Pushing Film

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Good afternoon everyone,

I read past posts relative to pushing films. In particular, someone wrote:"for Delta 3200, expose at 1600 and push one stop". What does it mean excatly? Why do you do so? what do you tell the lab? Also, for the Velvia, some of you suggested to rate it at 40. Do you tell the lab that you have rated the film at 40? Is it different a if you want to underexpose your slide films (like some have suggested for color slides)?

Many thanks,

Arie

-- Arie Haziza (nhaziza@northrock.bm), May 05, 2002

Answers

Perhaps it would be good if you pick up a book on basic photography. Henry Horenstein's "Black and White Photography, A Basic Manual," though dated, remains a very good introduction to black and white photography. You can get it used for $6 from Amazon.com.

-- Charles (c.mason@uaf.edu), May 05, 2002.

I don't think it is enough to refer this question to basic photography sources. The problem is often that statements of how to expose film are inprecisely formed.

In the example of the Delta 3200, did the person mean that the film should be exposed at 1600 but processed as if it were exposed at 3200, thus in a push of one stop with respect to the processed speed? I think so.

I remember being a bit puzzled by the statement about rating Velvia at 40. I think that means that the film should, in the author's opinion, be exposed at 40 but processed at 50 (normal, not pushed).

I think Arie's question challenges us all to be as precise as possible.

-- Tom (therbert@miami.edu), May 05, 2002.


Actually, the first case as I stated it would result in a PULL of 1 stop.

-- tom (therbert@miami.edu), May 05, 2002.

When I was shooting slides for publication in magazines, I always rated Velvia at least 1/3 stop lower because slides that turned out even a bit too dark printed poorly. After shooting many rolls of it, I am not convinced that Velvia is a 50 ISO film--more like a 32 or 40.

When you push film, they leave it in the developer longer than the standerd developing time.

-- Andrew Schank (aschank@flash.net), May 05, 2002.


There are three terms commonly used in this connection, Arie, "rating", "pushing" and "pulling". Their use varies a bit between photographers, and the meaning isn't always clear when mentioned in text. In general, however, one can "rate" a film at something other than its stated ISO spec, such as rating (or, exposing) Tri-X at 320 rather than 400. Absent other comments, it would be assumed that the film so rated or exposed would be developed "normally".

Rating a film at something other than its stated ISO is based on the experience and/or processing tecniques of the individual photographer. In doing so, it should be understood that the ISO rating is derived based on specific lab test standards which often don't relate directly to actual image creation in the field.

Pushing and pulling are usually used to refer to the degree of development. Pushing one stop, for example, would mean developing the film longer to compensate for a higher-than-normal rating or exposure. Thus, if you exposed ISO 400 Tri-X at 800, you'd then want to "push" the development by one stop. The amount of additional development time to equate to a one-stop push varies by film, and is determined by extensive lab testing. Conversely, "pulling" means decreasing the development time to compensate in the other direction. The objective in both cases is to produce a negative of "normal" density.

-- Ralph Barker (rbarker@pacbell.net), May 05, 2002.



Is Delta 3200 really a 3200 speed film? Or it like TMax 3200, which is actually an 800 speed film?

-- Richard (rvle@yahoo.com), May 05, 2002.

I find Delta to work best at about 1000, under "normal" processing. But I find TMax to work best at 1200 in normal dev, so go figure.

-- drew (swordfisher@hotmail.com), May 05, 2002.

Delta 3200 is approximately 1000 to 1200 ASA. Therefore, when it is exposed at 3200 and developed at the recommended time and temperature for that speed, it is actually being pushed about a stop and a half. But it is designed for pushing, and Ilford publishes development recommendations at a wide range of speeds. (See their web page, or the data sheet with the film.) I get my best results when I expose Delta 3200 at 1600, which is just slightly more than the real speed of the film.

-- Jack Matlock (jfmatlo@attglobal.net), May 05, 2002.

Howdy Doody! You can`t talk about `your`speed for an emulsion if you you don`t specify if your exposure meter is``corect`` (ever heard of the Wallace disc?) and linear. It doesn`t mean a thing to me if you state that you expose a 3200 emulsion 1600 or 6400 ISO.

-- Hans Berkhout (berkhout@cadvision.com), May 05, 2002.

Ok, so if a film is "rated" at 3200, but you say here it is really a 1200 speed film; why don't the manufacturers just say it is a 1200 speed film? So, if I were to use 3200 speed film, should I set my meter at 1200 speed? Wouldn't this make everything under exposed? Thanks Phillip

-- Phillip Silitschanu (speedin_saab@hotmail.com), May 05, 2002.


