Auto iso

Started Sep 23, 2013 | Questions thread
PenguinPhotoCo Veteran Member • Posts: 6,284
Re: Auto iso

Don wrote:

I have a shake problem with the shutter slower than 100,

Depends...if you do it right the flash will light the subject and freeze them - so you can drat the shutter and not get blur.
I find if i go much below 1/60 the subject's motion will be blurred - at a reception. For church formals I've gone as low as 1/4 second (camera on tripod) to capture ambient light and flash freezes the subjects just fine. 1/20 and 1/30th of a second is common for me for church formals.

if you enable high speed sink then the shutter can go above 250 on my camera. so if I set the shutter at 250 the lens at 2.8 and the exposure is dark if the auto iso is on the camera will use the lowest iso to compensate for my settings. So that means to me if I wanted to go to a 500 shutter speed the camera would make the iso adjustment, with or with out flash.

Wiht flash the light is on or off. Want more light? Then it's on longer. It's not a 'dimmable' type light source.
The shutter in our cameras moves and only a slit is open at any give time. It takes time for the shutter to travel over the sensor. If the shutter speed is raised above the x-sync value then the flash will be off before the shutter completes it's move - you'll see this as a black band on the image.

HSS has the flash 'pulse' or 'strobe' very fast. This is hard on the flash and batteries and in my experience is of limited value outside unless you are very close to your subject. Just not much power in HSS.
I find it easier to go for 1/200 (max on my 5d2) and up the aperture at iSO 50 and add fill flash to balance. Working in the shade helps a lot. Just pick your BG carefully and it works fine.

I do use TTL with the flashes and adjust them as necessary. It just seems you could shoot manual set the f stop to what ever depth you wanted and the shutter however fast for whatever you want for the ambient light or action and never worry about the exposure because the camera would adjust the iso to match.

eTTL means the flash thinks - 'what exposure are we aiming for?'
Auto ISO does the same thing.

So this in Av mode and shutter speed gets to play too.

You've introduced 3 variables there that you have no control who know what you're gonna get as an end result.

What does the camera prioritize?  I know canon's eTTL is fill flash until it's X dark then it changes to make the flash the main light. At that crossover point you get either version as it sees fit...unpredictiable results is the reality.

Canon's programming says in Av mode the shutter can drop as low as 30 seconds. Not 1/30 but a FULL thirty seconds. Hence my use of M in darker environments. Where Im' usually at 1600. Auto ISO I don't think goes that high.

That would force me to use Av or Tv modes with auto ISO...and there will be three things changing at will. Will my shutter speed drop? Or ISO go up? Or just blast the subject with more flash?

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