Question about auto ISO

I know this is probably buried in the archives somewhere, but I couldn't find a

good answer.

 

My K10D, when set to auto ISO for, let's say, a 100-800 range, always selects

the lowest ISO, even when it then tells me I need to use the flash.

 

For instance, if I mount the 50mm/f1.4 lens and set the mode dial to P, it will

give me, let's say, a shutter speed of 1/60, an aperture of 2.0, an ISO of 100,

and give me the flash warning. If I take the ISO off auto and set it to 800,

it will give me 1/125 and f2.8, and I don't need the flash.

 

Do other people have this problem? I may be nuts, but it seemed to be that the

camera always used to select the highest ISO but now it's selecting the

lowest. Changing the Program Line in the Custom menu doesn't seem to affect

the ISO, although it will affect the other parameters. Yes, I have updated to

firmware 1.3.

 

Any info or insight would be appreciated.

 

Thanks

That doesn't really sound like a problem, though I imagine you're pretty close to the threshold where the sensitivity would have been automatically changed--the Auto ISO logic will generally raise the sensitivity only as a last resort. Your 50mm lens would theoretically allow hand-holding at 1/60 and it still had aperture to spare. It would appear that the 'use flash' warning comes on a little sooner than the ISO bump.

 

The camera will generally always select the lowest ISO value it can for maximum image quality even though in some cases a borderline shutter speed may be a bigger risk to the image than one stop of sensitivity. If you don't like what it's doing, change the ISO range (200-800?), use manual ISO, or perhaps try one of the other modes like Sv or TAv.

 

I would tend to agree with you--given 1/60 & f/2 @ISO 100, I'd probably rather use a moderately higher ISO to get a slightly higher shutter speed, a little more aperture for DOF/lens sharpness, or both (though in your example, I think ISO 400 would be enough--2 stops, one stop shutter, one stop aperture) You might want to try Sv--I recommend configuring Sv to use ISO on the front e-dial and P-shift on the rear e-dial.

What is the point of auto-ISO, if the camera is going to stick at the lower ISO and nag you to use the flash? If I set it to specifically use ISO 100, that's different. But, when you select auto, aren't you telling the camera that you want the sensitivity to float, so that you can handhold the camera and avoid using the flash?

Barry did not say that f/2 1/60th settings at ISO 100 was giving him underexposed images.

 

To me, giving a flash message and actually firing the flash automatically are two completely different things. It's a suggestion vs an action.

I don't have a K10d, but still think often about picking one up. In Canon land when in program mode the camera will "program shift" when you spin the selector dial. Changing shutter speed & aperture stepping though exposure equivalent options. (Canon does not have the ISO priority function). It seems the Pentax should allow a quick step through equivalent exposures in Program mode; that's not uncommon. Am I wrong?

Rob, not sure why you're mentioning anything about underexposed images.

 

<P>I didn't focus on the flash warning much in my previous response because I personally pretty much ignore it--I <i>think</i> I know based on the shutter speed and aperture whether or not I want it. Good points are being raised though--you'd expect that the warning would be more in sync with what the other automatic features on the camera are doing--sort of like the left hand not knowing what the right hand is doing.

 

<P>The other thing is that if the flash <i>is</i> enabled, the ISO might <i>also</i> be raised to make the flash more effective. I haven't tried this particular scenario recently however.

<<Rob, not sure why you're mentioning anything about underexposed images.>>

 

Because the thread is about the camera's metering system and it's belief that a flash is needed based on the shift ISO algorithm. I was trying to illustrate the difference between a suggestion and a requirement.

 

Barry believes that the camera should avoid giving a flash warning/indication by raising the ISO. But if the images are not underexposed then you should take the warning under advisement and continue shooting.

"Barry believes that the camera should avoid giving a flash warning/indication by raising the ISO. But if the images are not underexposed then you should take the warning under advisement and continue shooting."

