Auto ISO and Fill flash

[Ted]

Have recently got a D90 and been using my 50mm 1.8 indoors in low light. The function that makes it so easy to use is auto iso which i'm sure you are all familiar with......set max iso and min shutter speed and fire away.

It's great and exposes everything perfectly.....except for when I try and use fill flash to reduce shadows. I set the flash (in camera flash, not external) to -1.3 ev and instead of auto iso keeping all things the same and letting fill flash do its job, it massively under exposes.

I have tried compensating by setting the exposure level to +1.3 (and keeping the flash at -1.3) and this seems to help but there must be a better/easier way of using Auto iso, adding some fill flash and getting a well exposed result.

Any thoughts on how to do this?

Thanks

 

[puddleduck]

Turn of AutoISO for flash.

I'm not sure if the D90 has shooting or custom banks - if so define a Flash bank, with AutoISO turned off.

Otherwise just add an Auto ISO / On Off control to My Menu.

 

[Ted]

I thought that might be the case ....

What are your thoughts on the +1.3 exposure compensation? It seemed to work ok in the limited tests i ran

 

[Richard King]

why on earth use auto ISO? you are throwing all creative control out of the window

There are not that many basic settings on a camera to keep tabs on..

apeture, shutter speed, white balance, ISO and flash power. If your really want to know how to balance flash or fill flash, work through the 101 tutorials on the stobist website, and consign auto ISO to the naughty corner

 

[Ted]

why on earth use auto ISO? you are throwing all creative control out of the window

In the situations where I want creative control then of course i'll turn it off but there will always be occasions where convenience and speed are king and thats when Auto iso cant be beaten.

 

[puddleduck]

I thought that might be the case ....

What are your thoughts on the +1.3 exposure compensation? It seemed to work ok in the limited tests i ran

Dunno - I don't really understand flash :nuts::nuts:

Sounds plausible!

 

[pxl8]

More to the point, why is auto ISO affecting flash exposures? Surely it's only concerned with the ambient light and not what the flash is doing?

 

[puddleduck]

More to the point, why is auto ISO affecting flash exposures? Surely it's only concerned with the ambient light and not what the flash is doing?

This is exactly what is happening.

AutoISO just does what it does, and doesn't measure any contribution from the flash. It meters unflashed (pre-flash)

So you can end up with ISO3200 etc, even with flash.

Best to disable it.

 

[Richard King]

More to the point, why is auto ISO affecting flash exposures? Surely it's only concerned with the ambient light and not what the flash is doing?

because due to the nature of the setting it is trying to balance the normal exposure settings (apeture / shutter speed) against ISO. Exactly how much flash wil it decide to throw in - thats the 100$ question - it depends on the equation they used

 

[Ted]

More to the point, why is auto ISO affecting flash exposures? Surely it's only concerned with the ambient light and not what the flash is doing?

just been googling it and a couple of comments came up from forum members like:

Nikons auto ISO defaults to your manual ISO setting (when you turn the flash on) and only raises the ISO when the flash is uncapable of illuminating the scene.

Late Canon cameras (40D,50D and 5DmKII) use ISO 400 as default all the time, with or without flash. When both camera and flash together are uncapable to aceive correct exposure , the ISO will be adjusted up or down. Nikon's auto ISO default is 200.

Any truth in that?

Apparently if you use flash it will always resort the default iso setting.....off to check my exif data

 

[Ted]

Indeed. All images taken with auto ISO on and with flash were ISO 200. All other shots iso 3200......thus the underexposure

If you try the same thing with a canon it will default to ISO 400.

seems turning it off is the only solution