Can 'auto ISO' be used when using a flash?

[paul_b]

I'm curious how it actually works. I have a Nikon D3100 and a fixed Nikon SB400 speedlight.

The problem is when i use the flash indoors in the evening my subject (my poor child) always seems to get overexposed by the flash like its throwing too much light on to her. I have 'auto ISO' set to on and was wondering if that is the culprit?

What i'm interested in is this: To get the correct exposure does the camera first automatically adjust the flash power before considering the needed auto ISO adjustment or vice-versa. Could this be why i seem to be getting too much flash light? Can 'auto ISO' be used when using a flash?

 

[ShootRaw]

I would manually set your Iso...Use your in camera meter to balance your exposure..Once at 0 under expose it a few clicks and then add your flash..

 

[gqtuazon]

I'm curious how it actually works. I have a Nikon D3100 and a fixed Nikon SB400 speedlight.

The problem is when i use the flash indoors in the evening my subject (my poor child) always seems to get overexposed by the flash like its throwing too much light on to her. I have 'auto ISO' set to on and was wondering if that is the culprit?

What i'm interested in is this: To get the correct exposure does the camera first automatically adjust the flash power before considering the needed auto ISO adjustment or vice-versa. Could this be why i seem to be getting too much flash light? Can 'auto ISO' be used when using a flash?

Hi Paul. Try using bounce flash first and use ISO 800 for indoor. Let us know how that works.

 

[Jonathan]

The amateur (me) says yes you can, but (as mentioned already) use the flash sympathetically and bounce the light off the ceiling or wall by angling the flash. That will give you a gentler light. Never use it like a spotlight.

 

[WayneF]

Can 'auto ISO' be used when using a flash?

Probably it can be done, but you may not want to.

Flash and Auto ISO on Nikon DSLR has gone through three variations (making explanations difficult).

1. Older ones, from D70 to D300, never increased ISO if flash was recognized with Auto ISO. They always stayed at lowest value, simply because we were using flash instead. Good plan, there is much to be said for that.

2. Then from D300S and later, it changed. I believe (not positive) your D3100 is in this group. Then Auto ISO did its thing, adjusting for the ambient light level (resulting in very high ISO indoors), and then the flash power level had to adjust for this high ISO situation. Several things wrong with that, flash pictures ought not always be high ISO. And the ambient incandescent light was orange, and caused white balance problems.

3. The very latest models (D800, D600, D7100, and I really don't know what else) would only advance ISO by two stops (for example, only to ISO 400) when flash was used. This was reasonable for bounce, and ceased doing the absurdly high ISO.

You can determine your cameras ISO mode this way: With flash turned off, and Auto ISO on, indoors where you need flash, compose your picture and half press shutter to see what ISO is. Probably pretty high ISO in dim places where flash is needed. Then reach up and turn the flash power switch On. What does ISO do at half press?
1) will stay the same, low. 2) will remain at the sky high value. 3) will advance only 2 stops over minimum (4x value).


2. Above should work, exposure wise, just with very high ISO, and possibly orange. We need more info, etc, to explore why not, but really, it seems a moot point. You surely do want to turn Auto ISO off with flash.

 

[paul_b]

Wow great advice thank you so much, I've learnt a lot.



Here's my plan now:



Ok, with Auto ISO on and with external flash the camera was giving me an Auto ISO value of 200. So this must of meant that because the ISO was low the camera was using more flash power instead and probably explains why my subject was always blown out with too much flash light.


So, therefore i'm turning Auto ISO off and using ISO 800 for indoors in the evening. So now I need to work out my ideal settings (maybe i can program them so i can reach them with just a touch of a button or 2?)


I therefore with ISO 800 need to work out my other shooting settings with a combination of shutter speed (minimum to stop camera shake from my non VR 35mm f1.8 prime lens), aperture, and flash power, taking into consideration that i need to balance ambient light with flash power.


I would imagine im going to need about 160th of a second to prevent camera shake and maybe even 200th of a second (max for my flash).


So i have my first 2 values - 160th or 200th of a second (shutter speed mode) and iso 800 (if ambient light is not enough then i will need to reduce shutter speed). I would imagine i would need to go right down to f1.8 for the widest aperture to let in the most light thus reducing the need for flash power from the flash. So my indoor evening values would be 200th sec shutter speed, f1.8 aperture and ISO 800. The only thing that remains is to work out how much flash power i need and if the default looks ok. The SB400 is obviously an automatic flash, but flash power can be adjusted in camera. I'm going to use bounce flash (straight up, as i have to get quite close with this lens). Its probably advisable to reflect some of it forward using a white buisness card poked into the flash unit to reduce those bottom shadows.


So i'm now experimenting with test shots and see what the images look like at the default flash power and then either decreased or increase it.

 

[WayneF]

Ok, with Auto ISO on and with external flash the camera was giving me an Auto ISO value of 200. So this must of meant that because the ISO was low the camera was using more flash power instead and probably explains why my subject was always blown out with too much flash light.

