Reciprocity Failure of Ilford HP5 Plus

Hi, I requested from ILFORD a chart to help with reciprocity failure of ILFORD HP5 Plus sheet film. I got the chart in no time but the longest exposure time was something like 35 seconds. And there it ends. Can anyone who uses Ilford HP5 Plus sheetfilm give me some advice how to properly compensate reciprocity failure when the lightmeter reading is 1, 2, 5, 10 minutes? I have recently started to use my TOYO 4x5 and 8x10 as pinhole cams, so exposeures readings of 5-10 minutes is quite common.

Thanks, Erich

Hi Erich, how are you developing this film with these long exposures? David

From a table on side of my meter, here are my times for HP5 which I develop in pyro: indicated: 30" 1' 2' 4' use: 2'25" 6'20" 28' 2hrs 10' develop: -14% -18% -24% -30%

Hope this helps (and stays lined up so you can decifer it.

1' - 7'37", 2' - 16'14", 5' - 53'18", 10' - 132'. Also note that a development d ecrease of an average 30% is recommended.

I have no idea where I got the chart those times came from or if they're valid .