[The Squirrel Mafia]

I'd have no problem setting the auto ISO from 100 to 12800 & use ISO 25600 in a pinch on the K-3/3II.

I do always try to shoot as low ISO as possible, but I'm fine with images up to ISO 12800. The post processing program that one uses & one's skills at using it will also determine the camera's ISO limit.

[luismpg]

depends on the end use and the subject, but iso3200 is pretty much my limit unless i really have no choice. However, i typically stick to 80-400. Most of the things i shoot i can either light artificially or use a long exposure + tripod.

For kicks, i looked at how many photos i had taken (and kept) at each iso on my k5iis, i've grouped a few together:

iso	# of photos
80/100	4393
140/200	3157
280/400	2005
560/800	1259
1100/1600	570
3200	987
6400	135
12800	6
25600	1
51200	1

for 12,154 total photos. The "3200" count is a little inflated from several late night sequences that involved 20 to 200 or so photos stacked together into one final image (typically fireflies).

really nice

[leekil]

It all depends on the target of the image. If you are going to make a 4"x6" print then you can go to 6400 in dim light and maybe even 12k and beyond in better light. As your print size increases then you will want to lower your maximum ISO. Imaging Resources has a chart detailing the maximum recommended ISO for various print sizes.

Pentax K-3 Review - Image Quality

Scroll almost all the way down and you will find a section about print quality.

Interestingly the K-1 was rated 2(!) stops ahead of the K-3 for print quality in it's review. I wouldn't have thought it was that large of a difference.

[BigMackCam]

Imaging Resources has a chart detailing the maximum recommended ISO for various print sizes.

Pentax K-3 Review - Image Quality

Scroll almost all the way down and you will find a section about print quality.

That's a useful reference if shooting JPEG, but I'd argue you can easily go much higher than they recommend by shooting RAW and processing in something like Lightroom. The loss of detail in the red fabric in those sample shots, for instance, is typical of Pentax's in-camera JPEG engine (the new K-70 seems to do much better than previous models in this regard). Careful RAW processing would have kept much more detail in that at considerably higher sensitivities (I can retain red fabric detail with the Pentax Q at ISO 3200 without too many problems ).

[JimJohnson]

When I can shoot at 100 ISO, I certainly do so - but otherwise I pump up the gain to whatever I have to do to support a reasonable aperture and shutter speed. Inside a Disney ride, I wanted a photo of my grandson (with his father). The riders were in near total darkness so I ran the ISO to the max and still fell short on shutter speed for a moving ride. But I captured my grandson's reaction and that is what counted to me at that time. So what if it would never win a prize in a photo contest?

K-3 with 18-135, ISO 51200, f/4.5 1/4, handheld

[lotech]

3200 no doubt, WB and noise will start to deteriorate over that, I do shoot extreme low light that calls for 12800 and above, but the image will shift crazy to deep yellow and even red randomly.

[Rondec]

Typically I would use 100 to 3200 as my auto iso. If I am shooting in really dark situations, iso 6400.

Bear in mind that iso performance is going to be a lot better if you nail your exposure. If you are under exposed and have to brighten parts of your image, you will see noise very, very quickly at even iso 3200. The bigger issue than noise is dynamic range. It just gets really poor at high isos and you may end up being better to convert to black and white.