) or I did something wrong?

Asked by garik

Answer

What you're seeing is longitudinal chromatic aberration (otherwise known as axial colour), whereby the light at the edge of the bokeh disc undergoes a colour shift depending on whether it is in front of or behind plane of focus. The reason for this is that light of different wavelengths focus at different distances along the axis of the lens.

This is very common of ultrafast lenses like your 50 f/1.4 and is exacerbated by strong contrasts such as shooting against the open sky. Unlike Lateral Chromatic Aberration (where colours are shifted outward regardless of depth) which can be fixed easily in software, occurrence of Longitudinal Chromatic aberration depends on depth information, which is absent from the image. As such it is more difficult to correct automatically (though some software such as Capture NX2 and DXO offer this feature). It does however reduce rapidly on stopping down.

In a nutshell there's nothing wrong with the lens, it's just this type of subject/shooting environment is not ideal for f/1.4 lenses.

Answered by Matt Grum

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What is Chromatic Aberration?

Question

What is Chromatic Aberration? Is it a physical part of the lens, or just an optical illusion?

Asked by WireGuy

Answer

Chromatic Aberration is a distortion that occurs when a lens focuses different colours slightly differently.

It is caused by the refractive index of the lens (the amount that the lens bends light) being slightly different for different colours, so I suppose you could say it is caused by physical properties of the lens. It is possible to produce higher quality lenses that exhibit this effect to a lesser extent.

Wikipedia has a very detailed article on chromatic aberration.

Answered by Simon P Stevens

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Is it technically possible to build a camera body to correct for lens defects?

Question

Most lenses tend to be expensive because the lens needs to be very complicated in order to correct for various optical effects (aberration, etc). Is it possible to build a sensor and processor combination which would fix defects produced by cheap lenses? I'm assuming the processor knows exactly the parameters of the len's defects.

Answer

Not only is it possible, but it's becoming commonplace. The micro-four-thirds system makes extensive use of it, and some compact cameras now do too. (I imagine that if they don't yet, most super-zooms will within a few years.) Digital Photography Review has a good article on this at http://www.dpreview.com/articles/distortion/ , and it's worth reading even if you don't like that site's reviews in general.

Correcting distortion and lateral chromatic aberration is an option in my Pentax K-7, but although it doesn't impact shot-to-shot time (unless you fill the buffer), it takes a few extra seconds per image.

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Is there an easy way to force chromatic aberration?

Question

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.

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.

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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.

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ADDENDUM ADDENDUM

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

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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!

Answer

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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How do I use the Chromatic Aberration correction tools in Lightroom?

Question

When I upgraded from a 1000D to a 550D, my 18-55mm started to show more significant Chromatic Aberration. This is probably due to the 8mpx difference between the two cameras.

Due to this, I've started playing with the CA controls of Lightroom and can't get it. I don't know really how it works, and no matter how much Red/Cyan or Blue/Yellow corrections I set, the image still shows CA.

Do you have any advice with this function?

Also, what does "Defringe" tool do?

Answer

Chromatic Aberration can be a bit tricky, and in many cases you can't actually correct the fringing, only the color cast, caused by CA. In LR 3, you have two ways to correct lens aberrations. The first, and most simple, is to use a lens profile which should automatically correct for ALL lens aberrations in your shot, including CA, distortion, and vignetting. The other option is to manually correct for those aberrations.

Manually Correcting

To manually correct for aberrations, go do Develop mode and expand the Lens Corrections panel. Click "Manual", and scroll down to the Chromatic Aberration section. You have three controls here, the Red/Cyan and Blue/Yellow sliders, as well as a Defringe options list. When using the sliders, the general idea is to shift the slider toward the opposite color of CA that you are seeing in your photos. In many cases, you will only have one axis of CA, however in the worst case you may have both axes. When both axes of CA are present in an image, you might see other colors, such as green, which require an adjustment of both sliders to fully correct.

To make life easier when correcting CA, try this little trick. Hold down the ALT key and adjust one of the sliders. This will limit the photo to just the two color channels affected by that slider, making it a lot easier to see the effect of your corrective adjustment.

The Defringe options allow you to limit where LR applied "defringing". CA is an optical effect that results from the divergence in the way different wavelengths of light focus. Particularly around the edges of objects, this can cause a slight halo or blurring, creating a soft fringe around the edges of those objects. Defringing attempts to correct this halo. Sometimes correction of CA itself will be sufficient and leave no halo, however if one is left behind, you can try the Highlight Edges or All Edges options. All Edges may leave unslightly "hard" edges, or double edges with a thin hairline of dark between the object and another edge. If that occurs, try Highlight Edges.

Correction via Profile

In addition to manual correction of optical aberrations, you can also use a lens profile to correct for all aberrations at any focal length. LR 3 comes with numerous lens profiles out of the box, and it is also possible to create your own. You have some ability to adjust the three types of lens aberrations corrected by a lens profile, but not as much control as with manual.

If your lens is not included in the list of profiles out of the box, you can use the Adobe Lens Profile Creator to create your own. The process can be a little tedious, but it can be handy when you have a LOT of images to correct on a regular basis.

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