What causes dark halos?

[JPD]

On some black and white photographs there are "halos" around dark objects. They are the opposite to the halos that sometimes appear around bright objects that the anti-halation backing used on film and plates are meant to minimize. What causes the "dark halos"? Is it a film or lens problem?

Example and illustration:

 

[Nicholas Lindan]

Dirt or haze on the enlarging lens.

 

[JPD]

Dirt or haze on the enlarging lens.

No, it can be seen on the negatives. Clean camera lenses...

 

[MattKing]

What agitation scheme are you using when developing? Is this a print or a scan?
Dark halos in a positive means lighter areas (less development or less exposure) on the negative, or, it means flare in the enlarging or scanning system.

 

[removedacct1]

I've only ever seen this happen on "exotic" ortho films like MZ3.

 

[JPD]

What agitation scheme are you using when developing? Is this a print or a scan?
Dark halos in a positive means lighter areas (less development or less exposure) on the negative, or, it means flare in the enlarging or scanning system.

This is Efke 100 in 6,5x9 sheet film developed in a combiplan tank turned upside down two times every 30 seconds. It's a scan.

The lens on the camera was a Goerz Dagor 6,8/130 fully open.

 

[ic-racer]

Lens flare. See response #2 above.

 

[koraks]

Lens flare. See response #2 above.

You'd say so. But he says he can see it in the negative. Beats me; 9 out of 10 cases I see like this it's a scanning issue these days.

 

[JPD]

You'd say so. But he says he can see it in the negative. Beats me; 9 out of 10 cases I see like this it's a scanning issue these days.

Yes, I'm sure it can be light scattering in the negative during scanning sometimes.

Maybe in this case it had to do with the Dagor being fully open? I was a test shot of the lens mounted on a 6,5x9 camera. I should have taken another one stopped down, but it was my last sheet at the time so I didn't.

 

[koraks]

Regardless of lens type, I don't see how a dark area could ever flare. It sounds like something that defies the laws of physics, or a pocket-sized black hole. So it either has something to do with development (although equally puzzling, a sort of negative edge effect...), or your observation that it's in the negative isn't entirely reliable.

 

[brbo]

Combination of soft taking lens and film/developer? I'd guess that if you used a high acutance developer you'd not notice the softness that you call dark halos...

 

[Lachlan Young]

This is Efke 100 in 6,5x9 sheet film developed in a combiplan tank turned upside down two times every 30 seconds. It's a scan.

The lens on the camera was a Goerz Dagor 6,8/130 fully open.

Spherical aberration and flare from the lens, halation from the film stock, halation from a cheap scanner. Some combination of these is likely. Combiplans aren't a good choice for adequate agitation, but that's a different story. & unlikely what's going on here.

 

[Lachlan Young]

I'd guess that if you used a high acutance developer you'd not notice the softness that you call dark halos...

This is a bad guess. The differences between visually acceptable 'high' acutance and more 'normal' developers are largely much less than people want to talk themselves into thinking they're seeing. High acutance development can rapidly produce quite visually unacceptable prints (under double blind tests) compared to D-76, for example, but the act of controlling for this zeros out a lot of the differences. Getting the level of fill/ flare seen in the image is much more likely halation related

 

[Don_ih]

Overdevelopment? The highest density is in the surrounding bright areas. Where the edge of the bright area is against the dark area, less "bunching" of grain occurs than in the middle of the bright area, since no grain from the dark area will push against the adjacent bright area. So, it's not that there's a dark halo around the dark thing but that the bright area around it is actually too bright.
Or that's my guess.

 

[ic-racer]

You'd say so. But he says he can see it in the negative.....

Then he should show us too; rather than showing a print on an analog photography site.

 

[grain elevator]

Optical aberration in the taking lens (spherical or chromatic)? These entail that not all the light is actually focused at the film plane. So some of the light from the bright areas leaks into adjacent dark areas, we know that kind of halo. But doesn't it mean that mean that so to speak that unfocused light that falls not on the bright area (where it would be focused with a perfect lens, originating on the bright object), but in the dark area, is "missing" in the adjacent bright area?
Maybe this is sort of brain fart. Could be such a.an effect exists tlbut is all but invisible because what light suffices to noticeable brighten dark areas is unnoticeable in bright areas.
Btw I see no such halo in the left picture, it's just slightly out of focus.

 

[JPD]

I wish I had saved the negative. I have seen the same effect on a couple of photos on flickr.

Spherical aberration could be it. Dagors are known for their slight focus shift, so when parts of the lens have a different focus plane and you shoot wide open that could result in a blurry image combined with a sharp, and then you get a kind of softening effect.

Yes, the Combiplan tank isn't perfect. I use developers and dilutions that allow me to have longer developing times for even development.

 

[koraks]

I wish I had saved the negative

That's a pity.

All the talk about lens aberrations is fascinating for sure, but none of those defects are capable of making miniature black holes in a negative. My money remains on the defect not actually having been present in the negative at all. We'll never know, I suppose.

 

[grain elevator]

YOu

That's a pity.

All the talk about lens aberrations is fascinating for sure, but none of those defects are capable of making miniature black holes in a negative. My money remains on the defect not actually having been present in the negative at all. We'll never know, I suppose.

A black hole isn't the only possible explanation. Do consider that unfocused light also contributes to the density in the highlights. More unfocused (or rather nearly focused) light reaches highlight areas further from the edge with a dark area.

 

[koraks]

You'd have to have corresponding highlight halos in that case as well. They're not present in the example.

 

[grain elevator]

You'd have to have corresponding highlight halos in that case as well. They're not present in the example.

I clearly see them. Not sure if they're as strong as they'd be expected for the effect, but they're there. In the right image. I see no halo at all in the left one.

 

[koraks]

Maybe, maybe not. I still see nothing that proves or disproves this happened during image capture.