Reciprocity failure question

<p>For exposures 4 minutes and above for Fuji Provia 100F, Fuji's data sheets suggest two things: (a) +1/3 stop exposure compensation (b) a color correcting filter to compensate for color shift.</p>

<p>My question is, is the +1/3rd stop needed if I were to dispense with the filter i.e. if I plan to do color correction in post.</p>

<p>Thanks</p>

<p>Shifting in color on slide film is pretty messy... What lighting are you using... if at night don't worry... if day with that long then try it both ways..... but I don't think it will mean much.. as I have never used the filter to get what I want in something that long. </p>

<p>"Colour correcting" means discarding some colour in excess and enhancing some colour in defect. Therefore, the colour in excess may mean excessive highlights with lesser detail, while the colour in defect may lead to enhancing grain while overexposing that colour.<br>

Overall, it is a little bit like underexposing the film and then correcting it with photoshop: it is possible, and if the difference is small the end result is almost unnoticeable, but it is not optimal.</p>

<p>I haven't used reversal film for years, and I'm surprised this stuff has such good reciprocity characteristics. Ain't technology grand? My take on it is:</p>

<p>(i) Yes, give it the extra 1/3 stop if you're doing critical work. That recommendation would be for after you have dealt with the effect of filtration, but the CC2.5 is pretty negligible.</p>

<p>(ii) Having said that, you could get away with just shooting it according to the straight meter reading, and forgetting about reciprocity failure. In that case, the 1/3 stop of underexposure would give you a bit more density and saturation. (In the old days, many of us used to shoot Kodachrome 64 at EI80 for this reason.)</p>

<p>(iii) Your Provia only needs 2.5G of color correction at four minutes, which is an amazingly low color shift. If you're scanning, this will be easy to correct in the computer.</p>

<p>(iv) YMMV, so run a test roll before doing anything important. If circumstances allow, you might bracket a bit-- maybe one exposure right on the straight meter reading, and one opened up an extra 2/3 stop.</p>

<p>(v) Come back and tell us how you made out with this. </p>

When I used to used film for

astronomical imaging, we chilled

it to about -40 degrees to lock

in color balance ad reduce

reciprocity failure. If you're

doing a lot of this, I'd suggest

a hypering tank to

hypersensitize the film. 92%

nitrogen and 8% hydrogen formung

gas mix at about 90 degrees and

15 psi.

<p>Compared to more neutral portrait films I found Provia to have an annoying cyan cast upon long exposure. Like everything it is digitally correctable.</p>

<p>The recommended compensation for exposure up to 4 minutes is to increase exposure by 1/3 f/stop and to mount a CC 2.5 G correction filter (Green).<br>

Some thoughts:<br>

When processing color film, photofinishers do their best to control the process to maintain uniformity of ISO speed and color balance. The best any lab can achieve regardless of due diligence is ± 0.05 density units on a day-to-day basis however the average is more likely ± 0.08 density units.<br>

f/stops relate directly to density:<br>

1 f/stop = 0.30 density units<br>

2/3 f/stop = 0.20 density units<br>

1/2 f/stop = 0.15 density units <br>

1/3 f/stop = 0.10 density units<br>

1/6 f/stop = 0.05 density units<br>

1/12 f/stop = 0.025 density units (consider just barely perceivable) .</p>

<p>It is likely that the processing activity will be maintain a the 1/3 f/stop level. In is not likely that the processing will be maintained to 1/6 f/stop. No lab has achieve day-to- day ± 1/12 f/stop process control.</p>

<p>The color balance will likely vary ± 0.08 density. Mounting a 0.025 Green correction filter is good advice but:</p>

<p>On any given day with due diligence taken into account the process will drift:<br>

Too red<br>

Too Green<br>

Too Blue<br>

Too Cyan<br>

Too Magenta<br>

Too Yellow<br>

By ± 0.08</p>

<p>The 0.025 G filter will only help if the process drifts too Magenta (the complement of Green).</p>

<p>Bottom line: Do not worry about it.</p>

<p>Just to clarify:<br>

CC (color correction) filters are labeled in density units. Common usage is to omit the decimal point. Thus a 0.30G (1 f/stop) is referred to simply as 30G. A 2.5G or 2 1/2 G is actually labeled 0.025G. These are density units. Density is expressed in logarithmic notation. Each 0.30 units = 2x change = 1 f/stop. </p>