reciprocity faillure longer than 35 sec

How can I know the reciprocity failure for longer exposures than described by the manufacturer? Ilford for exemple provide only on information for reciprocity faillure up to 35sec which would be 2min30sec compensation. But sometimes I want longer than it.

I will have to test?

I've not found any comprehensive data on long reciprocity failure times for various films, so I would suspect you'll have to do your own testing. That said, I've been using Fuji Acros 100 in my pinhole camera in no small part because it has no reciprocity failure up to 120 seconds.

Test or check some of the night photography blogs or forums, at least from those that still shoot film. I use exclusively Acros for my night shooting since using something like Delta 100 would require times 3-5x more than Acros due to reciprocity. That said a lot of my semi-urban night shots with some lighting are in the 2-5 minute range at f/5.6 with Acros and more rural ones with little to no light (other than stars ir perhaps the moon) up to 8-12 minutes sometimes.

Examples:

This one I believe was around 6 minutes, Acros, f/5.6. That's light spillage from downtown San Francisco on the horizon. That smooth medium grey there was actually crashing waves over time. Otherwise it was very dark being 11pm or so and up north on the coast.

Pt Bonita Hasselblad500CM 80Planar 150Sonnar Acros D-76 5min45sec 22C 05-2007 VS 9000 23 A by rich8155 (Richard Sintchak), on Flickr

This one a more urban setting with a decent amount of artificial light was actually quite darker than the image appears, but that's the look I wanted. About 2 minutes at f/5.6:

Portero Hill, China Basin ContaxRX 35PCDistagon Acros @100 Diafine 5min 20C 08-2006 26 by rich8155 (Richard Sintchak), on Flickr

This one, seriously in the middle of nowhere in the eastern Sierras. 15 minutes, f/5.6:

Dechampeau Ranch, Bodie FujiGW690III Acros Xtol 1-1 23C 10min 08-2006 02 by rich8155 (Richard Sintchak), on Flickr

Do an APUG search on reciprocity failure. This has been discussed countless times. Howard Bond did a major test on many of today's modern films and his information can be found via APUG as well.

Best.
Shawn

Here is few.

http://www.seeinglight.com/reciprocity.shtml

http://www.willwilson.com/articles/0403Bond_Reciprocity2.pdf

I used to shoot with Fuji across too but since I start to print my photos in darkroom I realised that the black is not black enough for my taste.
Now I am shooting with Delta 100.

deisenlord said:

Here is few.

http://www.seeinglight.com/reciprocity.shtml

http://www.willwilson.com/articles/0403Bond_Reciprocity2.pdf

Click to expand...

Thank you very much.