Good protection, completely neutral

I absolutely can not stand it when the front lens is unprotected, gets me every new lens out of the box, a filter missed. So far, I preferred those that also included a UV protection, which was certainly not a disadvantage in film photography. The pictures came out a little warmer than without a filter and the like usually. In the recently purchased Pentax 300mm lens I wanted as little interference as it gets and I came upon this by the manufacturer as a "neutral" advertised Protector (no filter). Before mounting, I briefly made some comparison pictures without Protector and then immediately the same scene again with Protector. Even with the most precise test no difference can be established. Therefore, full satisfaction.