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Author Topic: Why is auto exposure so useless?  (Read 108187 times)

Justinr

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Re: Why is auto exposure so useless?
« Reply #160 on: August 27, 2015, 02:30:49 pm »

I'm not reluctant to believe that you took some "poor exposures" using AE.

All that's of interest is understanding what led to those "poor exposures".

I can honestly say that all the under exposed files from that day have been deleted. I will look to see if I have kept any from elsewhere. 
« Last Edit: August 27, 2015, 02:33:05 pm by Justinr »
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Justinr

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Re: Why is auto exposure so useless?
« Reply #161 on: August 27, 2015, 02:43:18 pm »

I believed you the first time. Are AE "poor exposures" so unlikely that you won't be able to make some more tomorrow?

That depends on whether I get my tax return done which I was meant to be doing today! But If time allows over the weekend I might try it again to see if I can establish a pattern between shutter/aperture priority etc.
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telyt

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Re: Why is auto exposure so useless?
« Reply #162 on: August 27, 2015, 03:00:28 pm »

I'm not Justinr but I do have some example photos.  They're not AE photos because I gave up on the concept many years ago (but then I've only been doing this for 45 years)

From experience I'm pretty sure AE (the camera's suggested exposure) would have clipped highlights:








I know which highlights I wanted to keep from clipping; the camera didn't




whether the bird is against a light background or a dark background the exposure I care about is on the bird;
why would I want to diddle with an exposure compensation dial to fix the camera's exposure error when I know what exposure I want and I don't have to diddle at all?





These sorts of exposure scenarios happen so often that it's much simpler to set exposure manually than it is to think "is this where I should compensate or switch to manual, or can I let AE do its thing?".
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Justinr

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Re: Why is auto exposure so useless?
« Reply #163 on: August 27, 2015, 03:03:25 pm »

I'm not Justinr but I do have some example photos.  They're not AE photos because I gave up on the concept many years ago (but then I've only been doing this for 45 years)

From experience I'm pretty sure AE (the camera's suggested exposure) would have clipped highlights:








I know which highlights I wanted to keep from clipping; the camera didn't




whether the bird is against a light background or a dark background the exposure I care about is on the bird;
why would I want to diddle with an exposure compensation dial to fix the camera's exposure error when I know what exposure I want and I don't have to diddle at all?





These sorts of exposure scenarios happen so often that it's much simpler to set exposure manually than it is to think "is this where I should compensate or switch to manual, or can I let AE do its thing?".

Well I wish you were Justinr then I could lay claim to those shots!  :)
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Isaac

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Re: Why is auto exposure so useless?
« Reply #164 on: August 27, 2015, 04:38:07 pm »

These sorts of exposure scenarios happen so often that it's much simpler to set exposure manually than it is to think "is this where I should compensate or switch to manual, or can I let AE do its thing?".

As I said -- full-time live view plus raw means that most-of-the-time all I need to do for my "correct" exposure is check the live view histogram -- so I use Manual.

However, that leaves me unpractised in the AE adjustments my camera provides; and when the light in-the-frame is changing rapidly I've wished I could off-load exposure-time or ISO adjustments to the camera -- so I can pay attention to what's happening.

(As-it-happens my camera doesn't allow me to set a reduced range of exposure-time / aperture / ISO; and that's really what I'd like, because I'm going to be able to do a lot with the raw file -- as-long-as the exposure is fast-enough and the ISO is low-enough -- but the camera doesn't know what I'm going to do with the raw.)
« Last Edit: August 27, 2015, 08:44:02 pm by Isaac »
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tom b

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Re: Why is auto exposure so useless?
« Reply #165 on: August 27, 2015, 06:45:20 pm »

Rob, welcome back!

Cheers,
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Tom Brown

Slobodan Blagojevic

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Re: Why is auto exposure so useless?
« Reply #166 on: August 31, 2015, 01:16:28 pm »

Justin,

I found a solutions for you:

jjj

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Re: Why is auto exposure so useless?
« Reply #167 on: September 03, 2015, 04:21:35 pm »

why would I want to diddle with an exposure compensation dial to fix the camera's exposure error when I know what exposure I want and I don't have to diddle at all?
These sorts of exposure scenarios happen so often that it's much simpler to set exposure manually than it is to think "is this where I should compensate or switch to manual, or can I let AE do its thing?".
Yup. Manual is usually much easier than AE. Set correct exposure and....well that's it.

Nice pics BTW.
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Rob C

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Re: Why is auto exposure so useless?
« Reply #168 on: September 03, 2015, 05:16:39 pm »

Yup. Manual is usually much easier than AE. Set correct exposure and....well that's it.

Nice pics BTW.


That was why I suggested using a hand meter: once you know the correct exposure for the highlight, you got it all as with trannies.

