High ISO problem

[social_lurker]

This is probably me making a schoolboy error, but if someone could confirm this I'd be greatful:

I went out dog walking last night with my new(ish) nifty fifty and although it was early evening (about 7pm) it was still very bright. I wanted to play with the shallow DOF and obv as it was sunny set the WB and ISO to 100. Using the aperture priorty, I was getting 1/2000 and 1/4000 shutter speeds.

I was obviously walking around with the dogs and the camera was slung over my shoulder and about 3/4 of the way around I checked the settings and the ISO had moved to 1600. I hadnt intentionally changed the ISO, so could I have knocked the on switch (or not turned it off) and would it be the ISO button got pushed and changed? Or is there another setting that I have knocked (or is my camera spontaneously changing things?)

It's a 400d btw.

 

[admirable]

The fact that you were getting 1/4000 should have rung alarm bells! I would have checked everything!

I think it's quite hard to change the settings accidentally.

 

[pxl8]

How do you change the ISO on the 400D? Is it a case of scroll through and then press SET or similar? Maybe you selected it but didn't confirm it by pressing SET?

 

[social_lurker]

I did think it was a bit strange, but then again its the first outing on a fast lens in bright daylight, so at f1.8 I didnt think too much about it (especially as I wasnt really out taking pics just a few snaps of the dogs and random hedgerow flowers). I mean 1/1000 at f4.5 isnt uncommon, so the few extra stops could have given me that sort of speed.

I'm just a little puzzled as to how the ISO changed: It would require me to have left the camera on (possible), then to knock the ISO button and the arrows across to 1600.

edit: Actually, pushing the ISO button once moves the setting up one. So at 100, one push of the ISO button would move it to 1600.