Auto ISO on 7D (1 Viewer)

This morning I have been playing around with auto iso for the first time ever on my 7D. I was using AV mode f5.6 and evaluative metering ( + 1/3 ev). The shutter speeds I am getting are between 1/640 and 1/800 which is ideal for hand-holding my 300/2.8 + 1.4 tc with I.S. on. How does this work? is the shutter speed relative to the focal length of the lens you are using?

First results are encouraging and it could be useful in variable light situations I guess. I am a bit concerned about the intermediate ISO being used as they can apparently result in more noise than the next full ISO up according to what I have read. Having said that I have noticed lately that a lot of top shooters seem to readily use intermediate ISO - how much of a problem is this on the 7D in your experience?

I just found this on another site about it.
Rob
According to the Canon 7D User manual, page 63, when the 7D mode is set at Auto, CA, P, Tv, Av or M mode, the ISO will float between values 100 and 3200, depending on the exposure. I believe that Highlight Tone Priority changes the available values to ISO 200-3200 (but I don't know this for sure.)

It also appears that exposure compensation is affected, but I'm not sure just how it is affected in the 7D.

I also believe that the shutter speed in Av mode is selected using the closest available shutter speed according to the reciprocal of the focal length.
__________________

GYRob said:

I also believe that the shutter speed in Av mode is selected using the closest available shutter speed according to the reciprocal of the focal length.
__________________

Click to expand...

Interesting about the focal length and shutter speed in Av mode Rob. I have just been playing around with a couple of lenses and this is what I am mostly getting getting:-

420mm = 1/640 to 1/800 sec
200mm = 1/250 to 1/320 sec
70mm = 1/100 - 1/125 sec

This seems to be working out at around focal length x crop factor (1.6) which is quite nice!

Hi Roy,

my understanding is that the camera does indeed serve up the ISO necessary to give a 1/FL shutter speed when using Auto ISO.

Keith Reeder said:

Hi Roy,

my understanding is that the camera does indeed serve up the ISO necessary to give a 1/FL shutter speed when using Auto ISO.

Click to expand...

Maybe its the next speed faster or something like that Keith as I seemed to be getting FL x 1.6 (ish).

What's your take on intermediate ISO's Keith? - I took some shots of a Dunnock on auto ISO this morning and there were almost all an intermediate ISO value and yet they look very clean - mind you it was good light so nothing over ISO 800.

Intermediate ISOs - there's good and bad, Roy.

Some intermediate ISOs are actually higher ISOs "overexposed". This like ETTR, so you get less noise from them.

But you lose DR headroom with these ISOs - they're effectively exposing to the right in the camera, meaning less DR "wiggle room" for us - the histogram is already shoved over to the right.

Intermediates that are derived by - in effect - underexposing an ISO then pushing, will be noisier but will have more headroom.

The second post here is an excellent explanation, and applies to the 7D as well as the 40D.

Keith Reeder said:

Intermediate ISOs - there's good and bad, Roy.

Some intermediate ISOs are actually higher ISOs "overexposed". This like ETTR, so you get less noise from them.

But you lose DR headroom with these ISOs - they're effectively exposing to the right in the camera, meaning less DR "wiggle room" for us - the histogram is already shoved over to the right.

Intermediates that are derived by - in effect - underexposing an ISO then pushing, will be noisier but will have more headroom.

The second post here is an excellent explanation, and applies to the 7D as well as the 40D.

Click to expand...

Got it Keith, That link is a good read. It uses the nearest ISO which means over or under exposing depending on which is nearest - swings and roundabouts I guess.

I too have been playing around with the ISO settings recently on my 7D, Roy. I have now disabled intermediate ISO values having used them from the start. I have also increased the maximum to 6400 from the default limit of 3200 plus activated the shift facility so that the camera will drop down one ISO setting if not on auto ISO. I'm sure however you are aware of these features.

I have been regularly alternating between setting the camera to auto ISO and fixing it to one value, 400. Still can't decide if one route is better than the other of whether in fact it's best to change 'on the fly' with the Q button as conditions dictate at the moment of shooting.

I feel I still have a lot to learn about ISO and it's effect on getting the optimum exposure (ettr) so it's good to hear the views and findings of others.

Nick

NixAvianPix said:

I too have been playing around with the ISO settings recently on my 7D, Roy. I have now disabled intermediate ISO values having used them from the start. I have also increased the maximum to 6400 from the default limit of 3200 plus activated the shift facility so that the camera will drop down one ISO setting if not on auto ISO. I'm sure however you are aware of these features.

I have been regularly alternating between setting the camera to auto ISO and fixing it to one value , 400. Still can't decide if one route is better than the other of whether in fact it's best to change 'on the fly' with the Q button as conditions dictate at the moment of shooting.

I feel I still have a lot to learn about ISO and it's effect on getting the optimum exposure (ettr) so it's good to hear the views and findings of others.

Nick

Click to expand...

Hi Nick, I have always had intermediate ISO values disabled so that I only ever dial in full ISO's but this does not effect Auto ISO as it will still use an intermediate value !!!, from what I read there is no way to stop this - unless you know different Nick?

What's this shift facility so that the camera will drop down one ISO setting if not on auto ISO all about? I have not come across this one before.

Roy, I stumbled across this feature that's available on the 1D bodies (ISO safety shift) just a couple of days ago and so was curious to see if it's there on the 7D. Found safety shift at Cf I.6 (although does not mention ISO). However, I haven't had a chance to try it out yet or find any more helpful info on it.

Didn't realise that auto ISO uses intermediates even if they are disabled. I guess the only way round this is to set the value manually and use ec to adjust as per Keith's linked article.

Nick

Ps: thanks for the info on 300 f2.8 and Black Rapid the other day.

NixAvianPix said:

Roy, I stumbled across this feature that's available on the 1D bodies (ISO safety shift) just a couple of days ago and so was curious to see if it's there on the 7D. Found safety shift at Cf I.6 (although does not mention ISO). However, I haven't had a chance to try it out yet or find any more helpful info on it.

Didn't realise that auto ISO uses intermediates even if they are disabled. I guess the only way round this is to set the value manually and use ec to adjust as per Keith's linked article.

Nick

Ps: thanks for the info on 300 f2.8 and Black Rapid the other day.

Click to expand...

Thanks for that Nick - I have just been looking at this safety shift. It is supposed to be handy when a subjects brightness changes erratically and correct auto exposure cannot be obtained. It say the Camera will change the exposure setting automatically to obtain a correct exposure. I am not sure in what circumstances you would use this or what it actually does - I will delve into this more.
EDIT Just been reading about this safety shift and can now see how its works - not sure it would be a lot of use in bird photography if you shoot in AV mode and have your lens wide open (or there about's) as there would not be a lot of headroom to change the aperture.

As for normal shooting I have no problem in the setting the ISO I want and also using exposure compensation (practising ETTR) - that is my normal shooting style anyway. My 'standard' birding ISO is 400 and then I just up or down it to suit the light. The only time I deviate from this is if I am specifically shooting BIF then I will usually switch to manual and meter the ambient light at around 18% grey and just alter the shutter speed to suit the tone of the bird.

I was just curious more than anything about auto IOS just to see if there are any advantages to it and if so in what circumstances.