Ilford FP4+ reciprocity correction?

[l2oBiN]

I am trying to identify reciprocity correction factors for the Ilford FP4+ film and have come across two separate recommendations by Ilford themselves?.

For a 5s measured exposure time, The FP4+ technical data sheet indicated the time corrected for reciprocity to be ~12.5s (https://www.ilfordphoto.com/amfile/f...roduct_id/690/)

The same 5s exposure would result in ~8s time corrected for reciprocity if the technical data sheet on reciprocity is followed.
https://www.ilfordphoto.com/wp/wp-co...mpensation.pdf

Which values are correct?

[interneg]

The second document specifically about reciprocity is the up-to-date information. It's based on new testing, not a generic recommendation like the data sheets used to give.

[l2oBiN]

If that is indeed the case, then the reciprocity is significantly better than the data sheet recommended graph!

+1 stop at 15s
+2 stop at 68s (~1m)

Not bad!

[Pere Casals]

If that is indeed the case, then the reciprocity is significantly better than the data sheet recommended graph!

First generic document is more "conservative".

Reciprocity is difficult to calculate because shadows have a higher failure than the mids or the highlights.

You can use a factor that corrects well exposure to reach the same density in the negative for the mids, but then shadows may be lost.

So while the second document is technically correct you should be aware that you may want additional corrections to ensure that you record well your shadows, increasing exposure and performing a compensating development for the additional contrast LIRF provocates.

Specially with contrasty scenes (night photography) you should make some bracketing tests to know how the factor fits your taste.