Okay. I tested the reciprocity characteristics of Efke 25 4x5 sheet film and I have to say that I was suprised at the results. Before I started the test I quickly searched the internet for any reciprocity characteristics listed for this film. This is what I found: 1/2 no exposure compensation required 1 sec give 1 stop (2x) 10 sec give 2 stops (4x) 100 sec give 3 stops (8x) No development compensation was listed with this data so I thought maybe Efke 25 doesn't need it (just like my beloved HP5+). My own testing indicated that it indeed doesn't. But, the above exposure compensation data was way off compared to mine. Mine is as follows: 1/2 sec no compensation required 1 sec give 1/6 stop 10 sec give 1/3 stop (1.2x) 100 sec give 2/3 stop (1.5x) How can my findings be so different I thought to myself? I decided to expose a sheet outside of the back stairs. I adjusted the metre's reading and placed the shadow under the 2nd step on zone III. That was 16 seconds. My data says that I should give an additional 1/3 for reciprocity. I noted that the wall fell on about zone IX and eventually made the exposure. I guess I should explain how I did my testing. I have a zone wall (inspired by Hutchings' zone board in his pyro book) in my darkroom. I made 1/4, 1, 10, and 100 second exposures of my zone wall. The aperture was only adjusted going from the 1/4 sec exposure to the 1 second exposure. For the 10 and 100 second exposures appropriate ND filters were placed in front of the lens. The 4 sheets of film were developed in pyrocat-HD, 5ml+5ml+500ml in BTZS for my normal time. The negative looks good and the shadow density under the second stair's step is zone IIIish. The zone IX density was very close too, indicating that development compensation is not necessary for this film. I only tested out to 100 seconds. Things could be different beyond that. I was under the impression that Efke 25 was an old school film requiring very hefty reciprocity compensation. Maybe it's an old school film but with new school reciprocity characteristics. It would be nice for others to pipe in with their reciprocity (gettin' tired of typing this word...) compensation data... I'll try and attach my test curves and a poorly scanned negative of the back steps of my house.