Naturally, that assumes the direction of the light remains pretty much the same for the shots you are about to make, as it was for the reading.

Either way, Matrix or hand meter, you gotta use your brain, at least a bit.

Rob C

jjj

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Re: Why is auto exposure so useless?
« Reply #169 on: September 03, 2015, 06:18:19 pm »

I use manual exposure for concert lighting, which is anything but static.
Get the base exposure correct and you capture the lighting as it was intended.
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BradSmith

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Re: Why is auto exposure so useless?
« Reply #170 on: September 03, 2015, 06:56:57 pm »

Let's see if I understand this correctly.   We can't trust the camera's auto exposure ability.  I have heard it is "USELESS".   So we'll shoot manually.   That's the solution!!!      But how do we know if our manual exposure is correct while we're shooting? 

Oh wait, of course, I've got it!   We'll check the histogram to be sure our manual exposure is correct.  I guess it must be OK to trust the camera's determination of what the histogram should look like.  Right??  Or maybe the camera's histogram can't be trusted as we've seen discussed here many times before ("We want a RAW histogram, not some crummy jpg rendered histogram that isn't accurate!!").

Hmmm.  OK, NOW I've got it!  We'll review the captured manually exposed image on the camera's LCD to be sure the exposure is correct.  It must be OK to trust the camera's jpg rendering on that little 3" screen.  Right??  or maybe we can't trust either the camera's jpg conversion from the RAW data or the LCD's ability to faithfully show the camera's converted jpg on the LCD !!   

After all, if we can't trust the camera's auto exposure capability to generate a file we can use, why should we trust anything else that the camera does that might help us get to an exposure that we decide is correct?

Further variations on this theme:
Why trust the incident meter because......
Why trust either the camera's or my hand held spot meter because......
Why trust that my monitor's rendering of the image file because........

Brad



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jjj

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Re: Why is auto exposure so useless?
« Reply #171 on: September 03, 2015, 07:58:58 pm »

I don't think you really understand what auto or manual exposure means.
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Slobodan Blagojevic

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Re: Why is auto exposure so useless?
« Reply #172 on: September 03, 2015, 08:21:52 pm »

I don't think you really understand what auto or manual exposure means.

I can't wait to be enlightened (pardon the pun) ;)

dwswager

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Re: Why is auto exposure so useless?
« Reply #173 on: September 03, 2015, 09:28:14 pm »

There I was standing in the middle of field covering a major classic tractor event for a couple of magazines. It was an overcast day that threatened rain although it was the middle of summer and yet, despite the multitude of settings I tried to obtain a reasonable exposure, nothing seemed to be working. I turned to a fellow writer who I know is also very fussy about his cameras and images, he too was struggling while a third colleague also confessed that only a fraction of his pictures were useable due to poor exposure. Thinking about it afterwards I decided to try manual and rely on the good old histogram and since that happy moment around 90% of my pictures are now 'keepers'  (how I hate that word!). Using flash is going to be a problem as I can't see anyway of selecting an intensity setting on my flash head and adjusting aperture or ISO to achieve the desired result, but for all other purposes taking a few test shots to get the right exposure seems to work just fine. Just for the record I was using a Nikon and the others Canon and to further rub salt into the wound many people were getting better exposures on their smart phones!

I've attached a few taken using manual exposure.

The fallacy is that there is some magic "CORRECT" exposure.  There is not.  What you want is some rendering of the subject you prefer, but the camera doesn't know that.

I'm not saying that auto exposure will yield "EXPECTED" results under all conditions, but you can get closer to that goal.  First, you have to calibrate the camera.  Shoot known exposures and make the appropriate adjustment.  Now you must dial in the adjustment with all shooting.  Second, you need to pick the appropriate metering mode (Matrix, Center Weighted, or Spot) depending on conditions.  Also, in changing light conditions (moving subject and/or moving camera) then it takes some time for the camera to calculate and set the camera.
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Petrus

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Re: Why is auto exposure so useless?
« Reply #174 on: September 04, 2015, 05:30:42 am »

Let's see if I understand this correctly.   We can't trust the camera's auto exposure ability.  I have heard it is "USELESS".   So we'll shoot manually.   That's the solution!!!      But how do we know if our manual exposure is correct while we're shooting?  

Oh wait, of course, I've got it!   We'll check the histogram to be sure our manual exposure is correct.  I guess it must be OK to trust the camera's determination of what the histogram should look like.  Right??  Or maybe the camera's histogram can't be trusted as we've seen discussed here many times before ("We want a RAW histogram, not some crummy jpg rendered histogram that isn't accurate!!").

Hmmm.  OK, NOW I've got it!  We'll review the captured manually exposed image on the camera's LCD to be sure the exposure is correct.  It must be OK to trust the camera's jpg rendering on that little 3" screen.  Right??  or maybe we can't trust either the camera's jpg conversion from the RAW data or the LCD's ability to faithfully show the camera's converted jpg on the LCD !!  

