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Occasional Contributor
Posts: 16
Registered: ‎10-19-2014

Auto Exposure Bracketing in Auto ISO

I have a 7D Mark II, but I understand this is the same with other cameras.

 

When you set auto ISO in manual mode, and change exposure compensation, it changes ISO.  Good.

 

When you set auto ISO in manual mode, and use auto exposure bracketing, it changes shutter speed.  Not good.

 

I understand the thinking here, even if I think it's wrong, so instead of just "fixing it", I'd recommend a custom function for selecting which you want it to do.  In my case, I actually want manual mode to behave like manual mode rather than behaving like Av mode which is the current behavior with AEB in manual mode.  If I had wanted the behavior to be like Av mode, I would have set it in Av mode!

Esteemed Contributor
Posts: 2,994
Registered: ‎06-11-2013

Re: Auto Exposure Bracketing in Auto ISO


Lee_Jay wrote:

I have a 7D Mark II, but I understand this is the same with other cameras.

 

When you set auto ISO in manual mode, and change exposure compensation, it changes ISO.  Good.

 

I think you may find this depends on the camera mode.  Generally the camera follows something called the "program line".  In auto & semi-auto exposure modes, it tries to find a "safe" exposure (trying to find a reasonably safe shutter speed based on focal length of the lens and trying to find a safe f-stop given the aperture range of the lens.)  If the camera cannot open the aperture further AND slowing the shutter speed (relative to the focal length) would be unwise... then the safest thing to do is change the ISO.  

 

But the computer has "options" and, in my experience, which option it chooses depends on how much wiggle room it has with each element of the exposure (ISO, aperture, and shutter speed.)  You can read articles about how the "program line" works and realize the logic (what the camera will change is predictable -- and is based on which elements of the "exposure triangle" are already constrained.)

 

When you set auto ISO in manual mode, and use auto exposure bracketing, it changes shutter speed.  Not good.

 

The general recommendation in the industry when bracketing is that you should alter the shutter speed -- which is why the camera alters the shutter speed.

 

When you "bracket", the assumption is that you intend to use the bracketed data to merge for purposes of an HDR type result.  If you alter the aperture, then you change the depth of field.  This would be bad because you want all the samples to have identical depth of field with the ONLY variable being the amount of light collected.  If you change the ISO then you change the amount of noise and this may also be undesirable because you get a brighter exposure to integrate into the HDR result... but the "brighter" photo is now also noisier and that degrades the quality of the result.  

 

BUT... if you only change the shutter speed... you're generally safe.  The depth of field and noise levels should be consistent across all exposure samples in you bracketed series.  This means you may need a tripod.  That's probably ok, because bracketing doesn't work well for "action" photography (each image captures something completely different and you want a series of shots that captured the same thing... with only the exposure being different.)  This means you PROBABLY should be using a tripod anyway (otherwise you have to "register" (align) the frames because you didn't use a tripod... then crop.)

 

So... if you're using a tripod (and you should be) then the safest and best option to vary for a bracket image is... the shutter speed.  And that's exactly what the camera does.

 

I understand the thinking here, even if I think it's wrong, so instead of just "fixing it", I'd recommend a custom function for selecting which you want it to do.  In my case, I actually want manual mode to behave like manual mode rather than behaving like Av mode which is the current behavior with AEB in manual mode.  If I had wanted the behavior to be like Av mode, I would have set it in Av mode!


There's nothing magical about bracketing.  Some cameras have a built-in HDR mode which combines the images for you.  Some have a built-in "bracketing" mode which simplifies the task of gather a series of images where each has a slightly different exposure value (but doesn't combine them).  But it turns out photographers have been bracketing for years before any camera had any built-in feature for "bracketing".

 

Take a shot, alter your ISO, take another, alter the ISO again, and take another (then reset back to the original ISO).  The camera cannot stop you from doing that.   If you use the automatic bracketing feaure, it's going to use the shutter speed as the variable because that's the control that most photographers want to use -- and it's the method that would be taught in photography books and photography schools.

 

Tim Campbell
5D III, 5D IV, 60Da
Occasional Contributor
Posts: 16
Registered: ‎10-19-2014

Re: Auto Exposure Bracketing in Auto ISO

[ Edited ]

I understand just fine, and I have a perfectly valid reason for wanting this. What I don't understand is why I need two different modes, Av and M to behave the same in this case (Auto ISO). I put it in manual because I don't want shutter speed to change. If I wanted it to change, I would have used Av. If I'm in manual with fixed ISO, that's another story and something has to give (and shutter speed is the logical one). But AEB in manual with auto ISO should do exactly what I'm asking it to do and exactly what it does with manual EC applied - change ISO, not shutter speed.

