Hi, this system with no negative effect on the lens, will not damage it. 

Black soft filters can be used to reduce blemishes and wrinkles in people or objects by reducing the resolution of the image. They can also be used to increase contrast and create a halo or glow effect for specular light sources in a scene. 1. soften the light effect of the actress's facial details, 2. It can effectively reduce some wrinkles and spots on the face of the actor, but at the same time maintain the details and clarity of the character's hair and eyes. 3. It also plays an important role in film shooting. Excellent black mist filter does not affect the color temperature, the use of dim scenes with a hazy age will create the atmosphere of the scene well. 

This is fixed focus. 

Unlike a tube it won't effect your focus distance nor effect your quality like a doubler. The lens will have more of an effect than anything else. On my Sony a7, I must be sure to use a full frame lens since the sensor is 35mm size 

Hi, the K&F black soft filter 1/4 has the same effect as Tiffen black pro-mist filter 1/4, just difference in name , thanks.