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Re: [OM] SC vs MC (how to tell them apart)

Subject: Re: [OM] SC vs MC (how to tell them apart)
From: Moose <olymoose@xxxxxxxxxxxxx>
Date: Fri, 22 Aug 2003 13:37:09 -0700


Joe Gwinn wrote:

I just tried a simple experiment on a 55mm f/1.2 MIJ Zuiko.

All Zuikos are made in Japan and so marked. The vast majority are marked on the side of the mount near the rear. The only time "miJ' (reflecting the capitalization in the marking itself) is meaningful in describing a Zuiko is in the case of the last version of the 50/1.8. In this version, the serial number was relocated to the mount, swapped with the 'made in Japan' notice, which moved to the front ring. These are referred to as 50/1.8 miJs as the most convenient way to distinguish them from earlier versions. By referring to a 55/1.2 as 'MIJ', you cause confusion as to whether the later reference to a 50/1.8 MIJ actually refers to that last version of the 50/1.8 or some other version.

I also tried the same experiment on a 50mm f/1.8 MIJ Zuiko. The reflections in this lens are all kinds of colors, including white.
Not surprisingly, the more expensive lens (55mm f/1.2) has almost all green 
reflections, and the same shade of green at that (showing tight process 
control), while the cheaper lens (50mm f/1.8) has all colors (looser process 
control) including white (uncoated surface?).

Assuming this is actually one of the last versions of the 50/1.8, it's coatings are considerably more sophisticated than those on a 55/1.2, as it was designed much later than the 55mm, at least 10 years, during a period when the development of coating technology moved rapidly. The original 50/1.8 was a so-so lens developed in roughly the same time/technology frame as the 55/1.2. The 50/1.8 went through several versions covering the whole range of OM lens development. The 55/1.2 was apparently never changed to MC, instead being replaced with the 50/1.2. Compare a 50/1.2 and a late 50/1.8 and I'll bet you find very similar reflection colors.

I agree with Lee about the impossibility that this is a matter of poorer process control on the less expensive lenses. As to the multiple color business, I quote myself:

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"I've heard lots of people refer to the colors of the reflections, as though the presence of several different colors shows MC. I don't see why that would be true. In the case of the design of a lens before MC, the designer would still want to balance the color response of the lens. If all surfaces were given the same coating thickness, the lens would have significantly higher transmittance around the color most effected by that coating thickness, resulting in a lens with unnatural color balance. Would not the designer use different thicknesses of coating on different surfaces to achieve a roughly balanced transmittance across the visible spectrum? Of course, they must have done so based on the color characteristics of the lenses produced. Since the color of the reflection from a SC lens surface is determined by the subtraction of light around the effective range of the coating thickness, this results in different colored reflections from different lens surfaces.

It is further true that individual MC coatings are not equally effective across the whole spectrum. A 2 layer coating can only be even theoretically fully effective at 3 wavelengths, and possibly only 2 in many actual applications. So MC lenses continue to have multiple different colored reflections.

I have gazed into the depths of at least 3 pairs of Zuiko lenses to compare SC to MC reflections. Although there were some (surprisingly smaller than I expected) differences in the color of the various sizes and depths of reflections, the most noticeable difference was the clearly lower overall brightness of the reflections of the MC lenses, vs. the SCs."

The earilest SC lenses tend to show overall yellow reflections, while later ones show a number of different colors. This certainly shows the results of improvements in coating technology and sophistication, but not necessarily in the number of coatings per lens surface."
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Moose



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