hi fellows, i have just started to use the glass neg mask on the de vere 504. anti newton on top plain on bottom.first two prints from 35mm last night look good, no dust either, result. however i need some advice on several points. 1. should i be so worried about scratching the glass, is it ok to close them together with no neg or tissue paper between? 2. do minor scatches come into focus anyway? 3. how can i center the neg acurately, i dont want to stray too far into the edge of the lens image circle. 4. and thats just what i know i dont know, so please enlighten me to the virtues of the glass. thanks for any help.