Preflashing question

[davet]

I still don't understand. You're just adding an ND filter at FB+F (or more if you preflash higher) of the neg. How is the paper going to know?

 

[Donald Miller]

I still don't understand. You're just adding an ND filter at FB+F (or more if you preflash higher) of the neg. How is the paper going to know?

There is another thing to consider here...that is the density range of the camera negative. That is ultimately what will determine the contrast.

Adding uniform ND will not change the DR of the camera negative. Wheras when one preflashes and then determines the second exposure of the negative on highlight placement rather then shadow exposure, the DR is compressed.

 

[lee]

Don,
you said, "Wheras when one preflashes and then determines the second exposure of the negative on highlight placement rather then shadow exposure, the DR is compressed."

When one applies this technique is there any development considerations to be dealt with other than just a normal development time?

lee\c

 

[Donald Miller]

Don,
you said, "Wheras when one preflashes and then determines the second exposure of the negative on highlight placement rather then shadow exposure, the DR is compressed."

When one applies this technique is there any development considerations to be dealt with other than just a normal development time?

lee\c

Lee,

That depends on the brightness range (contrast) of the actual scene/subject. An example would be a brightness range of twelve stops. If one preflashed at a Zone III exposure. the effect would be to raise a Zone I placement to a Zone III 1/3, a zone II placement to a III 1/2, a Zone III placement to a Zone IV, a Zone IV placement to a IV 1/2.

So we have effectively raised the lower values and then we can place the second exposure Zone XII value on a Zone X placement (keeps from shoving the high value densities onto the shoulder) and give N-1 development. Thus a twelve stop brightness ratio is compressed to a seven stop density range on the camera negative.

The net effect of doing it this way is that the contrast compression is shared by both the shadows and to a far lesser degree on the highlights.

Sometimes there is no need to alter development at all. Other times in extreme conditions one may alter by N-2. I try to keep changes in development at a minimum...I prefer good highlight tonal separation at the expense of shadows...so long as shadow detail is present...and this method does provide for that.

As I mentioned this depends on the actual conditions prevalent at the time of the exposure. I have used this method to expose fourteen stops of brightness range and arriving at a negative that was capable of printing on Grade 2 1/2 paper.

 

[ChuckP]

Don't forget that fogged film is really what pre exposure is. But it is caused by an exposure to non image light. All you're doing with the sandwich is cutting the light hitting the paper. Does it matter if you sandwich a piece of film exposed to .3 density or just change the fstop by one stop? If you measure light through the .3 density film all areas will be one stop down. Highlights and shadows. The amount of light lost in the highlights will be much greater then the shadows. But the contrast isn't changed or the scene tonal relationships.