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07-14-2011, 09:46 PM   #1
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Auto ISO with ext flash defaults to high?

Hey guys, for those with a k-5, I was wondering in the situation with an external flash like a Metz 36 does the Auto ISO usually default to a low ISO like 400 or does it tend to hit high ISO's in low light situations. I only ask because I noticed my k-x in Program mode shoots ISO 6400 in dark situations when I know the flash is capable of lighting the room enough to hit ISO 400 with no problem.

I noticed another k-5 thread where tilting the flash for bounce causes overexposure, but thats not exactly my problem here. Thanks for any feedback ahead of time.

07-15-2011, 12:26 AM   #2
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Yes, Pentax changed their Auto-iso behavior when they introduced the K7.

Before (K10, K20, etc), the iso was kept to a low value (something around 400-800) IIRC...

But now, the camera nearly meters for the ambient, leaving only one or two stops for the flash, which often hasn't a low-enough burst to accomodate the resulting high sensibility...

And even more troublesome : both the K7 and the K5 have a upped-up Controller flash burst (surely to ensure proper communication in broad daylight), making wireless useless when you want to balance ambient and flash...
07-15-2011, 10:40 AM   #3
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QuoteOriginally posted by wutsurstyle Quote
Hey guys, for those with a k-5, I was wondering in the situation with an external flash like a Metz 36 does the Auto ISO usually default to a low ISO like 400 or does it tend to hit high ISO's in low light situations. I only ask because I noticed my k-x in Program mode shoots ISO 6400 in dark situations when I know the flash is capable of lighting the room enough to hit ISO 400 with no problem.

I noticed another k-5 thread where tilting the flash for bounce causes overexposure, but thats not exactly my problem here. Thanks for any feedback ahead of time.
the ISO number has become the "number I watch" on the K-5 more than anything else. If you are going to trip the mother of all strob lights (or a pan of flash powder) there is no special reason to let the camera default to an ISO of
32000.......

When I was using the K10 or even the older *istD, I found the 'auto ISO range' setting very useful, but neither had much range, but the K5 has so much potential range that I find that I need to 'dial it in' pretty regularly.

to my tastes, there is about half a dozen usable F stops of range in the ISO and howyou use that will have more than a trivial impact on the ultimate photo.
07-15-2011, 01:17 PM   #4
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I agree. Their choice to allow more ambient light fill the picture rather than your dedicated fill-in flash strobe is a bit counter-productive. I can tell a difference between "color of light" when I forcefully shoot at ISO 400 compared to ISO 6400. It gets warmer with higher ISO's and I can see where one would want that..but if I go that route I might as well go Available Light all the way. I very much prefer it default to low ISO's for cleaner images especially if my flash can provide the light. That way one has more control with a studio setup. Its a good thing changing ISO is so easy for us.

07-26-2011, 07:00 AM   #5
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The problem with auto selection of too high ISO is that the flash guide number increases and minimium distance increases too.

If subject is positionned before the minimum distance then it is burned.

High auto ISO with flash is available in large rooms (sports).

For portrait, you will have better results with low ISO : the background will be darker (lower Guide Number). Manual setting of ISO (and aperture) will give you the capacity to control the background ambiance, lighter or darker. Remember the relation between ISO and Guide number. It's a key to make great photos with flash.


With my K5 and AF 540FGZ i have great results for portraits inside with the flash oriented vertically and with the white reflector.

Last edited by pscl57; 07-26-2011 at 07:32 AM.
07-26-2011, 09:01 AM   #6
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What it means? I have no idea...but I accidentally took this using the K5 and the 540 flash mounted off the camera. Never noticed that I was at ISO 12,800. Turned out OK for me...not near as good as Mom's Cherry pie turned out though!
[IMG] [/IMG]

Regards!
07-26-2011, 03:47 PM - 1 Like   #7
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OK here's the deal. In auto or semi auto modes which includes Av, Tv, TAv, Sv, the camera will meter for ambient and use you flash as fill only. Unless you are outside on a sunny day intending to use you flash as fill to just lift the shadows cast by the sun, this is not what you want.

