Having a separate quadrant each factor would be ideal so that each influence can be identified and measured. Unfortunately I'm restricted to the four quad.
Agree. In the end the result is the same. My only preference all along would have been to present the effects of non-image forming light in quadrant 2, or on its own, rather than in quadrant 1. Just a personal preference I guess (the way it is presented on p. 160 in Henry's book, for example).
all it is supposed to do is alter the toe of the H&D softening the contrast
and increasing the ISO but not to detectably alter the shoulder (the degree of change in contrast and ISO would depend upon the film).
Any film and it's response to light remains constant as long as development remains constant. The film curve, doesn't change just because we use two exposures instead of one.
The whole point of flashing is that it is such a small amount of exposure itself that it has only an insignificant effect higher up the curve than
where it is targeted. But down there it does by definition add density and lift the toe of the film, hence diminishes the pace of shadow and
textural separation. Whether this is good or bad depends on what you are trying to achieve, the specific film, and the lighting ratio. But the risk is ending up with mud down there if you overdo it.
What I'm getting at and what Stephen's charts show is that subject placement changes, the shape of the curve does not.
Surely there is compression, yes the relative distance between tones changes vertically, but that's not because the shape of the curve changes; it's because the extra exposure has pushed the tones furthar right on the normal curve.
If you photographed a reflection step wedge without a pre-flash and then photographed it with a pre-flash and then charted two two results, you would get a different shape curve for each in chart.
the whole point of pre-flashing is to alter the distribution of the tones on the toe of the curve which does change the resulting curve.
The whole point of pre-flashing is to improve the shadow detail in the print without affecting the highlights.
BTW even if the characteristic curve was a universal law of physics, fully continuous and whatnot, a preflash would not translate into a linear shift, neither sideways nor upwards. Remember, it's a logarithmic scale in both axes.
There is a disconnect between making a test chart/curve and making an actual print.
If you photographed a reflection step wedge without a pre-flash and then photographed it with a pre-flash and then charted two two results, you would get a different shape curve for each in chart. what has remained fixed is the development. But we already know that. So what you are saying is kind of correct in one way but wrong in another because the whole point of pre-flashing is to alter the distribution of the tones on the toe of the curve which does change the resulting curve.
The confusion is that you are talking are talking about a film speed/contrast curve whereas everyone else (mostly) is talking about a tone dstribution curve. The two are subtely different in concept. So I guess both sides of the argument are correct.
No just different placement. This is exactly what Shephen's chart shows in quadrant 2.
To get a different curve you have to change the assumptions of the math involved. Change the Log scale or factor out the fog or some such thing.
The basic film curve doesn't change.
I would rephrase that:
In Stephen's chart it's obvious that the whole toe of the film curve gets buried with flare and pre-flash.
Pre flash pushes everything usable rightward on the curve, all the way onto the straight line.
Quadrant 1 shows the curve I think your are suggesting.
You can superimpose one over the other to illustrate your point but the scales used to define each of those curves, are different.
That's one way of looking at it. The other is that film or paper doesn't have a curve. The curve is a mathematical construct after the event which means there is no pre-existing curve to place anything on. The curve construct after the event just shows what happened and in the two scenarios I gave above, the first would produce a different curve than the second.
Your concept is that there is a pre-existing curve which youn are predicting. But if you change the parameters to the curve then it should be obvious that the curve will change. What I don't think you have grasped is that a single exposure, and the basis of your curve prediction, follows the exponential laws of exposure. By adding a pre-flash (double exposure) you break those laws so that the rules for constructing your predicted curve change. Result = new curve.
But that is not a valid hypothesis?Actually my premise is just that for a given film, in a given development scheme, that: a given amount of exposure, will produce a given amount of density.
...
But that is not a valid hypothesis?
BTW even if the characteristic curve was a universal law of physics, fully continuous and whatnot, a preflash would not translate into a linear shift, neither sideways nor upwards. Remember, it's a logarithmic scale in both axes.
Well a different analogy is a pin ball machine.
If you need four balls in the win zone and they don't stay in the zone long the game goes on 'for ever', but if you cheat and super glue in three the first time another drops in you win cause you cheated.
A preflash is cheating but the process is more complicated.
And to be fair Athirils results look better than any I get.
I find it ineffective for simple underexposure and normal processing times, combined with a strong push is what gets it there. I based it off an article about Tri-X and heavy pushing to get detail you otherwise simply cannot get.
Jerry, as you sure know, density is a logarithmic measure of absorption. My statement stands as I wrote it. No densitometer I am aware of can measure density without forming the logarithm of measured light.Not true. The characteristic curve describes the relation between density (linear) to the log of exposure. So the plot is logarithmic on one axis and linear on the other.
I would also like to comment on a subtle erroneous notion that pops up from time to time on APUG and elsewhere. That is that a relationship is somehow "unreal" because it is non-linear. Not all relationships in nature are linear. For example the decay of a radio-isotope is not linear but logarithmic.
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?