Editing 126 film (section)

== Technical details ==
[[Image:126 holburn.jpg|thumb|upright=1.5|left| A photo of the [[Holburne Museum of Art]], [[Bath, Somerset|Bath]], taken with 126 film and illustrating the square format.]]

In 1963, [[Kodak]] introduced a new film, encased in a plastic cartridge, for which they re-introduced the "126" designation. (The number was originally used for the unrelated [[126 film (roll format)|126 roll film]] format from 1906 to 1949). The term "126" was intended to show that 26&nbsp;mm square images were recorded, using Kodak's common 1xx film numbering system.  However the image size is actually 28×28&nbsp;mm,<ref name=PM-1963>{{Cite magazine |url=https://books.google.com/books?id=CeMDAAAAMBAJ&pg=PA208 |title=Comparing the new quick loaders |author=Brown, Kevin |pages=112–115;208;212 |magazine=Popular Mechanics|publisher=Hearst Magazines|date=October 1963}}</ref><ref>{{Cite web|url=http://kodak.3106.net/index.php?p=207&cam=1188|title=Kodak Instamatic 314|website=kodak.3106.net|access-date=2019-12-06}}</ref> which usually was reduced to approximately 26.5×26.5&nbsp;mm by masking during printing or mounting. At the nominal 28&nbsp;mm square size, the image diagonal is {{#expr:28*2^0.5 round 1}}&nbsp;mm, which is close to the {{#expr:(24^2+36^2)^0.5 round 1}}&nbsp;mm diagonal of a 135 film frame (24×36&nbsp;mm); the [[crop factor]] or [[equivalent focal length]] multiplier is {{#expr:1/((28*2^0.5)/((24^2+36^2)^0.5)) round 2}} based on the diagonal measurements.

The 126 film cartridge and format were defined in [[ISO standard#International standards and other publications|ISO]] 3029, which has since been withdrawn.<ref>{{cite web |url=https://www.iso.org/standard/8115.html |title=ISO 3029:1983 Photography — 126-size cartridges — Dimensions of cartridge, film and backing paper |date=August 1983 |publisher=International Standards Organization |access-date=2 March 2023}}</ref>

Like the [[120 film|120]] format, there is a continuous backing paper, and the frame number is visible through a small window at the rear of the cartridge. Cameras for this type of film are equipped with a large rectangular window in the back door, through which is visible not only the frame number, but also a portion of the label showing the film type and speed. The cartridge has a captive take-up spool, but no supply spool: the film and backing paper are simply coiled tightly and placed in the supply end of the cartridge. The positioning of the image is fixed by the cartridge. The film is 35&nbsp;mm wide, but unlike [[135 film]], it is unperforated, except for one registration hole per image, similar to the earlier [[828 film]]. The camera is equipped with a sensing pin which falls into this hole when the film is fully advanced to the next frame, at which point the winding knob or lever is locked, so as to prevent winding past the pre-exposed frame lines.
<gallery mode=packed widths=350px>
Image:126 film negative strip (small).jpg|A strip of 126 negatives, showing the square format and single perforation. The film is pre-exposed with frame lines and numbers, a feature intended to make printing and viewing easier.
File:Sample 126 Film.jpg|126 negative strip (converted to positive) with numbered leaders on a roll of 20 exposures from the 1970s showing the manufacturer text [[Cellulose acetate film|"Kodak Safety Film"]] indicating acetate base (non-nitrate).
</gallery>

The top edge of the cartridge above the film gate has a square notch in a specific position that signaled the [[film speed]]. Some of the higher-end cameras used this notch to determine the correct exposure, or to set the [[light meter]], if so equipped. Although the actual films manufactured in 126 cartridge format had speeds varying between ISO 64/19° and ISO 400/27°, the standard defined 20 different speeds, spanning from ISO 20/14° to ISO 1600/33°.<ref>{{Cite web|url=https://www.flickr.com/groups/instamatic/discuss/72157594480288222/|title=126 cartridge ASA sensitivity. cartridges notches position list|date=January 14, 2007|website=[[Flickr]]|access-date=December 6, 2019}}</ref>

[[File:Kodak Instamatic X-15 2015-11-28 penultimate roll of 126 film.jpg|thumb|right|[[Kodak Instamatic]] X-15 with open door and loaded 126 film cartridge]]
The film was originally available in 12 and 20 image lengths; at the time regular production stopped it was only available in 24 exposure cartridges.  The exposed film is stored on the take-up spool and does not need to be rewound, making the cameras very simple to load and unload. Kodak published instructions for assembling a simple [[pinhole camera]] using a 126 cartridge with typical household materials.<ref>{{cite web |url=https://archive.org/details/how-to-make-a-pinhole-camera-kodak/ |title=How To Make and Use a Pinhole Camera, publication no. AA-5 |date=April 1980 |publisher=Consumer Markets Division, Eastman Kodak Company}}</ref>