correcting for "mid grey" metering.

I understand that my camera meter measures to a tone approaching mid grey. There or thereabouts anyway.

I was being quizzed by a pro 'tog a few days ago and kept answering wrong. I'd appreciate those more knowledgable explaining why I keep correcting it the wrong way.

Lets say I've metered a white and it tells me its f/16 at 1/125s. I am using a tripod and want to stay at f/16, so its the shutter speed I wish to alter. Lets also assume (as did my pro 'tog) that we have a 5 stop range.

Assuming I want to move " two stops", which way does the shutter speed get altered? My natural inclination is to think I want the mid grey paler, so less exposure, which makes me think a shorter speed, so 1/500s. However As I got it wrong every time, its going to be 1/30s?

I would have sworn blind I knew all this stuff, so its embarrassing to find I don't!

1/125 -> 1/500 is two stops faster on the shutter speed which is two stops less light yielding a Grey tone that's darker.

For "Paler" (and by that I assume you mean brighter) you would want to slow your shutter to get more light so 1/30 would be the right answer.

Less exposure makes the gray darker. I have no idea why you would go the other way. Perhaps if you keep in mind the concept of using a gray background. If you add enough light you can make it appear white, or remove enough light you can make it appear black.

Someone else might be able to say it more clearly, but here's my attempt:

You are not metering "in relation" to medium grey; the camera is attempting to MAKE whatever you are metering from a medium grey. This means that if you are metering a white subject, the camera will UNDER expose your shot, in an attempt to render that object as medium grey. Since white is brighter than medium grey, you need to increase the exposure time in order to make the white brighter and achieve the appropriate color.

Lowner wrote in post #14235090
I would have sworn blind I knew all this stuff, so its embarrassing to find I don't!

You do know this stuff

It is perfectly natural to first double and redouble 125 into 500, temporarily forgetting that we are dealing with fractions.

40 years experience and I still make the same "mistake" before realising that I've just shortened the time the shutter is opened and have to redo the calculation.

gonzogolf wrote in post #14235119
Less exposure makes the gray darker. I have no idea why you would go the other way. Perhaps if you keep in mind the concept of using a gray background. If you add enough light you can make it appear white, or remove enough light you can make it appear black.

I think thats my problem, I want to go the wrong way all the time. My thinking is that less exposure lightens the image, just as a negative would be less dense back in the days of film. I need to think in slide terms maybe?

DunnoWhen wrote in post #14235237
You do know this stuff

It is perfectly natural to first double and redouble 125 into 500, temporarily forgetting that we are dealing with fractions.

40 years experience and I still make the same "mistake" before realising that I've just shortened the time the shutter is opened and have to redo the calculation.

Its not the correction from 1/125s via 1/250s to 1/500s thats the problem, thats "two stops" less exposure. My problem is (I think) as I've answered gonzo, I'm wanting to apply the change in the wrong direction.

Do you shoot Av/Tv? Could you correct it by setting the custom setting that makes the Canon work like a Nikon? (Reverse dial direction in Av/Tv) And, slightly off topic, are you an Engineer, by chance?

Lowner wrote in post #14235446
Its not the correction from 1/125s via 1/250s to 1/500s thats the problem, thats "two stops" less exposure. My problem is (I think) as I've answered gonzo, I'm wanting to apply the change in the wrong direction.

One of the ways I found that made life easier was to change the way in which the camera was set up with respect to turning the front dial.

By default, if one turns the front dial to the right, the exposure bar indicator goes to the left causing under exposure.

To me this seems opposite to the way my mind works. For me, right should equal light and left, darkness.

I've therefore gone into the custom functions and reversed the default option to work for me.

Edit.

I type too slowly on this new fangled iPad (classic) gadget

That can certainly work if your brain is wired for "Up Is Louder (Brighter)"

Snydremark wrote in post #14235511
Do you shoot Av/Tv? Could you correct it by setting the custom setting that makes the Canon work like a Nikon? (Reverse dial direction in Av/Tv) And, slightly off topic, are you an Engineer, by chance?

Yes, I was in electrical engineering from the age of 16 to 50. After that I became a sailing instructor but to this day I still think like an engineer!

Its not the correcting of the camera, as already mentioned the histogram is our friend. No, its the sheer frustration of continually getting it wrong when questioned. Time after time after...........!

Lowner wrote in post #14236060
Yes, I was in electrical engineering from the age of 16 to 50. After that I became a sailing instructor but to this day I still think like an engineer!

Its not the correcting of the camera, as already mentioned the histogram is our friend. No, its the sheer frustration of continually getting it wrong when questioned. Time after time after...........!

All I can say is that I'm glad your sport of choice wasn't one of those based at Old Sarum.

Lowner wrote in post #14236060
Yes, I was in electrical engineering from the age of 16 to 50. After that I became a sailing instructor but to this day I still think like an engineer!

Its not the correcting of the camera, as already mentioned the histogram is our friend. No, its the sheer frustration of continually getting it wrong when questioned. Time after time after...........!

Hahah...I only ask because the directions that one needs to dial things for exposure adjustment seem to make more sense to the engineers I know in the reverse direction of the way Canon's cameras work. So, it's long been my assertion that Nikons were build/designed by engineers

So, your frustration is just in the verbal, Q and A area rather than in the actual camera usage? Am I understanding that right?

Lowner wrote in post #14236060
Yes, I was in electrical engineering from the age of 16 to 50. After that I became a sailing instructor but to this day I still think like an engineer!

Its not the correcting of the camera, as already mentioned the histogram is our friend. No, its the sheer frustration of continually getting it wrong when questioned. Time after time after...........!

I was just about to mention about the gauge of wire and conductors. I have been in the electrica industry for 32 yrs.

DunnoWhen wrote in post #14236079
All I can say is that I'm glad your sport of choice wasn't one of those based at Old Sarum.

Flying has never interested me, unlike sailing, first in dinghies then offshore racing & cruising which has been a lifelong passion. But I live only about a mile from the perimeter of Old Sarum.