EMS-ULTIMA, equipped with enhanced silver coated mirrors, is coming soon. The graph above shows its extraordinary reflectivity.
Dark blue line shows the relfectivity of one reflection, and light blue line shows that of two times reflectons. Note that the scale of the bottom of table is not “zero”, but “75 percent”.
Now that EMS has achieved not only the diffraction limited resolution but also the practically total reflection of the incoming light, there will be no reason even for the most conservative users to dispense with EMS in their visual observation.
I believe it declares the advent of the new age of visual Telescopes.
It has been well known that Silver inherently has very high reflectivity through the visible spectrum except for the violet. But at the same time, it is also widely known that Silver degrades rapidly. So a Silver coating has not yet replaced aluminum in spite of its attractive features.
Not yet, but not “not from now on”.
Now, EMS-ULTIMA is breaking the age long stereotype as a past one. Recently developed enhanced silver coating has achieved super high reflectivity through the total visible spectrum including violet and enough durability allowing the continual use in the air at the same time, and I have developed the way to realize it on the mirror of EMS overcoming many difficulties.
The average reflectivity through the visible spectrum per one mirror is as high as 98.5 percent, and 97 percent of the incoming light is secured even after 2 times of reflections.
Following is the history and process I have traced before reaching this ultimate goal.
Attaining erect image at the right angle viewing with only two reflections itself is unexcelled feature of the EMS that cannot be substituted by any other devices. Judging from the least possible number of the reflection,”2″ of EMS, compared with the traditional devices of 4 or 6 times reflections, originally I did not think it urgent to additionally improve the reflectivity of the mirrors. So, I had chosen the traditional mirror of the highest visible reflectivity with time proven durability, among those that were available at that time.
The answer was “enhanced aluminum coating” that is the aluminum coating over coated by some layers of dielectric to boost the reflectivity of the normal aluminum and at the same time to enhance the surface durability.
Dielectric coating is becoming popular recently for its alleged remarkable reflectivity. But, regrettably, recent investigations showed that it is not suited for the purpose of higher index-angle, such as 60 degrees of the EMS, and thicker light cone of brighter optics of F/5 or shorter that should contain rays of wide range in index-angles. Dielectric coating is very critical about index-angles and causes unwelcome polarization, and we should know that the perfect reflection is given only under the optimum condition originally intended in the plan. Even by customizing the layer thickness and increasing the number of coatings up to hundreds layers to overcome the degradation at the higher index-angle, unwelcome byproduct effect will balance out the merit of its original super high reflectivity, along with the inflation of the cost.
Concretely speaking, there is a tendency of shortening the width of the peak plateau of the reflectivity, peak shifting to the shorter wavelength direction (violet shift), and cause drastic down turn at the longer wavelength or the counterpart.
I have done some experiments on three kinds of coatings to check which is the most excellent and suitable choice for my purpose. Seeing the results of the experiments will help you understand why I have chosen the enhanced silver coating as the ultimate one for my EMS.
The largest image of the camera lens is the direct, number 1, reflection image and next to left will count up to 5,7,9,….times reflected images. Left photo is enhanced aluminum and the right is enhanced silver. いずれの写真も、右端の大きなカメラレンズが１回反射の像で、３回反射の像はどちらかのミラー の陰になって撮影できず、５回反射以降の像が写っています。写真に番号を振りました。左に行くほど 反射回数が増えます。 可視光線平均としては95％の高反射率を誇る増反射アルミであっても、 赤い光線の落ち込みによって、カラーバランスがどんどん崩れて行くのが顕著です。 また、デジカメのレンズ部だけでなく、ミラーを保持する私の指先も写っていますが、 銀ミラーでは、その健康な血色が20回反射を超えてもまったく褪せないことは驚きに値します。
Test2: multiple reflection experiment-2;
Two mirrors faced to each other in such a way that forward end touch each other like a book slightly opened. The set stayed on my visiting card. In this experiment, dielectric one showed worst in contrast, though brightness was rather good. (direct image is marked by a red circle.)
Test3:transparency test on dielectric mirror; テスト３：誘電体多層膜の透過テスト；
I found rays passing through dielectric coating. If it reflects 98 percent of the incoming light, 2 percent of the light seems to go through it. I thought it very unwelcome feature when I aim at the superb image contrast. The photo witnesses the fact of the diode flashlight passing through the dielectric mirror.
From top to bottom, dark blue line represents one reflection by enhanced silver, light blue that of two reflections, red line one reflection by enhanced aluminum, green line that of two reflections.
You will find not only the extraordinary high reflectivity of the enhanced silver, but also the remarkable flatness of the line. Through these experiments, I have studied the fact that the flatness of the line is as important as the highness of it.
(No image processing has been done on the above photos of experiments except for trimming. And I must add that the silver sample mirrors were almost two years old since deposition at the experiment.)
I musn’t forget to extend my sincerest appreciaton to some of my friends who have assisted me devotedly. They have given me a lot of information about the silver coating and even have done durability experiments.
Above all, their encouragement helped me a lot to keep up going wih this difficult project.