ISO set incorrectly on automatic SLR

[DramaKing]

I shot a roll of Tri-x with a Pentax SF10, which automatically reads the DX code and sets the ISO. When I began shooting with it, I noticed that the meter was drastically overexposing the scene (1/60 or 1/125 at f/3.9 in mostly sunny conditions). I developed the roll, and the negatives were too dense as I had expected. According to the manual, the camera defaults to ISO 100 when it can't read the ISO. This was also the first time using b&w film, so maybe it needs to read the barcode information on color negs?

 

[Nicholas Lindan]

ASA 100 exposure for 'sunny conditions' would be f8-f16 at 1/125th. Your exposures are more like ASA 8 or so.

Try cleaning the DX contacts in the camera with a pencil eraser. If you can, set the film speed manually on the camera and check that the camera gives the same exposure as it does with DX readings.

And, as always, suspect the batteries - they are the highest failure rate item in the exposure chain.

 

[BlueWind]

You may also fool the camera with a simulated code
http://www.imageaircraft.com.au/DXsim/
Regards
Joao

 

[wiltw]

1/400 f/16 (Tri-X Sunny 16) to 1/100 f/4 (actual) is -6EV...ISO 6 (400, 200, 100, 50, 25, 12, 6)

 

[RalphLambrecht]

I shot a roll of Tri-x with a Pentax SF10, which automatically reads the DX code and sets the ISO. When I began shooting with it, I noticed that the meter was drastically overexposing the scene (1/60 or 1/125 at f/3.9 in mostly sunny conditions). I developed the roll, and the negatives were too dense as I had expected. According to the manual, the camera defaults to ISO 100 when it can't read the ISO. This was also the first time using b&w film, so maybe it needs to read the barcode information on color negs?

Will you make prints in your own darkroom?

 

[Leighgion]

A modern roll of Tri-X will definitely be DX coded and in that way no different than a roll of color negative film. Something's definitely amiss. Has the camera read DX codes accurately prior to this?

 

[DramaKing]

The funny thing is that color film works fine. There is of course greater latitude in color film, but I still haven't noticed any serious incorrect exposures in either ISO 400 or 100 film. I'll try cleaning the DX contacts, though, and see if that helps.

I know that there is encoded information along the bottom, but I realized that this must be developed before becoming visible so the camera cannot read this. I can't really think of any other difference, so I'm pretty stymied right now.

Will you make prints in your own darkroom?

No, I'm still not set up for printmaking. I've got a PF 1800 film scanner set up, and I just got an Omega B22 off eBay. Someday, I'll have a full darkroom put together, but right now it's still just hopes and dreams.