Inverse square law

I'm beginning to learn some basics of lighting. So this may well be wrong, but the physicist in me couldn't help itself.

Several of the lectures I've listened talked about the inverse square law. The problem is, it doesn't apply: or at least not strictly to the problem they describe.

The inverse square law models a point light source radiating uniformly in all directions. At a distance x from the source, the energy falling on an area y is the proportion of the power of the source of area y relative to the surface area of the sphere of radius x.

If you double the distance from the source, the surface area of the sphere at 2x is now four times as large (A=4/3Πr²) since surface area increases in r². So y is now 1/4 of the area of the larger sphere and so receives only only 1/4 of the energy emitted by the source.

But often the lighting being used and measured in the studio isn't from a point source; it's collimated with umbrella reflectors, so the energy doesn't fall off as the square of the distance. The ultimate in collimated sources is a laser; absent scattering all the energy emitter at the source hits the target. The same principle applies to theatre spot lights or search slights.  

That being said, I am guessing that for soft boxes the inverse square law is a fairly good approximation since each point on the front of the box might be considered as a point source. But in any setup in which light from the source is focused, the inverse square law won't apply.

Disintermdiation

This post probably doesn't belong here, since it's really about digital: specifically my prediction that the Internet will render prints obsolete, and with them the need for mass market dedicated cameras. Aside from some niche uses, most people will take pictures on their smart phones, and upload them directly to a website, such as Facebook, where they will be viewed; the images will never be printed from beginning (capture) to end (viewing). Smart phones are better positioned to do this than cameras since they are already connected to the net. If the highest resolution needed is that needed to view a picture on a large screen TV, then a 20+ MP dedicated camera looses out to an 8MP smart phone. I give the mass market segment of the dedicated camera industry another 10 years.   

Reducing the number of variables

For the moment I have decided to scan all my black and white negatives with a simple rule. Turning off the scanner software's auto exposure, the bottom of the histogram will be 0 and the top 255, with an gamma of 1.25 and the tone curve set to linear.

This allows me to 1) reduce the number of variables so that I can learn more easily the effects of manipulation in GIMP, and 2) should, in theory, be a more constant, predictable and and perhaps accurate representation of the characteristics of the film itself.

Another comparison

A small portion of the same scene.

First the LX3:

then the RZ:

Colour printing

I'm glad I'm not printing this in the darkroom: I've tried over 20 variation of the scan settings, which, if this were colour paper, would have cost a small fortune. I'd have been ducking in and out of the darkroom to see what I'd done, and since it takes a while for my eyes to adjust, this takes time and introduces error. I also couldn't have been writing this at the same time as the print was developing (the scanner is scanning at the moment).

Here are the thumbnails of some of the variants. The differences between them are generated, in some cases, by very small changes in the scan settings (e.g., from 236 to 237 in one of the blue channel parameters).  In just one panel - the AD coding 'histogram', there are 5 settings per channel, so there are a lot of variables to mess with.     


This is the final product. It probably has slightly more blue in the highlights than the original scene, at least as I remember it (it was late evening as the sun was setting and the light was fairly yellow), but it seemed more pleasing to me than a possibly more accurate representation.

Fuji Reala 100

Two rolls of color negative film came back today. It's much harder to work with than black & white because the film itself is so dense which means the information is compressed into a much smaller range. That makes the tonal gradation rougher and reduces the margin of error. This is visible in the 'sudden' transitions between adjacent tones. Here is a comparison with my LX-3.  First, LX3 image:

Next the film version (Fuji Reala 100).

I'm not too happy about either image to be honest. The lower one seems to me to have a little to much cyan, while the upper is a shade too yellow. The lower image could also be a little flatter. But this was my first attempt and it's much harder than black and white - obviously - since there are many more variables. But this is all about learning the craft. The road is long, but the path is clear (sounds like a quote but Google won't tell me whose).

P.S. Seems I left the white balance setting on the LX3 to "house with shadow", which according to the user's manual is for "when taking pictures outdoors in the shade", which wasn't the case here. So the odd tint in the LX3 is my fault. More tests (and care) are clearly warranted. 

Digital Analog(Digital) Comparison

Two images of the same scene. The top one was take with my Lumix LX3, the lower image with the RZ-67 and Acros 100.

The film was scanned at 1200 dpi which gives it about the same sized file and resolution as the digital end-to-end below.