Adox CHS Art 100 reciprocity times

[Jarvman]

Can anybody point me to the reciprocity times for this film or should I just wing it using the times for FP4?

 

[AlanC]

I have found that reciprocity failure definitely kicks in suddenly with this film. If I calculate that I need an exposure of 1 second, I give it 2 seconds or I know I will underexpose. But if a half second exposure is needed, giving it 1 second will overexpose it.

Alan Clark

 

[Lee L]

It's quite absurd that even in 2009 some manufacturers don't publish data sheets!!

Here's the unpublished data sheet, hidden on the Ilford web site on the FP4+ page link to the fact sheet:
http://www.ilfordphoto.com/download.asp?n=474&f=2006216115141521.pdf

The problem isn't that they don't publish tech info, it's that by all accounts from users who test it, the reciprocity information is outdated by a third of a century or more.

Lee

 

[Markus Röhling]

According to http://www.adox.de/ADOX_Filme/ADOX_CHS_Filme/ADOX_CHS_100/ADOX_CHS_100.html the CHS has a very low reciprocity failure:

Das Reziprozitätsverhalten des efke ist so hervorragend dass es bei Belichtungszeiten unter einer Sekunde vollständig vernachlässigt werden kann !
Ab einer Sekunde sollte nach der folgenden Tabelle verlängert werden.

1/2 Sek. keine Verlängerung notwendig

1 Sek. plus 1/6 Blende (1,2x)

10 Sek. plus 1/3 Blende oder Zeil mal (1.3x)

100 Sek plus 2/3 Blende oder Zeit mal (1.5x)

Diese Werte sind Startwerte für den ersten Versuch.
Je nach Aufnahmebedingungen können auch höhere Werte nötig sein !
Diese Werte wurden unter “optimalen” Bedingungen ermittelt und sind verglichen mit anderen Filmen extrem niedrig (fast kein Schwarzschildverhalten messbar). Dennoch kann es notwendig sein von diesen Werten abweichende Belichtungszeiten anzuwenden.
Nach unseren Tests ist keine Veränderung der Entwicklung notwendig !

Markus

 

[Lee L]

Thanks for the link Markus. I'll throw in a table based on the information you linked to. I usually look at reciprocity data in two ways, the traditional Schwarzschild exponent used in Michael Covington's revised formula, and with another formula that seems to fit very well with a wide range of data from people doing careful reciprocity measurements.

For this note and the attached chart, the variable x will be the time in seconds as metered, and the variable y will be the adjusted exposure time in seconds, which allows for the compounding effects of reciprocity failure when adjusting time rather than aperture.

The Schwarzschild exponent from the Adox supplied data would be 0.90, used as the variable 'p' in the formula y=((x+1)^(1/p))-1

The exponential equation I've found very useful is y=a*x^b+x Running a regression on the information found in Markus' link gives values of
a = 0.18028451729247
b = 1.2215054850993
for Adox CHS100.

The attached chart uses these equations to calculate new exposure times in seconds in the second and third columns based on the metered exposure time in seconds in the first column. The fourth column is the difference in the adjusted exposure times in stops, just as information on how the two methods diverge, which is only by 0.23 stops when adjusting from an initial exposure of 960 seconds.

You can plug these formulae into your own spreadsheet and format it as you like.

There will be batch-to-batch variations in reciprocity characteristics, and your particular usage will probably vary from these calculations, but they are a good starting point for finding your own results.

Lee