I have been having persistent and irritating dust problems ever since getting my 4X5 about a month and a half ago. I have tried many different strategies to deal with it and have not yet been able to completely solve it. Here is what I have come up with. The last test I did was with four holders, two sheets in each. All of my holders (I have 10 total) were purchased used from KEH in bargain condition. All were dusty to some degree when I got them. Before loading, I thoroughly cleaned the four holders with a slightly moist lint free cloth and then canned air. I did my best to get the air in the felt trap area at the top. I also cleaned the inside of my bellows and my back on the camera in case there was dust hanging out there. (It did look like there was some dust and I cleaned it as thoroughly as I could) I then loaded the film with as much care as possible not to set the holders on the counter in the loading room and to avoid contact with anything at all that could introduce dust. The results of the test were that of the eight sheets, four sheets, from two holders, were acceptably free of dust and four were really bad. I have come to the conclusion that I have a couple of holders that have some dust which I have not been able to clean out, probably in the light trap. I did not do anything to be able to tell which holders they are, and I have 6 others that have not been tested, so just avoiding the holders isn't much of an option. The question comes down to: Is it possible to clean old holders in a meaningful way, especially in areas such as the light trap where dust may hide? There is no visible difference between the holders, but a massive difference in the amount of dust that was on the negatives. Also, does anyone see something that I may have missed in my cleaning and loading regimen that would make such a difference, especially something which could vary like this from holder to holder? Thanks for reading my long post and thanks for any help you might be able to provide. Paul.