I don't think this could be easily modelled, as there are too many variables, including things you couldn't know, like sky conditions over the horizon after sunset. Heavy clouds over the horizon could kill the light faster than expected.
Originally Posted by Loose Gravel
Also, the sun sets at different angles at different latitudes at different times of the year. So the rate at which it drops below the horizon changes, which changes the length of twilight according to season and location.
There are good working models of twilight, so you could do something with that, dependant on latitude and time of year, but I think combining that with unknown sky conditions over the horizon would be too complex and involve variables that the photographer couldn't observe in the field.
Has anyone come up with tc,1 coefficients for additional films like color print, transparency and the multitude of other films that have appeared on the market in recent years?
That one must be my first post here but, I watch the forum for some time now.
I have tried to gather as much info as i can and create a calculator for film reciprocity times...
The programme is still under dev and might be unstable but you can get the general idea...
I implemented the equation
tr = tc,1*(tm^1.62) + tm
where tc,1 coefficients are the following
KODAK TMY T-MAX 400 ........0.061
KODAK 400 TX TRI-X 400 ......0.169
KODAK TMX T-MAX 100 ........0.069
ILFORD HP5 Plus 400 ............0.101
ILFORD 100 DELTA ...............0.046
ILFORD Pan-F Plus 50 ...........0.140
ILFORD FP4 Plus 125 ............0.110
KODAK PLUS-X 125 ..............0.210
KODAK Technical Pan ...........0.140
ILFORD SFX 200 ..................0.450
ILFORD XP2 Super 400 .........0.050
KODAK T400 CN ..................0.030
KODAK TMZ T-Max P3200 .....0.310
for EFKE CHS ART I used ADOX suggestion:
1/2s -> +0 stop
1s -> +1/6 stop
10s -> +1/3 stop
100s-> +2/3 stop
the general equation I used for that case is
tr = tm + (tm * 2^log(tm)) / 6
dev language C#.Net
requires Microsoft Framework .Net 2
win xp or later
in order to upload the file I changed the extension to .pdf
after you download the file just replace the .pdf part by .rar, unzip the file, paste both contained files in one folder and run the "film_reciprocity.exe" file
if you think that it can help I might also develop it for mobile phones...
I would appreciate any feedback
If you have any additional equations for more films I will be glad to add them
Last edited by celetron; 11-19-2009 at 11:05 AM. Click to view previous post history.
Whose reciprocity data did you use for each of the Kodak and Ilford films?
Actually I used the data you uploaded at GainerMethod.pdf.
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Thanks for the reply. The data from Reeves referenced in that post has been taken off the web, and that link in my post is dead. Reeves is no longer using film, and the test data from his page is about 10+ years old. The post of mine that you drew from is now almost 5 years old. So some of the films are likely to have changed a bit. TMY has been reformulated, although the few who have mentioned it say reciprocity is similar to the older version.
Quite possibly, but for the moment that is all the data I have. I guess I could run my own tests but it'll take ages... Maybe I should develop another version with the ability the users to add their own films and coefficients.
Originally Posted by Lee L
I'm not implying that there's better data around now, only that people who read this need to confirm or adjust through personal testing. If there is better data, I haven't seen it. And I'm disappointed that Reeves took down his color and B&W film information.
Originally Posted by celetron
Bond's methods were exhaustive. Reeves uses a rather short and simple test that I use. It's outlined in his and Michael Covington's books on film Astrophotography. (Be aware that the Covington book 2nd ed. has a typo that I found last year in one equation used to calculate reciprocity, so check his website for the errata page.) This method uses a 1/8 second exposure, then 128 second exposures under the same conditions but with a 10 stop neutral density filter and some bracketing. The amount of bracketing in stops that produces the same density at 128 seconds (with filter) as the 1/8 second exposure (without filter) is used to calculate a Schwarzschild exponent. This is a check at a single data point, but it's very good at giving a useful indication of the relative degree of reciprocity failure in a film. You could also use other ND filters of different values to get more data points, but 128 seconds is a good start.
This testing takes only one reference frame and then however many bracketing shots you feel you need, at whatever step rate in stops would be useful to you. Four frames and reasonably careful work will give you a very good start.
Just an observation: I have the original Howard Bond article, "Black-and-White Reciprocity Departure Revisited," and in it, Bond states clearly that Kodak provided him with sheet film. Since 400TX does not come in sheets, he must have tested the 320TX, not the 400-speed-roll-film version that seems to be mentioned everywhere in the thread. Unfortunately, the usually careful Bond only identifies the film he tested as "Tri-X," with no other details. Since it was sheet film he was testing, however, we must assume that it was the 320 version and, therefore, revise all the earlier references to "400TX" in this thread to read "320TX."
Nevertheless, this is a fine thread with much useful information.