[BB_Zone28]

This is a follow up to a much earlier post on another thread, so hopefully what I've learned may be useful "words to the wise" so to speak.

Over a year ago I apparently stumbled onto what likely caused my original K5 to get effectively stuck at a higher minimum ISO setting regardless of dialing in lower ISO settings. It happened after buying a K5II to supplement my original K5 a couple of years ago.

One day I forgot and left the K5II in the front seat of my car on a warm day. The K5II was very warm to the touch, but not extremely hot and when I was out later that day shooting with it I noticed it was overexposing everything at ISO 100 and had to turn the dial up to about ISO 1600 to get better-but-slightly-clipped highlights.

I was dreading the thought that this may have been what really caused the problem with my original K5 and now I've done it to my K5II also.
However, after sitting for several days indoors at normal temperatures the K5II settled down and returned to "normal" performance regarding ISO settings. Apparently the K5II was able to recover from a single heat exposure event.
Now I'm very careful to not to do that again.

That led me to suspect the reason my original K5 is stuck at roughly ISO 800- 1600 "minimum ISO" even when dialing in lower ISO settings was probably due to leaving it in my car during a summer for a few weeks while driving around town and parking in various place, even though the camera was in a bag in the back floor board covered from direct sunlight.

I'm not sure what actually happened internally to the camera to caused the end result observed with the effective ISO minimum setting. My guess is the heat exposure possibly caused something to happen within the sensor electronics to affect the gain settings that track along with the dialed ISO setting???

CONCLUSION: Heat exposure inside a car is most likely what caused my original K5 to become permanently stuck at a higher "minimum ISO setting," although dialing in higher than ISO 1600 settings still seem to boost ISO like you would expect, it just won't return to the lowest ISO settings when dialing it below about ISO 800-1600.
PS: In case anyone was wondering, noise performance appears to be about the same as it was before heat exposure, so the original K5 has basically become a dedicated night/low light DSLR.

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Last edited by BB_Zone28; 03-25-2019 at 11:07 PM.

[steve_k]

If you are over exposed at iso 100. I would expect you to be more over exposed at iso 1600. Do you mean shutter speed?

[rangercarp]

If you are over exposed at iso 100. I would expect you to be more over exposed at iso 1600. Do you mean shutter speed?

If he is setting the camera at ISO 100 but it is actually shooting at 1600 it would be overexposed by 4 stops. When he sets it to 200 it overexposes by three stops. When he sets it to 1600 is exposes properly.

[UncleVanya]

If you are over exposed at iso 100. I would expect you to be more over exposed at iso 1600. Do you mean shutter speed?

He is suggesting that the sensor ignored the changes to ISO until he reached 1600 or higher. So at 100, it metered as if 100 but exposed as if 1600.

[BB_Zone28]

If he is setting the camera at ISO 100 but it is actually shooting at 1600 it would be overexposed by 4 stops. When he sets it to 200 it overexposes by three stops. When he sets it to 1600 is exposes properly.

"RC", you're comment is correct. Heat damage apparently made the lowest obtainable actual ISO response, regardless of lower dialed in values, become stuck at approximately ISO 1600, or said another way, dialing down the "ISO setting" below the ISO 1600 number didn't reduce the actual exposure response of the camera as you should expect when reducing the ISO setting.

The combined set of exposure settings (shutter, aperture, ISO) recommended by the camera meter presumed the lower ISO setting, but the image would be overexposed. The camera's meter and image exposure results only seemed to work correctly once I dialed in ISO 1600 or higher.

---------- Post added 04-20-2019 at 10:20 AM ----------

He is suggesting that the sensor ignored the changes to ISO until he reached 1600 or higher. So at 100, it metered as if 100 but exposed as if 1600.

"UV", you've explained it in the most simple and clear manner!!!