编辑“︁DX碼”︁（章节）

==DX相機自動辨識==
[[底片暗盒]]外印有可供相機辨識的CAS條碼 (DX '''C'''amera '''A'''uto '''S'''ensing)，讓相機可以自動決定[[ISO值]]、內含的張數和曝光寬容度。第一部可自動讀取DX碼的的相機是1984年的 Konica TC-X SLR <!-- first DX-enabled SLR, sources differ regarding date of introduction: 1983, 1984, 1985? -->和 Pentax Super Sport 35 (PC 35AF-M)。<ref name="Pentax_PC35AF-M">{{cite web 
 |title=History of Innovations 
 |url=http://old.pentaximaging.com/world_of_pentax/history_of_innovations/1980-1989/ 
 |publisher=Pentax 
 |accessdate=21 July 2011 
 |quote=1984: Pentax introduces its second leaf-shutter sport model, the Super Sport 35 (PC 35AF-M). The new addition offers all of the features of the Sport 35, plus a built-in auto winder, fully automatic loading and automatic film speed setting using the Kodak-pioneered DX coding system. The Super Sport 35 is the world's first non SLR camera to incorporate the DX film sensing system. 
 |deadurl=yes 
 |archiveurl=https://web.archive.org/web/20120328024322/http://old.pentaximaging.com/world_of_pentax/history_of_innovations/1980-1989/ 
 |archivedate=2012-03-28 
 |df= 
 }}</ref> .<!-- Left hidden as source code comment only for now: Pentax claims the A3 / A3000 was the first DX-enabled SLR in 1985, but the Konica TC-X seems to be earlier in 1983 or 1984. Other DX-enabled SLRs were introduced in 1985 as well: Minolta 7000 (1985-02)in  and 9000 (1985-09), Nikon F-301 / N3000. <ref name="Pentax_A3000">
{{cite web
 | title = History of Innovations
 | url = http://old.pentaximaging.com/world_of_pentax/history_of_innovations/1980-1989/
 | publisher = Pentax
 | accessdate = 21 July 2011
 | quote = 1985: The Pentax A3000, a fully automatic SLR, is introduced. Its automated features include: exposure, film loading and winding, and film speed setting with DX-coded film. The A3000 was the world's first 35mm SLR camera to utilize the DX film sensing system. This new SLR also allows for creative flexibility with features such as: aperture-priority, backlight compensation and a 12-second self-timer. The camera's Pentax KA bayonet lens mount makes it compatible with more than 50 Pentax lenses.
 | archive-url = https://web.archive.org/web/20120328024322/http://old.pentaximaging.com/world_of_pentax/history_of_innovations/1980-1989/
 | archive-date = 2012-03-28
 | dead-url = yes
 }}
</ref> -->

CAS的原理是在金屬製的底片暗盒上，將導電或絕緣的塗料印成 2x6 的格狀，而相機上的電子接點就可以讀取條碼。大多數相機只讀取一部分的條碼，通常是[[ISO值]]的部分。還有一些入門相機只讀取更少的接點，就能分別出最常用的ISO值。例如100, 200, 400, 800僅憑S1和S2接點即可分辨。

===電子接點===
在底片暗盒上印有二列六行的長方形區域。把凸出的捲軸朝左邊時，最左側兩格接點都是基點，它們總是印著導電材料。上排剩下的五格用以編列32種可能的ISO值，但只有 ISO 25 到  5000 、以 1/3 EV 遞增的24種數值被編碼。這些編碼並不嚴格遵守二進制。

第二排的頭三碼可以分辨底片是 12, 20, 24 或是 36 張裝。最後兩碼編了四種曝光寬容度。

多數相機只讀取第一列的[[ISO值]]。

圖表狀（捲軸朝左）：

{| class="wikitable"
|-
| bgcolor="#7fff7f" | G
| bgcolor="#ff7f7f" | S1
| bgcolor="#ff7f7f" | S2
| bgcolor="#ff7f7f" | S3
| bgcolor="#ff7f7f" | S4
| bgcolor="#ff7f7f" | S5
|-
| bgcolor="#7fff7f" | G
| bgcolor="#ffff7f" | L1
| bgcolor="#ffff7f" | L2
| bgcolor="#ffff7f" | L3
| bgcolor="#7fffff" | T1
| bgcolor="#7fffff" | T2
|}

G是接地點，S是ISO值，L是底片長度，T是曝光寬容度。