Auto ISO, Manual and AEB

[rpcrowe]

Setting up my Canon 7D on manual exposure and auto ISO, I cannot seem to set it up to shoot Auto Exposure Bracketing.

Am I doing something wrong?

Ideally, it would seem if I set the camera on manual + auto ISO and then set it up for AEB, the exposure bracketing should take place by bracketing the ISO...

Why would I want to do this? Perhaps when doing a series of night shots at a fair or equivalent event.

[tao2]

Setting up my Canon 7D on manual exposure and auto ISO, I cannot seem to set it up to shoot Auto Exposure Bracketing.

Am I doing something wrong?

Ideally, it would seem if I set the camera on manual + auto ISO and then set it up for AEB, the exposure bracketing should take place by bracketing the ISO...

Why would I want to do this? Perhaps when doing a series of night shots at a fair or equivalent event.

Hi Richard,

not a Canon user but ah'd reckon that it behaves similarily tae my Sony ( and many other DSLRs). Ah need tae use PASM or full AUTO tae enable some functions. Auto bracketing being one . Ah have tae press the shutter button shot by shot if in Manual mode.

P mode sets exposure and allows Auto brck. but will adjust both aperture and shutter speed tae achieve correct exposure. A mode allows adjusting shutter speed and vice versa for Shutter prio + Auto brck.

Some Minolta/ Sony cameras will shift shutter speed in Manual but if holding AEL button or using a custom on the AEL button then they shift Aperture value.

Regardless of Auto ISO, Manual mode only allows a setting of ISO 200

. This may be yer problem (in quotes).

[DanK]

Boab, Canons don't behave that way.

Richard, I had never used auto ISO with AEB on my 7D, so I just tried it. I set it to manual and did three shots, first 1 stop intervals and then 2 stop intervals. It worked fine, selecting ISO=3200. (I'm in a poorly lit room.) However, the bracketing is done with shutter speed rather than ISO. It seems to set the ISO based on the neutral exposure and then holds it there, changing shutter speeds to get the bracketing. I don't know why it is set to work this way.

Dan

[rpcrowe]

I was really hoping to set a standard shutter speed and f/stop and then have the bracketing done by adjusting the ISO. No big problem if I can't. I am not even sure that I would like to have it that way, it was just an experimental thought!

[Greg Lehey]

I was really hoping to set a standard shutter speed and f/stop and then have the bracketing done by adjusting the ISO.!

A frequent use of AEB is for HDR images. If you're interested in that, take a look at http://wiki.panotools.org/A_simple_a...o_HDR-blending for one method. In general you take a number of images at different exposures (typically 2 to 3 EV apart, depending on whom you ask) and then merge them together with something like enfuse (http://wiki.panotools.org/Enfuse). The agreed best way to take the images is with same ISO and aperture, varying only the shutter speed. That way the images are closest in appearance to each other; only the exposure is different. If you change the ISO rating, you'll change the noise between the images. If you change the aperture, you'll change the depth of field.

Your application (night shots) is a good choice for HDR. Take a look at this image (bigger at http://www.lemis.com/grog/photos/One...ns.jpeg&size=2) for one example.

[William W]

. . . I had never used auto ISO with AEB on my 7D, so I just tried it. I set it to manual and did three shots, . . the bracketing is done with shutter speed rather than ISO. I don't know why it is set to work this way.

I am reasonable certain that’s the functionality with (mostly) all Canon DSLR’s capable of Auto ISO (not sure about the newer 1 & 5 Series Cameras).

What is fact -

AEB has previously (i.e. before Auto ISO) been dictated by the CAMERA MODE viz: -

In P Mode: AEB will bracket on EITHER SHUTTER SPEED or APERTURE or BOTH
In Av Mode: AEB will bracket on SHUTTER SPEED
In Tv Mode: AEB will bracket on APERTURE
In M Mode: AEB will bracket on SHUTTER SPEED

*

What is my supposition

When Auto ISO was developed the AEB functionality was kept intact because it was too difficult and/or not seen as necessary to develop Auto ISO as a “Camera Mode Function”.

This also makes a 'limitation' on many Canon DSLR's if one wants to use EC, when the camera is set in M Mode and when Auto ISO is activate.

WW

[Black Pearl]

I don't think ISO bracketing is a common feature - my Fuji can do it but I have to go into the menu and ask specifically for it. That said most sensors these days are pretty much ISO free so you don't need to alter it for a given shutter speed/aperture when taking the shot as changing it in your raw software gives the same result.

[Davejl]

Presumably AEB would either be used to try to achieve a single well-exposed shot, or a series of shots for merging into an HDR image. I use it for the latter, with fixed aperture and ISO (selecting the lowest) and the camera alters the exposure time. This generally means a static subject and a camera support. I can't really see why it would be desirable to bracket a series of shots by aperture. Nor am I sure why it would be desirable to bracket by ISO. If to avoid camera shake or subject movement in poor light, is it not better simply to set a fast enough shutter speed together with auto iso?

[Dave Humphries]

Hmmm, interesting thread Richard,

I can understand why you might think it would work like that and how, to maintain a certain aperture (for consistent DoF) and shutter speed (for consistent handling of any movement in the image), it would be useful.

However, if we think about why we bracket, (arguably) it ought to be* to allow us to capture a scene with a wider dynamic range than the sensor can handle.

