[quote="Michael A. Smith"]
"I use a NuArc frame. I bought it for the 18x22s. Before then I had an old spring back contact printing frame for my 8x20s. I have tested and there is no difference in sharpness between the NuArc and the contact printing frame."
But bear in mind that some processes have much different requirements in terms of the amount of pressure need toi maintain good contact between the negative and the sensitized material. With relatively thin factory coated papers, such as AZO, good contact can be had simply by placing a thick plate of glass over the sandwich. However, when working with alternative processes where the paper is a fairly thick piece of drawing or water color paper one needs much greater pressure to maintain good contact.
In carbon printing, where one works with a very thick and sifff piece of carbon tissue, it is virtually impossible to get adequate pressure with a contact printing fraame, even when well adjusted.