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Author Topic: Biased auto ISO  (Read 2950 times)

Tijn

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Biased auto ISO
« on: March 12, 2012, 09:58:27 AM »
When I started out with my first DSLR about 6 years ago, I was mostly shooting with automatic exposures in "P" mode. The camera would pick a nice combination of shutter speed / aperture for correct exposure (auto ISO wasn't an option in my body yet). When I saw that some portraits I'd been shooting in bright daylight turned out to be f/11 at 1/400sec shutter speed, I decided to use "aperture priority mode" (aV) instead. It gives me the control over aperture that I want, but it's the absolute opposite of something completely "auto": it's totally fixed. The middle way is to use 'portrait mode' which will hide all the settings it chooses but pick larger apertures. It uses a bias.

On my current body (the 60D), there's an "auto ISO" function; but it too tends to be too biased on low ISO values / slow shutter speeds. The only way to customize this auto ISO setting on my current camera is that you can set an upper limit to the auto ISO it is allowed to pick.

Since learning about the workings of these "auto" modes, I've always had the idea of factually customisable auto ISO playing through my mind, being able to bias it manually. I've yet to see this in Canon cameras. Currently, auto ISO is coupled with "minimum shutter speed" and will always bias ISO value first, and only start to increase it when shutter speeds become really slow. The minimum shutter speed is coupled with the focal length (at least for the 5D mk2), but it's not customisable.

Now what I read recently, on the Nikon D4, was the following:

Quote
"In the D4, Nikon has (at long last) added an 'Auto' option to the minimum shutter speed options, which allows the camera to automatically set the minimum shutter speed based on its knowledge of the focal length that you're working at. This response can be biased in 5 steps, from 'slow' to 'fast' depending on whether you'd like the camera to err on the side of slower or faster shutter speeds. A small change but one that (along with the D4's extremely wide ISO sensitivity span) finally makes Auto ISO more like the 'set and forget' function that it should have been long ago."
-Barney Britton, DPReview

I think it would be great to have a customizable / auto ISO bias setting in-camera. And having seen some of the abilities of the Magic Lantern software I'd be curious whether something like this functionality would actually be possible to make.

Example:

In aV mode (fixed max aperture), biased auto ISO doing two things:
(A) Take a low ISO setting;
(B) keeping the shutter fast between 1/200 and 1/8000.

Now say that you could change the weight of A versus B (i.e. a low ISO having more weight, or a fast shutter having more weight), and that you could change the minimum/maximum range of B. You could perhaps even give weights to individual ISO values to be able to not make it pick the dodgy 1/3rds, or to further reduce the value of the superhigh ISO's.

Setting a fixed aperture value in aV, you'd be able to shoot with auto ISO on, with the camera picking much more useful/appropriate 'auto ISO' settings to start from. It would make Auto ISO much more useful for me in aV mode.
Action sports: give a bit more priority to fast shutters (for action, 1/1000 @ iso 400 is better than 1/250 @ iso 100). General outdoor: moderate bias on low ISO. More landscape-focused: big bias to the low ISO.

I'm not sure if this is quite what the Nikon D4 is said to do in the quote above, but I'd personally very much love to have the option of customising the auto ISO to be biased, as described here.

Positron

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Re: Biased auto ISO
« Reply #1 on: March 12, 2012, 10:20:51 AM »
As far as I can tell, what you're suggesting should be possible with custom firmware, and probably should be included as an option in the official firmware for all cameras in the first place.

I can also say, that as a computer science major with 15 years of programming experience, I cannot figure out Canon's API for the life of me. The function and variable names are quite descriptive but the documentation is downright abysmal. If not for that I'd gladly make an attempt at creating it myself.

neuroanatomist

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Re: Biased auto ISO
« Reply #2 on: March 12, 2012, 10:25:23 AM »
I do like the idea. 

The 5DIII would seem to come closer than previous non 1-series bodies, in that you can specify a minimum shutter speed in Av mode (instead of it being fixed in relation to focal length).  So for example, you can set 1/160 s as a floor even with a 35mm lens, with Auto ISO (settable upper bound), and it won't go lower than that shutter speed or higher than that ISO - and if both are at the ends, it will just underexpose the shot (but there's often a Safety Shift custom function that will override that if enabled).  With that configuration, it's still not the bias you're talking about - in the above example, I bet it will keep it at ISO 100 until the shutter speed bottoms out at 1/160 s, then start to lift the ISO higher as needed.

The 1-series bodies are more customizable - you can set a range for Auto ISO, for shutter speed in Av mode, and for aperture in Tv mode (useful when you have an f/1.2 lens but subjects thicker than eyelashes). 

