topic Re: Strange settings when using auto ISO in EOS DSLR & Mirrorless Cameras

Strange settings when using auto ISO

gwinegarden — Tue, 17 Mar 2020 18:12:10 GMT

I was just looking at some photos that I took recently and found some of the picture very noisy. When I looked at the metadata, the settings were a bit strange.

I was using a t5i with the Canon 55-250 IS STM lens. The camera was set to Apeture priority @ f11 and Auto ISO. An example of the settings, on the noisy photos, was 1/400 with ISO 6400!! This seems odd. I can see why it might pick that ISO at 1/400 but why choose that speed? The others had similar settings.

On other photos, all seemed more correct e.g. 1/100 @ ISO 320 & 1/160 @400.

To me, the issue is that the camera is selecting too high a shutter speed, at certain times. I do not know if Auti ISO has anything to do with it.

Any thoughts would be, greatly, appreciated.

Re: Strange settings when using auto ISO

Waddizzle — Tue, 17 Mar 2020 20:14:49 GMT

@gwinegarden wrote:
I was just looking at some photos that I took recently and found some of the picture very noisy. When I looked at the metadata, the settings were a bit strange.

I was using a t5i with the Canon 55-250 IS STM lens. The camera was set to Apeture priority @ f11 and Auto ISO. An example of the settings, on the noisy photos, was 1/400 with ISO 6400!! This seems odd. I can see why it might pick that ISO at 1/400 but why choose that speed? The others had similar settings.

On other photos, all seemed more correct e.g. 1/100 @ ISO 320 & 1/160 @400.

To me, the issue is that the camera is selecting too high a shutter speed, at certain times. I do not know if Auti ISO has anything to do with it.

Any thoughts would be, greatly, appreciated.

You can go into the menus and limit the range of ISO settings the that the camera can use in ISO Auto mode.

When I am using Av mode, I prefer to dial in an ISO value. I do not want the camera to control more than one leg of the exposure triangle, because undesirable things can happen, just as you have experienced.

You need to be careful of when you lock in focus in One Shot mode because it also locks exposure. This can be an issue when you focus and recompose, or when you use spot focus, which only meters with the center AF point in your camera.

Re: Strange settings when using auto ISO

gwinegarden — Tue, 17 Mar 2020 20:22:43 GMT

Thank you. I realise that I can limit the ISO (I had set it to 6400) but this does ot explain what I believe s the issue which is why it chose 1/400.

As I indicated, I am not sure if this is a metering issue or is caused by the Auto ISO being on (or both). The camera was checked out a year ago, by Canon.

I will be avoiding Auto ISO from now on.

Re: Strange settings when using auto ISO

Waddizzle — Tue, 17 Mar 2020 20:31:31 GMT

@gwinegarden wrote:
Thank you. I realise that I can limit the ISO (I had set it to 6400) but this does ot explain what I believe s the issue which is why it chose 1/400.

As I indicated, I am not sure if this is a metering issue or is caused by the Auto ISO being on (or both). The camera was checked out a year ago, by Canon.

I will be avoiding Auto ISO from now on.

The problem is less using Auto ISO, and more of an issue in allowing the camera to select two legs of the Exposure Triangle. I doubt if your camera is malfunctioning. May I suggest that you try using Manual mode with ISO Auto.

Also, I almost never shoot at f/11, not even for landscape shots. I take advantage of the hyperfocal distances of lenses. The only time I will use f/8 is with a Sigma 150-600mm "C" lens, which has an aperture range of f/5-6.3.

Re: Strange settings when using auto ISO

Waddizzle — Tue, 17 Mar 2020 20:38:22 GMT

As a couple of regular members are fond of saying, "The camera will do exactly what you ask it to do."

Re: Strange settings when using auto ISO

gwinegarden — Tue, 17 Mar 2020 20:50:24 GMT

Well, I, certainly, did not ask it to choose 1/400 at f11.

Re: Strange settings when using auto ISO

Waddizzle — Tue, 17 Mar 2020 20:55:18 GMT

@gwinegarden wrote:
Well, I, certainly, did not ask it to choose 1/400 at f11.

What are you trying to photograph?

ISO is not exactly "exposure", as it is supposed to correspond to the type of film yo would use. Exposure comes form aperture and shutter speed. In digital camera, ISO is basically just a gain setting, albeit a slightly complicated gain setting.

Re: Strange settings when using auto ISO

kvbarkley — Tue, 17 Mar 2020 21:05:34 GMT

It might be trying to maintain a shutterspeed based on the 1/f rule, does the shutterspeed/iso depend on the focal length?

1.6 * 250 is 400.

Re: Strange settings when using auto ISO

gwinegarden — Tue, 17 Mar 2020 21:08:43 GMT

Possibly, but that would be counter=productive as the lens is IS. But, stuff happens.

