Manual versus auto exposure

Apologies in advance but I wasn’t sure whether this question fits this forum but as it’s about light I’ll post anyway .

It seems to me that people fall in to two camps. Those that never or rarely trust the camera's auto exposure and those that do. I was wondering what benefits people felt manual exposure gives.

To me it seems that they are essentially equivalent IF you continue to use the camera's exposure level indicator as the guide to the scenes exposure. In Auto mode you can change the exposure compensation amount to the desired value and in manual mode you obviously change shutter speed or aperature.

I agree you could spot meter the scene and work out your own overall setting that works for your composition but again this could easily be set via the exposure compensation particularly if you use Tv or Av modes leaving one variable (ignoring ISO).

In what situations can one method or the other be considered superior and more importantly why?

I prefer an auto mode with EC because I can evaluate and make an exposure correction once for a subject and then shoot multiple shots with correct exposure. Also, as lighting changes (clouds passing by being one example) I don’t have to mess with exposure. This frees me to concentrate on composition and on using aperture and shutter for effect rather than exposure.

I learned photography using a manual-only Canon F1. I'm definitely no stranger to using manual mode for every shot. When the light is steady, such as a sunny day or a stadium lit with stadium lighting, then you can set exposure with a gray card and forget about it for a while. Manual mode is fine for those times. Otherwise, I can't see any good reason to use manual mode in changing light.

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geekperson said:

Apologies in advance but I wasn’t sure whether this question fits this forum but as it’s about light I’ll post anyway .

It seems to me that people fall in to two camps. Those that never or rarely trust the camera's auto exposure and those that do. I was wondering what benefits people felt manual exposure gives.

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If you are completely lazy and ignorant, you let the camera do its job - automatically. T his may involve selecting a "scene" on the dial.

You may also make your choice of shutter speed or aperture and let the camera select the other - automatically.

Manual operation means the exposure is determined without the aid of the camera. There are three tried and true means of doing this:

1. Experience or intelligent guesswork

2. Use a meter

3. Follow the instructions on the little piece of paper in the film box

The only reason for using any of these methods today is that the camera was made when these methods were in vogue, and does not have a built-in meter.
Anything else is automatic. And if a camera has exposure metering, you use it.

Muyltiple flash photography in a studio is a possible exception.

geekperson said:

It seems to me that people fall in to two camps. Those that never or rarely trust the camera's auto exposure and those that do.

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That may be true to some degree, but a genuinely competent camera operator will use both, depending on circumstance not on just personal preference.

geekperson said:

I was wondering what benefits people felt manual exposure gives.

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Auto exposure and manual exposure modes provide the same benefits: more accurate exposures for more efficient operation. They provide the same benefits but under different circumstance.

If the light is changing often, an auto exposure mode will probably be best. If the light is constant then manual exposure will be better.

geekperson said:

To me it seems that they are essentially equivalent IF you continue to use the camera's exposure level indicator as the guide to the scenes exposure. In Auto mode you can change the exposure compensation amount to the desired value and in manual mode you obviously change shutter speed or aperature.

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But in manual mode you set both the shutter speed and the aperture. In auto exposure modes you either set neither, or just one or the other. And then, with either manual or auto you can set Exposure Compensation and/or ISO. ISO can also be in Auto mode, separately from the exposure mode.

geekperson said:

I agree you could spot meter the scene and work out your own overall setting that works for your composition but again this could easily be set via the exposure compensation particularly if you use Tv or Av modes leaving one variable (ignoring ISO).

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But that is independent of the metering mode (spot, weighted, or whatever).

With Tv and Av modes you control only one variable. Setting shutter speed controls motion blur, setting the aperture controls DOF and may affect lens sharpness (e.g., diffraction). With manual exposure (especially if Auto-ISO is enabled, you control both.

geekperson said:

In what situations can one method or the other be considered superior and more importantly why?

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Depends on what is most important to the picture. Or maybe it would be better to say it depends on what is not important to the picture, and that can be left to an Auto mode!

For example, on cameras with Auto-ISO you set the range over which you can accept the noise. For shots, for example with sports or waterfalls, where the shutter speed is the single most important parameter, use Shutter Priority and let the camera auto set everything else. For portraits the DOF is important, so use Aperture Priority.

