I've been persisting for a couple of months trying to get really good boards using photo resist. I prefer the dry film method because poorly exposed boards can be stripped and recoated quite easily, which is good when you're at the left hand side of the learning curve!
I've found the best method for applying the resist is using a laminator; I tried modifying a cheap home office laminator, but the rollers are too small, not firm enough and the A4 (8") width is too limited. I browsed ebay and located a professional pouch laminator, this has heated top and bottom rollers, a heated platen and a pair of output rollers; it has variable temperature from around 80C to very hot, but has fixed roller speed and although it has motor on-off, it doesn't have a connection for a foot pedal which would be a worthwhile upgrade.
The method I use is to mist the board with DI water, remove the inner protective layer from the dry film for about 10mm (3/8") and apply the leading edge to the copper clad, preferably outside the area to be exposed, although I have been lucky and been able to use the leading edge to within 3mm (1/8") of the board edge. Lay the board on a piece of heavy paper that's 30 to 50mm (1 1/4" to 2") longer than the board, ensuring the film does not overhang the edges of the paper anywhere, or you will end up with film stuck to the lamionator's rollers. Ste the laminator to a low tempertaure initially; run the leading edge of the paper into the laminator then stop the motor. Now peel back the inner protective layer until you can easily hold it, then lift the film so that it's vertically oriented directly from the input to the laminator. Start the laminator's motor and carefully hold the protective layer taut to prevent wrinkles and ensure it seperates from the dry film before it enters the rollers. This takes a bit of practice, but I've got it to a point where I don't have to strip and recoat any boards now.
A very important point is to make sure the copper is absolutely clean before coating; I scrub the board with a green pot scourer to remove any oxide, then thoroughly clean it with dish soap until water forms a film on the board and doesn't bead up.
Note that the photopolymer layer in the dry film is highly sensitive to oxygen and will not readily polymerise in the presence of oxygen, so you must leave the outer protective layer on the film until it's ready to be developed. This film is very thin and is UV transparent, so doesn't affect the exposure process.
I'm going to follow up with how I get really good photo masters, without resorting to using an imagesetter (I used to have access to machines that could image to 3600 lpi and produced extremely accurate films with an ND of > 5.0; as a development engineer, I could spend entire days running off random jobs on these machines, but alas I'm no longer in that job).
AA9GG