Thanks for your input. I always shoot in Av mode and I was aware that I can override auto ISO with the front dial. I'm just lazy and wanted to stop bothering about ISO at all.

My/the need to raise ISO manually is only determined by the two formulas I mentioned above, so I would prefer to just set them inside the custom menu, instead of relying on a mysterious default formula and keeping in mind to override it each time it differs from my requirements.

It leads to a workflow where you set your own shutter limits beforehand and auto ISO works to provide them for you. You don't have to examine Av, Tv and ISO, but you can concentrate on DOF (Av), focus and composition.

However, as I said, my urge might be related to my own lazyness and my unwillingness to process additional data in my head. No need for Pentax to act on it, if their users prefer to do it the manual way. But it could attract new customers, as it is a unique feature for someone who upgrades from a lower class and it underlines the value of in body SR.

Wow, thank you. If I may add another suggestion which is not too off-topic as it also relates to SR:

Auto ISO allows to set the upper and lower ISO limit. But the algorithm which chooses the respective ISO is not quite transparent and might be inadequate in many cases. I think that is one reason why many people refrain from using auto ISO. But with only two further settings auto ISO can be a very powerfull facilitation.

1. relative shutter limit (vs. camera shake)
This resembles the classical rule of thumb, but takes SR into account and allows for individual customization. The lowest ISO is used. It is only raised, if shutter speed is slower than 1/focal lenght*X seconds. Adjusting this X allows the user to consider his own hand holding skills in combination with SR. If you're steady X=0.4, if you're shaky X=2.

2. absolute shutter limit (vs. motion blur)
If camera shake is not the problem, the other reason for lifting the sensitivity is the movement of the subject. Steadiness is of no use here, as a fast shutter is needed anyway. As this limit varies from occasion to occasion, it should be possible to custumize it for the respective photo session in the term of 1/Y seconds. If you're shooting a still life Y=1, friends in a restaurant Y=30, playing kids Y=125.

ISO is only raised if the low light leads to shutter speeds that conflict with either of these rules. And only as far as necessary to stay within these limits.

The purists might say that they prefer to adjust everything manually. I can agree with that in regard to focus and aperture as they are artistic decisions. But in most cases sensitivity has no artistic influence, but is only used to fight the problems of camera shake and motion blur. I believe that the two settings I suggested above could explicate the algorithm behind auto ISO and should, in most cases, allow for adjustments that eliminate the mentioned problems and let you concentrate on the artisic part of photography.

I'm happy for everyone who wants to comment on this. And even happier for everyone who can pass this on to Pentax, so they can consider implementing it in a firmware upgrade.

Thanks.

I just registered to express my full support for that idea. I have been suggesting such a "force SR mode" for a potential firmware upgrade on Pentaxforums, but nobody seemed to be interessted, back then. It is especially valuable, if you hand your camera out to older people/mothers/etc, who have shaky hands, but no sense for only tipping the shutter and waiting for the SR-signal to pop up.

If someone here has contacts to Pentax, please pass this on! It should be less than an hour of work for the camera software department.