ISO the poor relation to Av and Tv in the exposure triangle

"correct" exposure is achieved through choosing appropriate aperture, shutter speed and ISO. In any "auto" mode elements of this "triangle" can be varied and others allowed to be calculated by the camera to achieve the metered exposure. Sometimes the metered exposure can be varied (compensated for).

What amazes me is that these three things are treated so differently by the camera controls. In paritiular Iso seems to be the poor relation. I guess this is because historically you had to change film to change iso, but now I can't see this legacy should affect us.

I imagined that someone would have developed a means to literally push the triangle around (some kind of joystick?). Or at least have three wheels. On the 5d mk3 you cannot set the iso and (dynamically) see the effect on Av and Tv (they are blanked out!).

When I got the 5D I thought wow when I saw all the iso choice, then it struck me that what I often wanted to do was "Manual" i.e. set Av and Tv and Auto Iso which you can, but then you can't set a compensation value (e.g. +/- 1 stop) - or can you?

I think if a more equitable approach were taken the controls would be easier, quicker and less prone to error (I occasionally forgot I left compensation on or left iso very high or occasionally low).

What do do you think? Are we clinging to old ways for no reason or am I just not learning to adapt myself to the tools I have?

Martin

Good question. Personally I am mostly shooting with just a cheap little rebel T3, so I don't have a lot of experience with the more effective control layouts. I would like the multiple dials to make changes a little faster, but I don't find it to be exceptionally slow even on the low end bodies.

I rarely think of ISO as my primary change, but that could in part be the really limited useful ISO ranges on the camera I use the most. (Basically limited to 100, 200, 400. 800 becomes pushing it in most conditions I find, and I start to dislike the grain. The few options higher don't get prettier.)

It is still less flexible in many cases than your shutter speed or aperture, so having a dedicated control for it doesn't seem that useful in my mind. For a two dial system I could see having a button/toggle to switch between aperture-shutter speed and ISO-EC. Beyond that, I don't see it as very user friendly for control layouts. The more buttons and dials you get, the easier it becomes to accidentally bump something.

I have just moved from the 500D (T1i) which (like Luckless's T3 I think) only has one "wheel" so it can be very confusing what you are changing and it takes multiple button presses to set Av and Tv - at theast the 5d has the second wheel so you can change Tv and Av a bit more easily.

I agree I think all canon model controls are needlessly complex to use. In some ways a steb backwards from mechanical film cameras where the controls are more intuitive and separate - aperture on the lens (too late to change the eos sytem!)

Canon almost fixed this on the 1D4 and 5D3 by giving a functional "aperture and shutter priority mode" when you use M mode with auto ISO selected. There are still defects:
1. No exposure compensation available in this mode which kind of kills it.
2. The mode doesn't work if you turn on a flash because the ISO then inexplicably locks to 400 for no good reason.

Someday Canon will realize that these are digital cameras and will give a true "aperture and shutter" priority mode to go with the existing Av (aperture and ISO priority) and Tv (shutter and ISO priority) modes.

IMO they really need to do this, because having ISO as the dependant variable is usually best as ISO has the smallest effect on the image. I usually want to pick the other two as I care about DOF and blur a lot more than noise.

JeffreyG wrote in post #14857787
Someday Canon will realize that these are digital cameras and will give a true "aperture and shutter" priority mode to go with the existing Av (aperture and ISO priority) and Tv (shutter and ISO priority) modes.

God, I hope they wake up soon and get it done. In the early days of digital, the range of "useable" ISO settings was pretty limited. Not so today. Of course they need a way for the user to select a minimum and maximum, with a safety shift of aperture or shutter speed on each end, but I really don't understand why it hasn't been done already.

When I shoot in Manual mode (which is most of the time), I adjust ISO to react to changing light. No reason the camera can't be designed to do that.

You know what? You're right. There should be a simple dial for each, and a small button to lock it if you don't want to bump it.

So easy a caveman could think of it. So why haven't the camera manufacturers. A print button? Really? Come on.

JeffreyG wrote in post #14857787
....having ISO as the dependant variable is usually best as ISO has the smallest effect on the image. I usually want to pick the other two as I care about DOF and blur a lot more than noise.

Couldn't put it better. I'm relieved I'm not alone in thinking this!

Does Canon do feature requests?

JeffreyG wrote in post #14857787
...IMO they really need to do this, because having ISO as the dependant variable is usually best as ISO has the smallest effect on the image. I usually want to pick the other two as I care about DOF and blur a lot more than noise.

Not everyone thinks this way. I prefer to set ISO as a constant specifically because it affects the fundamentals of the image, whereas other things (DOF, action, etc.) are more highly variable with the subject.

Auto ISO would seem to meet most of your expressed needs, since you care little about selecting a specific ISO.

RTPVid wrote in post #14861488
Not everyone thinks this way. I prefer to set ISO as a constant specifically because it affects the fundamentals of the image, whereas other things (DOF, action, etc.) are more highly variable with the subject.

