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FORUMS Photography Talk by Genre General Photography Talk 
Thread started 13 Dec 2013 (Friday) 06:15
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Auto ISO

 
ejenner
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Dec 13, 2013 13:10 |  #16

frugivore wrote in post #16524339 (external link)
I envision a system where the base exposure would be perfect with every single shot (using the ETTR concept), with EC and different metering modes needed only for taste.

So in thinking about this, there is a problem. But first when using LV, I agree this should be easy and if you can put Magic Lantern on your camera you can get this.

Out of LV, the problem is that the metering doesn't sample all of the image. And canon cameras (at least most up until now) actually only sample a relatively small number of zones.

So if Canon had an ETTR feature with its current models (not sure about 1Dx) they could easily try to ETTR only to blow out some highlights. Of course I don't really know
how bad this might be in practice.

Still I certainly do think they could do something a lot better.

If you want 'auto-ISO' for the 5DII I suggest also looking at Magic Lantern. There is a module that lets you 'auto expose' but it's not really auto becasue you have complete control over what aperture/SS/ISO the camera will use as the light level changes. I really need that for the 7D, but alas the developer doesn't have a 7D to make the required code.


Edward Jenner
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frugivore
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Dec 13, 2013 13:59 |  #17

ejenner wrote in post #16524762 (external link)
So in thinking about this, there is a problem. But first when using LV, I agree this should be easy and if you can put Magic Lantern on your camera you can get this.

Out of LV, the problem is that the metering doesn't sample all of the image. And canon cameras (at least most up until now) actually only sample a relatively small number of zones.

So if Canon had an ETTR feature with its current models (not sure about 1Dx) they could easily try to ETTR only to blow out some highlights. Of course I don't really know
how bad this might be in practice.

Still I certainly do think they could do something a lot better.

If you want 'auto-ISO' for the 5DII I suggest also looking at Magic Lantern. There is a module that lets you 'auto expose' but it's not really auto becasue you have complete control over what aperture/SS/ISO the camera will use as the light level changes. I really need that for the 7D, but alas the developer doesn't have a 7D to make the required code.

Are you referring to auto-ETTR? From what I understand, this is based on an existing RAW histogram, so you wouldn't get that perfect exposure on the first shot.

The metering zone may not cover the entire frame, but that's what we're working with now. So at least the algorithm will be more accurate than it is now.

Why don't you send your 7D to the dev to make the code? :D




  
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John ­ Sheehy
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Dec 13, 2013 16:09 |  #18

Blaster6 wrote in post #16524077 (external link)
Just did a shoot with my 6D last night. M with auto ISO worked like a charm. I knew I needed 2.8 and at least 1/250 with variable light so that pretty much gave me ISO as the only setting to play with.
The 6D allows you to set a range for min & max auto ISO too so no worries about unexpected noise.

A high limit to auto ISO will not save you from noise in M mode. In M mode, the photon noise is determined by scene lighting, f-stop and shutter speed. The only role ISO plays is that the lower the ISO, the more read noise you get, especially at the lower range of ISOs. That's not a typo; that's the way it really is. The lower the ISO, though, the more room you have for highlights, so there is a tradeoff.




  
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ejenner
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Dec 13, 2013 22:58 |  #19

frugivore wrote in post #16524879 (external link)
Why don't you send your 7D to the dev to make the code? :D

I have seriously considered it, I've been using it a lot though. I was hoping someone else would give him the info he needed from the 7D.

About auto ETTR - yes out of LV you have to take multiple exposures. In LV you can use the raw histogram to dial in the exposure without using auto ETTR. I think though with LV on it does this in one go, but I haven't used it much.


Edward Jenner
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Savethemoment
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Dec 14, 2013 06:06 |  #20

JeffreyG wrote in post #16523906 (external link)
Anytime I am in shifting light levels, I use M mode + auto ISO. In my mind, this almost makes it so I never use Av (my previous choice for shifting light).

The best way to think of it is that with digital we had two modes:
Av = Aperture and ISO priority mode.
Tv = Shutter speed and ISO priority mode.

So obviously there is a missing mode. Where is the aperture and shutter speed priority mode?

Canon has now kind-of given us this missing mode by letting us shoot M-mode + auto ISO. What is still missing though is some way to input exposure compensation and a way to make it keep working if we also use flash.

The mode currently does not work with flash. The ISO just defaults to 400, which makes it now M-mode with fixed ISO (and just what the heck is the point of that?)

It is frustrating that with almost two decades of digital SLR cameras, Canon has still not quite adapted their thinking to a control scheme that recognizes ISO as just another variable. The control scheme of the camera is still kind of based around the film system where the ISO was set when you loaded a roll and could not be changed from shot to shot.

