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03-24-2009, 01:20 PM   #46
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QuoteOriginally posted by Confused Quote

According to the infallible Wikipedia
Is this sarcasm right

03-24-2009, 01:21 PM   #47
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QuoteOriginally posted by Confused Quote
Hi again thibs

According to the infallible Wikipedia, the most common aspect ratios are 66*cm (square) and 64.5*cm (rectangular). The last time I checked, 6cm = 60mm, 4.5*cm= 45mm ?

Best regards
Well 645 format is not 6x4,5 cm. Weird I know. Most if not all 645 cameras use 120 and/or 220 film.
645 aspect format with a 120 film (Pentax 645 case) is 56x41,5mm, no 60x45mm.
120 film - Wikipedia, the free encyclopedia
03-24-2009, 01:28 PM   #48
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Medium format size

QuoteOriginally posted by cousinsane Quote
645 is just an aspect ratio, not the actual image size. It's more intuitive than calling it 5641 format
Yes, it is quite confusing.

What MF meant to mean is just that the 120mm film format was used (or 220mm film yielding more exposures).

This film (introduced 1901 by Kodak) is roughly ~6cm wide (between the top and bottom edges). The precise figures are:
  • 62.64mm size of the film roll, probably excatly 60mm for the film inside.
  • 56.00mm exposable area (frame size, corresponding to 24mm in 135mm film).
The possible lengths (by aspect ratio when referring to the width as "6") include:
  • Name: 4.5, 6, 7, 8, 9, 12, 17, 24
  • Actual size [mm]: 41.5, 56, 70, 77, 84, 118, 168, 224
Note how the 67 format is actually much larger than the 66 format...
The length of the 645 format (41.5mm) was choosen to yield a 1.35:1 aspect ratio for 56mm width. So, it actually is a 644 format

Source: 120 film - Wikipedia, the free encyclopedia

So, we have this by comparison:

MF:.. 56.0 x 41.5 / 69.70 / 2324 / 0.62 / 1.00 / 149
FF:.. 36.0 x 24.0 / 43.27 / 0864 / 1.00 / 1.61 / 400
K10D: 23.5 x 15.7 / 28.26 / 0369 / 1.53 / 2.47 / 937
K20D: 23.4 x 15.6

How to read:
Format: size / image circle / surface / crop of FF / crop of MF / ISO noise (FF=400)

(I avoid to speak about APS-C here because Canon's APS-C is smaller than Pentax's...)

135mm film is 35mm wide; but image size is only 24mm wide, not 35mm...
So, 120mm film (56mm of 60mm) actually makes better use of the available film surface than 135mm film (only 24mm of 35mm). Due to ease of handling (the perforation).

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