Consider that if we adjust aperture or shutter speed between the bracketed shots, we can meet that need because we are physically changing how much light reaches the sensor.
However, if we only change ISO, it does not address that need. (If we shoot RAW, we can do as much recovery in PP as may be possible)

* sometimes though, we might bracket as a 'safety net', we take three exposures, hoping that one of them will be correct, only ever intending to use one of them - and in this instance, yes, it would be useful if the AEB worked the way you wish; i.e. M + AEB + Auto-ISO = different ISO used on each shot.

e.g. Consider a night shot at say, a fairground/amusement park, we have the subject and know we want a certain length of blur of the moving lights within the exposure (and obviously a fixed DoF), but would rather judge which was the best exposed shot in PP on a big monitor because at the time on a camera's LCD this won't be easy and with such a scene, the histogram will be almost useless.

Cheers, Dave

[DanK]

It is what it is, so you are stuck with AEB using shutter speed when the camera is set on manual. However, depending on the nature of the night shot, I don't see that as necessarily a problem.

What I am about to write applies only if you have time, e.g., you are shooting a scene that is reasonably stable.

First, when shutter speed isn't an issue, most people I know who do night photography opt when they can for base ISO and long exposures, to get the cleanest image. With a Canon, you can use long-exposure (subtractive) noise reduction if the exposure is long enough to get noisy.

Except in extremely dark settings, you can get a very close estimate of the exposure by boosting the ISO a lot, getting a properly exposed shot, and then doing the arithmetic to compensate for a lower ISO by slowing the shutter. A few test shots at high ISO, and you should be set to go. It is particularly easy to do this with ISOs of 100 an 6400 because the math is simpler.

If you are willing to accept point light sources as specular highlights, it isn't very common in my experience to need either HDR or exposure fusion (not the same, and I use the latter) in night photography. Excepting the specular highlights, the histogram is generally narrow enough. It's a different matter if the point sources can't be blown out, e.g. if you want details in the moon and on the ground. If you do need to bracket for this purpose, you can easily enough do it manually.

Of course, none of this holds true if you are trying to capture something transient.

I'm just taking a brief coffee break now and won't be at my real computer until tomorrow to check, but I believe that none of the shots below was bracketed.

[rpcrowe]

Dave:

This is exactly the reason that I would consider using AEB.
“* sometimes though, we might bracket as a 'safety net', we take three exposures, hoping that one of them will be correct, only ever intending to use one of them - and in this instance, yes, it would be useful if the AEB worked the way you wish; i.e. M + AEB + Auto-ISO = different ISO used on each shot.”

I pretty well have my technique for shooting night cityscapes down pat. But, I would have considered the “safety net” technique for shooting people available light at night in “fair-ground conditions”.

Specifically, I plan on shooting the Lunar New Year celebrations at Qualcomm Stadium, in San Diego, CA, tomorrow afternoon and evening...
http://www.lunarnewyearfestival.org/

I plan on using both a Canon 7D camera and a 5D2. Perhaps, I will carry two 7D cameras AND the 5D2. This is really the first time that I will use my 5D2 in low light photography. It is as much an experiment as an attempt to get some decent shots of the above celebration.

I like my 17-55mm f/2.8 IS lens for low light photography on my crop cameras. However, I do not have an equivalent image stabilization equipped lens that is capable of full frame work. My fastest lenses for full frame work are: EF 50mm f/1.8 Mark-1; EF 40mm f/2.8 Pancake and my EF 135mm f/2.8 SF lens (shooting without any softening dialed in).

This is a far greater load than I usually consider carrying: my "normal" setup for most aspects of photography is a pair of 7D cameras + the 17-55mm f/2.8 IS and 70-200mm f/4L IS lenses...

I investigated renting a Tamron 24-70mm f/2.8 VC lens from a local rental outlet but, their copy was booked for the time that I desired it (I will guess for the same celebration I plan to shoot)...

[DanK]

Sorry, Richard, I misunderstood what kind of shooting you wanted to do.

[Mike Buckley]

I was really hoping to set a standard shutter speed and f/stop and then have the bracketing done by adjusting the ISO.

Would that happen if you didn't confiture Auto ISO?

[William W]

Would that happen if you didn't [configure] Auto ISO?

You'd have to change the ISO manually, between each shot - (see my Post #6)

[William W]

. . .

This is exactly the reason that I would consider using AEB . . . “* sometimes though, we might bracket as a 'safety net', we take three exposures, hoping that one of them will be correct, only ever intending to use one of them"

I like my 17-55mm f/2.8 IS lens for low light photography on my crop cameras. However, I do not have an equivalent image stabilization equipped lens that is capable of full frame work.

That's interesting. For my "travel record shots" when on holiday - (these intended as JPEGS as a visual diary on slideshow monitors) - I often use AEB, typically set ±⅔Stop. These photos include a lot of low light and night time shots and these 'visual diary' shots were the main reason why I bought the 24-105/4L IS for my 5D Series Cameras.

At the time I thought it was an extravagance buying the 24 to 105 when I had a 24 to 70/2.8 and 70 to 200/2.8, but I have to say I use the 24 to 105 much more than I ever expected, and mainly for the IS and the IS allows this type of bracket shooting to be much easier when getting to the slower shutter speeds and so I can maintain a lower ISO.

For your uses though and depending upon the AEB RANGE you select, if you want to use M Mode and AEB, (obviously) you'll simply need to set an ISO to accommodate the slowest Shutter Speed - with a 5DII that shouldn't be too much of a problem in regard to being discontent with the (high) ISO you'd need to choose, even if the range of AEB you choose is one stop - a lot depends on what the RANGE of the AEB is to be.

WW

[rpcrowe]

The handy thing about using AEB on my Canon DSLR cameras (and I suspect on some other cameras also) is that I can have the camera set on burst mode and it will shoot three bracketed shots with every press of the shutter button and then stop until the next time the shutter is pressed. This makes shooting sequenced AEB shots extremely quick and easy - especially if I have my 7D on high-speed burst.