ISO 200 seems unexpected. I would have expected higher. Settings could affect that. What were your Auto ISO settings for Minimum ISO and for Maximum ISO? (Normally) it cannot go below minimum or above maximum.

But... the TTL flash is still automatic metered exposure, regardless of camera settings like shutter speed or ISO. TTL is metered, and the design is that the TTL flash power level is set to be what it needs to be, to be correct for whatever situation. It is not always precise, but if we want to pursue it, we will need more information about why the subject was blown out. A sample picture of the problem would help, along with either Exif or details of ISO, shutter, aperture, distance, any special conditions, etc. Was it direct flash or bounce? Direct flash is sometimes blown out a little. We control what the TTL automation does with Flash Compensation, specifying either +EV or -EV changes to the results we see.

So, therefore i'm turning Auto ISO off and using ISO 800 for indoors in the evening. So now I need to work out my ideal settings (maybe i can program them so i can reach them with just a touch of a button or 2?)

If bounce flash, the SB-400 (a lower powered flash) may need ISO 800 if like f/4 under a ten foot ceiling. For direct flash though, that seems higher than necessary, ISO 200 is probably fine.

I therefore with ISO 800 need to work out my other shooting settings with a combination of shutter speed (minimum to stop camera shake from my non VR 35mm f1.8 prime lens), aperture, and flash power, taking into consideration that i need to balance ambient light with flash power.

There are several ifs and buts about flash. Making up example numbers, but for example, if with the flash turned off, often the indoor scene typically meters say f/5.6 at 1/2 second. You reach up and turn the flash on, and it changes to f/5.6 at 1/60 second (in camera A or P mode). This 1/60 is NOT sufficient exposure for the ambient, which we just said needed 1/2 second. The 1/60 is Nikons Minimum Shutter Speed With Flash... if using flash, we have no need that it be 1/2 second. But that makes the ambient be about five stops underexposed (we are after all using flash instead).

So... in that case - any camera shake caused by the "slow" 1/60 second is too dark to be visible.. it is "don't care". Instead the flash duration is vastly faster, and will stop the motion (of camera shake, or from the moving subject too). Hot shoe flashes are called speedlights for this reason.

I would imagine im going to need about 160th of a second to prevent camera shake and maybe even 200th of a second (max for my flash).

It is common to use camera Manual mode M with flash indoors. Obviously, if it meters 1/2 second without flash, the ambient is not a consideration any more. And shutter speed does NOT affect flash exposure at all. But instead of always using 1/60 second, we can choose another shutter speed, faster to block all ambient (typically orange from incandescent), or slower to allow some of the ambient in. Our choice in camera M mode. The flash is still fully automatic TTL mode, regardless.

 

[paul_b]

Here's some sample images to show to problem - i assume the settings are visable to view, if not i'll upload the RAW files

 

[paul_b]

ps both pics are bounce flash straight up (no point in angling the bounce as its a 35mm prime lens so i have to get quite near to the subject)

 

[paul_b]

Ok, probably 'blown out' was the wrong choice of words, but to me she looks certainly overexposed by flash.

 

[WayneF]

Hmmm. I guess I cannot help, because I would not call that overexposed. It looks pretty good to me. Speaking of the bottom image, there is nothing at 255 (right end of histogram). The background window starts becoming visible at 240 (we can't help windows much). The yellow shirt starts showing about 225. The face not until about 205. (I am holding ALT key while shifting Adobe Levels White Point. Holding Adobe Raw Alt key with Exposure shows this too, but it is calibrated in -EV instead of RGB). My notion is these are fine exposures, very good.

But if you want it darker, then add just a bit of -EV Flash Compensation, maybe -1/3 EV. However, my guess is that a factor might be that many LCD monitors are shipped with brightness too high. Mine has been calibrated to be not quite so bright. I would check that first.

My other notion (just a preference) is that I see no need of f/1.8, esp not at ISO 800. Maybe it was just to blur the background (again, a preference, yours is as good as mine). You probably are down on the floor with her (so ceiling is that much higher) and if on the floor, I would have used ISO 400 f/4 for bounce with a SB-800 and ten foot ceilings. But the SB-400 has about one stop less power, and ISO 800 might be about right at f/4. That is speaking more of capability than preference.

The bounce shows well in the room background, but in close subject, there is quite a bit of direct spill, and to me, the shadows are direct instead of bounce. Another rule of thumb is that proper perspective of human faces means we need to stay back 6 or 8 feet. Zoom in all you want for head and shoulders, but for perspective, standing closer often tends to make closer noses look too large, etc. It does look OK here though.

