Bergger Pancro 400 Reciprocity Characteristics

[lumiere_et_son]

I like Bergger Pancro 400 in 4x5 and became curious about how it behaved with long exposures. Now that it is available in 135, I am able to expeditiously and affordably experiment.

Knowing that most films follow an exponential curve, I set up a target in dim light and shot a few rolls of 135 at various exposure times to determine the "right" exposure. I tested this method on FP4+ (for which Ilford has published power law reciprocity characteristics, thanks Ilford!) beforehand.

174584

I controlled exposure of the target using a tungsten fresnel lamp and CTB+ND gels. The "meter" I used for this was a Canon 5d Mark III (which is my typical long exposure meter). I first determined that the digital camera exhibits "correct" reciprocity across shutter/aperture/ISO settings, and would meter by taking a test shot of the target at high ISO, wide open, followed by a series of exposures on Pancro 400 135 using a EOS 1N with exposure times bracketing Bergger's guidance (e.g. +1.3 stops for 10-60 second exposures). "Correct" exposure was based on negative density compared to a short-exposure (1/4 sec) sample. As expected, the film's reciprocity characteristics follow a power law.

The result was a correction factor of 1.36 (i.e. Corrected Exposure Time = Metered Exposure Time ^ 1.36), determined using a least-squares linear regression of log exposure time.

Pancro 400 appears to have at least a stop of latitude in both directions, which makes Bergger's guidance totally decent for exposures of metered time less than c. two minutes.

[Drew Wiley]

You might need to modify that for nominal daylight exposure.

[lumiere_et_son]

Not sure precisely of your meaning - this is for long exposures (>1 second). Testing was done with c. 5500K light.

[Drew Wiley]

OK. You apparently daylight balanced the light.

[lumiere_et_son]

Yes - In an otherwise dark room, I used a 3200K tungsten fresnel light with a CTB gel to convert to 5500K (and dim) and another ND gel to dim it further. Decent approximation of moonlight, and also I'm eventually planning to do this for Velvia, Provia, Ektar, and Portra, and want to use an X-Rite target to see how the colors shift for those films with long exposures.

[Drew Wiley]

I didn't bother to photograph our "blood moon" not long ago. But I did watch it. Within a few hours there were plenty of posted preposterous Fauxtoshoppy scenic composites containing it. I had a suitable lens, but no fast color film.

[Moogie]

Thanks a lot for your effort and providing this useful info.
I just started using Pancro 400 and was looking for exactly something like this to fill the gaps from Bergger's data sheet.
Miguel

[SMBooth]

This test by Australian photography David Tatnall may help.
https://viewcameraaustralia.org/2017/06/28/review-bergger-pancro400-sheet-film/

[lumiere_et_son]

Shane, many thanks for the link.

I ran a regression on David Tatnall's data and a combination of his and mine, and found the following factors:

My data : 1.36
David's data: 1.29
Combination of both: 1.34

Less than a half stop difference between the two through 120 sec (metered). I'm comfortable with this film for long exposures.

I'll probably run Vevlia, Provia, and Portra through the same setup while I still have it up, since my process is 90% automated.

[Tim V]

Does anyone have any examples of ultra long exposures shot on Bergger Pancro 400 to share? Would love to see the look.

[Thalmees]

Thanks so much Lumiere.
Is the same data applicable to HP5+? Still have some.
To everyone: What's the merit of Pancro 400 over other equivalent films?
Asking because I stopped purchasing Kodak sheet films a year or more ago(due to escalated price), at the same time I purchased a considerable amounts of Acros100(fro Japan lower prices) and FP4+ old prices.
Due to the recent increased ILFORD prices, my next purchase for ISO400 will be Arista or Pancro. Unfortunately, Shanghai does not make ISO400 films as far as I know.
Regards.