I agree with Patrick
one note, when we focus we are focusing on the emulsion or grain , which is important to note, if the glass carrier holds the film flat and if the enlarger is aligned I see no issues.

I have tried the glass only on the top of the neg, it has caused me problems in the pass therefore regular glass bottom AN glass on top for me.
Humidity in the darkroom will solve a lot of issues and a good cleaning workflow of the glass and negative.

Quote Originally Posted by Patrick Robert James View Post
I have been using glass carriers for the last 15 years. Combined with a laser alignment tool, the glass carriers deliver the best overall sharpness without a doubt. Cleanliness is certainly an issue, especially if you use a condenser enlarger, but it is worth it in my opinion. I would love to replace the lower glass in my Saunders 4550xl glass carrier with coated glass but haven't found any likely candidates yet. I doubt I would see much improvement at this point with the coated glass but every little bit helps.