Reciprocity qustion efke25 and hp4+

[tormod]

Hi!

New to pinhole, and therefor I don't event know where to start..

I manly use 3 types of films, efke 25, hp4/5+
To day I'm thinking of taking my new camera out for a walk, and did a search on internet to find out if there was any important thing I need to know.
I have read about the reciprocity factor before, but never really used it because I'm not used to so long exposures.

On the hp4+ and the hp5+ I have found the date cheat, but stupid as I am I cant figure out what to do when I passes the timelimet on the datasheat.
On the efke film I have found nothing..

Could any of you help me with some information?

tormod

[Lobalobo]

As it turns out I have the same question. I'm looking for a Reciprocity Failure Chart for Adox 25 for use in an f/154, 4x5 pinhole camera.

[noseoil]

Last I heard, Efke 25 had pretty good reciprocity characteristics. This is what I was told, but haven't worked out the numbers for myself. Most of my shots fall under 10 seconds. Use this for a start and see what happens. good luck, tim

1 - 10 seconds use +1/3 stop
10 - 100 seconds use +2/3 stop
100 - 1000 seconds use + 1 stop

[Greg_E]

Check out Pinhole Designer, it has some reciprocity values for some films. In the exposure tab enter you f number, and chose your film. Then you can print out a chart of times compared to what a meter will read at f22.

[JBrunner]

There is some information on Efke(Adox) 25 here:

http://www.jandcphoto.com/index.asp?...on=Custom&ID=1

A rough reciprocity guide is at the bottom of the page.

Developing times should be normal, as you are compensating the exposure, not the developing (although you could, to some degree, with penalties), for the reciprocity failure.

True reciprocity numbers for a given exposure/stock/developer can only be arrived at by testing.

[Lobalobo]

Thanks for the information.

[Lobalobo]

Also, thanks for recommending too the Pinhole Designer, which I tried, but which does not have Efke or Adox.

[tchamber]

Since the Ilford film is sixteen times faster than the Efke/Adox film, reciprocity will be less of an issue. Your exposures will be quite short in good light, perhaps only a second or so. With the Efke you can be looking at *very* long exposures.

[Guillaume Zuili]

Why don't you try on a roll with few exposures and see what's good for your dev time ?

[Lee L]

Since you're talking about pinholes, you'll need to adjust times rather than aperture.

Given the Efke data sheets and tests in books on astrophotography, your films have the following Schwarzschild factors:

Efke 25 0.79
FP4+ 0.79
HP5+ 0.83

So HP5+ has less reciprocity failure and the others "fail" at the same rate.

Use the following formula to calculate a corrected time from the metered time.

corrected time in seconds = (metered time in seconds + 1)^(1/p)-1

where p is the Schwarzschild factor for the given film.

You could plug the formula, Schwarzschild factors, and a range of times into a spreadsheet and generate a custom table or chart to carry along.

Here's a good thread with lots of different takes and several options on ways to calculate exposures for reciprocity failure:
http://www.apug.org/forums/forum37/11566-reciprocity-misbehavior.html

BTW, it's not true that slow films will fail more rapidly than fast films. Ektar 25 was considered an excellent astrophotography film in part because it had very little reciprocity failure. Slower films with little reciprocity failure very quickly become effectively faster than fast films with mediocre reciprocity characteristics. If you want a B&W film with the least reciprocity failure, go with Fuji Acros.

Lee