It used to be that I'd switch between Programmed Auto Exposure if the lighting of each shot might be different, or manual if I could set it once for the next series of exposures. Most of the time I used Manual Exposure just because that suited the most common circumstances where I'm doing photography. But with Auto-ISO that has changed. I almost always use Manual Exposure with Auto-ISO enabled. Instead of switching back and forth to Programmed Auto Exposure I'm much more likely to change the range of ISO's that Auto-ISO is allowed to use. The only time I switch Auto-ISO off is when I want some specific effect of a given ISO. (The grain in high ISO's can be interesting for BW images; and for something meant for a poster sized print or needing very high dynamic range the ISO might be locked at 200).

As you can see, which is most likely to be used and how often it might be changed by any one photographer depends on what kinds of photography they do (and to some degree the functionality of the camera too).

Thanks that's very helpful.

I've got into a habit, over time, of almost always using Av mode with the ISO that gives me the quality I want which fits the type of photography generally I do. Occasionaly I use Tv.

Lesson for me is to try experimenting more, move from my comfort zone and add back that extra degree of freedom you highlighted.

geekperson said:

To me it seems that they are essentially equivalent IF you continue to use the camera's exposure level indicator as the guide to the scenes exposure. In Auto mode you can change the exposure compensation amount to the desired value and in manual mode you obviously change shutter speed or aperature.

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You did not mention flash, which is quite a different subject.

Assuming the continuous ambient light, there are different auto modes (A, S, P, etc), but yes, if you simply always center the meter, auto is the same as manual, just less convenient. Or, you can choose to compensate either way, or you can choose to meter different areas of the subject.

For TTL flash, the camera meter does not show the flash metering. Meter only reads ambient light. But flash is independent of shutter speed, things work rather differently.
http://www.scantips.com/lights/flashbasics.html

Then camera Manual mode allows setting the continuous light exposure to be fixed for any background ambient (often to eliminate it, using maximum shutter sync speed), and the TTL metering handles the flash power level exposure (still automatic in TTL flash mode - but still can be compensated).

Or in a studio situation, it is normally much more precise and convenient to set the flashes to manual power level. Then they are always the same, always the same as you individually set them up to be.

geekperson said:

Thanks that's very helpful.

I've got into a habit, over time, of almost always using Av mode with the ISO that gives me the quality I want which fits the type of photography generally I do. Occasionaly I use Tv.

Lesson for me is to try experimenting more, move from my comfort zone and add back that extra degree of freedom you highlighted.

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If it is practical I prefer to use manual on my flash but that is only 10% of the time for me. An example is a studio shot. I trust TTL to a certain degree and I say that only because I am forever adjusting the FEC. Then again I could not live without it.

As far as exposure goes your histogram is a great tool. Put something white (if you can) in the image. The info on the right side of the histogram are your whites. Adjust manual flash power or FEC until that info as far to the right as possible without touching the far right wall. Here is your optimal exposure.

When you are shooting in low light like indoors I would suggest not to shoot in AV or TV. Learn to use your camera in manual and the flash can be on TTL. AV and TV are more for outdoor fill flash situations.

Indoors. In manual for starters set your ISO to 400, shutter to 1/160 and aperture to 5.6. When you depress your shutter your light meter will more than likely show you are underexposed. Ignore it as there is likely very little ambient light to record. It is the flashes job to provide light for your subject. This is where the histogram comes in play.

You can decrease your shutter speed or change ISO to change the background (ambient) light if you wish. The aperture and flash control the exposure of the subject.

You have far better control in manual. You set a shutter speed and forget about it (for now) and now you can open and close your aperture for the desired effect and the TTL on the flash will compensate. Again check the histogram and adjust FEC as desired.

Here is a great video that show how you camera and flash work together. It is a pocket wizard ad but the first 4 minutes have some good animations. It also gets into HHS.

http://www.pocketwizard.com/inspirations/tutorials/pocketwizard_controltl_optimiz/

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The solution is always simple. Getting there is the hard part.

apaflo said:

geekperson said:

It seems to me that people fall in to two camps. Those that never or rarely trust the camera's auto exposure and those that do.

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It happens that 1/125th @ f/8 is the same exposure however you get there: therefore it doesn't matter HOW you get there. This is equally true whether 1/125th @ f/8 happens to be the correct exposure, or not.
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Regards,
Baz

"Ahh... But the thing is, they were not just ORDINARY time travellers!"