Here's a post I did in another thread to answer exactly the same question ===================================================

Yes that is typical, the camera is exposing for purely ambient light in auto or semi-auto modes, and does not take flash exposure into account in that mode. Obviously if ambient gave you the exposure you wanted then you wouldn't even be using flash. So, do not shot in auto or semi-auto modes whilst using pTTL on the flash unless you are only doing subtle fill flash. Indoors is not for fill flash.

So, put the camera in manual mode, ISO ~400 to 800, shutter say ~1/100, aperture to taste (usually wide though). You want the meter to be saying you are under exposing by 1 to 3 stops (this indicates how much ambient light will be let in, the more negative the darker the ambient). The flash should be in pTTL mode. Aim the flash preferably at a wall so light will bounce off that and illuminate your subject. Push the shutter. The camera will then instruct the flash to achieve overall correct exposure. Then chimp and if your subject looks to bright or dim after this then use the FEC compensation on the flash to adjust. Typcially I end up dialing in -0.3 or -0.7 FEC. If ambient is too dark or bright then use ISO, aperture or shutter to adjust, this will alter the mix between ambient and flash but not the total overall exposure (only FEC will do this). The more ambient you let in (slower shutter, higher ISO, wider aperture) the less flash power will be used.

Remember, in pTTL mode the camera will use the flash output to achieve overall correct exposure. The more negative the meter says the scene is, the more light will have to be dumped by the flash to achieve correct exposure (hence the greater the ratio of flash to ambient).

All this sounds complex but is actually very easy once you try it and get the hang of it. The results are fantastic so it's worth mastering.

The best site I've found on using TTL mode on the web is this one http://neilvn.com/tangents/. The think "the strobist" is the best site for off camera manual flash photography if you don't want to use pTTL.

Good luck and have fun experiementing

Last edited by twitch; 07-26-2011 at 03:57 PM.
07-27-2011, 06:34 AM   #8
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Thank you for your clear response and your advice.
Perhaps the best explanation I've read about it

07-27-2011, 04:31 PM   #9
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QuoteOriginally posted by twitch Quote
OK here's the deal. In auto or semi auto modes which includes Av, Tv, TAv, Sv, the camera will meter for ambient and use you flash as fill only. Unless you are outside on a sunny day intending to use you flash as fill to just lift the shadows cast by the sun, this is not what you want.

Here's a post I did in another thread to answer exactly the same question ===================================================

Yes that is typical, the camera is exposing for purely ambient light in auto or semi-auto modes, and does not take flash exposure into account in that mode. Obviously if ambient gave you the exposure you wanted then you wouldn't even be using flash. So, do not shot in auto or semi-auto modes whilst using pTTL on the flash unless you are only doing subtle fill flash. Indoors is not for fill flash.

So, put the camera in manual mode, ISO ~400 to 800, shutter say ~1/100, aperture to taste (usually wide though). You want the meter to be saying you are under exposing by 1 to 3 stops (this indicates how much ambient light will be let in, the more negative the darker the ambient). The flash should be in pTTL mode. Aim the flash preferably at a wall so light will bounce off that and illuminate your subject. Push the shutter. The camera will then instruct the flash to achieve overall correct exposure. Then chimp and if your subject looks to bright or dim after this then use the FEC compensation on the flash to adjust. Typcially I end up dialing in -0.3 or -0.7 FEC. If ambient is too dark or bright then use ISO, aperture or shutter to adjust, this will alter the mix between ambient and flash but not the total overall exposure (only FEC will do this). The more ambient you let in (slower shutter, higher ISO, wider aperture) the less flash power will be used.

Remember, in pTTL mode the camera will use the flash output to achieve overall correct exposure. The more negative the meter says the scene is, the more light will have to be dumped by the flash to achieve correct exposure (hence the greater the ratio of flash to ambient).

All this sounds complex but is actually very easy once you try it and get the hang of it. The results are fantastic so it's worth mastering.

