Todd,
You need to establish if the optics on the Dimension 400 are suitable for FM (is the laser spot size small enough to generate what micron size spot you desire). Another variable is the plate itself, does it have the resolution to maintain FM spots and maintain them consistently. The linearity of the plate will also come into play as to whether you can get the proper exposure. Kevin gives a good example on how the exposure will effect the plate. The question is can the plate and CtP combination provide the desired results. I would recommend you ask Presstek what the specifications are and has FM been certified on this combination. I did not see them posted on their website but may have missed it.
With 2nd order FM, the spots size you choose is what you will get up to about 15% until it makes the transition to larger size. The tighter the clusters determine the additional shape you receive. So if you choose 20 micron, it will be 20 micron spot up to around 15%. As you go from 1% to say 5%, they are all 20 micron but you have a tighter cluster at 5% and tighter at 10%. So if you can not hold a 20 micron, you will be missing from 1% to about 15%.
You may also consider a Hybrid Screening. You still will need to control the exposure for the Highlights and Shadows but depending on screen ruling, the transition in spots size to AM will be less than the FM.
But before you spend too much time, find out if the CtP and plate are certified to image the FM. If not, you may be chasing your tail. If they are, then Presstek should be able to guide you on set up.
Hope this helps.
Regards,
Mark
