Explaining the copy lights

Max Hoever · May 29, 2007

Does anyone know a place to look for a deeper article about copy lights?

I don't really find anything online and the books I found can't help me as well.

...for example "Image Control" by Hirschfeld - I thought that one could help me, but it also stays very much on the surface.

I wanne know how the machine technically works. and for example which light (RGB)i have to de- or increase to work against or for any of the six colours RGB and YCM!

Thanx very much...

Brian Pritchard · May 29, 2007

Does anyone know a place to look for a deeper article about copy lights?
I don't really find anything online and the books I found can't help me as well.

...for example "Image Control" by Hirschfeld - I thought that one could help me, but it also stays very much on the surface.

I wanne know how the machine technically works. and for example which light (RGB)i have to de- or increase to work against or for any of the six colours RGB and YCM!

Thanx very much...

I presume that you are interested in Grading and Printing Lights. I am sorry if I have misunderstood you.

You can find some information on Grading on my website at http://www.brianpritchard.com/GRADING.htm.

On that page there is a colour diagram that shows you what the effect of increasing the Red, Green and Blue lights for Colour Reversal grading and Neg to Pos grading. The Model C type lamp house which is the most common printing lamp house has three light valves which used to be mechanical and are now electronic. The white light from the lamp is split into red, green and blue light by dichroic mirrors and a light valve controls each colour before the three colours are recombined into the printing light. The valves have a range of 50 lights which can be raised or lowered by another 24 lights by means of trims.

I could email you a picture of a lamp house if that would be helpful.

Brian

Max Hoever · May 30, 2007

Yes, printing and not copy lights was what i meant!

Thanks for the answer, I haven't yet read the info on your page, but anyway I would be glad, if you could also send me the picture!

mhoever@gmx.de

THANK YOU

Max Hoever · May 30, 2007

On that page there is a colour diagram that shows you what the effect of increasing the Red, Green and Blue lights for Colour Reversal grading and Neg to Pos grading.

super, the colour diagram explained to me, what I somehow always knew but never was sure of. Its really good to find simple explanations who bring it to the point!

THANKS FOR THAT

Clive Tobin · June 3, 2007

...The valves have a range of 50 lights which can be raised or lowered by another 24 lights by means of trims....

Nobody asked me for further confusion, but each printer point is .025 log E or 1/12 of an F stop of actual light intensity. Since color positive stock has a gamma of about 3, this 1 point exposure change makes a density change of 1/4 stop in the flesh tone area of the print.

Labs generally adjust the overall light so that a Light 24 or 25 across (that is 25-25-25 for Red Green and Blue respectively) gives normal results from a normal original. This is done through changes in the voltage, filters and trims.

This is controlled for negative-positive printing with the LAD (Laboratory Aim Density) system which was described in the literature by this forum's contributor John Pytlak.