Re: Strange settings when using auto ISO

gwinegarden — Tue, 17 Mar 2020 21:09:41 GMT

In this case, I was shooting an icy stream.

Re: Strange settings when using auto ISO

Waddizzle — Tue, 17 Mar 2020 21:54:51 GMT

@gwinegarden wrote:
In this case, I was shooting an icy stream.

Have you ever used a Depth Of Field chart or table. Check out dofmaster dot com. They have a DoF field table.

Depending upon your focal length and distance to the subject, you could probably use a wider aperture setting, and avoid high ISO issues altogether. My advice is to not let the camera control more than one leg of the Exposure Triangle.

If you want to use Av mode, then dial in an ISO value. Do not use ISO Auto in Av mode, which means the camera controls both ISO and Tv. I only use ISO Auto in Manual mode, which means I control both Av and Tv.

Re: Strange settings when using auto ISO

ebiggs1 — Thu, 19 Mar 2020 16:39:08 GMT

I do say, "The camera will do exactly what you ask it to do." And I think it applies to your case as my friend pointed out you have chosen to let the camera control two of the necessary settings for proper exposure. The only thing you told the camera is it can not change the aperture. You said, camera select whatever ISO or SS you want to. It did exactly that!

I came from a time where a photographer had to set everything. This background has me using little of the 'auto' features. One of my favorite modes is Av. However, I almost never use auto ISO. It is my least favorite auto setting. I want to know where the ISO is all the time.

Re: Strange settings when using auto ISO

ebiggs1 — Thu, 19 Mar 2020 16:55:14 GMT

"I can see why it might pick that ISO at 1/400 but why choose that speed?"

Along with setting an upper or lower ISO limit, you need to also set limits on SS, fastest and slowest. What camera are you using? Did I miss that? Some cameras allow you to set the minimum shutter speed automatically based on the focal length of the lens. The camera uses the reciprocal rule to do this.

It's good to know the limitations of auto ISO. For example, there is a risk of creating overexposed images, or underexposed, as the camera would not be able to drop or increase the ISO enough.

Re: Strange settings when using auto ISO

gwinegarden — Thu, 19 Mar 2020 18:32:17 GMT

I was using a T5i which does not have SS limits.

I might have noticed, in the viewfinder, but if I see 1/400 @f11 I would not. normally, look at the ISO.

To me, the main question is why it selected 1/400 @f11. That, of course, cause the high ISO.

Was it due to the focal length of the lens? Doesn't make sense, to me, especially, as the lens is IS.

Is my sensor nuts? Maybe, but was checked out a year ago.

Does auto ISO cause strange behavior?

Anyway, I don't often use auto so I will stay away from now on unless, absolutely, necessary.

Thanks

Re: Strange settings when using auto ISO

ebiggs1 — Thu, 19 Mar 2020 19:02:25 GMT

"Was it due to the focal length of the lens?"

It could be. I don't have a T5i to try. Check your manual.

"Doesn't make sense, to me, especially, as the lens is IS."

The fact the lens has IS, has no factor in this issue. What lens were you using?

I personally don't like auto ISO but most (all) of my pro friends that shoot for the Kansas basketball games all use it. They are telling me I need to use it, too. I think it is pretty common in all of professional sports anymore. I don't see, at this point in my life, any good reason for me to use auto ISO.

Re: Strange settings when using auto ISO

gwinegarden — Thu, 19 Mar 2020 20:05:00 GMT

I did some research. Canon does use the focal length to determine SS and does not consider IS.

Re: Strange settings when using auto ISO

Waddizzle — Thu, 19 Mar 2020 20:35:09 GMT

@gwinegarden wrote:
I did some research. Canon does use the focal length to determine SS and does not consider IS.

Correct! Not every lens has IS, so having IS does not factor into the behavior.

BTW, we still do not really know what exactly you are doing. For example, we do not know what focal length you are using, how much available there it, how far away is your subject, etc.

Re: Strange settings when using auto ISO

ebiggs1 — Thu, 19 Mar 2020 21:29:29 GMT

"...we still do not really know what exactly you are doing."

The more info you supply the more accurate the solution will be.

Re: Strange settings when using auto ISO

gwinegarden — Fri, 20 Mar 2020 15:39:23 GMT

My research gave me the answer. But, I do not understand why the camera does not take IS into consideration.

Oh well. Once burned.

Re: Strange settings when using auto ISO

kvbarkley — Fri, 20 Mar 2020 16:12:49 GMT

If the info is given to the camera - does DPP tell you whether IS was used? - it can be three states: No Lens IS, IS present but off and IS present but ON. It is probably easier to ignore IS, since that gives you a more conservative answer. After all, how many stops do you allow for IS? 2? 3? 4? There are many IS's and they all have different abilities.

Remember to, that IS came after the invention of the EF lens, and before digital. The whole point was to make it as invisible to the camera as possible.