Jump to content

LAD method for black and white film


Luca Zonca

Recommended Posts

Hello everyone,

The other day my cinematography professor mentioned the Laboratoy Aim Density Control Film method for black and white film. It wasn't very clear to be honest and, since I can't find anything online, I was hoping someone could help me understand this better.

The explanation revolved around the formula: DLAD = D0 + 0.70, where D0 is the minimum density of the film, and 0.70 is the LAD number given by Kodak for B/W film stocks. My professor concluded saying that the result is the value of the normal exposure and so, in this way, we can understand how our material is different from the normal exposure. With normal exposure he's referring to the 18% gray, but I'm not really following here. Does that mean that the result of that formula is giving us the density of a film at 18% gray? And if so, is there a standard value for that density?

Can anyone help me?

Thanks in advance

Link to comment
Share on other sites

  • Premium Member

I can't help in that I've never even heard of the LAD method......I'm sure people in here will know.....I use the zone system with a light metre and that's worth learning....will follow this thread to hopefully learn about that

Link to comment
Share on other sites

LAD is basically a quick one-measurement check for under-/overdevelopment. Originally intended for color neg. As far as I remember, Kodak recommended slightly different gray patch densities for various stocks, all of them around 0.8-1.2-1.6 RGB Status M.

For B&W, 0.7 over base and fog sounds like a safe grey density. Optimum exposure depends on the post process (and, to some extent, the stock) though. In the photochemical world, a "correctly" exposed negative would print at midrange printer lights. DI is much more complicated and you have to test to figure out the densities that yield the best scan. 

Link to comment
Share on other sites

  • Premium Member

Laboratory Aim Density is a typical Kodak crutch in the pursuit of getting a grasp on as many labs as possible. Forget about it.

If prints are to be projected, the calculation goes backwards from screen to set. You want to define an albedo of the screen, a reflectance factor of, say 1. That would be the best mat white surface, closely matched by a whitewashed wall.

Maybe 0.8 reflectance. Then you define a screen luminance that allows you to produce a certain contrast between no light and full light. You produce the contrast by the density range of the print. You most certainly want to reproduce nature in that model cinema, deepest blacks and brightest snow or clouds. The range is limited by the amount of silver developable with a given print stock. Kodak X302 yields about log 3.0 max. dens., maybe log 3.2.

You can hammer too much light through the film. In that case the shadows begin to shine. With too little light the midtones sump out towards the shadows.

The best attainable positive image on the print defines, still going backwards, the contrast of the negative. In full consequence the last liberty that remains in your hands is the lighting of the set, of the object. Only very few cinematographers want to understand this context. If you wish a richer image on the screens, you need denser prints, at least a print film that can be processed to a max. dens. of log 3.5 and up. The lab is the not-to-be-envied executor between the producer and the theater people.

There are black-and-white films available with which a max. dens. of log 4 to log 5 is feasible, mainly sound recording stocks.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...