I think a lot of this also depends on the developers used (for the b&w). Please state what developers you guys/girls are using. Just saying that you pushed this film or pulled that film, or that this film is really iso such and such, is meaningless, without the processing information. Unless you're really using a high end custom lab, you're going to get b&w processing that basically sucks, and that's why you get these idiot numbers that are all over the place. Slide film, I can see, because it's going into some E6 soup, and that is that. Actually there are some really experienced darkroom users on rec.photo.darkroom that know what they're talking about.

-- Glenn Travis (leicaddict@hotmail.com), May 05, 2002.

Thank yoy for the answers but I am still confused.

-- Arie Haziza (nhaziza@northrock.bm), May 06, 2002.

Thank you for the answers but I am still confused.

OK, let me try again.

In theory, the ISO rating for a film rates the film's sensitivity to light, and should result in an exposure that will produce a negative of normal density and normal contrast when developed for the "normal" time in any given developer. (Normal development times vary for each developer, but each has a specified "normal" time determined by testing.) The ISO standard, however, describes a scientific lab process that doesn't match real-world photo-taking circumstances. As a result, the ISO rating for a film is often different than what will produce negatives of normal density and contrast in normal shooting situations. Thus, many people adjust the ISO rating to something that actually works for them in practical situations. Most often, the sensitivity of the film is somewhat less than the stated ISO rating. For example, many people find ISO 400 Tri-X to have a sensitivity that equates to ISO 320 under normal picture-taking situations. Thus, they "rate" the film at ISO 320, develop it "normally" (make no adjustment to suggested development times for a given developer), and achieve "normal" negatives.

When thinking about this, remember the generally-accepted basic concept: exposure determines density and development determines contrast. You can adjust them in concert to achieve "normal" density, but with a corresponding effect on contrast.

So, if you under-expose the film by one f-stop, you can over-develop by one f-stop to compensate, resulting in a negative of "normal" density, but higher contrast. This equates to "pushing" the film by one f-stop. Continuing with the Tri-X example, if the film has a real sensitivity of ISO 320, set your meter to 640 (resulting in a one-stop underexposure), and extend, or "push" the development (develop longer) to compensate. The result is a printable negative having greater-than-normal contrast.

Or, you can over-expose by one f-stop, and under-develop by one f-stop, resulting again in a neg of normal density, but with less contrast. This would equate to "pulling" the film, as the ISO 320 film in this example would be exposed at ISO 160 (over-exposed by one stop), and the development reduced ("pulled") to compensate.

Pushing is more common than pulling, as people are often faced with low-light situations where they want a higher-speed (more sensitive) film, but are forced to use what they have in the camera. In making that decision, they are also forced to accept negatives of higher-than-normal contrast as a result of the compensating over-development. Over-development also increases grain, and that also should be considered when making the "push" decision.

Thus, think of "rating" as setting your meter to something other than the ISO rating claimed by the film manufacturer, but developing for the normal time (or, telling your lab to do so). And, think of pushing and pulling as affecting the development time to compensate for the different-than-normal exposure. So, if you "push" the film by one stop, tell the lab to "push" the development by one stop.

-- Ralph Barker (rbarker@pacbell.net), May 06, 2002.


There's more. Did you meter the shadows or the hilights? How accurate is your meter. How good is your thermometer if you developed your own film? How consistent is your developing process. What is the acid alkaline balance of your water? Which developer and how well mixed or consistent is it? With color was the range of the scene beyond the range of the film? Did you want shadow detail or hilights? What kind of light color temperature, warm tungsten or noon daylight? And on and on. There is an axis where consistency and creativity cross to produce excellent or not so good images. Ben Hogan said 'the more I practice the luckier I get'. Good luck.

-- Gil Pruitt (wgpinc@yahoo.com), May 06, 2002.

Thank you very much Ralph, I appreciate your consideration, I start to understand. That is where this group is very good at, it changes from those wars of words that I witness too often sadly. On a similar note, it is my understanding now that if I want to underexpose Velvia (to add some saturation), I have to set the sensitivity to say ASA 64.

-- Arie Haziza (nhaziza@northrock.bm), May 06, 2002.


Ralph, that's the best short description of the process that I've come across. Well worth a cut-and-paste to a text file.

-- Preston Merchant (merchant@speakeasy.org), May 06, 2002.

" . . . On a similar note, it is my understanding now that if I want to underexpose Velvia (to add some saturation), I have to set the sensitivity to say ASA 64."

Yep, your understanding is correct.

-- Ralph Barker (rbarker@pacbell.net), May 07, 2002.


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