I will try with an other camera then..
I will try with an other camera then..
The Formapan 100 data sheet also seems accurate, not tried Formapan 200 much.
Forma have provided the contrast, fog and ISO dependency for time and temp for three developers.
formapan 400 datasheet
Then you need an adjustment for your developer, meter/shutter and metering technique.
Digital truth is closer to 'Analogue Porkies'
Rodinal @ 20C 1+100 stand will be in the 250-320 range with low contrast, but you may not like the rendering, I set my Weston to 250. Pour in the Rodinal invert a few times and set the kitchen timer for 60 minutes. Id also temper the following solutions to 1C, cause the Forma is not as prehardened as Kodak or Ilford film.
Most of my shooting is high contrast.
The actual ISO speed (formerly ASA) is a property of the film only. If you go to the actual ISO specification document, the number is based on exposure at the "toe" of a negative film, where it first starts to show density above the base level. The development details will affect strongly the slope of the curve above the toe, and therefore the exposure required to reach the standard 18% density grey level. Still the best description of how to rate film speed for specific applications can be found in Ansel Adams works on the Zone System.
With that film, anything is possible. I was shooting Arista EDU 100 at the box speed and getting terrible results. Found out later that the film is actually Fomapan, and that I needed to shoot it at ISO 50. When I did that it looked much, much better. Tri-X is another film that seems to not be rated correctly by the maker, as pretty much everyone will tell you that it is really a 200-250 ISO film, and my tests say just that. Of course, it being Tri-X, you can shoot it all over the place and get great results.
The maker of the film gives you what they consider to be the correct ISO, but what developer you use, how you meter the shots, how you print the negs, etc will determine YOUR optimal ISO. There really is no other way to do it except to shoot a test roll. What I consider to be the optimal ISO is not what someone else agrees with, nor should it be.
I shot a roll of Tri-X yesterday w/ my FT QL using a yellow filter, and metered it w/ a hand held meter at ISO 125. Then developed it normally. The shots came out perfect. On my NiKon N8008s and using the same yellow filter, I set the camera's TTL meter to ISO 320. These values came about by shooting test rolls and noting the results, and they differ from one camera to another. A dull, cloudy day will also require something different from a bright sunny day. Sometimes I shoot Tri-X at ISO 50 w/ a yellow filter because I personally like that sort of look sometimes. So it just depends on what you want on the finished end. Everything is done to suit my eyes, not anyone else.
The ISO speed point is determined based on a set of criteria when the film is exposed and developed under a specific set of conditions. The ISO speed point is for a fixed density of 0.1 above B+F such that the density increases by 0.8 at an exposure 1.3 log H higher than the speed point. This is what is commonly referred to as the "ISO triangle". Therefore development and a gradient are part of the standard. The Zone System is a related but different methodology, not necessarily a "better" one.
Well, too many angels on the point of this pin. Just shoot a test roll or two under controlled conditions using different ISO settings, take careful notes, develop consistently, and you're there.
Shoot at box speed and develop to your own requirements.
In comparison to manufacture's specs are you using minus development, stand...?
Are you "zoning"? If so details?
Spot meter or incident?
Are you using old Petzvals or newish multicoated lenses?
Is part of that rating a safety factor?
My intent here is not to put you on the spot c6h6o3, but to help marciofs understand how you made your choice and at least some of considerations that go into the decision.