The idea of a bias is certainly doable, and Canon uses it - just not in their dSLRs.  My PowerShot S95 and S100 have a user-selectable Auto ISO range (like your 60D), but also have a Rate of Change setting for Auto ISO (Slow, Standard, Fast).
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JerryKnight

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Re: Biased auto ISO
« Reply #3 on: March 12, 2012, 10:53:42 AM »
I agree that the past implementations of auto ISO have been fairly useless without more customization, and this probably contributes to the fact that most photojournalist photographers (and photojournalist-style wedding photographers) use Manual mode. If you let the camera guess, then you can get burned when it guesses wrong, and a lot of times, you don't have time for a second attempt. I've used Av maybe once at a shoot, but if I could rely on it more, I might use it more often. I would think most portrait photographers would use Manual as well, but more for consistency.

What I would like to see is auto ISO in Manual mode. ie. Set aperture and exposure, and have the camera choose the proper ISO to make the exposure correct. Might be a little dangerous if you forget to update your settings, but that's already something Manual shooters have to stay on top of. Maybe it could have a "High Auto ISO" warning indicator somewhere. EDIT: Maybe this has been done already. I haven't investigated it thoroughly yet.

I would also like to have way that I could take one picture on Av and then have the camera transfer the exposure settings (including auto ISO?) to the Manual mode. Then I could adjust everything manually, but not have to hunt so much for the starting point.

But honestly, I think Manual photographers feel more comfortable having full control over every setting. It will take time for them (and me) to trust a camera's judgement.
« Last Edit: March 12, 2012, 11:04:27 AM by JerryKnight »

ejenner

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Re: Biased auto ISO
« Reply #4 on: March 12, 2012, 12:11:46 PM »
Well, Canon do make a camera with this functionality.  The S95.  Granted you only have 3 settings, one for basically tripod work (or very steady hands), one 'normal' and one 'high speed'.  You don't have a minimum shutter speed option though, just a max ISO.

Amazing what Canon will put in their P&S that they don't seem to want to put in DSLR's.

neuroanatomist

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Re: Biased auto ISO
« Reply #5 on: March 12, 2012, 12:30:10 PM »
What I would like to see is auto ISO in Manual mode. ie. Set aperture and exposure, and have the camera choose the proper ISO to make the exposure correct. Might be a little dangerous if you forget to update your settings, but that's already something Manual shooters have to stay on top of. Maybe it could have a "High Auto ISO" warning indicator somewhere. EDIT: Maybe this has been done already. I haven't investigated it thoroughly yet.

Not the high ISO warning part, but newer cameras have a functional auto ISO in M mode (not the 5DII, but the 7D, 1D IV, 60D, and some of the newer Rebel/xxxD bodies, and the later ones of those (60D and on) let you specify an upper limit for the Auto ISO that's more restrictive than what is normally the max (ISO 3200 on those cameras).  I'd love to be able to have Auto ISO stop at 1250 or so on my 7D...
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Mt Spokane Photography

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Re: Biased auto ISO
« Reply #6 on: March 12, 2012, 01:51:14 PM »
When I started out with my first DSLR about 6 years ago, I was mostly shooting with automatic exposures in "P" mode. The camera would pick a nice combination of shutter speed / aperture for correct exposure (auto ISO wasn't an option in my body yet). When I saw that some portraits I'd been shooting in bright daylight turned out to be f/11 at 1/400sec shutter speed, I decided to use "aperture priority mode" (aV) instead. It gives me the control over aperture that I want, but it's the absolute opposite of something completely "auto": it's totally fixed. The middle way is to use 'portrait mode' which will hide all the settings it chooses but pick larger apertures. It uses a bias.

On my current body (the 60D), there's an "auto ISO" function; but it too tends to be too biased on low ISO values / slow shutter speeds. The only way to customize this auto ISO setting on my current camera is that you can set an upper limit to the auto ISO it is allowed to pick.

Since learning about the workings of these "auto" modes, I've always had the idea of factually customisable auto ISO playing through my mind, being able to bias it manually. I've yet to see this in Canon cameras. Currently, auto ISO is coupled with "minimum shutter speed" and will always bias ISO value first, and only start to increase it when shutter speeds become really slow. The minimum shutter speed is coupled with the focal length (at least for the 5D mk2), but it's not customisable.

Now what I read recently, on the Nikon D4, was the following:

Quote
"In the D4, Nikon has (at long last) added an 'Auto' option to the minimum shutter speed options, which allows the camera to automatically set the minimum shutter speed based on its knowledge of the focal length that you're working at. This response can be biased in 5 steps, from 'slow' to 'fast' depending on whether you'd like the camera to err on the side of slower or faster shutter speeds. A small change but one that (along with the D4's extremely wide ISO sensitivity span) finally makes Auto ISO more like the 'set and forget' function that it should have been long ago."
-Barney Britton, DPReview

I think it would be great to have a customizable / auto ISO bias setting in-camera. And having seen some of the abilities of the Magic Lantern software I'd be curious whether something like this functionality would actually be possible to make.

