Speedlites and auto iso

Weetobix

Weetobix

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Name
James
Edit My Images
Yes
I'm using a Canon 5D mk3, mostly to shoot weddings, and like to use auto iso for versatility. But when I use a flash, the iso gets set to 400 automatically, no matter how dark it is, meaning I have to then set the iso to something more useful manually, just for the shots I want with the flash.
Any idea why it should do this and if there's any way to change it?
 
What flash?
 
The way that Canon's flash algorithms work Auto ISO would be a nightmare for them to try to compute (like stapling a jelly to a cloud). The flash needs some fixed settings so it knows where it's working from.

I've never noticed this because as soon as I fire up the flash indoors I switch to Manual mode and a fixed ISO because balancing with a fixed ambient exposure is my main aim.

I just wonder what Nikon do, as they've been much better at Auto ISO historically.

I wonder if it's in the custom functions or advanced flash menu.
 
DG Phototraining said:
No idea !!!

When Auto ISO first came to my cameras I played with it a bit, but have ignored it ever since - hang on though, I'll check :D

Dave
Click to expand...
When Canon first did it, it was rubbish, but I have to say on the 6d it's fantastic (until I need to shoot in M)
 
Well that was interesting lol

Sat editing in a fairly dark room I set it to auto ISO and the ISO shot up to 8000

I then popped a flash on camera and composed the same shot and the ISO went down to 1600

I've no idea why it choose that ISO as the subject was easily within the range of the flash where even at 100 ISO the flash would have been powerful enough

I doubt that helps at all though :D

Auto ISO is now once again confined to the 'dustbin'

Dave
 
If you take a pic of a bright sky the ISO will drop to 100
 
When using a Speedflash as a main point light source it's important to consider that the ambient lighting around you is now a secondary factor. The power of the flash and distance of the flash is determined by its Guide Number (GN) which does not require the camera to need a high ISO to record the image. Typically I will use no more than a 200 ISO 'manually set' and that is sufficient for most subjects. It is also the optimum setting for quality for most Nikon processors.

By dividing the GN of the flash by a working Aperture that will give you the maximum subject distance. Now, if you set the ISO manually to 400 ISO that will reduce the recycling times of the flash.

A general rule of the thumb for experimentation, and a starting point try a manual setting of ISO to 200, aperture to f/16 and shutter speed to 1/250. Without changing this settings move closer, or further away from the subject until you are happy with the final image. Having tried this. The next logical step is to remain static and open up / close down your aperture until you once again happy with the results.

Shooting at 1/250 is going going to freeze your subject but by reducing the camera speed will also start to bring in the ambient light and background. How much of this is entirely dependent on the slowness of the shutter speeds of 1/30, 1/15 will yield some good results.

In short, Auto ISO takes all the thinking away from the photographer but also stifles creativity and enforces certain limitations.
 
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