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03-24-2011, 05:48 AM   #1
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K5 Flash and Auto ISO

I just received my K5 and still learning it. Is there a way for the auto iso functionality to start with the lowest iso and move up if my flash output isn't strong enough? From my quick test, when I have the flash on set to p-ttl and auto iso on, camera seems to default to the highest iso.

03-24-2011, 09:16 AM   #2
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it's not using the highest possible. It selects ISO to correctly expose even without flash, assuming you want the flash jut to fill in. Which is reasonable, because for what else would set the ISO to auto?
03-24-2011, 10:04 AM   #3
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That make sense, I've only had the K5 for a few hours. Is there a way to set an ISO and have it move up as necessary to compensate for the flash?
03-24-2011, 11:34 AM   #4
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Perhaps you could describe your situation.

Are you using the on-camera flash or an off-camera flash? What are you shooting under which circumstances?

Are you finding that ISO 400 is occasionally not enough but don't want to shoot regularly at 800 to avoid the occasional manual bump to 800?

I have to admit I'm lazy - I pick a reasonable (for me) ISO and aperture, letting the camera and flash figure it out from there. For many of us, a special effort to keep ISO very low isn't of much value on a camera like the K-5.

03-24-2011, 01:32 PM   #5
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From your quick test Charley, the conditions might be that the best results for the exposure are at the high ISO the camera had chosen, because any lower and the flash may not have been powerful enough to expose for the image. This too is a guess without knowing any further detail.

But normally it is expected that auto ISO chooses the lowest possible ISO for the exposure. If you really want a particular ISO, just select it rather than using auto ISO.
03-24-2011, 02:53 PM   #6
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QuoteOriginally posted by glanglois Quote
Perhaps you could describe your situation.
I am using on camera flash (I have both the 360 and 540) in
Flash Mode - normal p-ttl.
TAv mode- Shutter 180
Auto iso range - 100-6400.

I would like the camera to use ISO 100 where possible. If I set the aperture too small and the flash isn't powerful enough, I would like the ISO to move up to the necessary value to properly expose. Or if I fire off 2 consecutive shots, while the flash is fully recharged, I would like ISO to go up.

This is the behavior of my Nikon D700. This way, I can get the best quality shot, but if my flash is not ready or the room is too large or I set the aperture too small, I still get a shot.

Hope that explains things.
03-24-2011, 03:27 PM   #7
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OK I admit the other scenario makes sense too. But I have no idea how to influence this besides setting the auto ISO to slow mode. I'm used, from Canon SLR and Fuji bridge camera, to use the flash when body is set to manual exposure and the flash automatics lights the rest.

Anyway still I do not think that lowest possible ISO equals best quality shot when flash is in play. Increasing ISO puts more natural liht inplay and shoud yield better result in most cases or action and report photography. When you want nimimal natural light and light all flash, that is usually in controlled conditions where manual ISO is prefered anyway. What would you shoot this way?
03-25-2011, 10:53 PM   #8
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I tried the slow mode for auto ISO and it had no impact. I did notice that the auto ISO behaves differently for Av and TAv modes. In TAv it was even more aggressive about using the higher ISO.

I agree that the lowest possible ISO may not equate to the best quality. But I'm in a situation where the flash is powerful enough to take the picture at ISO 100 and it's take a picture at ISO 6400. I can lower the range of auto ISO, or keep it at ISO 400-800 to be safe that I have enough light and the flash recycles fast enough. Otherwise, auto ISO basically isn't useful with a flash.

QuoteOriginally posted by elho_cid Quote
OK I admit the other scenario makes sense too. But I have no idea how to influence this besides setting the auto ISO to slow mode. I'm used, from Canon SLR and Fuji bridge camera, to use the flash when body is set to manual exposure and the flash automatics lights the rest.

Anyway still I do not think that lowest possible ISO equals best quality shot when flash is in play. Increasing ISO puts more natural liht inplay and shoud yield better result in most cases or action and report photography. When you want nimimal natural light and light all flash, that is usually in controlled conditions where manual ISO is prefered anyway. What would you shoot this way?


10-09-2011, 10:03 PM   #9
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I hope it's OK to revive this thread from March.
I have a K7 and I really wish there were some way to set a separate or maximum ISO range for when using the flash.

For example I may have the camera set to auto ISO in Av mode (say up to 3200) to take advantage of any natural light.
Then I decide to pop up the flash / or use my AF360 and I'd like the camera to go to a more moderate ISO of say 400-800.

I'm sure this is not currently possible, but it would be very convenient. Any solutions??? Maybe contact Pentax with a request for a firmware change?

Last edited by calsan; 10-09-2011 at 10:04 PM. Reason: spelling mistake
10-09-2011, 10:27 PM - 1 Like   #10
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In any auto modes (ie anything other than "manual") the camera will meter to ambient and ignor flash. So if you dont want that then don't use an auto modes when shooting pTTL. So the solution is to shoot in manual mode on the camera, pTTL on the flash. It's not that hard, it's way easier than shooting manual mode without flash because with pTTL the camera will still meter the scene and put out the right amount of flash power to correctly expose the pic (obviously within the limits of the flash). So if the meter is saying you're underexposing 2 stops, the camera will instruct the flash to pump out 2 stops worth of light, how easy is that!

So just put the body in manual mode, dial in the ISO you want, hit the green button to get initial settings, then adjust the aperture and/or shutter to underexpose 1 to 3 stops (keep shutter <=1/180 unless you really need HSS). Much more underexposed and you'll get the black tunnel background effect.
10-09-2011, 11:23 PM   #11
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Thanks, twitch.
Still, not so convenient - actually the real reason I'm asking is because I lent the camera to my wife at a wedding and there's no 'point and shoot' mode I can leave the camera in, without having to explain ISO and aperture and so on. [People's eyes glaze over.] Therefore I set it to auto iso 200-3200, but that stuffed up the photos she took with the flash. Green mode only goes 100-800 iso so a point and shoot will appear to 'perform better' in natural light.

BTW, your flickr photos are very good. Especially like the architectural style shots with the 15 & 21. You obviously travel a bit.
10-10-2011, 01:58 AM - 1 Like   #12
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QuoteOriginally posted by calsan Quote
Therefore I set it to auto iso 200-3200, but that stuffed up the photos she took with the flash.
I use one of the five USER slots to set up a "General-Flash" setting. Here I use ISO80-ISO400 as the initial auto-ISO range settings as this holds the ISO down to a reasonable setting. Because of the K-5's auto-ISO behaviour with flash, it's really a fixed medium-ISO setting, but may come in handy if the lighting changes and you don't need flash. If I'm far away and getting too much flash underexposure I'll raise the upper ISO limit. If it's a daylight fill-flash situation, I'd use a low fixed ISO.

I use a Sigma DG530 Super. In a recent set of bounced flash tests, I was happy with +1 FEC in-camera and +0.5 to +1 boost in the flash unit to get a good exposure. This is pretty much the same comp as what I used with this flash on the K20D. Users of other flash units may need different flash comp settings. This was in a house in various rooms and hallways. In a very large room or hall you have to raise the ISO dramatically, if bouncing is possible at all.

Not P&S simple, but a good starting point.

Dan.

Last edited by dosdan; 10-10-2011 at 04:27 AM.
10-10-2011, 03:56 AM   #13
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Thanks Dosdan
That's a fantastic idea.
I just have to explain "use USER for with flash and P for without flash." Mode dial is pretty basic to explain and won't cause any trouble.
EASY peasy.

I've 'liked' both you guys for your help.
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