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white fringe

evan north , Dec 06, 2011; 12:09 p.m.

hi, under certain conditions with various lenses some of my photos show some white fringing along high contrast edges of the subject. is there a way to avoid it in the first case or can i get rid of it via processing? thanks, evan.

Responses


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Craig Meddaugh , Dec 06, 2011; 12:34 p.m.

I don't see any objectionable white fringing. There might be a little due to the jpeg conversion process, but no real problem. All that I do see is some lateral chromatic aberration along the high-contrast edges, especially the defocused edges. That is normal for just about any lens and can typically be easily handled in post-processing.

Tom Mann , Dec 06, 2011; 12:50 p.m.

I see a bit of CA along some of the high contrast edges, artifacts that look like excessive use of the recovery slider in ACR, but, to be honest, not very much at all of the usual white halos from oversharpening.

Over-sharpening (either in-camera, or in post processing) or excessive use of the "recovery", "fill" and similar sliders in image editing programs cause similar, but not identical problem. There is extensive discussion of the 1st here on photo.net, less discussion of the 2nd.

While there are ways such problems can be repaired after the fact (eg, http://photo.net/digital-darkroom-forum/00ZbNk?start=1 ), the procedures are either complicated or very time consuming. It's vastly preferable never to let the problem happen in the first place by (a) proper adjustment of in-camera sharpening, (b) a light touch in post processing, and (c) lenses with better CA, or do a partially automatic fix of the CA using LR or ACR.

Tom M

Jerry Coffin , Dec 06, 2011; 01:37 p.m.

It's really only visible when you expand it up to 100%, but there are what look to me like halos from slightly excessive sharpening. For example, at the upper-left and lower-right corners of this section:

At least to me, these do look like they're a result of sharpening (post-processing), not anything the lens has done. There is an effect called "halation", where you get a "halo" around a bright area in a photograph, and that is a result of the lens. At least to me, this does not look (at all) like halation though. In particular, the halos are most obvious around relatively dark areas, where halation is around bright areas.

Tom Mann , Dec 06, 2011; 01:59 p.m.

I agree that there are halos that look like they are from over-sharpening, but, IMHO, not all that serious, at least compared to some of the horrible examples we regularly see here on photo.net.

There clearly is also edge corruption due to excessive use of the "recovery" slider in ACR or LR, or excessive adjustments of the luminosity of individual colors using ACR, LR or in PS (see attachment to next message). There is also CA (see following post). IMHO, none of these are terribly bad.

BTW, Jerry, in standard photography usage, halation (http://www.wisegeek.com/what-is-halation.htm), which typically spreads highlights over a substantial fraction of the frame, is absolutely not the same as over-sharpening halos (which typically extend only a few pixels away from the high contrast edge).

Tom M

Tom Mann , Dec 06, 2011; 02:03 p.m.

Edge corruption described in previous post.


... as described above

Tom Mann , Dec 06, 2011; 02:04 p.m.

CA


CA

Jerry Coffin , Dec 06, 2011; 03:38 p.m.

Yes, Tom, I described halation about the same way you did, and specifically said this does not look like halation. I was pointing out that while a lens can produce a halo-like effect, it's quite a different one from what we see here.

Tom Mann , Dec 06, 2011; 03:52 p.m.

Hi Jerry -

I was just trying to clear up any ambiguity, specifically, your statement, "There is an effect called "halation", where you get a "halo" around a bright area in a photograph, and that is a result of the lens."

Halation (in the conventional use of the term) is never a result of the lens -- it is the result of light bouncing around and scattering in between the layers of old film emulsions before the mfgrs began to incorporate an anti-halation layer.

Lenses can produce veiling flare, ghost images, rather nice softening by undercorrected coma, but never halation.

Cheers,

Tom M

Jerry Coffin , Dec 06, 2011; 11:08 p.m.

Tom: Ah, good point. I should have been more precise -- I shouldn't have said it was the lens, though my point was primarily that it was not what we're seeing here, which stands.


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