Example:

In aV mode (fixed max aperture), biased auto ISO doing two things:
(A) Take a low ISO setting;
(B) keeping the shutter fast between 1/200 and 1/8000.

Now say that you could change the weight of A versus B (i.e. a low ISO having more weight, or a fast shutter having more weight), and that you could change the minimum/maximum range of B. You could perhaps even give weights to individual ISO values to be able to not make it pick the dodgy 1/3rds, or to further reduce the value of the superhigh ISO's.

Setting a fixed aperture value in aV, you'd be able to shoot with auto ISO on, with the camera picking much more useful/appropriate 'auto ISO' settings to start from. It would make Auto ISO much more useful for me in aV mode.
Action sports: give a bit more priority to fast shutters (for action, 1/1000 @ iso 400 is better than 1/250 @ iso 100). General outdoor: moderate bias on low ISO. More landscape-focused: big bias to the low ISO.

I'm not sure if this is quite what the Nikon D4 is said to do in the quote above, but I'd personally very much love to have the option of customising the auto ISO to be biased, as described here.

That is a great feature, and one that i have wanted for a long time.  You can sort of get the same thing with a Canon camera, its just not as simple.

The Canon 5D MK III finally brings auto ISO to the manual mode,  Set shutter speed and aperture, and it will raise or lower ISO for you to get the right exposure.

The 5D will also let you set a upper limit to ISO, which keeps it from jumping up higher than you want.

With the 5D MK III you also have three saved settings, so you can have a preset for landscape, low light, and fast moving subjects, or whatever you would like.

The Rebels have settings for the type of shot(landscale, low light, fast subject, etc, and bias shutter speeds and or apertures and thus ISO accordingly.   It may not be obvious to some exactly what is going on.

Personally, I like Nikon's idea.  However, I do not expect different companies to make identical cameras with identical features, we have a choice to get what we value most, but we don't get everything in one body.

JerryKnight

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Re: Biased auto ISO
« Reply #7 on: March 12, 2012, 03:10:36 PM »
What I would like to see is auto ISO in Manual mode. ie. Set aperture and exposure, and have the camera choose the proper ISO to make the exposure correct. Might be a little dangerous if you forget to update your settings, but that's already something Manual shooters have to stay on top of. Maybe it could have a "High Auto ISO" warning indicator somewhere. EDIT: Maybe this has been done already. I haven't investigated it thoroughly yet.

Not the high ISO warning part, but newer cameras have a functional auto ISO in M mode (not the 5DII, but the 7D, 1D IV, 60D, and some of the newer Rebel/xxxD bodies, and the later ones of those (60D and on) let you specify an upper limit for the Auto ISO that's more restrictive than what is normally the max (ISO 3200 on those cameras).  I'd love to be able to have Auto ISO stop at 1250 or so on my 7D...

...

That is a great feature, and one that i have wanted for a long time.  You can sort of get the same thing with a Canon camera, its just not as simple.

The Canon 5D MK III finally brings auto ISO to the manual mode,  Set shutter speed and aperture, and it will raise or lower ISO for you to get the right exposure.

The 5D will also let you set a upper limit to ISO, which keeps it from jumping up higher than you want.

With the 5D MK III you also have three saved settings, so you can have a preset for landscape, low light, and fast moving subjects, or whatever you would like.

The Rebels have settings for the type of shot(landscale, low light, fast subject, etc, and bias shutter speeds and or apertures and thus ISO accordingly.   It may not be obvious to some exactly what is going on.

Personally, I like Nikon's idea.  However, I do not expect different companies to make identical cameras with identical features, we have a choice to get what we value most, but we don't get everything in one body.

This is good news. I've been shooting with the 5D2 so long, I've gotten behind on the complete features of the other bodies.

I like the custom registered settings (C1-C3) but I wish it were easier to register the settings on the go. In my shooting, I often line up a shot beforehand, and I'd like to be able to quickly register it and continue shooting other things and switch to the C1-C3 setting when needed. The current menu navigation is too cumbersome for me.

I agree that we shouldn't expect all features to act the same across brands or even the major model lines (Rebel, 60D, 5D, 1D) but I really, really, really like seeing as many options as possible. Even if some options are obscured in custom functions and I never use anything but the default setting, I like seeing the ability to change it. More options the better. That's how I got into back-button-focus before getting a camera with a dedicated AF-On button.