Quote Originally Posted by andrew.roos View Post
Hi Mike

Welcome to APUG and thanks for posting this.

However note that the reciprocity failure chart that Ilford provides in the Delta 100 data sheet is not accurate. It is extremely unlikely that these films (which include both conventional and CCG emulsions) have identical reciprocity failure characteristics, so I expect it is sloppiness on Ilford's part copying and pasting the graphs rather than actually performing the measurements.

My "rule of thumb" based on these measurements is that no correction is required for exposure times up to 4 seconds. For exposures longer than 4 seconds, add an additional 1/3 stop of reciprocity failure correction for each stop of (metered) exposure over 4 seconds.

So you are suggesting, I think: 1.The OP's findings are clearly and substantially wrong
2. Ilford has been incredibly lazy over reciprocity testing.

I have no idea how difficult such things are to ascertain but given that Ilford tries to meet customers' requirements to an extent that other manufacturers do not, it seems quite incredible that Ilford hasn't bothered to check on these matters when it is within individuals ability such as Howard Bond to ascertain reciprocity. Why not be as lazy with development times and simply cut and paste ID11 times for say HP5+ for all its films and all its developers? I don't think we are suggesting that Ilford has done this

Might it be that the methodology used was different?

Maybe Simon Galley will respond. I would if my company were accused of cutting and pasting our of laziness