From: rspeirs@javelin.sim.es.com (Ron Speirs)
Subject: Re: Changing DX code
Organization: Evans & Sutherland Computer Corporation
Date: Wed, 12 Aug 1992 17:55:14 GMT

In article <1992Aug12.071330.926@bio.vu.nl> hermanh@bio.vu.nl (Herman Hillebrand) writes:
>I want to fool my camera (Pentax P30t) for B/W photography by changing
>the DX code on the film cartridge. I would like to change ISO/ASA values.
>Can it be done? How?


There is a way to override a camera with automatic DX coding:  Recode
the cassette yourself.  I posted this quite some time ago, but I guess
there are a lot of new people on the net.

[Flames to the camera manufacturers for designing cameras (at
least SLR's) without DX override].

Here is the key to the DX code: 

		 ________________________
		|                        |
		|                        |_
		|________________________| |
		|12 |11 |10 | 9 | 8 | 7  | |
		|___|___|___|___|___|____|_|
		| 6 | 5 | 4 | 3 | 2 | 1  |
		|___|___|___|___|___|____|	
		|________________________|

ISO		SENSING AREA
SPEED		2	3	4	5	6

  25		-	-	-	X	-
  32		-	-	-	-	X
  40		-	-	-	X	X
  50		X	-	-	X	-
  64		X	-	-	-	X
  80		X	-	-	X	X
 100		-	X	-	X	-
 125		-	X	-	-	X
 160		-	X	-	X	X
 200		X	X	-	X	-
 250		X	X	-	-	X
 320		X	X	-	X	X
 400		-	-	X	X	-
 500		-	-	X	-	X
 640		-	-	X	X	X
 800		X	-	X	X	-
1000		X	-	X	-	X
1250		X	-	X	X	X
1600		-	X	X	X	-
2000		-	X	X	-	X
2500		-	X	X	X	X
3200		X	X	X	X	-
4000		X	X	X	-	X
5000		X	X	X	X	X


NUMBER OF	SENSING AREA
EXPOSURES	8	9	10

(non-std)	-	-	-
   12		X	-	-
   20		-	X	-
   24		X	X	-
   36		-	-	X
   48		X	-	X
   60		-	X	X
   72		X	X	X


EXPOSURE	SENSING AREA
 RANGE		11	12

+- 1/2		-	-
+- 1		X	-
+2, -1		-	X
+3, -1		X	X

NOTE:  An "X" under the sensing area indicates an electrically
conductive area.  A "-" under the sensing area indicates an
electrically insulated area.  Areas 1 and 7 are always conductive.

Use electrical tape to insulate; use copper or aluminum tape to
make conductive areas.  Remember that cameras might depend on
conductivity between conductive areas because the cassette is made
of metal.  So put the metal tape down first, then put on the
appropriate patches of insulating tape.

________________________________________________________________

There is another way to approach the task:  I recently rolled some bulk
Vericolor 400 and Ilford XP-1 for a friend with a Point & Shoot camera.
There were 27 short rolls of each film and I didn't feel like putting
foil tape on each cassette.  Since each of these films is ISO 400 and
my friend wasn't going to shoot anything else in the near future, I 
decided to recode the CAMERA.  Examining the cavity where the cassette
goes, I found contacts for areas 1, 2, 3 and 4 only.  Of course, area
1 is always conductive, leaving only three areas for ISO setting.  
Looking at the ISO table, we see that this camera is not able to
differentiate between the ISO's between multiples of 25; (ISO 80, 64 
and 50 will all set to 50, ISO 160, 125 and 100 will all set to 100,
etc).  This is probably just fine for negative film, but may not be
accurate enough for slide film (ISO 64 would be set to 50).  

Anyway, I put conductive copper tape (sticky side up) between areas
1 and 4, insulating areas 2 and 3, and then covering over that with
insulating tape.  I told my friend that as long as he was shooting my
bulk loaded cassettes, everything would be OK.  If he wanted to shoot
something else, then remove the tapes.  Judging from the results, this
method works just fine.  Those of you with non-override
cameras might consider this approach.

PS:  I'm glad my camera is pre-DX.

Ron Speirs, Evans & Sutherland Computer Corp., Salt Lake City, Utah