Occasional Contributor
Posts: 7
Registered: ‎11-29-2016

Re: Auto Exposure Bracketing in Auto ISO

The reason for needing ISO Bracketing is quiet simple. Flash.. Since Shutter speed effects only abient light, if someone is trying to create a HDR portrait, the only real option is ISO since aperture is not recommend at all for any bracketing.  So yes there needs to be an option to allow one to switch from Shutter Speed to ISO Speed..

Respected Contributor
Posts: 1,852
Registered: ‎02-17-2016

Re: Auto Exposure Bracketing in Auto ISO

I don't think having the noise level changing for an HDR shot is such a good idea.

Honored Contributor
Posts: 5,038
Registered: ‎08-13-2015

Re: Auto Exposure Bracketing in Auto ISO

[ Edited ]

JoeJackson wrote:

The reason for needing ISO Bracketing is quiet simple. Flash.. Since Shutter speed effects only abient light, if someone is trying to create a HDR portrait, the only real option is ISO since aperture is not recommend at all for any bracketing.  So yes there needs to be an option to allow one to switch from Shutter Speed to ISO Speed..


Using Auto ISO during a series of AEB shots for HDR kind of defeats the whole purpose of taking a series of shots.  For HDR, you actually WANT to have under/over exposed shots.

 

For many of my HDR shots, my series of shots might look like this +1, 0, -1, -2, -3.  The shots are not centered around zero.  Adjusting the ISO over that wide of a range, 4 Ev,  would only introduce noise.

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"I don't rent software. I use Photoshop CS6, ACR 9.8 and Lightroom 6.8 ."
Occasional Contributor
Posts: 7
Registered: ‎11-29-2016

Re: Auto Exposure Bracketing in Auto ISO

Yes I am fully aware of the downside of using ISO bracketing. I am a professional headshot and landscape photographer. However you still miss the point that this is the ONLY way to bracket for flash..  In addition this is an option on many other cameras.   Besides bracketing 100 200 400, or just 100 320 is not going to introduce any signifigant noise that anyone will notice.  This technique is used by many well known photographers like Joel Grimes to get HDR portraits, while still using studio strobes..

Esteemed Contributor
Posts: 3,510
Registered: ‎06-25-2014

Re: Auto Exposure Bracketing in Auto ISO


JoeJackson wrote:

Yes I am fully aware of the downside of using ISO bracketing. I am a professional headshot and landscape photographer. However you still miss the point that this is the ONLY way to bracket for flash..  In addition this is an option on many other cameras.   Besides bracketing 100 200 400, or just 100 320 is not going to introduce any signifigant noise that anyone will notice.  This technique is used by many well known photographers like Joel Grimes to get HDR portraits, while still using studio strobes..


Forgive me if this is a stupid question, but if you're in a studio situation, where you presumably have full control over the lighting, why do you need to use HDR techniques at all? I had always assumed that those were nothing more than an imperfect workaround for situations where you can't control the light. What am I missing?

Bob
Boston, Massachusetts USA
Honored Contributor
Posts: 5,038
Registered: ‎08-13-2015

Re: Auto Exposure Bracketing in Auto ISO


JoeJackson wrote:

Yes I am fully aware of the downside of using ISO bracketing. I am a professional headshot and landscape photographer. However you still miss the point that this is the ONLY way to bracket for flash..  In addition this is an option on many other cameras.   Besides bracketing 100 200 400, or just 100 320 is not going to introduce any signifigant noise that anyone will notice.  This technique is used by many well known photographers like Joel Grimes to get HDR portraits, while still using studio strobes..


Okay, I already got it.  Instead of varying shutter speed, keep SS constant and vary the ISO. 

 

I'm no studio pro, but my in my avid and enthusiastic opinion, you're do something unconventional.  Some folks might even say wrong, instead of unconventional.  I think you're introducing noise when you do not have to.

 

I have had occasion to take a series of outdoor shots at some location, and when I get back home I realize that the shot had more dynamic range than what the camera could handle.  Sometimes you just don't see it in bright sunlight on the camera's LCD.  In these cases, I'll create a series of JPEGs with slightly altered exposre values, and use them to create an HDR photo. 

 

This works best when the series of expsoure changes are not centered at "0".  For example, I might create +2, +1, 0, -1 exposures when some areas are too dark.  Sometimes I will not create exposres that vary by equal steps.  I might skip the "0" exposre in the previous example.  And, yes, this introduces noise, too.

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"I don't rent software. I use Photoshop CS6, ACR 9.8 and Lightroom 6.8 ."
Honored Contributor
Posts: 7,925
Registered: ‎12-07-2012

Re: Auto Exposure Bracketing in Auto ISO

B from B said, "... why do you need to use HDR techniques..."

 

HDR increase the dynamic range of the camera no matter where you shoot.  That is what the "D" stands for.

 

 A side form that, auto ISO is not only silly it is a dumb idea.Smiley Frustrated IMHO, of coures, as always.

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