As ISO is usually the least important variable (of aperture, shutter and ISO) it really should be the dependent variable most of the time.

Exactly. I love auto ISO in AV and TV modes. But I was shooting in a mix of broad daylight and deep/dappled shade during the week and had my camera in manual, & auto ISO, with a flash in the hot shoe. When checking the first couple of shots - which were in sunshine, with the flash for fill only - I was surprised to see that they were at ISO 400. Then I remembered that in manual mode, with flash, this is what auto ISO will give you regardless. ISO 100 was what I wanted & would have been perfect for those particular shots (in the shade & at smaller apertures I was happy for auto ISO to select a higher value).

So I cursed mildly and took it out of auto ISO, meaning I had to think about all three settings for each shot rather than only two. In a fast-changing environment where there were between 1 and 8-9 people in each shot - sometimes still, sometimes dancing, as well as in and out of the shade that was a PITA.

I'm not sure if this is something which might be fixable in a firmware update, or if we'll need to wait until it's eventually improved in a new model. My guess is the latter :confused:


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John ­ Sheehy
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Dec 14, 2013 08:39 |  #21

Savethemoment wrote in post #16526278 (external link)
So I cursed mildly and took it out of auto ISO, meaning I had to think about all three settings for each shot rather than only two. In a fast-changing environment where there were between 1 and 8-9 people in each shot - sometimes still, sometimes dancing, as well as in and out of the shade that was a PITA.

I'm not sure if this is something which might be fixable in a firmware update, or if we'll need to wait until it's eventually improved in a new model. My guess is the latter :confused:

Canon seems to be either dense or sadistic. From the time of my first DSLR, the 10D, it became quite obvious to me that a camera should be able to let the user control or float all of the parameters that control both absolute and relative ambient and flash exposure, in any combination. Manual exposure (Av & Tv) with auto-ISO and EC (ISO bias) with normal flash fill was one the things I expected to see in the upgrade to the 10D. I am still waiting; it has been very painful watching every other manufacturer make this mostly work, while Canon has covered their eyes and ears and pretended to be cutting-edge. I stay with Canon, because of my lens and peripheral collection, but I do not recommend Canon to anyone getting started in a DSLR platform.




  
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lar55
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Dec 14, 2013 22:04 |  #22

JeffreyG wrote in post #16524221 (external link)
1D Mark IV
7D
5D Mark III
1DX

I would also assume the 70D works the same as these, and possibly the 60D as well but you need to check it.

I don't know if any of the Rebels have this or not, or when they would have gotten it.

60D and Rebel T3i (maybe older Rebels too) have Auto ISO with M, Av, Tv modes. Max ISO can be set, but there is no way to set the minimum shutter speed in Av. (Only 1DX, 5Dmk3, and 6D can do that apparently.) In Av + auto ISO, the 60D will keep the shutter speed above about 1/(lens focal length) until it hits the max ISO, then it will drop the shutter speed further.




  
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madasax
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Dec 14, 2013 23:29 |  #23

I use it for situations like others have stated. Just depends on what I'm shooting and the available light and how consistent the light is. I'd rather control aperture abd shutter speeds and just keep an eye on iso to make sure its not to high. Again it depends a lot on what I'm shooting and for what reason.


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mark48
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Dec 16, 2013 08:54 |  #24

Thanks Roy, for starting this thread. I never gave auto ISO much thought but am going to try it in AV mode to see if it works for me. I really appreciate learning new things from time to time.




  
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tat3406
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Dec 16, 2013 23:15 |  #25

I started used Auto ISO since 1100D in M mode. I always shoot in M mode, if the environment light always change, I turn ISO to Auto and most of the time is useful. 6D is more user friendly than 1100D I used before, I can change metering mode on the spot.
If Canon can make EC for it then will be perfect mode.


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Blaster6
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Dec 17, 2013 08:34 |  #26

John Sheehy wrote in post #16525138 (external link)
A high limit to auto ISO will not save you from noise in M mode. In M mode, the photon noise is determined by scene lighting, f-stop and shutter speed. The only role ISO plays is that the lower the ISO, the more read noise you get, especially at the lower range of ISOs. That's not a typo; that's the way it really is. The lower the ISO, though, the more room you have for highlights, so there is a tradeoff.

So what you are saying is if I need a specific aperture and shutter speed in a poorly lit area I can increase my ISO and that will result in less noise? Flash is not an option so I will not be changing the scene lighting.

