# Tips and Tricks

### Pinhole Calculation

As per Newport.

D = Fw/a , where

D = Pinhole Diameter F = Objective lens focal length w = Wavelength of laser (sorry no greek letter on my keyboard) a = Beam radius at input to lens

More.... "Newport Pinhole"

### Calculating Laser Power vs Film Requirement vs Exposure Time w/Sample

Joules = Watts x seconds thus 1 mW = 1mJ/1 second

1 inch = 2.54cm 1 square inch = 6.45cm^2

For a film requiring 100 mJ per cm^2

Plate length(2.54 cm) x width(2.54 cm) = 6.45 cm^2

Laser putting out 10mw = 10mJ per second

10mJ per second /6.45cm^2 = 1.55mJ per cm^2 per second

100mJ per cm^2/1.55mJ per cm^2 per second = 64.5 seconds

This is just a basic starting point based on the film energy requirement. Adjustments need to be made for laser light losses, processing etc....

### Detecting the Emulsion Side of the Plate

Most of these can be tried with a used piece of film plate with the lights on for practice. Note: These tricks rely on the fact that only one side is gelatin; with the Fuji film both sides are gelatin.

If you breathe on the plate, the side that does not fog will be the emulsion side (no condensation occurs on the emulsion side because the gelatin absorbs the moisture). (This does not work for the Fuji film as it has gelatin on both sides.)

Look at the edge of the glass with a safelight - the cleanest (non-ragged) edge is the emulsion side.

With a bit of practice you can detect the difference in the dark by rubbing your thumbnail along the edge.

If all the plates are oriented the same way, you can label the box emulsion this side ->

The two finger method: moisten your thumb and index finger and pinch them together a few times. Now do the same motion with the plate between them, and it should be easy to feel which side is the sticky emulsion side.

### Got old plates?

I have stacks of failed plates.

Do yourself a favor now that you have some scrap plates: Spray paint one of the ruined jobbies white and use that as a dummy plate when setting up. Both sides and the edges. You will find this very useful when it comes to carding off light that would otherwise enter the edges of the glass as well as for checking the quality of your reference beam. A clean white surface is also nice for making sure that you have no specular reflections from shiny places on your object(s)...