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Old Jul 21, 2008, 11:47 PM   #1
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Hey everyone, a quick and hopefully easy question. I have two old Minolta film lenses (1985, the "Beercan" lens) and I when I look at the lenses under the light in my room, one lens shows an orange/green reflection while the other shows a blue reflection. What could this possibly mean? Is the coating possibly worn down on one of them?

Thank you so much.

Edit: Looking at the kits lens with my Sony Alpha, that always shows the blue reflection. I wonder why the one of the older lenses is different.
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Old Jul 22, 2008, 5:00 AM   #2
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Lens coatings have changed somewhat over the years, so what you are seeing isn't unusual. Keep in mind, also, that the coatings are designed for each lens and lens element, in order to reduce chromatic aberration, and work together, so that the coating on the objective will be different than the internal lens elements. Coatings also reduce internal reflections (but can't eliminate them completely) and the refected color from the glass corresponds at least indirectly, to the color(s) the coating is designed for.

If you shine a white LED light into your lens, and look at the various reflections from the different lens groups, you will see different colors reflected from the different groups and elements in the lens. Theoretically, it will all add up to a fully compensated lens.

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Old Jul 22, 2008, 7:45 AM   #3
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To supplimentVTphotog's excellent explanation, I'll say that Minolta had a history of insuring that their lenses all had the same color properties, sometimes even at the expense of sharpness and contrast. (Remember that this is the age of film, and having multiple lenses all of which shared a common color made the photographer's job a lot easier.) The techniques employed to achieve that goal changed from series to series (The Beercan is a member of the first series of Maxxum lenses, and so is likely to have a slightly different color than lenses from subsequent series.) and that could account for the color differences you see in the lenses you have.

Sony seems to have abandoned that philosophy and gone for sharpness and contrast while relying on the in-camera and post processing for any color variations. (Hence the reliance on Zeiss for many of their newer lenses.)

See Historical perspective on Minolta lens design philosophy for more detailed info.
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Old Jul 23, 2008, 12:25 AM   #4
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Thank you both very much for your detailed answers. I have been trying to learn much about coating and how it greatly influences the image quality of a lens. I am trying right now test right now to see whether or not it is single-coated or multi-coated.

Thanks again for the help! I can always count on this forum and the people here for great information.
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