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The rear element of a lens has some peripheral haziness on the front surface (inaccessible when the lens is fully assembled). Based on lens diagrams, I believe it is between the two rear-most elements, but I cannot figure out how to separate them from the housing.

What is the likely cause of the haziness? Since the haziness is peripheral and on the rear element, what effect is this likely to have on images? If I cannot separate the elements (because they are stuck in the housing), can anything be done to clear it up?


The lens is a Kiron 28-105mm f/3.2-4.5 Macro MC. When I first examined the lens, the haziness appeared to cover the entire area of the front of the rear element, though it was definitely worse peripherally:

haziness

After disassembling the lens and heating the rear lens group, the haziness seemed to shift, or lighten, to cover only the peripheral portion of the lens. It also didn't look quite as bad as before.

peripheral haziness

  • Could it be en.wikipedia.org/wiki/Apodization – xenoid Jan 18 at 22:35
  • @xenoid Are you asking if it's intentional? I don't think it is. But I do suspect it may have effects similar to an apodization filter. Consequently, this might end up being a real-life example of Can lens defects, such as scratches or fungus, improve image quality? But to confirm, I'd need to obtain a pristine copy of the lens for comparison. – xiota Jan 18 at 22:48
  • Yes I am... Assuming it's accidental, why would it be only on one lens? Is the width constant around the lens? Can you show a frontal shot? – xenoid Jan 18 at 23:09
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    The two most common causes of haziness on the inside of a lens are fungus and element separation. Your case sounds like the latter. – Mark Ransom Jan 19 at 4:59
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    Whatever it is, a Kiron 28-210 I've owned since 1986 shows a similar haze on the rear element of the group directly behind the aperture diaphragm. There's also quite a bit of it on the rear of the front group in a swirly "water stain" looking pattern. I haven't used the lens since the late 1990s. At that time the glass looked pretty good. – Michael C Jan 20 at 17:59
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Peripheral Haziness

Pretty sure it's not mold. There were no signs of mold elsewhere in the lens.

Doubt balsam separation because the lens diagram indicates that the elements are separate (259, 261). It also does not look like pictures of balsam separation that I have seen, which have a fine crazing pattern.

My current hypothesis is out-gassing of lubricants, though I cannot confirm it. The lens also suffers other related effects. The aperture was oily and sticky. Other elements had a greasy film, though there wasn't such haziness elsewhere in the lens.

Lens Diagram

Sharpness

According to online discussions of this and similar lenses, a good copy of this lens (Kiron 28-105/3.2-4.5) should be sharper than a Vivitar Series-1 28-105/2.8-3.8 (Cosina), and similar to a Vivitar Series-1 28-90/2.8-3.5 (Komine). Despite the peripheral haziness of the rear element, this Kiron lens appears to follow the reported pattern.

Normally, lenses with a narrower magnification ratio are expected to be sharper than those with wider magnification ratios. This lens appears to be a touch softer than a Kiron 28-210/4-5.6, which was tested at 90mm instead of 28mm because of the minimum focusing distance.

Sharpness Comparison

Color and Contrast

Compared with the aforementioned lenses, color with auto white balance does not appear to be significantly affected. If it were a significant concern, custom white balance could be used. Contrast appears to be slightly reduced.

Veiling Flare

Compared with the aforementioned lenses, this lens appears to be more susceptible to veiling flare when used indoors and pointed toward large windows. However, all of the comparison lenses had some difficulty with this environment.

Apodization and Bokeh

Bokeh from this lens may be a touch softer than the Komine lens, which is what is expected from lenses with apodization filters. The effect is subtle.

Apodization Kiron Apodization Komine

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