Push or pull that is the question?

greenspun.com : LUSENET : B&W Photo - Film & Processing : One Thread

Hi All, I've been reading AAs book and looking into his concept of N+x and N-x development of Ilford films. My question is Ilford specific: What is the best way to do N-1 with Ilford films. I've just read over their data sheets and it appears I could use FP4(125ASA) expose it at 400ASA and then push process it for 200ASA film, or use HP5(400ASA) shoot it as 400ASA and then process it in Perceptol (this has a note saying it will not produce as good negatives as standard developing). Any comments would be greatly appreciated.

Thanks, Anthony

-- Anthony Wyatt (anthony_wyatt@hotmail.com), December 27, 2001

Answers

What is your purpose of pushing or pulling? Contrast manipulation, or simply want the best image quality you can get?

HP5+, TMX and probably many other recent films tolerate overexposure and overprocessing much better than older films, including currently sold Plus-X. This is particularly so with HP5+ in XTOL or my D-76Ad, and TMX in Microphen or HC-110. I usually simply have to expose longer during printing without too much contrast adjustment, and I don't get noticeable increase in grain in highlight area. (PX needs contrast adjustment and I see much bigger grain in the sky, reflections, etc.)

I simply recommend to expose and process normally, and make necessary adjustments during printing process. It's a matter of finding the right combination of film, developer, and paper for the kind of images you are looking for.

I'm not against zone system, but I never felt like I need it except for a few exceedingly rare extreme cases.

-- Ryuji Suzuki (rsuzuki@rs.cncdsl.com), December 27, 2001.


Exposing film at a higher ISO rating than normal, and using the increased development times recommended for the higher ISO speed, is by definition N+ ("push") processing. Push development doesn't really increase the speed of the film as Adams measured it (approximate density of .1 over base film and fog for a Zone I exposure); it merely increases contrast of the negative. This is because increased development has little effect on the shadow areas (Zones I-III) and a much greater effect on the highlights (Zone VII and above). So I believe that you are barking up the wrong tree if you want N-1.

To achieve N-1, Adams would usually cut the normal ISO speed by 1/2 (increasing exposure by 1 stop) and cut development by about 15-20%. To exactly determine the processing required for N-1 development and exposure, here is a procedure that can be used:

First, expose an image of a gray card (Zone V) by giving the film 3 stops more than the meter reading. This will give you a Zone VIII image on your negative. (If you know that your meter is not calibrated to 18% gray, then adjust accordingly.) You should develop this roll of film normally (N). Then take another exposure (on another roll or another sheet film) of the gray card and give the film 4 stops more than the meter reading. This will be your N-1 exposure (Zone IX that you will “pull” back to Zone VIII). Develop the N-1 roll (or sheet) about 20% less than the first roll (N). For the N-1 exposure rate the film a bit lower in ISO speed (1 full stop from normal is recommended).

Print the Zone VIII image on the first roll (N film development) in your enlarger. Experiment with different print exposure times until it comes out as Zone VIII, a slightly off-white with a hint of texture (Adams’ or other books will show you what Zone VIII should look like). Note the enlarger exposure time and print development time carefully.

Then print the image from the N-1 roll (that was given 1 stop more film exposure and 20% less development than the N image) using the exact same enlarger exposure time and same print development time as the first print. Compare the 2 prints. If the second print (N-1) is lighter than the first print (N), reduce your film development time for N-1 and try again. If the N-1 print image is darker the N print, increase your film development time. When the prints match in Zone VIII values, you have “pulled” the negative highlights by one Zone (IX to VIII) and now you have your N-1 film development time.

Conducting your own tests to determine N-x processing is important because your enlarger light source (condenser, dichro, cold-light, etc.) has an impact on the final print contrast you are trying to achieve. Also, your personal film development technique (agitation, total solution amount, etc.) effects negative contrast.

-- Michael Feldman (mfeldman@qwest.net), December 27, 2001.


> I've been reading AAs book and looking into his concept of N+x and N-x development of Ilford films.

I think you're getting the concepts confused; pushing is the intentional underexposure and appropriate (over)development in order to make a printable (but high contrast) neg, which your FP4 example would result in, while your HP5 example is simply going to give normal contrast but at a lower speed because of the developer used.

N+ and N- development otoh is simply adjusting neg contrast to fit the subject brightness range so that the neg can be printed on a "normal" paper grade.

I've found that roughly a 20% development time change is a good starting point, depending on the film. Note that EI doesn't change a whole lot; N-1 needs only 1/3 to 1/2 stop more exposure and N+1 may not need any less exposure to match speedpoint density with normal development. However, you may want to give more exposure for N- to get the shadows up on the straighter part of the curve.

There's no need to get really retentive about this; such minor changes can be handled by using different-contrast papers. There are of course differences but they're subtle.

A very good book on the subject is _Beyond the Zone System_ by Phil Davis.

-- John Hicks (jbh@magicnet.net), December 27, 2001.


Thankyou all for your responses. I'm off to do more reading and lots more development :-)

Thanks again, Anthony

-- Anthony Wyatt (anthony_wyatt@hotmail.com), December 28, 2001.


Moderation questions? read the FAQ