After the lens has been optically coated, the outer frame is coated with GT-7-2 and cured by baking. There are unknown particles on the surface.

Place in 100% dust cleaning agent PTC-21(H), 25°C, 40KHz ultrasonic wave, 30W/L, and shake for 1 minute. It was found that the dirt was completely washed away. And the GT-7-2 frame ink is not damaged; the lens surface does not have any fine lines.

Place in 50% fine dust cleaning agent PTC-21-H, 25°C, 40KHz ultrasonic wave, 30W/L, and shake for 1 minute.
Before cleaning, the surface of the lens can be seen covered with particles.

置於50%微塵清洗劑PTC-21-H，25℃，40KHz超音波中，30W/L，震盪清洗1分鐘。
清洗後，發現髒汙已完全洗淨。而且GT-7-2外框油墨也沒有受傷；透鏡表面也沒有任何細紋。

置於25%微塵清洗劑PTC-21-H，25℃，40KHz超音波中，30W/L，震盪清洗1分鐘。
清洗前，透鏡表面可看到佈滿particle。

After cleaning. It is much cleaner than before washing, but there are some dirt on the surface that cannot be completely removed.

In order to avoid that the lens may be worn or polluted, the cleanliness is so poor that it cannot be completely cleaned. Take another lens for testing.

Repeat the test. Before cleaning, the surface of the lens can be seen covered with particles.

Place in 25% fine dust cleaning agent PTC-21-H, 25°C, 40KHz ultrasonic wave, 30W/L, and shake for 1 minute.
After washing, it is much cleaner than before washing, but some dirt on the surface cannot be completely removed. (pointed by the red arrow)

in conclusion. If cleaning at room temperature (25°C), the recommended cleaning concentration is above 50%.