Pentax ist - Manual (Page 130)

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A number of dedicated accessories are available for this camera.
AA-Battery Grip BG-20
Battery grip powered by size-AA
batteries. Usability is enhanced with
the shutter release and AE lock
buttons for vertical positioning of the
camera.
ACCESSORIES (OPTIONAL)
Battery life ( Using 24-Exposure film rolls)
The number of 24-exposure film rolls that can be taken with a
new set of alkaline batteries is indicated below.
Number of film rolls
at 20
°C( 68°F)
General existing light photography approximately 75 rolls
Flash photography with 50% of
shooting uses flash
approximately 30 rolls
Flash photography with 100% of
shooting uses flash
approximately 20 rolls
Bulb exposure time approximately 12 hours
Cable Switch
Cable switch CS-205
Lengths:0.5m
When you use the camera in cold climates, it is recommended that
you use the camera without the BG-20, since the performance of
alkaline batteries, such as those used in the BG-20, deteriorates in
cold environments.