It's an interesting video but I reckon things are not so easy.
Of all the Harman Direct Positive Paper I've used about half of it has gone to testing rather than taking pictures. This may be the underlying business model for this expensive material. Problems I've yet to definitely solve:
How to filter the light meter so it sees the same light that the DPP sees.
How to calibrate the pre-flash; what colour light, how much. Preflashing DPP changes its contrast AND its light sensitivity.
The effect of preflashing seems to fade after a while. The paper appears to re-set toward its original characteristics of speed and contrast after hours or days.
How to sort out all of the above while using a yellow filter for a more "panchromatic" tonal response. I'd like to reduce the "dark complexion" characteristic of blue sensitive materials.
How to formulate a developer that stays strong. I suspect DPP releases a lot of iodide (restrainer?) when processed. Ordinary Dektol 1+2 (stock plus water) seems to lose power quickly.
How to do accurate 2, 3, or 4 second exposures. That's where my DPP seems to lead for studio portrait work. Hand timing is least repeatable at these speeds and mechanical timing is not easy or cheap to come by.
How to stretch the exposure latitude of DPP. Even 1/3 stop changes are pretty obvious and 1/2 stop wrong means a re-shoot.
Experiments continue.
Much like conventional paper negatives, Harman DPP is blue and UV sensitive. Unless someone builds a UV light meter, I don't think matching the spectral response of the meter to the paper is practical.
I've pre-flashed in the darkroom using a very similar tungsten lamp that is used in enlargers, since that kind of light has worked well for print paper (i.e. paper negative media) for a century or more. And I continue to use it the same way for Harman, except that through testing I've come up with an exposure that works for me.
I too have noticed that pre-flashing fades, but especially if you give it too little exposure. With paper negatives I've also done post-flashing, just prior to development, but the contrast control effect is not quite as strong. Some people pre-flash in-camera, using some kind of diffuser on the lens, just before the main exposure. To do so you'd have to work out what fraction of a full exposure you need.
I tend to pre-flash paper negatives so they have a faint light gray tone if then developed. For Harman, I give it enough for a faint exposure above pure paper black (which is what you get from fully developing it without exposure).
Regarding using yellow filters, I know many people swear by this for paper negatives, but I never have. These materials are slow enough as it is, especially Harman. To tackle the dark skin tones on portraits, give it more exposure than normal. This is what I've learned through years of using paper negatives, you meter the scene, then apply exposure compensation to account for colors that might not expose well, especially on the brown/red end of the spectrum.
For developer exhaustion, I do one-shot for Harman. For paper negatives I'm more apt to employ used developer and develop by inspection, but not if I'm using the Jobo tank in the kitchen, then it's one-shot also. When I say "one-shot" I'm referring to using a rotary tank. That large Jobo for 8-by-10s only takes 100mL of solution. Amazingly economical.
Okay, regarding reciprocity failure, Leon over on Filmwasters suggests that Harman DPP has a reverse reciprocity curve, implying that sub-second exposures will be under-exposed compared to longer. You saw the comparison I made in the video between the tests done at 1/15s and the 8-by-10 timed by hand for (I think) 3 seconds. They were fairly close, considering the innaccuracies with hand timing shutters.
So yesterday I went out with the 8-by-10 and made two exposures, both at ISO 7.5 as per the video tests. I used two different aperture sizes, the large size (I think 9mm) being metered at 1 second and the smaller size (3mm) being metered at 4 seconds. The 1 second exposure was slightly too bright, but not nearly like the print you saw in the video; I attribute this to timing errors with a hand-operated shutter (literally using the dark slide over the lens). The 4 second exposure came out beautiful, just like what the tests in the video would have indicated. It's easier for me to accurately time a 4 second exposure (using the sweep second hand on my wrist watch) than a 1 second exposure.
So if there is reverse reciprocity effect, you think it would have shown up between these two rounds of image making, where on the one hand I exposed a 4-by-5 at ISO6, 1/15s and f/5.6-8, and the second day I exposed an 8-by-10 at ISO7.5, 4 seconds at f/80-ish. Both images came out nearly identical, from scenes nearly the same lighting, using the same (or nearly) ISO rating, with the same metering technique. Between 1/15s and 4s there should have been a difference, but there wasn't.
Finally, as for the suggestions to use incident metering, I've been shooting paper negatives for decades, and have always found reflective metering, off the principal subject of interest, to be more accurate.
~Joe
