What causes red/blue glow around black/white borders

[wolfestone]

I've noticed this with my camera, and also with other cameras. I've tried searching google, and this forum but I'm not having any luck (probably because I don't know the correct name for this issue).

This picture shows what I'm talking about, it's a very pronounced brightly colored 'glow' where white meets black in a photo. Interestingly, on the bird picture it was a blue glow, whereas on the rock photo it was red.

My uneducated guess would be that this is something to do with the way the sensor captures red green and blue, but I could be way off.

If anyone could clue me in as to what causes this, and if there's anything you can do about it short of fixing it in post, I'd really appreciate it.

 

[Patrice]

Chromatic aberration. Different wavelengths focus at different places. It's a function of lens design and lens correction. Some lenses are better than others at correcting for it as are some camera processing algorithms.

 

[Dao]

That is called "Chromatic Aberrations" or CA in short.

It is a characteristic of the lens. Better optical quality lens has better control on CA.

 

[clanthar]

It is, as noted, a lens characteristic but it is also exacerbated by mismatching lens resolution and sensor resolution. You'll see the problem is more common and more severe with smaller sensor cameras where the resolution of the sensor exceeds that of the lens.

Joe

 

[wolfestone]

Thanks very much for the info. I'd heard the term before but didn't know what it meant.

My camera (eos rebel xt) is a smaller sensor camera as far as I know. Is lens resolution ever quantified with a number or specification? I'm assuming this is the 'size' of image it projects onto the sensor area, and that having this as close as possible to the sensor size is desirable?

thanks again for the help it's much appreciated.

 

[ann]

Which software are you using? These can be corrected in RAW with PS

 

[KmH]

Is lens resolution ever quantified with a number or specification?

Yes.

where
θ is the angular resolution, λ is the wavelength of light, and D is the diameter of the lens aperture.

Optical resolution - Wikipedia, the free encyclopedia

 

[wolfestone]

Which software are you using? These can be corrected in RAW with PS

I have photoshop CS2 and the adobe camera raw plugin. I don't often shoot in raw though, but I would definitely be interested in learning how you go about correcting this.

 

[Josh66]

What you are seeing is commonly refered to as 'Purple Fringing'.

Purple fringing - Wikipedia, the free encyclopedia

It's mostly due to extreme contrast.