 

[FastGlass]

Yes you can use auto ISO when using I-TTL or manual flash. When using flash, the cameras light meter doesn't care if your using flash or not. It's going to expose for ambient light
regardless. So if your shooting in low light and you have your auto ISO enabled than yes the camera is going to choose a high ISO to obtain correct exposure when the other settings such as aperture and shutter can't be adjusted any more than what their allowed. So when using a flash in I-TTL. Once the shutter is triggered, the magic of the I-TTL system reads the light that is bounced off what ever subject your focus point is on and it decides how much light from the flash is needed. All this is completely separate from the cameras internal meter. If you want your background to fall into blackness than set your shutter so that no ambient light is recorded. The flash will still expose the subject correct. Remember when using flash, you have two exposures to deal with. Ambient and flash .

 

[FastGlass]

Also you should think about adding a gel to your speedlight to better match the existing ambient light. The background looks to be on the orange side of color.

 

[paul_b]

For me i think her face has a whitish colour to it rather than her natural skin colour, and not much definition.

 

[WayneF]

For me i think her face has a whitish colour to it rather than her natural skin colour, and not much definition.

Maybe a bit less yellow would help the skin color, but I think that is White Balance, not exposure. My own rule of thumb for printed portraits is that the highlight on skin ought not to be more than 235 to 240. Yours just barely makes 200.

Mixed lighting is always a bear to deal with. High ISO does increase capture of the orange incandescent ambient (which I only assume is present). Your pictures show shadows BELOW the far room furniture, from above, but I don't know if that was bounce flash, or the incandescent room light. If exposure was set for room light, it is no doubt only the room light. f/1.8 and high Auto ISO is just not my own style with flash.

So there are two philosophies. Nikon's Auto ISO will use high ISO to expose the indoors ambient, and the flash becomes fill level, not the main lght. That leaves things orange. Standard way to deal with that is to use an orange CTO filter on the flash, to make it orange too, and then to use Incandescent White Balance to correct both. Nikon added such filters to their SB-900 and SB-700 flashes about the time they allowed Auto ISO to go so high with flash.

Or, we can continue to simply use conventional low ISO 100 with flash. This keeps the ambient more dim, underexposed, not orange, and then the white flash lights everything of interest. Bounce lets that also be the room background, but bounce generally needs a little more ISO to help the available flash power. It need not be ISO 3200 however.

Correcting WB: Buy a $5 Porta Brace White Balance card from B&H (or if available, other genuinely white things, like cheapest printer copy paper, or white ceramic dishes, are nearly as good - far better than nothing). Take test picture with it in the scene, illuminated by the SAME light as the subject. Use the WB tool in Raw to click it to correct the WB to be perfect. Then same picture without the card is corrected the same (both at once, one click). It doesnt get any better than that.
See White Balance Correction, with or without Raw

 

[paul_b]

interesting - thanks for taking the time to explain that to me

 

[paul_b]

Can the problem in that specific photo now is has been shot be rectified in Lightroom or ACR using the standard white balance tool? i.e temperature and tint, or do i have to go advanced (i'm not) and actually reduce just the orange or yellow?

Why does a high iso increase the orange? (sorry i could Google it but other readers may find it interesting to read it here)?

 

[WayneF]

Can the problem in that specific photo now is has been shot be rectified in Lightroom or ACR using the standard white balance tool? i.e temperature and tint, or do i have to go advanced (i'm not) and actually reduce just the orange or yellow?

It can be corrected, but you need some known white thing in the scene to use the WB tool. Clicking WB on that white shoulder strap is close, but I think not quite exact (try it). Clicking a Known white thing says "Computer, I know this is white. Make it be white", and it removes whatever color cast is there (from the entire image). When a white thing is white, that is perfect WB. If it really was not quite white, result will be off a bit (but maybe still better?)

Or you can simply adjust it by eye to be pleasing, by sliding the sliders. This becomes arbitrary, but pleasing.

Why does a high iso increase the orange? (sorry i could Google it but other readers may find it interesting to read it here)?

Because the high ISO fully captures the weak incandescent, which is orange, so we see the orange. Auto ISO sets up all settings (including ISO) to properly capture what the light meter sees, which is 100% ambient... and incandescent is orange.

Then automatic TTL BL sets the flash power level to work into that setting, as weaker fill flash, not as main light. The ambient incandescent is the main light.

Snap off one test picture, flash or sunlight, but using Incandescent WB. Or just click Tungsten WB in Raw on such a flash or sunlight picture. See? It is blue, because it removed expected orange.
Our human brain hides it from us, but it is orange in a picture.

Low ISO shuts out the weak ambient, underexposes and ignores the weak ambient, and only the stronger white flash contributes light into the picture. Not orange.

 

[paul_b]

Can the orange luminance also be reduced in the HSL panel in Lightroom (i assume its the same in ACR) - is that an option too?

 

[WayneF]

Sure, shifting colors for correction can arrive at the same result

HSL is sort of a standard graphic tool, where WB (Temperature and Tint, which are the -a and -b Lab color coordinates) is more oriented to what cameras need (leaving Luminance to Exposure).

But shifting colors is shifting colors.