What is Base+fog+0.1 speed of XP2 ?

Hi,

 

May I know what is the "true speed" of XP2 defined by Adams such

that at N-4 exposure, the film has a density

of "film base + fog + 0.1" ?

Have you done an experiment for this ? Thanks in advance.

Others may disagree but I've long contended that the Zone System, as such, does not apply to color films, negative or slides.

 

Strictly speaking, the Zone System is equal parts exposure and development. Color films are fairly resistant to being influenced by development. I suspect that C41 process chromogenic monochrome negative films are the most resistant.

 

I don't see how "N-4" could be achieved with XP2 Super. It's already a low to moderate contrast film. Instead, it would make more sense to regard the film as being at its minimum contrast as-is and work up from there with filters - yellow, orange, green, red, etc. - as suitable for the conditions.

I believe you can measure the foot speed of a chromogenic

negative film using sensitometry just as effectively as you can

measure Silver based B&W films. This has nothing to do with

development . It is often stated that the real film speed of

professional C41 films is lower than the box speed whish is why

pany rate Portra 160nc at EI:100 and NPH (older version ) at

EI: 250. I would not be surprised if the real foot speed of XP2

was a little lower than what it says on the box but I have never

bothered testing it. It is only really relevant doing these tests

based around your own equipment, not using someone elses

figures.

"It is only really relevant doing these tests based around your own equipment, not using someone elses figures."

 

True. If Photographers ever had to a apply for research grants as real scientists do, they never get any money becaue of the "your mileage may vary" technical approach we accept.

Hi Lex,

 

I am not trying to vary the development of C41. The purpose of knowing the foot speed is that I can set up the ISO such that I can make a negative with zone I having at least some detail and texture rather than being empty at all.

Shoot a series of bracketed exposures at 1/2 stop intervals. Do it in various places, different subjects, a variety of lighting situations. See which speed works best for you.

My suggestion is pretty much like Al's. I'd set up a textured black object and a textured white object in even light, such as open shade (bath towels or other non-reflective material would probably be best).

 

Then I'd start exposing at ISO 50, working my way up in 1/2 stop increments as far as I cared to go - maybe to ISO 1600.

 

After getting the negatives back from the lab I'd inspect them with a loupe - the negatives, not prints - to evaluate the point at which the black object's texture can no longer be seen and the point at which the white object becomes so overexposed and dense that it wouldn't print well. Somewhere between those extremes is the working range for the film.

 

Or you can just take the advice of other people who've used the film enough to say with confidence that it works very well when exposed between ISO 200-400.

Thanks for all your response and assistance.

 

My final testing result is :

Rate XP2 super (Not old XP2) at ISO 200. Then I can get a negative with 0.1 density at zone I.

 

I used a light box and Sekonic 558 spot meter to do the measurement. And placed a 50mm MD lens on the film as close up lens such that the spot meter can focus accurately.

 

And I discover that the old XP2 is very different from new XP2 super. The contrast of new XP2 super has increased a lot.