kx - flash help

bnorikane · 11-16-2009, 08:24 AM

When I use the built-in flash in P mode, the camera often sets a very slow shutter speed, below a safe handheld speed even with SR. This is not consistent, but tends to happen in lower light with the kit lens or 18-250.

For example, in a slightly dark room

kit lens at 40mm,
4 feet from the focus point
flash up
mode set to P, SR on
iso set to 1600

camera set the exposure to 1/10 at f/4.5. 1/10 is many, many stops below what I expect for a flash shot in this situation.

http://picasaweb.google.com/lh/photo/A8G3Xrp5P1qcxSxEWETWwg?feat=directlink

Why is the shutter so slow with flash on?
The GN for the flash at 1600 is 48 according to the manual, so I should have been well within the flash range at f/5.6. I was maybe even too close.

I know I can shoot flash in manual instead of P, but for casual snapshots, I'm used to just shooting in P and popping up the flash when I want more light. My wife also uses this camera and will almost always shoot in P. I haven't seen this behavior with other cameras.

Any suggestions

Last edited by bnorikane; 11-16-2009 at 08:52 AM.

Eruditass · 11-16-2009, 08:45 AM

The camera prefers to use a weak flash output and get more ambient lighting in to make the image look better instead of the obvious flash look.

If you do not prefer this method, put it in Tv mode and change the shutter speed yourself - the flash will compensate its power quite well. Or you can stay in P mode and use program shift.

You can read more about flash at Strobist

bnorikane · 11-16-2009, 09:33 AM

Thanks Eruditass.

I will try Tv, but I was hoping that the camera would adjust the minimum shutter speed based on focal length instead of me remembering. The kx seems to set a minimum shutter speed in other auto modes and often does the right thing in P with flash.

I like weaker flash with more ambient, but I would cut it off close to the handheld/SR limit for the focal length. Other cameras seem to use a higher cut off, and the Kx sometimes sets a higher shutter speed, but not always.

Marc Sabatella · 11-16-2009, 11:24 AM

Originally posted by bnorikane

I will try Tv, but I was hoping that the camera would adjust the minimum shutter speed based on focal length instead of me remembering.

It does; it just doesn't in the particular way you expect. Remember, the flash duration is incredibly short - much shorter than the fastest shutter speed you can ever use with flash. So you can leave the shutter open for much longer than you could without flash and still have your subject be sharp. The camera chooses a slow shutter speed than 1 / focal length if it, for whatever reason, things you might want to have the ambient light fill the shadows so the picture doesn't come out so harsh. In most cases, what the camera suggests will work out pretty well - you don't really need 1 / focal length just for ambient light shadow fill to be effective. So I suspect you'd find that taking the picture as described above would have worked just fine. If you didn't want the ambient light to be filling in shadows, you shouldn't have chosen such a high ISO. I'm betting that's what caused the camera to assume you wanted the ambient light to play into the picture, and that's why it chose a relatively slow shutter speed. Had you chosen a lower ISO, it probably wouldn't have bothered.

bnorikane · 11-17-2009, 02:56 AM

Thanks Marc!

You and Eruditass have given me the pointers on what the camera is trying to do with TTL flash.

Is there any way to determine the flash output used on an image? I don't see it in the extended EXIF.

I will experiment with lower ISO. I'm experimenting a lot with higher ISO, as I've never had a camera where I've used anything over 400.

I set ISO 1600 because the Kx flash has a relatively low Guide Number, and 1600 bumps it up to GN 48. I didn't need the high GN for that shot as I was quite close.

I'm trying to find the settings that work for casual indoor holiday shots with the kit zoom, and with and without flash. The Kx great high ISO makes the non-flash pretty simple, but I'm struggling with the flash in any of the auto modes. I get some surprising results like blown out backgrounds (which seems physically impossible.)

My most consistent results have been shooting flash with camera in manual. The camera does a pretty good job adjusting the flash.

