purple (more bluish really) fringing

[ian.bertram]

Hi all,
this is not meant to show off my talent as a fabulous photographer- it's not the best by any standards- but I'm interested in the fringing in the hair. As I understand it, this effect is caused by my long lens (canon 75-300 is usm) and the very fine hair in the image showing the imperfections in the lens. Clearly it means I must rush out and buy the 70-200 L 2.8 is lens, but does anyone know how I can minimise it. The photo was taken on manual with a speedlight also on manual to pick out the performer (he was under cover and in shadow). The figures for the shot were 180mm, 1/250th, f5.7, iso 400, manual speedlight 580 around 1/2 power mounted on the camera.
Any thoughts?



Here's a close-up of the hair.

[surenj]

This is chromatic aberration caused by imperfections in how the different colors are refracts off the lens (I think)

1. You can stop down and see whether it improves
2. try software adjustment - LR or DPP
3. Get a better lens
4. Avoid shooting into high contrasty conditions like above

[ian.bertram]

Stopping down is a great idea, I'll try that.
I guess really my question is related to your point three... would this actually be eliminated in a more expensive lens? The 75-300 wasn't cheap at close to $1000, it's no kit lens, but would one of the L series lenses have taken this shot without the fringing?

[gstark]

I guess really my question is related to your point three... would this actually be eliminated in a more expensive lens?

Not necessarily. Unless that was a Nikon lens. (Sorry, couldn't resist)

A primary culprit here is the high contrast situation that you've found yourself in. Basically, your equipment cannot cope; it's almost an expected outcome, given the situation you're in.

Are you able to reduce the apparent contrast and observe if that makes any differences?

[ian.bertram]

Are you able to reduce the apparent contrast and observe if that makes any differences?

Absolutely. What I should have done (and will remember to do next time) is to set the camera for the background and use the flash to bring up the subject. I did that for the other photos and with a blue sky background rather than the completely over-blown white there's no fringing whatsoever. The issue is you never see this stuff until later when you look at them on your computer and then of course it's too late (till next time)

Unless that was a Nikon lens.

Is that a brand of camera? Never heard of it. Are they for people who can't afford Canons?

[gstark]

Are you able to reduce the apparent contrast and observe if that makes any differences?

Absolutely. What I should have done (and will remember to do next time) is to set the camera for the background and use the flash to bring up the subject. I did that for the other photos and with a blue sky background rather than the completely over-blown white there's no fringing whatsoever.

Exactly. When I'm at a music festival, outdoors, shooting the band from the stage looking back out to the crowd, that's exactly how I do it.

Remembering to shoot in this manner is really they key.

[DaveB]

I think you've got it here. I don't think it's chromatic aberration caused by the lens.
It's overexposure/blooming causing colour shifts at the edges of blown out areas (where the camera or RAW processor has to guess as to each of the R/G/B/G components because some of them are blown out).

In ACR/Lightroom you'll find the "Defringe: Highlight Edges" option (just near the chromatic aberration controls) which may help, but minimising the blown out areas is a better option.

[surenj]

I think you've got it here. I don't think it's chromatic aberration caused by the lens.

That's very interesting Dave. I learn something new everyday.

I had assumed it's CA when it tends to happen with my 17-85 at the wide end. The 17-50 Tamron (same settings) same scene I think didn't have much of this effect!

[DaveB]

The usual CA we see is a radial smearing of the colours (i.e. from the centre out, and getting bigger the further you go from the centre) so if there's a blue or cyan fringe on one side of an object there'll be a corresponding yellow or magenta fringe on the other side.
This definitely looks different to that.