Archived posting to the Leica Users Group, 2010/02/28
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Hi Neil, > > http://gallery.leica-users.org/v/nbeddoe/NightimeLondon/Noct+with+Filter.jpg.html > - with a Leica UV filter attached. > http://gallery.leica-users.org/v/nbeddoe/NightimeLondon/L1031963.jpg.html- > after I took the filter off. > The filter was clean. > > Yes, two fellow listers pointed out the exposure difference. There is yet another important factor, _which_ filter did you use? You may know that even a serious make like Hoya has got four grades of coating quality on their filters (including no coating at all, and several grades of multicoating) - having a clean filter does not mean it has been properly coated! Of course mutual reflections between lens elements and filter surfaces get more important when the lens has got many elements like the Nocti, but I only got effects comparable to what you show with the very cheapest filters. In particular some Skylight (!A, 1B) filters used a plastic coloured film sandwiched between two layers of glass and the results were consistently a disaster - I remember Genaco filters and the more recent Cokin rubbish. To give Hoya as an example, the non-HMC Hoyas are not really usable, and there is still a noticeable difference between simple HMC (4 quarter wave layers each side) and Pro-1 HMC (6 quarter wave layers on each side). I could never find any difference between "with" and "without" a Pro-1 - I don't have a Nocti and this should be an interesting test. Old Leica/Schneider/B+W filters were not particularly good on this respect. Jean --