Fieldscope III ED coatings puzzle

[Avron]

Hello everyone,

For those of you who have been following my exchange with Henry Link in the “Fieldscope III 60 HD vs. Pentax 80 ED thread” (Henry has been extremely generous in providing me with feedback) you know that, in the process of examining two MC II zoom eyepieces I found considerable variation in the colors of, and in the reflections from, their coatings. The coatings and reflections of one eyepiece have a distinct bluish cast, while in the other eyepiece the coatings and reflections have a distinct greenish cast. To add to the puzzle of how this is possible, I have now compared two Fieldscopes ED III-A and found exactly the same situation: one has a greenish, the other a bluish color cast in terms of their coatings. Can Henry or anyone else comment further on this? I purchased the eyepiece and scope with the bluish cast just under a year ago; the ones with the greenish cast were loaned to me just last week by Nikon Canada. (Nikon has allowed my choice of each scope and eyepiece. Their customer service is simply outstanding.) I am concerned for the following reason. Henry advises that Nikon coatings should be greenish. For that reason, I would like to hold on to the pieces with the greenish coatings. The bluish tinted scope, however, shows less spherical aberration in a star test. For those with angled, ED Fieldscopes and MC II eyepieces, would you be able to let me know what color their coatings show?

Thank you.

Avron

[henry link]

Avron,

The reflections I see from my zoom MC eyepiece are both blue and green, and a little magenta depending on the element that is reflecting and the angle of reflection. I wouldn't worry about the exact reflection color too much. A much brighter reflection from one eyepiece or scope should indicate a bit lower light transmission (at least through that particular element), but if you don't see a dimmer image when you look through that scope, then it's not enough to matter. Don't forget Kimmo's admonition about obsessing. Obsessing is hard work, better left to the experts. ;-))

I'd definitely go for the scope sample with lower spherical aberration, if everything else is equal in the star tests. Changing eyepieces shouldn't have any effect on how the scopes star test. Either way you have a great scope. Don't worry, be happy.

Henry

[Avron]

Hello Henry,

Thanks for responding yet one more time to my questions. But obsessing? Hmmm… Surely, by definition, such a thing is not possible when it comes to optics… ;-)

Avron

[Anthony Martin]

I have a pair of Nikon HG binoclulars and the light reflections from each objective lens are dissimilar. All the green, blue, magenta etc. elements are there at differing angles as Henry describes, but their relative intensities are distinctly different.

Tony.

[Avron]

Hello Tony,

I have been away from my computer for a few days and have not had a chance to thank you for your post. I can say that my wife's Nikon SE's behave similarly to your Nikon HG's in terms of sometimes showing different colors at different angles in the two objectives. The color intensity in the two objectives of the SE's is fairly consistent, however (at least to my eyes). It is interesting that the objectives in my Swarovski EL's are, in terms of color, consistent at most angles; they are also consistent in terms of intensity of color in the two objectives.

Avron

[Anthony Martin]

Hello Tony,

I have been away from my computer for a few days and have not had a chance to thank you for your post. I can say that my wife's Nikon SE's behave similarly to your Nikon HG's in terms of sometimes showing different colors at different angles in the two objectives. The color intensity in the two objectives of the SE's is fairly consistent, however (at least to my eyes). It is interesting that the objectives in my Swarovski EL's are, in terms of color, consistent at most angles; they are also consistent in terms of intensity of color in the two objectives.

Avron

Hello Avron

My wife uses EL's and I also have an pair of Leica 10x50 BA's which I use for astronomical work and the Nikon's are the only ones to exhibit such an effect. To my eyes it causes no adverse effect on the image quality.

Tony.