 

I agree, it's a recommendation, the camera would feel better about the shot if it could use the flash; that's it. I don't use auto-ISO because I like to control it manually. I think I've used the flash about 2 times in the last 7 weeks, even though I very often get the lightning bolt flashing at me. Maybe the K10D would like some flash, but I ain't givin' it to 'er. My shots have never been underexposed when I've ignored the warning.

I don't think underexposure is the issue here at all--the camera will expose properly in these cases. The issue is that the shutter speed is getting low enough that camera shake is likely to occur--so you'll get properly exposed image ruined by camera shake. The flash recommendation is to encourage you to use flash to allow your shutter speed to be raised.

<<I don't think underexposure is the issue here at all>>

 

Andrew, I did not say it is. Again, the point here is that the flash indicator is a suggestion. It is not a warning that you /need/ to add light to the scene.

 

<<The flash recommendation is to encourage you to use flash to allow your shutter speed to be raised.>>

 

How is using the flash going to raise your shutter speed?

Barry,

 

Have you observed the same 1/60th of a second shutter speed choice with longer lenses in Auto ISO mode?

Rob: I don't think I understand the question--the flash will provide additional lighting that will allow you to raise your shutter speed (whether automatically or manually) to a level more safely hand-holdable. I believe this may happen automatically when you turn enable the flash. The automatic settings will normally keep the speed to a slowish-but-still-hand-holdable speed to minimize use of flash power.

<<the flash will provide additional lighting that will allow you to raise your shutter speed>>

 

The camera is in P mode, per Barry's original post. Changing the shutter speed in P will also change the aperture.

 

<<I believe this may happen automatically when you turn enable the flash>>

 

I believe it is erroneous to assume this. If the lights levels are such that the camera is metering 1/60th and f/2.0 then the camera will more likely assume it is to be the dominant light source. It will then shoot with the flash at the existing shutter and aperture settings.

Andrew, Rob was asking why the shutter speed would go up when using the flash. You are saying that it will go up because instead of 60, you can shoot at, say, 200. But this means that the shutter time will actually go down, as the exposure time will be shorter, because you're going from 1/60s to 1/200s.

 

I really think photography should sort its vocabulary out, because "increasing the shutter speed" actually means "shortening the exposure". :-)

I wonder if the sub-program for faster shutter speed/action shooting were activated would the camera then provide a higher ISO more readily??

In case anyone is still reading this, I'm sorry I wasn't able to return. I don't see why the camera should give you "suggestions." It's making the settings for you. If it sets the shutter speed at half a second and leaves the ISO at 100, that doesn't make any sense, and it's not even a good suggestion. It should raise the ISO appropriately, but it does not.

 

Changing the sub-program to MTF doesn't seem to matter.

 

Cheers

Barry,

 

You understand how a camera meter works, right?

Miserere: That is exactly what I said. Raise shutter speed means faster shutter speed with shorter duration. Of course, unless you're using P-TTL high-speed sync, 1/200 is out of reach on the existing *ist/K-series bodies. One can get by with a briefer shutter opening because of the additional light provided by the flash. In the particular scenario described (I didn't try it), I don't really expect the program logic even with flash to boost the shutter speed very far past handholdable--the automatic logic tends to try to keep the flash output mild.

 

Barry/Michael: The different program lines tend not to vary that much at the extremes of limited and excessive light and it appears to only start raising ISO after shutter speed is barely hand-holdable and the aperture is wide open. I think this is somewhat unfortunate as the image quality is still quite good at moderately elevated ISO that I'd hate to have the image damaged by camera shake--perhaps it would be nice if Pentax allowed some additional user tuning here. I know--we should be able to buy little cards containing "microchips" with different program lines and insert them into the body...oh, wait, the 1980's called, they want their technology back. :-) (From the Minds of Minolta)

 

I will also say that virtually everything that any camera light meter tells you is a "suggestion". In this case you're not happy with the AE logic's suggestion. Others might prefer that the sensitivity is only elevated once the shutter is at the hand-holdable boundary and the lens is wide open. Personally I would tend to agree with you that perhaps simultaneously applying a moderate ISO bump a little sooner would probably be a good idea. Fortunately for us the K10D offers excellent control to override it.