11-16-2009, 08:24 AM	#1
bnorikane Forum Member Join Date: Oct 2009 Location: Colorado Photos: Albums Posts: 91	kx - flash help When I use the built-in flash in P mode, the camera often sets a very slow shutter speed, below a safe handheld speed even with SR. This is not consistent, but tends to happen in lower light with the kit lens or 18-250. For example, in a slightly dark room kit lens at 40mm, 4 feet from the focus point flash up mode set to P, SR on iso set to 1600 camera set the exposure to 1/10 at f/4.5. 1/10 is many, many stops below what I expect for a flash shot in this situation. http://picasaweb.google.com/lh/photo/A8G3Xrp5P1qcxSxEWETWwg?feat=directlink Why is the shutter so slow with flash on? The GN for the flash at 1600 is 48 according to the manual, so I should have been well within the flash range at f/5.6. I was maybe even too close. I know I can shoot flash in manual instead of P, but for casual snapshots, I'm used to just shooting in P and popping up the flash when I want more light. My wife also uses this camera and will almost always shoot in P. I haven't seen this behavior with other cameras. Any suggestions Last edited by bnorikane; 11-16-2009 at 08:52 AM.

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11-16-2009, 08:45 AM	#2
Eruditass Veteran Member Join Date: Jul 2009 Photos: Gallery Posts: 2,207	The camera prefers to use a weak flash output and get more ambient lighting in to make the image look better instead of the obvious flash look. If you do not prefer this method, put it in Tv mode and change the shutter speed yourself - the flash will compensate its power quite well. Or you can stay in P mode and use program shift. You can read more about flash at Strobist

11-16-2009, 09:33 AM	#3
bnorikane Forum Member Join Date: Oct 2009 Location: Colorado Photos: Albums Posts: 91 Original Poster	Thanks Eruditass. I will try Tv, but I was hoping that the camera would adjust the minimum shutter speed based on focal length instead of me remembering. The kx seems to set a minimum shutter speed in other auto modes and often does the right thing in P with flash. I like weaker flash with more ambient, but I would cut it off close to the handheld/SR limit for the focal length. Other cameras seem to use a higher cut off, and the Kx sometimes sets a higher shutter speed, but not always.

11-16-2009, 11:24 AM	#4
Marc Sabatella Veteran Member Join Date: Sep 2006 Location: Denver, CO Photos: Gallery Posts: 10,685	Originally posted by bnorikane I will try Tv, but I was hoping that the camera would adjust the minimum shutter speed based on focal length instead of me remembering. It does; it just doesn't in the particular way you expect. Remember, the flash duration is incredibly short - much shorter than the fastest shutter speed you can ever use with flash. So you can leave the shutter open for much longer than you could without flash and still have your subject be sharp. The camera chooses a slow shutter speed than 1 / focal length if it, for whatever reason, things you might want to have the ambient light fill the shadows so the picture doesn't come out so harsh. In most cases, what the camera suggests will work out pretty well - you don't really need 1 / focal length just for ambient light shadow fill to be effective. So I suspect you'd find that taking the picture as described above would have worked just fine. If you didn't want the ambient light to be filling in shadows, you shouldn't have chosen such a high ISO. I'm betting that's what caused the camera to assume you wanted the ambient light to play into the picture, and that's why it chose a relatively slow shutter speed. Had you chosen a lower ISO, it probably wouldn't have bothered.

11-17-2009, 02:56 AM	#5
bnorikane Forum Member Join Date: Oct 2009 Location: Colorado Photos: Albums Posts: 91 Original Poster	Thanks Marc! You and Eruditass have given me the pointers on what the camera is trying to do with TTL flash. Is there any way to determine the flash output used on an image? I don't see it in the extended EXIF. I will experiment with lower ISO. I'm experimenting a lot with higher ISO, as I've never had a camera where I've used anything over 400. I set ISO 1600 because the Kx flash has a relatively low Guide Number, and 1600 bumps it up to GN 48. I didn't need the high GN for that shot as I was quite close. I'm trying to find the settings that work for casual indoor holiday shots with the kit zoom, and with and without flash. The Kx great high ISO makes the non-flash pretty simple, but I'm struggling with the flash in any of the auto modes. I get some surprising results like blown out backgrounds (which seems physically impossible.) My most consistent results have been shooting flash with camera in manual. The camera does a pretty good job adjusting the flash.