In dig­i­tal pho­tog­ra­phy, chang­ing the ISO val­ue is a mat­ter of a few sec­onds, but what about ana­log? Each film is nom­i­nal­ly pro­duced with a spe­cif­ic ISO, less often with a small range (for exam­ple, 200–400). What if you need to set a dif­fer­ent sen­si­tiv­i­ty when shoot­ing? There are push/pull process­es for this. You can get the result from anoth­er val­ue!

Pho­to: www.richardphotolab.com

What are push/pull processes?

ISO — expressed in num­bers, the val­ue of the film’s light sen­si­tiv­i­ty, its sus­cep­ti­bil­i­ty to light. The high­er the val­ue, the high­er the sen­si­tiv­i­ty. How­ev­er, light con­di­tions do not always cor­re­spond to the declared val­ue on the coil. For exam­ple, film is rat­ed ISO 800, but you’re shoot­ing in strong light­ing con­di­tions, in bright, back­lit sun­light. ISO 100 would be fine for this type of shoot­ing. You can under­ex­pose film in high light con­di­tions, but get the desired ISO of 800 in devel­op­ment by doing a push/pull process.

By set­ting the ISO val­ue in the cam­era set­tings, you also affect the shoot­ing set­tings: a large ISO val­ue can be com­pen­sat­ed with a short shut­ter speed, a small ISO val­ue with a long shut­ter speed.

Image: blog.dehancer.com

Push process — this is an inten­tion­al under­ex­po­sure of films with its sub­se­quent re-devel­op­ment. In sim­ple words: in your hands you have a coil with a nom­i­nal val­ue of iso 400, and you have to shoot in poor light­ing con­di­tions. You can com­pen­sate for this with long expo­sures, but this is not always con­ve­nient. In this case, you can set the set­tings to the desired ISO 800: this will pre­vent long expo­sures, tell the cam­era that the light­ing con­di­tions are per­fect, and the shots will not receive the prop­er amount of light in such con­di­tions and remain under­ex­posed and dark. This is exact­ly what the sub­se­quent push process com­pen­sates for with a slight­ly longer film devel­op­ment. The frames in the final will not be so dark, and the infor­ma­tion in the shad­ows will be pre­served.

Pull process — this is over­ex­po­sure of the film with sub­se­quent under­ex­po­sure. This process is reversed: let’s say you took ISO 200 film, but the day is sun­ny enough that you can set ISO 100. In this case, you over­ex­pose the frames by let­ting in a lit­tle more light, shoot­ing them at 100, and low­er­ing the expo­sure by one stop in the devel­op­er . By devel­op­ing at the orig­i­nal ISO 200, you can over­ex­pose the film, result­ing in light rec­tan­gles instead of pho­tographs.

Why are these processes needed at all?

A log­i­cal ques­tion, giv­en the abil­i­ty to choose the nec­es­sary film based on the con­di­tions of future shoot­ing. How­ev­er, these process­es can have both a tech­ni­cal side and a cre­ative one.

PUSH film development process

Key fea­tures: con­trast increas­es, grain increas­es, col­or sat­u­ra­tion increas­es, col­or dis­tor­tion may occur.

Image: blog.dehancer.com

Do not for­get that chang­ing the ISO val­ue based on shoot­ing con­di­tions is easy only on dig­i­tal cam­eras. In the case of film, some­times you have to adapt to these con­di­tions based on what is already there. Push-process allows you to com­pen­sate for short expo­sures in low light.

Sec­ond­ly, the push process some­times allows you to get a more inter­est­ing result in the pic­tures. With its help, the con­trast of the image is enhanced, a pleas­ant grain­i­ness is added, and on col­or films it is pos­si­ble to enhance some of the shades in the frame.

PULL film development

Key fea­tures: the con­trast is reduced, the elab­o­ra­tion of details is improved, the col­or repro­duc­tion is more sub­dued.

Image: thefindlab.com

The pull process helps to return the nec­es­sary detail. Only in this case when shoot­ing with a lot of light, which threat­ens to over­ex­pose. Pull will pull out details in the high­lights and reduce the con­trast of the pic­ture. Sec­ond­ly, the pull will make the pic­ture soft­er, reduce the con­trast and make the col­ors less bright, lead­ing to pas­tel shades. A kind of styl­is­tic device too.

Table of the pos­si­bil­i­ty of using the push / pull process, tak­ing into account the film rat­ings. source: lighthousefilmlab.com

What is important to consider?

• The­o­ret­i­cal­ly, these process­es are pos­si­ble on any cam­era, how­ev­er, tech­ni­cal­ly, not on each. When apply­ing the over/under expo­sure tech­nique fol­lowed by a push/pull process, your cam­era should be able to man­u­al­ly con­trol the ISO val­ue set­ting. Almost every coil has a DX code, which is auto­mat­i­cal­ly read by the cam­era and based on which the cam­era sets the val­ue. On many cam­eras, this para­me­ter can­not be adjust­ed, while oth­er cam­eras have the abil­i­ty to enter the ISO para­me­ter man­u­al­ly.

• Films are dif­fer­ent. Push / pull process is not suit­able for every one of them. First of all, this applies to col­or films, where the col­or can be great­ly dis­tort­ed dur­ing such devel­op­ment.

• Pre­dictable results are pos­si­ble with over­ex­po­sure and under­ex­po­sure with­in two val­ues. No longer rec­om­mend­ed. In the table above, you can com­pare the val­ues ​​and capa­bil­i­ties giv­en, tak­ing into account the res­o­lu­tion of a par­tic­u­lar film.

Pho­to: thedarkroom.com

• Best results are obtained on black and white films. They have a greater dynam­ic range and are more amenable to under or over expo­sure. In addi­tion, films of the pro­fes­sion­al seg­ment are more tol­er­ant of push/pull process­es, since they ini­tial­ly have a high­er qual­i­ty of the mate­r­i­al to which this cor­rec­tion will be applied. Rec­om­men­da­tions include Ilford HP5, Ilford PAN 3200, Kodak Tri‑X, and Kodak col­or Por­tra series.

• Be sure to indi­cate when hand­ing over to the devel­op­er how many steps you need to make this or that process. This is impor­tant for the preser­va­tion of your frames and their com­pe­tent devel­op­ment. If it is dif­fi­cult for you to count, then just tell the employ­ee what ISO val­ue you shot at. Based on the nom­i­nal, this will help you choose the right devel­op­er and cal­cu­late the cor­rect time to devel­op your film.