As for lens cleaning solutions, after several tries, including a product offered by a major filter manufacturer, I have grown weary of using them. Can’t shake the feeling that they indeed tend to create more problems than they solve (what you so aptly call ‘rainbow’ smearing certainly rings a bell).
Rarely end up with anything worse than a little dust, some raindrops, or the occasional fingerprint on lens surfaces anyway. And for that, given the quality of today’s nano coatings, a clean (!) microfiber cloth and perhaps a little breath (or drop of tap water applied to the fabric) will do the trick for me most of the time. Lens brushes I find hard to keep 100 percent fat-free, and those which are not, will leave streaks on surfaces.
When dust starts to accumulate on my K-7/WR lens combo, I put Pentax’s weather-sealing to the test and – dare I say it – simply rinse it with tap water. Then I carefully dry it with a microfiber cloth and have a squeaky-clean camera.
Started out doing photography at the age of 6 using an uncle's old 1940 kodak brownie box camera. At 15 years of age, I decided to buy my very own 1975 Praktica SLR camera. I now shoot with a Nikon D850. I do unpaid TFP and commercial paid work.