Minolta MC 1,4/50 experiences

Started Mar 10, 2013 | Discussions thread
eques
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Re: "Glowy" lenses usually caused by haze, scratches, or fungus
In reply to Letsgokoulos, Mar 10, 2013

Letsgokoulos wrote:

eques wrote:

Thank you for your detailed answer.

ProfHankD wrote:

john-photoguy wrote:

I bet that there is a haze (or dare I say fungus) on the inside of the lens,

Many older lenses are slightly "glowy" -- which is what you're complaining about. Teleconverters and glass adapters greatly magnify the effect, often producing IQ usable only as a special effect.

The glow can come from many factors, ranging from incorrect reassembly of the lens after cleaning to sensor reflections. Some lenses also have a little glow by nature of their optical design, but generally not as severe as what you're showing. For a sharp image with heavy glow the most likely culprit is some type of diffuser in the lens:

  • Haze is simply the deposition of diffusing material on (inner) lens surfaces over time. Most lenses suck air through as you focus, and humidity, volatile organics, and other materials go along with it, condensing and accumulating on inner surfaces over time. I've also seen a lens where oil had spread out onto an element near the aperture iris. Cleaning internal surfaces is problematic, but the only fix.

I could not make out any haze on the internal lenses. The lenses look clear to me. But of course I am no expert.

  • Contrary to popular belief, scratches don't have much impact on lens sharpness, but they do cause refractive problems like glow. The impact of surface scratches can be reduced by filling them with light-absorbing material, such as black paint, but that is feasible only for very deep scratches. Scratches in the rear element usually impact IQ far more than ones in front.

There are no visible scratches.

  • Fungus, with its well-known white branching structures, will reflect a little light.

There is no visible fungus in the lens.

  • However, it's after a long-term fungus infection that the real glow issue starts -- especially after the fungus is removed. Fungus emit chemicals that can etch lens glass (certain glasses more than others; for example, some older Canon lenses seem to be particularly vulnerable), leaving the equivalent of many-faceted micro scratches after the fungus has been removed. Once etched, no simple repair is possible.

This seems to me the only possibility left.

Note that dust usually doesn't cause glow because typical dust particles block light, rather than causing refraction. Close visual inspection of the lens with a penlight should tell you which problem you have....

Peter.

Peter, a long-term fungus should be visible with a pen-light. If you are absolutely positive that the glass is cristal clear with a pen-light, I would think the only other possibility is light leak, most likely with the adapter. Your pictures are focused, so it is not a problem with focusing. The glass is clear, so it is not a problem with altered glass... so what else could it be ?

I tried stopping down today: at F4 and F5,6 contrast is high and resolution great. This points in the direction of some plaque on the lenses, I suppose.

If you have the chance to mount the lenses on someone else's adapter and camera, try it.

I'll try tomorrow after light-proofing the adapter, which works ok with other lenses.

Keep us informed...

Marc

Thanks for your interest and help.

Peter.

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