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bw-man
6-Feb-2017, 20:25
What is the difference between 13X18 film and 5X7 film? (accurate to 0.1mm)
Why are there two very similar specifications?
Hope to get the answer, thank you.

Emmanuel BIGLER
7-Feb-2017, 01:28
Hello from Europe

13x18 cm size was very popular in Europe until the 1960's. You can still find today a choice of B&W in 13x18 cm.
There are two standards, the "Imperial" 5"x7" and the European 13x18 cm.
Although (to the best of my knowledge) the USA have been independent from the British Crown for more than 2 centuries, the Imperial 5"x7" size of film is still in use in Northern America ;)

5"x7" converted into metric makes a theoretical size of 127 mm X 177.8 mm to be compared to 130 x 180 mm of 13x18 cm. Off by 2 - 3 mm on each side.

Actual film sizes are slightly smaller, but 5"x7" film is definitely smaller than 13x18 cm by a 2 - 3 millimeters, 5"x7" film does not hold inside a classical 13x18 cm film holder.
FidelityTM in the USA used to make both sizes, 5"x7" and 13x18 cm. They are clearly labeled and definitely different inside. Outside dimensions are the same, at least for modern double-sided film holders designed for the International view camera 13x18 / 5"x7" back.
There are many old European and American holders made before WW-II that do not comply with the International standard, this is another story.

13x18 cm cut film does not fit at all inside any 5"x7" imperial size film holder.
5"X7" cut film can enter inside an 13x18 cm film holder, but you need some tricks to maintain the film properly (e.g. double-sided adhesive tape at the back), but if you do nothing special, a 5"x7" film will be too loose and will immediately fall outside the holding grooves of a metric 13x18 cm holder.

However, classical Linhof 13x18 cm holders, with their pressure plate, can hold 5"x7" film if you rotate the film slightly before letting it be pressed by the spring-loaded back plate.

bw-man
8-Feb-2017, 06:21
Emmanuel BIGLER:
Thank you for detailed explanation of 13X18 film.
Because China does not have this kind of film, so in the forum post.
Do you use 13X18 ? If there is an exact size (0.1mm), please let me know. Thank you!

Emmanuel BIGLER
8-Feb-2017, 07:40
Quoting Jim Jones (on APUG), one member of this LF forum:
The ASA standard for 13x18cm film is from 12.7 to 12.9 X from 17.7 to 17.9 cm. (http://www.apug.org/forum/index.php?threads/5x7-film-dimensions.20233/)

i.e. 13x18 cm is actually from 127x177 to 129x179 mm

The same discussion mentions 125 X 176 mm for TMY 400 in 5"x7" format, hence actual sizes are off by 2-3 mm between actual 5"x7" and actual 13x18 film.

Randy Moe
8-Feb-2017, 08:39
Perhaps China used plate sizes for a while. http://camerapedia.wikia.com/wiki/Plate_Sizes

I have 'modern' 1/2 Plate film holders that use only 1/2 plate film but the holder itself fits in the same camera as 5X7 holders. Perhaps 13X18 holders follow suit.