reciprocity and reduced devolment times

[atlcruiser]

Hi All,
I am dealing with some arista 100 (foma 100) and found the tables for reciprocity through a search here.
The times are LONG :) I have also seen recommendations to reduce dvelopment time but as much as 30% with the longer exposure times. All of that makes sense to me if i use a home made sort of sliding mental scale with the amount of decreased dvel time based on the incease in expsure time. A little less for slightly longer times to a lot less for long times.

So now the queston: I have a scene that will be N-1, lets say that N-1 equals 10% less time. I also read off of my reciprocity chart and figure that I need -20% based on the lenght of exposure. Does this make -30% overall develpment?

Sounds reasonable?

Am i making this too complicated? :confused:

[Lenny Eiger]

Am i making this too complicated? :confused:

Yes, IMO. If you expose more to deal with reciprocity you will get more, or an adjusted exposure. I don't believe it will affect the contrast at all, which is what development is about....

I suppose the case could be made that longer exposure affects the highlights more as they are mores sensitive overall, but I have never had issues with higher contrast because of longer exposure. I would keep to your development chart for the N#'s.

Lenny

[Brian C. Miller]

-30% sounds OK. What you need to do is make some test shots. Kodak Tri-X (PDF link (http://www.kodak.com/global/en/professional/support/techPubs/f4017/f4017.pdf)) has a massive reciprocity adjustment. I once made a test exposure where the lens was open for a couple of hours, and then I took a guestimate at the development time. It was good enough, and the shadow detail was good.

[Brian Ellis]

As you've pointed out, when you increase exposure time to account for reciprocity failure that causes an increase in contrast and requires a reduction in your normal development time if you want to produce a normal negative. With relatively small increases in exposure time the effect isn't enough to worry about. But my reciprocity and contrast tables indicate that with a metered time of 8 seconds the reciprocity adjusted exposure time for conventional (i.e. non-tab grain) films is 20 seconds and the contrast increase is the equivalent of N+1/2 development. The contrast continues to increase as the exposure times increase. My tables end with a metered exposure time of 15 minutes and an actual time of 2.25 hours, which creates the equivalent of an N+3 negative if you develop for your normal times.

My guess is that the answer to your question is no, you wouldn't just use your usual N-1 time to get an N-1 negative in a situation where you've also reduced your normal time by 20% to take the contrast increase caused by the reciprocity-adjusted exposure time into account. I wouldn't stake my life on it but my reasoning is that your N-1 reduction of 10% was 10% less than your time for a normally developed negative. But now you're not developing for your normal time, you're developing for 20% less than your normal time. So I don't think the 10% amount still holds true since it was 10% less than a normal time, not 10% less than a 20% less time. But I could be wrong and even if I'm right I'm not sure the difference between 30% less time and whatever the reduction really should be is big enough to matter.

[Jerry Bodine]

FWIW, I decided to looked up what AA had to say about the reciprocity effect in his book "The Negative." This is what I found:

"The reciprocity effect is not identical throughout the scale of negative densities. For a long exposure, the low values tend to be affected (i.e., underexposed) more than the high values, causing a decrease in their density, and there is thus an increase in contrast in the negative. It is therefore necessary to decrease development ... to avoid excessive contrast." He references Kodak data which provides a guide for b&w films.

For an indicated exposure time of 1 sec, use an adjusted time of 2 sec, and reduce development time by 10%.
For an indicated exposure time of 10 sec, use an adjusted time of 50 sec, and reduce development time by 20%.
For an indicated exposure time of 100 sec, use an adjusted time of 1200 sec, and reduce development time by 30%.

For more precise correction, individual tests should be conducted.

[Doremus Scudder]

Altcruiser

When you know the development reduction for a certain reciprocity adjustment, you should deduct that from your planned development time. Don't think of N- or N+ times as percentages of Normal, but rather as your planned development time and then adjust that accordingly

Example: Metered scene calls for N-1. Let's say, for the sake of simplicity, that that is 10 minutes (N might be 13 minutes, but that's not relevant here). Your reciprocity table says to reduce development by 20%. So, you subtract 20% from your 10-minute developing time to arrive at 8 minutes. That's the correct calculation.

Now the disclaimer: The data given in the post above is for older Kodak films. Howard Bond and others have done research on the newer films and found that they require very much less development adjustment than that, even though Kodak continues to publish the same information. Also, you are not using Kodak film. I cannot find anything from the manufacturer of Aristo that gives development adjustment amounts for reciprocity adjustments. Every film is different.

So... unless you want to test to arrive at your own adjustments for different amounts of reciprocity adjustment I would advise that you bracket.

I would take two identical negs and develop one at the planned development time and one at the time arrived at by applying the Kodak data. One of those negs will be in the ballpark and allow you to get a good print.

My experience is that less development adjustment is necessary than is usually stated. When BPF 200 was still around, I found it required almost no development adjustment for even very long reciprocity adjustments.

Hope this helps,

Doremus Scudder

[atlcruiser]

thanks for all the info. I guess it really boils down to test what you got and what works for you!

My experience is very limited in LF. I am finding that I need to apply more time to the exposure for reciprocity adjustment. Last night ended up with a exposure at f45, 4' meter, 7 min with the F4P+ chart. 13 min is my normal time. I dropped that down 10% for a 12.5 min devl time. I got a very thin neg with slightly blown highlights. If I am thinking correctly I underexposed and overdeveloped!

[David Schaller]

The problem really arises when the shadows fall on one side of the reciprocity line, and the highlights on the other. So the adjustment for the "reciprocity failure" or "effect" for the shadows increases the effective SBR. The best way to handle this is the same way you would handle a greater SBR, i.e., N minus something.

For example let's say that the shadow that you want to place in Zone III is 8 seconds, at the aperture you want, and the highlight you want (I use Zone VII, for this example, but it would be the same in principle if you want to use Zone VIII) at 1/2 sec. This would usually be a Normal range.

Then you apply the adjustment: for the 8 seconds you need to give 22 seconds for Zone III, that means that 11 seconds would be Zone IV, and 5.5 seconds would be the actual exposure time for Zone V. I would shoot it for 6 seconds. So now the 1/2 second Zone VII has received 1.5 seconds of exposure, which has moved it up to close to Zone IX. Therefore I would give almost N-2 development to bring that highlight back down to the Zone VII I want. If you had used the Zone VIII reading of 1/4 originally, that has moved up to almost Zone X (3/16 sec.), so the reduction in development would be the same.

This is how I figure it.
Dave