The best site I've found on using TTL mode on the web is this one http://neilvn.com/tangents/. The think "the strobist" is the best site for off camera manual flash photography if you don't want to use pTTL.

Good luck and have fun experiementing
Thank you very much, best explanation i've seen, why don't they put a simple statement like that in the manual, arrgh! But now i understand - much thanks.
07-27-2011, 07:00 PM   #10
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Twitch or anyone else that can explain,
Do Canon and Nikon systems basically work the same way with regard to ambient light, i.e. the camera will try to work out a solution wtih ambient light when in auto or semi=auto modes, but then will use flash to make up the difference?
(i know there are differences with the various TTL implementations, just wondering on the interface between ambient settings and flash?

Too many instructions for electronic stuff tell you what to do, but not the why of the way the software and mechanism is designed. The why is far easier to remember than 100's of specific situations, IMHO.
07-27-2011, 08:29 PM   #11
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QuoteOriginally posted by philbaum Quote
Twitch or anyone else that can explain,
Do Canon and Nikon systems basically work the same way with regard to ambient light, i.e. the camera will try to work out a solution wtih ambient light when in auto or semi=auto modes, but then will use flash to make up the difference?
Not so much "make up the difference" as meter for ambient plus put out a little bit of flash for fill. I believe Canon works the same way as Pentax, but not sure about Nikon. The way to test would be put a external flash on the Nikon/Canon camera, camera in Av mode and meter, make a note of ISO/Shutter/Ap. Turn on flash. See if any settings change.

Last edited by twitch; 07-27-2011 at 10:49 PM.
07-28-2011, 06:52 AM   #12
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I used to own a Canon T2i that would always attempt to default to Iso400 no matter the ambient lighting conditions. Only until the power guide of the flash was not capable of properly exposing the scene did the ISO start going beyond Iso400 in AutoIso mode. Not sure if anyone can cofirm. Just my 2cents.
07-29-2011, 11:03 AM   #13
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QuoteOriginally posted by twitch Quote
Not so much "make up the difference" as meter for ambient plus put out a little bit of flash for fill. I believe Canon works the same way as Pentax, but not sure about Nikon. The way to test would be put a external flash on the Nikon/Canon camera, camera in Av mode and meter, make a note of ISO/Shutter/Ap. Turn on flash. See if any settings change.
QuoteOriginally posted by wutsurstyle Quote
I used to own a Canon T2i that would always attempt to default to Iso400 no matter the ambient lighting conditions. Only until the power guide of the flash was not capable of properly exposing the scene did the ISO start going beyond Iso400 in AutoIso mode. Not sure if anyone can cofirm. Just my 2cents.
Thanks to Twitch, again,
for the first time ever, i finally think i understand flash usage . Its just so counterintuitive to realize that when putting an automated flash onto an automated camera body, is going to be better off with a manual exposure program - - i'm not crazy but it might help.

And i can understand what Canon is trying to do with the T2i. If one assume less knowledgeable entry level buyers, then why not automate the body up to 400iso, if the IQ is still pretty good at 400iso, before the body pops the flash, or forces the user to pop the flash. Its just that these automated features for the beginner can sometimes hamstring the user who knows a bit more.
07-29-2011, 11:35 AM   #14
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Flash usage is a complex process since it involves so many things, in fact if you count the bounce flash angles and wireless flash scenarios, there is an infinite number of ways that can make/ruin your photos. The best way IMHO to handle this is to set most of the parameters manually, so the automated processes by the flash and camera become much simpler. The approach I take when using it as fill flash,use Av mode with HSS either spot or center-weigh metering with EV to fine tune. When I use it indoors for bounce flash, use M mode with slow sync flash. I don't use auto-ISO in any of the situations. That's my 2cents.
07-29-2011, 11:41 AM   #15
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No flash expert here...dumb as a rock on flash.....but, I have always achieved the best results using M mode on the camera and manual on the flash too. It takes a few shots to get it all right, but usually it is fast and turns out well. For quick shooting where time is not available, the Pttl has worked good for me in most every case...just not as well as manual.

I often wonder what a real flash expert uses most often?
Regards!
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