Pre-flashing film - stability of pre-flash

[alanrockwood]

I am intrigued with the technique of pre-flashing to lift the shadows.

Question: If you pre-flash a roll of film, is the pre-flash effect stable or does it decay in a matter of hours/days/weeks?

Also, how much pre-flash is a good rule of thumb, e.g. equivalent to zone 1 or zone 2 exposure?

Thanks.

 

[alanrockwood]

I am intrigued with the technique of pre-flashing to lift the shadows.

Question: If you pre-flash a roll of film, is the pre-flash effect stable or does it decay in a matter of hours/days/weeks?

Also, how much pre-flash is a good rule of thumb, e.g. equivalent to zone 1 or zone 2 exposure?

Thanks.

Oops, I just discovered that I started a related thread a few years ago. Let's consider this a continuation of the discussion.

 

[koraks]

Do you want me to merge the threads?

As to the question: AFAIK latent image retention isn't absolute and appears to follow an exponential degradation curve. Much of it is lost in the first few seconds, then it all slows down but continues to taper off forever, basically, but it seems on a fairly stable plateau between half an hour and many months.

For repeatable results I'd suggest not waiting to use the pre-flashed film for longer than a few weeks or so. Also because the preflash will be kind of weak and I suspect the developable sites will be less stable than in a liberally exposed grain.

Forgive me for the somewhat speculative answer.

 

[eli griggs]

The method of pre-flashing b&w negitive film that I know of, is to preflash in camera, into the scene, with the lens in infinity and at the selective aperture for 5 - 10% of the actual exposure, using a Styrofoam cup, or, in my case, with a Series filter holder, with one or two filter sized sheets from plates installed, depending on the plate's thickness.

You can also just do the math and open-up the lens aperture, while focused and adjusting the shutter speed and I do not see any hang-ups in using a ND filter for a longer exposure, through the Styrofoam layer, say on a Hasselblad, TLR, or other leaf shuttered lenses that have a general top shutter of 500th of a second or less.

This might be a good technique for those participating in the current show me your Holga photography thread.

I'm currently using just one Styrofoam layer, but the do not have any examples to show since I rarely preflash these days, what I'm shooting most.

Cheers

 

[Andrew O'Neill]

I would say the pre-flash is stable, but I'm not entirely sure as I pre-flash in the field.
Depending on the film's toe, I usually don't go as high as Zone II. I have a video somewhere on my youtube channel, where I'm pre-flashing in the field...Luckily no people were around, and I was not arrested

 

[Ian C]

I've used the method of post #4 for years. This can be done just before or just after shooting the scene. If you use roll-film, you’ll need a camera that allows a second exposure on the same frame.

To do this accurately requires a metering test, first with no diffusion and then with the diffusion tool. Calculate how to obtain the desired difference in stops. This should be done ahead of time. The required actions are recorded in a small notebook you take with you into the field. Then you can quickly meter the scene and use the notes to pre- or post-flash as needed. I’ve used a piece from a sheet of white printer paper held over the front of the lens as my flashing tool.

In this way, when you use roll film, you can flash the scenes that need it and shoot the other frames without flashing on the same roll.

 

[grain elevator]

I thought the main reason why film doesn't come pre-pre-flashed and with the resulting higher sensitivity rating that any manufacturer would be glad to write on the box was that it isn't stable. But how long I have no idea.

 

[Helge]

I am intrigued with the technique of pre-flashing to lift the shadows.

Question: If you pre-flash a roll of film, is the pre-flash effect stable or does it decay in a matter of hours/days/weeks?

Also, how much pre-flash is a good rule of thumb, e.g. equivalent to zone 1 or zone 2 exposure?

Thanks.

It’s best done as close to exposure as possible and for as short a duration as possible (within reason, high speed reciprocity failure will set in at a point).
That will give you the least amount of ground fog.

When flashing for speed with slight push development in mind, I flash two stops below mid gray, or zone III.

In daylight to help extreme contrast, Zone II.