Keep in mind I am not at the lower range of ISOs -- I am in the 1600 - 6400 range. What you are saying is 6400 is cleaner? This does not make sense to me but I am willing to try anything if I am understanding you correctly.

In the past I have gotten a slightly cleaner final result from slightly underexposing and bumping the exposure a bit in post.


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RMH
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Dec 17, 2013 08:36 |  #27

I think what he'as saying is it's better to have the right ISO than set a limit and then need to push it 3 stops in post

I must admit, I don't really understand the need to shoot in M in this way - I've never really encountered a sitution where I wanted a speciffic shutter speed and still needed to adjust quickly, just a minimum shutter speed, so Av makes more sense to me, but that doesn't mean it doesn't exist - I only shoot photos of more or less stationary people, so my needs are not your needs :)

One thing I do find odd, and not quite right even on the 5D3 (though it doesn't actually affect me) is the choice of min shutter speeds -- it goes from 1/1250 down to 1 second. Really canon? You don't think anyone shooting sports would like to be able to set a minimum of 1/500 or 1/1000? And is 1 second really useful as a min shutter sppeed? If you're shooting that slow, you're probably on a tripod and taking a very considdered approach to your shooting, and probably in manual everything :S



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Roy ­ Mathers
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Dec 17, 2013 10:10 |  #28

mark48 wrote in post #16531257 (external link)
Thanks Roy, for starting this thread. I never gave auto ISO much thought but am going to try it in AV mode to see if it works for me. I really appreciate learning new things from time to time.


I've been using a digital SLR since the 10D was introduced and this is the first time that I've tried Auto ISO - it just shows that it's never too late to discover new tricks!




  
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John ­ Sheehy
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Dec 17, 2013 10:36 |  #29

tat3406 wrote in post #16533412 (external link)
I started used Auto ISO since 1100D in M mode. I always shoot in M mode, if the environment light always change, I turn ISO to Auto and most of the time is useful. 6D is more user friendly than 1100D I used before, I can change metering mode on the spot.
If Canon can make EC for it then will be perfect mode.

You can do it now, but not in the normal ways. For example, if you use a pinhole cap, and set the Camera to Tv and auto-ISO, you have fixed aperture and shutter speed, with floating ISO and EC (ISO bias) control. Same for a third-party lens with a manual aperture ring.

One could probably doctor a TC or extension tube to disable the aperture signals with the flip of a switch, so you can do a DOF-preview with a normal EOS lens, and then turn off the signals, so the aperture locks in place (but is no longer in the EXIF or camera display).

Desperate measures for desperate Canon minds ...




  
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John ­ Sheehy
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Dec 17, 2013 10:55 |  #30

Blaster6 wrote in post #16533993 (external link)
So what you are saying is if I need a specific aperture and shutter speed in a poorly lit area I can increase my ISO and that will result in less noise? Flash is not an option so I will not be changing the scene lighting.

In the lower range of ISOs on Canon DSLRs, the read noise relative to an absolute signal level peaks at ISO 100, at which it is almost 2x as strong as at ISO 200. With each doubling of ISO, the read noise reduces at a slower rate, until about 1600 to 3200, where it levels off, and the only benefit of a higher ISO setting is a brighter review image, and better cooperation from your converter, which may do strange things that it shouldn't when pushing deep shadows.

Keep in mind I am not at the lower range of ISOs -- I am in the 1600 - 6400 range. What you are saying is 6400 is cleaner? This does not make sense to me but I am willing to try anything if I am understanding you correctly.

If you're will to do the push in the converter (and your converter does it right), and you are willing to have a dark review image and a dark JPEG which won't push as well as RAW does, then "under-exposing" at these higher ISOs instead of using higher ones will give you an increase in highlight headroom, without any noise penalty. In that case, setting a max makes sense, in manual mode. There are more reasons to use a max in Tv and Av mode, because you may feel that a compromised shutter speed or DOF is a better choice than noise. Personally, I'd like an option to set manual Av and Tv values, and use auto-ISO, but have ISO thresholds settable which allow your Av and Tv values to break away, such as allowing a lens to open all the way to avoid ISO 51K, being that noise may reduce resolution as much as a wide-open lens (IOW, the value of maximum sharpness is not appreciated as well with a lot of noise).

In the past I have gotten a slightly cleaner final result from slightly underexposing and bumping the exposure a bit in post.

That is not likely if all other things are equal; the only benefit you should have from under-exposing a lower ISO is increased highlight headroom. Perhaps the converter in your case was doing more NR at the higher ISO setting, by default, and you didn't like it? Or maybe the situation was not completely equitable.




  
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