Ilford - new reciprocity failure compensation factors

[Michael R]

As you may have noticed, the reciprocity failure compensation graphs in Ilford's film literature are generic. A few years ago I had a discussion with Harman tech service about how frankly lousy Ilford's and Kodak's low intensity reciprocity failure (LIRF) compensation charts were/are. After some back and forth they decided to carry out new, film-specific LIRF testing. I followed along as Harman went through this process and the revised factors have now been publicly released. Notice most of the factors are substantially different than the old chart indicated.

https://www.ilfordphoto.com/wp/wp-co...mpensation.pdf

[Neal Chaves]

This doesn't seem to work for exposure times of one second or less. After my own tests, I never applied corrections at times of 1/4, 1/2, 1 sec but the old literature suggested doing so and many good negatives were spoiled as a result.

[Pawlowski6132]

Wow. Cool.

Good job Michael.

[IanBarber]

Good job Michael, can you work on Kodak now :-)

[Pere Casals]

Good job Michael, can you work on Kodak now :-)

Kodak gives separate LIRF corrections for each film, but not the factor. In general Kodak shows excellent technical documentation, I like that.

Ilford is prone to give more "photographer friendly" information, IMHO, also not a bad thing.


Anyway I like the LIRF specs from Acros

Sadly they are going to kill LF Acros. To me this is a big mistake coming from earlier big mistakes...

[Tin Can]

Yes, David, however I for one need definition of terms somewhere.

It wasn't until miles into this thread that LIRF was defined.

Now I know it's not the acronym for LIRF - Rome Fiumicino Leonardo da Vinci, an Italian airport!

[Pere Casals]

Great to know it !

[Pere Casals]

After reading it, IMHO it is also good they point those important factors:


"For very long exposures at very low light levels then
some other variables come in to play such as the
accuracy of the light measurement. This means that
some trial and error may be required.

You may also find that the contrast is increased with
long exposures. This is because of the light level
difference in light levels between highlights and
shadows in the image in effect giving different
reciprocity failure within the image. If this occurs, then
pulling the development may be required (reducing
development time) but will depend on the range of light
levels in the image."

The "some other variables ...such..." wording disclaimer is important. It is not mentioned, but I guess that also "other variables" as film batch and film aging may play a role. About metering, it can also be really challenging, for separate zones, and including flare from highlights to the shadows...

Perhaps because that complexity... manufacturers were not giving precise factors to encourage practical trials, rather than encouraging the counter... this is the easy way.

So IMHO this document is the right way, giving accurate factors, but still warning about the practical challenges a photographer may find.

[devb]

The "some other variables ...such..." wording disclaimer is important. It is not mentioned, but I guess that also "other variables" as film batch and film aging may play a role. About metering, it can also be really challenging, for separate zones, and including flare from highlights to the shadows...

Could the other variables include environmental factors like the spectral qualities of the light being captured?

[Pere Casals]

Could the other variables include environmental factors like the spectral qualities of the light being captured?

Yes, of course, as film spectral sensitivity is not flat. SPD (spectral power distribution) of light that our silver crystalls receive depends on the illumination SPD and on the spectral reflectiveness our subject has, and our filters. So at the end we have light with particular SPD reaching our silver crystals. Is SPD peak hits a valley in the film spectral sensitivity curve then we need longer exposure, with greater LIRF correction (Low intensity reciprocity failure).


I may be like the way exposure correction for a particular color filter depends on the light source, see here different corrections for same filter (for TMX) depending on if daylight or tungsten, page 20 : http://www.kodak.com/global/en/profe...JGWRQHIO3JXWJI


Also a great variation (Alaska -30ºC vs Death Valley +45ºC) of temperature will substantially change LIRF, it is lower with cold, as astronomers saw in 1930s, they were using "dry ice" cold backs.