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Perry Way
06-11-2010, 10:13 PM
This information I'm asking for is not on the Adox website nor is it found on any datasheet in the packaging.

Does anyone know what the reciprocity figures are for Adox CHS Art 25? Or even 50 or 100 would help because I'm sure there are similar characteristics between the various emulsions.

I just bought a 50 sheet box of 4x5 and it arrived today early. Now I want to shoot it, this is my first pack of Adox on 4x5. I intended on shooting tomorrow some pinhole stuff. I want to shoot this but I would like to be armed with some figures so I know how to meter my exposures for optimal effect. With the CHS series and particularly with 25 iso, I do not want to overexpose. Some films have a huge reciprocity (like Ilford, all of their films) and some have medium reciprocity (like most Kodak) and some have almost none at all (Kodak Ektachrome, Fuji Astia/Provia/Velvia).

I am thinking because the CHS series is not hardened and Ilford is like superhardened by comparison (development times are very extended for Ilford as compared to Kodak) that CHS has less reciprocity than any of the other films that appear in Pinhole Designer program.

Experience really counts the most. Anyone have experience on this? I want to make my trip tomorrow count because gas prices are back up again here on the Central Coast (California) and certainly don't want to overexpose.

Perry Way
06-11-2010, 10:42 PM
I just found this link: Adox reciprocity post on flickr (http://www.flickr.com/groups/efke25/discuss/72157603954208428/) and the gentleman provides this excerpt from the main dealer in Germany:

"Dear Mr David,

we're happy that you like Adox film. I don't have a proper chart here, but they exhibit very little reciprocity failure. The rule of thumb is as follows (measured time and the factor of correction):

1/2 Sek. no correction

1 Sek. plus 1/6

10 Sek. plus 1/3

100 Sek plus 2/3

Kind regards,
Benjamin Greiner"


How does this information measure up with anyone's experience?

rrankin
06-11-2010, 10:45 PM
Is that the same thing as the old Efke 25? If so, check

this
(http://photo.net/black-and-white-photo-film-processing-forum/008bb4)

Cheers, Richard

Perry Way
06-11-2010, 11:29 PM
Is that the same thing as the old Efke 25? If so, check

this
(http://photo.net/black-and-white-photo-film-processing-forum/008bb4)

Cheers, Richard

Just read that whole thread Richard. It is interesting how those figures are exactly the same as the ones posted by that other guy on Flickr.

Lee L
06-12-2010, 12:08 AM
If the adjustments given are accurate for this film, a bit of curve fitting (I use SciDAVis, which is free and open source) shows that the the following formula should work well.

adjusted time = 0.134353883987194*metered time^1.34968890243641+metered time

(trim to your desired level of pointless 'precision')

I usually make up a small spreadsheet to create a table showing standard meter exposure time readouts and the corresponding corrected exposure times using a formula of this form. I print out and carry the table in my camera bag and use it to determine exposure times corrected for reciprocity. A number of shots made at various corrected exposure times will quickly tell you if the corrections are suitable.

If you prefer to use a Schwarzschild or modified Schwarzschild formula, the approximate Schwarzschild exponent for the adjustments given is 0.90.

Lee

Perry Way
06-12-2010, 12:19 AM
This information is available but in German only:

http://www.adox.de/ADOX_Filme/ADOX_CHS_Filme/ADOX_CHS_25%20/ADOX_CHS_25.html

I think from what I can tell it appears this chart above is the same data Adox is posting, but again in German. I am wondering why this isn't in English....

Perry Way
06-12-2010, 12:21 AM
I usually make up a small spreadsheet to create a table showing standard meter exposure time readouts and the corresponding corrected exposure times using a formula of this form. I print out and carry the table in my camera bag and use it to determine exposure times corrected for reciprocity. A number of shots made at various corrected exposure times will quickly tell you if the corrections are suitable.

If you prefer to use a Schwarzschild or modified Schwarzschild formula, the approximate Schwarzschild exponent for the adjustments given is 0.90.

Lee

yeah Lee.. I got your chart you made on the CHS Art 100 off this post: http://www.apug.org/forums/forum37/67062-adox-chs-art-100-reciprocity-times.html#post874261

I believe the curves will be the same for iso 25 as it is for 100. What do you think?

Lee L
06-12-2010, 12:28 AM
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.
---------------------------------------------------------------
Loosely, but in essence correct:

Starting at one second, you should prolong exposure according to the following table.

1/2 second no exposure increase necessary
1 second open 1/6 f-stop or multiply time by a factor of 1.2
10 seconds open 1/3 f-stop or multiply time by a factor of 1.3
100 seconds open 2/3 f-stop or multiply time by a factor of 1.5

These values should be a starting point for further testing.
----end 'translation'-------

Lee

Lee L
06-12-2010, 12:35 AM
I believe the curves will be the same for iso 25 as it is for 100. What do you think?
A good place to start testing, but I haven't yet done so myself with these films. If you can find the right conditions, or can create them with ND filters and f-stop changes, you should be able to know if you're close in very short order. Just make a base exposure at a level that reciprocity doesn't come into play, then (with the same subject if possible) make exposures at a few longer times and then compare resulting negative densities.

You've probably also seen Gainer's method with a fixed exponent of 1.62, which should also serve just as well as mine, but has the option/advantage of making a sort of 'slide rule' chart for field use.

Lee