Are Exposure Comp. and ISO knobs functionally identical?

tomfrh · Mar 18, 2015

Hi,

On my 35mm and medium format cameras there are exposure compensation settings.

On a digital camera changing ISO changes your actual sensor amplification, and exposure compensation adjusts shutter or aperture or whatnot. However on a film camera is there any functional difference whatseover between say ISO 40 +0 and ISO 50 +1/3 ? (This example is for velvia 50. Like many people I set to ISO 40 as I find it a better baseline)

I am assuming not, and that as far as the camera and film is concerned it's identical, however I wondered if maybe the Program logic is perhaps altered in some way depending on the ISO, and that it might not map to the exact same Program combination in certain circumstances.

Regards,
Tom

AgX · Mar 18, 2015

The function of the compensating knobs is based on the setting done by the ISO knobs.

Ricardo Miranda · Mar 18, 2015

Tom

There is no distinction in that case as the result is the same.
Program and other auto-exposure systems relate to EV, not the ISO set.
See the program chart for your cameras if the manual has them. It should be something about it on the manual.

In many cameras. e.g. OM-2, the exposure compensation is concentric with the ISO. Changing the ISO also changes the compensation and changing the compensation factor effectively changes the ISO.

tomfrh · Mar 18, 2015

Thanks for your answers.

I was thinking they were one and the same function.

That's funny that on the Om-2 it's literally just another dial piggy-backing on the ISO dial, yet is presented as though it's an independent function!

My cameras are more advanced. The EC settings are physically separated from the ISO setting.

BrianShaw · Mar 18, 2015

Nikon (FE and F3) are same way - exposure compensation part of the ISO dial. I don't find that funny since that is what I always used and thought to be normal and quite rationale. To provide clarity to the conversation... what camera are you discussing?

E. von Hoegh · Mar 18, 2015

tomfrh said:
Hi,

On my 35mm and medium format cameras there are exposure compensation settings.

On a digital camera changing ISO changes your actual sensor amplification, and exposure compensation adjusts shutter or aperture or whatnot. However on a film camera is there any functional difference whatseover between say ISO 40 +0 and ISO 50 +1/3 ? (This example is for velvia 50. Like many people I set to ISO 40 as I find it a better baseline)

I am assuming not, and that as far as the camera and film is concerned it's identical, however I wondered if maybe the Program logic is perhaps altered in some way depending on the ISO, and that it might not map to the exact same Program combination in certain circumstances.

Regards,
Tom

What those ^^ guys said.
But, I've formed the habit (because most of my cameras lack built in meters) of simply using the aperture or shutter to compensate, because it's way too easy to forget to zero the compensator setting. The compensating function is really only useful on full auto settings such as on the OM 2 IMO.

Rick A · Mar 18, 2015

Exposure compensation dials only show you what you should already know. Take your meter reading, then open up or stop down accordingly with the aperture or shutter speed.

Mainecoonmaniac · Mar 18, 2015

As for my Canon F-1 (n). The exposure compensation knob just skews the exposure. I never use it. But I think it's for any auto exposure mode like shutter priority or aperture priority. The knob just compensates for back light exposure or other exposure that can throw off my center weighted meter. Though I have auto exposure capabilities, I only use my camera in manual mode because I know the sensitivity pattern on my focusing screen. If I my subject is back lit, I open up a stop or two or slow down my shutter speed a stop or two. In manual mode, the exposure compensation is a waste of time. If I set the compensation and forgot, it can screw up my exposures for the rest of the roll.

wiltw · Mar 18, 2015

tomfrh said:
Thanks for your answers.

I was thinking they were one and the same function.

That's funny that on the Om-2 it's literally just another dial piggy-backing on the ISO dial, yet is presented as though it's an independent function!

My cameras are more advanced. The EC settings are physically separated from the ISO setting.

Understand that changing ISO in dSLR is analogous to changing film sensitivity (emulsion). In BOTH, changing the EC control merely is putting in a OFFSET value so that more/less exposure is needed. An offset adjustment on a rifle scope causes you to move the end of the barrel to the right or to the left to compensate for wind or target motion. An EC adjustment on a meter -- whether film or dSLR camera -- causes you to move shutter/aperture for more/less exposure, usually to compensate for the fact that your subject is brighter/darker than the middle tone 18% grey card.

So if you stop and think about it, when in Manual mode with a camera, putting the indicator to the Right or to the Left is merely PUTTING IN AN OFFSET...effectively the identical action to using the 'EC' control of the film camera or dSLR in one of the auto control (Av, Tv, P) modes! And the OM-2 dial piggy-backing on the ISO dial is merely a mechanical way to achieve the SAME offset!

tomfrh · Mar 18, 2015

BrianShaw said:
Nikon (FE and F3) are same way - exposure compensation part of the ISO dial. I don't find that funny since that is what I always used and thought to be normal and quite rationale. To provide clarity to the conversation... what camera are you discussing?

I have Canon SLRs (EOS 1v and EOS 33) where you move the arrow against the scale for exposure comp, and Pentax 645N, which has an exposure compensation dial separate to the ISO setting. I also have canon DSLRs (Im just moving into film), where ISO changes sensor amplification, and EC adjusts shutter/aperture etc.

When i say it's funny, I just find it funny that there's one dial (ISO), with *another* dial on it (EC), both of which are adjusting the same underlying dial, and yet it's treated as two independent functions.

In any case, I now see that ISO setting and EC setting are really just meter calibrations, and that there's no real difference. Thanks for clarifying.

Are Exposure Comp. and ISO knobs functionally identical?

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