After all, if we can't trust the camera's auto exposure capability to generate a file we can use, why should we trust anything else that the camera does that might help us get to an exposure that we decide is correct?

Further variations on this theme:
Why trust the incident meter because......
Why trust either the camera's or my hand held spot meter because......
Why trust that my monitor's rendering of the image file because........

Brad

+1 !!!!

Basically what the AE does is that instead of you adjusting the exposure according to the reading the light meter in the camera (or hand-held meter) provides, the camera transfers the values automatically. So if you are using the camera's meter to adjust manual exposure, you are just complicated things unnecessarily.

So basically OP is saying his camera's light meter is not working properly.

For a true manual exposure you have to just shoot manual, and then check the exposures on your monitor or print them, then adjust accordingly. Trusting the histogram is not "pure manual exposure" just like Brad explained above. For me this is too slow, can not travel to the office between every exposure, and the auto exposure gives good enough result or even perfect result actually (+-1 EV tweaking latitude) 98% of the time, given the huge latitude modern cameras provide.

Just yesterday a colleague of mine showed a studio portrait which was underexposed 5 stops. The picture looked totally black unadjusted. With LR sliders it was possible to tweak the photo to be perfectly useable, nobody would notice anything unless pixel peeping. Camera was Nikon D4. So unless overexposing more than 1 stop just about anything AE provides is perfectly fine.
« Last Edit: September 04, 2015, 05:32:27 am by Petrus »
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Rob C

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Re: Why is auto exposure so useless?
« Reply #175 on: September 04, 2015, 06:30:03 am »

+1 !!!!

1.     Basically what the AE does is that instead of you adjusting the exposure according to the reading the light meter in the camera (or hand-held meter) provides, the camera transfers the values automatically. So if you are using the camera's meter to adjust manual exposure, you are just complicated things unnecessarily.

So basically OP is saying his camera's light meter is not working properly.

For a true manual exposure you have to just shoot manual, and then check the exposures on your monitor or print them, then adjust accordingly. Trusting the histogram is not "pure manual exposure" just like Brad explained above. For me this is too slow, can not travel to the office between every exposure, and the auto exposure gives good enough result or even perfect result actually (+-1 EV tweaking latitude) 98% of the time, given the huge latitude modern cameras provide.

Just yesterday a colleague of mine showed a studio portrait which was underexposed 5 stops. The picture looked totally black unadjusted. With LR sliders it was possible to tweak the photo to be perfectly useable, nobody would notice anything unless pixel peeping. Camera was Nikon D4. So unless overexposing more than 1 stop just about anything AE provides is perfectly fine.


1. You have to use a hand incident light reading method, because using a hand meter for reflected light reading takes you to the same situation as using the camera's meter, the latter probably even les accurate.

Rob C





Slobodan Blagojevic

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Re: Why is auto exposure so useless?
« Reply #176 on: September 04, 2015, 09:23:50 am »


..., because using a hand meter for reflected light reading takes you to the same situation as using the camera's meter...

Unless you are using it in the spot mode and know where to point it.

Rob C

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Re: Why is auto exposure so useless?
« Reply #177 on: September 04, 2015, 09:26:13 am »

Unless you are using it in the spot mode and know where to point it.


AFAIK, built-in camera ones don't go narrow enough; should be 1° for worthwhile control, but maybe things have moved on...

Slobodan Blagojevic

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Re: Why is auto exposure so useless?
« Reply #178 on: September 04, 2015, 09:32:59 am »


AFAIK, built-in camera ones don't go narrow enough; should be 1° for worthwhile control, but maybe things have moved on...

Both you and I are talking about hand-held meters.

dwswager

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Re: Why is auto exposure so useless?
« Reply #179 on: September 04, 2015, 09:42:34 am »


AFAIK, built-in camera ones don't go narrow enough; should be 1° for worthwhile control, but maybe things have moved on...

Incident or spot not really the issue.  The problem is expecting their to be a "TRUE" reading.  Move that spot meter around and you get different readings.  Which is "CORRECT".  Incident solves this to some extent by taking the reflectance difference of surfaces out of the equation, but try in dappled light!  

The point of auto exposure is efficiency in changing conditions and automatically setting the camera to the metered settings.  Still doesn't change the fact that it is 1) metering the correct thing, 2) the meter itself is accurate, 3) the camera response to the meter is in sync, or 4) that even if those things all worked out correctly, that the set exposure will be the one you like best.  Which is another reason that Exposure Bracketing exists as a feature on most cameras.  

No light meter in the world can know your mind.  You can help it along with a little preference compensation, but all you do is get close.  The extended DR of newer cameras is certainly helpful, but if post processing of RAW is involved, then you might want a totally different exposure for the file versus the finished image.

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