If you are saying that you specifically need the same ISO level used in every shot from a session, then auto-ISO (or some aperture and shutter priority mode) is obviously not the best choice for you.

But I'd guess most folks generally want the lowest ISO that they can use to get the shot for each shot, and they will take variation if it means they can use a lower ISO for shots in better light. If you are shooting in variable light and need to use an auto-metered mode (Av, Tv, P etc) then a mode where you pick aperture and shutter speed and the meter picks ISO is actually the best possible way to shoot at the lowest possible ISO level for any given shot.

If you think about it, such a mode lets you pick the biggest aperture you can tolerate for DOF and the slowest shutter speed you can tolerate for blur. The meter then comes back and gives you the lowest possible ISO for the light in each specific photo.

If you work in Av instead (for example) you can pick the same aperture but you need to set the ISO to whatever level will guarantee your minimum shutter speed for the lowest light shot you might take. This means that you have the ISO set higher than it needs to be for all shots not at this minimum light level.

That's true, except that auto ISO doesn't allow exposure compensation and it doesn't work when I turn on the flash. If Canon fixed that, I'm all set no matter what they want to call the mode.

It's not trivial that they don't have this quite fixed. I'd love to use auto ISO when dragging the shutter with flash, but the stupid mode stops working correctly in exactly this situation.

JeffreyG wrote in post #14865168
If you are saying that you specifically need the same ISO level used in every shot from a session, then auto-ISO (or some aperture and shutter priority mode) is obviously not the best choice for you.

But I'd guess most folks generally want the lowest ISO that they can use to get the shot for each shot, and they will take variation if it means they can use a lower ISO for shots in better light. If you are shooting in variable light and need to use an auto-metered mode (Av, Tv, P etc) then a mode where you pick aperture and shutter speed and the meter picks ISO is actually the best possible way to shoot at the lowest possible ISO level for any given shot.

If you think about it, such a mode lets you pick the biggest aperture you can tolerate for DOF and the slowest shutter speed you can tolerate for blur. The meter then comes back and gives you the lowest possible ISO for the light in each specific photo.

If you work in Av instead (for example) you can pick the same aperture but you need to set the ISO to whatever level will guarantee your minimum shutter speed for the lowest light shot you might take. This means that you have the ISO set higher than it needs to be for all shots not at this minimum light level...

Maybe you misunderstand what I do. I wasn't very clear about it. I don't generally use auto ISO. I set it to achieve the quality of image, and only boost it if necessary due to low light situations. So, I change it rarely during any one photo situation, so having it not on an independent wheel is not a big deal for me.

RTPVid wrote in post #14865562
Maybe you misunderstand what I do. I wasn't very clear about it. I don't generally use auto ISO. I set it to achieve the quality of image, and only boost it if necessary due to low light situations. So, I change it rarely during any one photo situation, so having it not on an independent wheel is not a big deal for me.

I think I do understand. Most of the time I just shoot M mode and I pick all of my parameters. But in some situations the light is really variable and an auto metered mode is very handy. Let me give you an example and see if we are thinking of the same thing.

Su ppose I am shooting a soccer (football) match where the stands are partially shading the field. As I track and shoot the action the players may abruptly run from full sun into shade that is a good three stops darker.

If I were to shoot this in M mode auto ISO I could set me lens wide open, set my shutter to my desired minimum (say 1/1000) and then the meter will give me ISO 400 in the sun and ISO 3200 automatically when they run into the shade.

Now imagine doing the same thing in Av mode. I still set the lens wide open but I have to shoot the match entirely at ISO 3200. That preserves my 1/1000 shutter in the shade but gives me the faster than needed 1/8000 shutter when the athletes are in the sun. I can't set the ISO to 400 in Av mode because then I would get 1/125 shutter speed every time the athletes went in the shade, and all the shade shots would be ruined by blur.

Tv mode has the same problem, I have to set the ISO to 3200 for all shots. Otherwise the camera meter will want to set the aperture bigger than wide open when the play is in the shade and my shots will be underexposed. And so at ISO 3200 and 1/1000 the camera will stop down my lens every time they run into the sun.

I hope this example shows how using a mode where the meter picks the ISO is the best way to shoot at the lowest ISO possible when using an auto metered mode in variable lighting.

Pentax already has this mode done properly on the main mode dial. So it can be done! Also in JefferyG's example of the football match, one team is in white the other black, so you might also want to dial some exposure compensation in, this again Canon doesn't allow.

Personally I would also like to be able to set up the camera in manual mode so that I can make all the exposure settings in relation to a particular EV setting say 1/125 f/5.6 @ ISO 100 but to be able to roll the front dial to adjust any two corners of the triangle together while maintaining the constant EV. Saftey shift of the other corner if one of the other two runs out of adjustment would be nice too. I often shoot in relatively constant light but need to change between slow and fast shutter speeds for subject blur requirements. You can do it in P mode, and of course Av and Sv effectively do the same but you are forced to accept the choices made by the camera meter. I would like the functionality while using a hand held incident meter.

Alan