Push processing confusion

[tim_shortt]

Recently I was in a low-light situation (flash not permitted), where

I needed to hand-hold. I had Tri-X 400. What is the difference

between the following two scenarios for negative film:

 

1. rating a 400 speed film at 800 at the time of exposure, and then

pushing it during development (typical 1 stop push, if I'm not

mistaken)

 

2. rating a 400 speed film at 400 at the time of exposure,

underexposing, and then push processing.

 

So would the difference between rating the film higher at time of

exposure versus mistakenly rating it at it's ISO make a difference in

the outcome? Also, is the nomenclature N+1, N+2, etc. (I think used

exclusively for B+W film) synonymous with the terms "push 1

stop", "push 2 stops"?

 

I know N+1, etc. refers to development times (longer affecting

highlights more, shorter time bringing contrast down by mostly

affecting highlights as well). But is this just a different way of

saying pushing and pulling for B+W?

 

Thanks,

Tim

[crackers_.]

No N plussses - it's too early and it's water in the aquarium. In the first case you're right. Look at it logically - you had a film that needed a threshold of light and you cheated it by one stop by doubling the exposure index; a one stop push.

 

In the second case the 400 film was cheated by one stop's exposure (I'm assuming only one) again so it too is a one stop push.

 

The first push was accomplished by setting the meter a stop high, the second by setting the shutter a stop high.

[crackers_.]

OIL. Oil in the aquarium - see.

[ellis_vener_photography]

Telling your meter that a film is twice as fast (1 stop faster) than it's known normal rating, exposing according to theresulting reading and then extending the development (pushing) is the same as telling your meter that the film is it's known normal rating, under exposing by one stop and then extending the development by the same amount of time in the first scenario.<P>Yes, you are correct: "N+1" is another, maybe more accurate way of saying "push the film 1 stop". I say more accurate because it refers directly to the development process as opposed to the metering process.

[m0002a]

Lots of confusion here.</p>

 

1. This will yield negatives that are underexposed 1 stop in the shadow areas. Adding additional development time (N+1) increases negative contrast. In a very low contrast scene, the underexposure of the shadow areas will not be a problem if there are no deep shadows.<br>

2. This will yield properly exposed negatives (not underexposed as you mentioned). Push processing (added more development) will increase negative contrast.</p>

 

The decision as to which of the above scenarios you should use depends on the contrast range of the scene. If the lighting of scene is very low in contrast (not much difference between the darkest area and lightest area of the scene as measured by a suitable meter) then option 1 would work OK since there are no deep shadows that will be underexposed.</p>

 

If the scene is fairly high in contrast (like a bright sunny day), then option 1 will generally yield underexposed shadows. Option 2 will yield properly exposed shadows, but overdeveloped (blocked, or too dense) highlights, which is the same as saying the negative contrast is too high.</p>

 

If the scene has normal contrast, then use normal development and film speed rating.</p>

 

The terms N+1, N+2, actually relate specifically to the Zone System and are used to increase negative contrast a specific amount as observed on the printing paper. An increase in film speed is <b>a consequence of</b>, and <b>not the purpose of</b> using N+1, or N+2. The purpose is to compensate for the contrast of scene by adding contrast to the negative during development. The N+1 (normal plus 1) specifically refers to making a Zone VIII value print as Zone IX value due to increasing the contrast with more development. N+2 makes a Zone VII value print as a Zone IX value, etc.</p>

 

Pushing is a vastly overused and widely misunderstood technique by beginning photographers. It�s better to just think of using more development to increase contrast and less development to decrease contrast. Which to use depends on the scene you are photographing. The above explanation is a bit simplified and some more reading on the subject will help you.

[ed farmer - mount laurel,]

Mark did a very good job of explaining N+ and N- development. However, he missed the point in your question 2. Of course, underexposure will result in underexposure. In general, both methods will result in the same amount of underexposure. However, the exposures are likely to be much more even if you reset your meter. Since you are processing the entire roll the same way, even underexposure will make for easier printing and a more consistent look.

[ed_pierce2]

I think the terms pushing and pulling are confusing...I know it confuses me. Determine the actual film speed and forget about that. If you underexpose, you can increase development...but it's not the same as 'proper' exposure. The contrast will be higher. This is because increasing development has more effect on the high values than the low values...thus higher contrast. I've read that some developers will produce a true increase in speed.

 

That said, N+1 essentially means underexposing by one stop on purpose and increasing development to bring the high values back up to where they would be if you'd gone with N.

[richard_cochran]

<cite>1. rating a 400 speed film at 800 at the time of exposure, and then pushing it during development (typical 1 stop push, if I'm not mistaken)

</cite>

<p>

Assuming it was a sunny day outdoors, this would be an

exposure of 1/1000 at f16.

<p>

<cite>

2. rating a 400 speed film at 400 at the time of exposure, underexposing, and then push processing.

</cite>

<p>

Assuming the same sunny day outdoors, this would <em>also</em> be

an exposure of 1/1000 at f16.

<p>

The film can't know or care how your meter was set. It

can only be affected by light levels, shutter speeds, and apertures.

At the same light level, same shutter speed, and same

aperture, you'll get the same results.

<p>

Setting the meter to 1 stop higher film speed is exactly

the equivalent of underexposing one stop.

[art_haykin]

In the simplest of terms: Pushing or pulling is done in the lab, and NOT in the camera. What is "pushing?" It is accomplished by overdeveloping the film (extended processing times). WHY push a film? To extend or increase its speed (ISO rating) for whatever reason, good or bad. OR, one can use a high energy developer like Acufine or Diafine (and others) which are designed for pushing. Some times pushing is employed when an error is made, such as forgetting to set the meter correctly.What is pulling? It is underdevloping the film by decreasing the processing time. Why is it done? To reduce contrast, or, again, in case of error. If I rate a 400 film at 800 by putting 800 on the meter dial, and then push that roll one stop in the lab, will I end up normal looking negs? Yes and no, depending on who you talk to. Extending the processing time in regular developers tends to increase the contrast more than anything else, but many would argue that point. No amount of "pushing" will create density (image on the neg) where none exists. Why do some rate a 400 film at a LOWER ISO when shooting, then have the film processed normally. This is to increase the overall exposure, which many find more satisfactory with negative films. The reverse is often true of positive (slide) films, where a BIT of underexposure is oftendesireable, for whatever reason. You will be hard pressed to ever find total agreement on all these matters of pushing, pulling, or rating films at different ISOs than the "normal" ones, so each shooter must arrive at his or her own standards and practices through testing. If none of this makes sense to you, you'd best hit the books.