A bit confused about exposure times

Maybe I'm missing the obvious, but what is the difference between 1/6th sec and 0"6 sec, or 0"3 sec and 1/3rd sec... etc on the LCD screen on a camera?
For example, is 0"5 sec the same as 1/2 sec, and if so, why are they displayed in different places?

Great question! The camera does shift from displaying the fraction's denominator of the exposure time (e.g. 60, 30, 15, 8, 4) to a real number (0"4, 0"5, 0"6, 0"8, 1", 1"3). When you see 6 in the LCD, it is really 1/6 or 0.17s. When you see 0"6, it is 0.6s - so these are different. I don't see 2, which would mean1/2, but I do see 2" to mean 2 seconds. As to why they use double quotes instead of a decimal, I suspect that it's for better visibility.

Does that make sense?

Miki G wrote in post #16212438
Maybe I'm missing the obvious, but what is the difference between 1/6th sec and 0"6 sec, or 0"3 sec and 1/3rd sec... etc on the LCD screen on a camera?
For example, is 0"5 sec the same as 1/2 sec, and if so, why are they displayed in different places?

Yes, 0"5 is half a second, but there is no 2 for half a second.

My camera goes down as fractions to 8 (1/8 or 0.125 of a second) then 4 (1/4 or 0.25 of a second) then switches to real numbers with 0"3 (0.3 of a second) 0"4 (0.4) 0"5 (0.5 or half a second).

Now, my camera is set to read in 1/3 stops. So from the last fraction 1/4, three more clicks should be a stop, and hey presto you count three clicks (0"3, 0"4, 0"5) and the third click is 1/2 a second as you would expect.

So, they are displayed in different places because fractions are easiest at "normal" shutter speeds (try writing 1/1000 the other way and you get 0"001 which would be confusing) but at shutter speeds slower than 1/4 fractions get complicated, 0"3 could be rounded to 1/3 and 0"5 is obviously 1/2 but what about the stop inbetween? 0"4 would be 2/5 (or 1/2.5).

You could count down as fractions 8, 4, 3, 2.5, 2, 1.6 etc. until you reach 1 second, but those are possibly less intuitive than decimals in that last few places. [Edited to add: Having just considered the use of the " instead of a decimal point being to avoid confusion with apertures, the same thing would apply here. You couldn't use 2.5, 1.6 etc. without risking confusion with an aperture setting, and you couldn't use the " as part of the fraction as you would get 2"5 and 1"6 as fractions of a second (1/2.5 and 1/1.6) but also as 1"6 and 2"5 (1.6 and 2.5) seconds.

So, they use decimals to keep confusion with aperture numbers, or times in excess of one second, to a minimum]

If you get confused though, just remember that each click on the dial is a third of a stop (or however you have your camera set) and don't worry too much about the actual numbers. Nothing funky happens, you don't get half a second showing up in two different places (as 2 and 0"5) the countdown is a continuous sliding scale moving in set divisions (third, half or full stops, whichever you have chosen to display)

frugivore wrote in post #16212484
As to why they use double quotes instead of a decimal, I suspect that it's for better visibility.

I just thought about that for a moment, I think it is probably to avoid it being confused with an aperture reading. With some of the shutter speeds being 1"6, 2"5, 3"2, if they were showing up as 1.6, 2.5, 3.2 they would look like aperture settings.

sandpiper wrote in post #16212723
I just thought about that for a moment, I think it is probably to avoid it being confused with an aperture reading. With some of the shutter speeds being 1"6, 2"5, 3"2, if they were showing up as 1.6, 2.5, 3.2 they would look like aperture settings.

I think you're right. Now if ISO value weren't in while numbers, we'd need another symbol to differentiate and we'd really be confused.

Thanks guys.
Great answers & they certainly make sense to me now. Cheers for clearing up my confusion.

I don't know why they just don't express it as a fraction all the time. On both of my camera's LCD screens, they express the shutter speed as a fraction, using the back slash : 1/4, 1/60, 1/320, etc.

When doing test images with a friend's Rebel last weekend, I couldn't find the shutter speed. Turns out it was because it was expressed in the way the OP showed, which is very confusing unless you're used to it and expect it.

I much prefer that fractions be expressed as fractions, as there is zero chance for confusion.

Hi guys

Part answer here. They use double quotes as that is an international standard for seconds, and a single quote mark for minutes. if its easier or not is debatable. I work in aviation and use time a lot, so to me its second nature. But we all do things different

Chris

Miki G wrote in post #16212438
Maybe I'm missing the obvious, but what is the difference between 1/6th sec and 0"6 sec, or 0"3 sec and 1/3rd sec... etc on the LCD screen on a camera?
For example, is 0"5 sec the same as 1/2 sec, and if so, why are they displayed in different places?

Just to note that although 0.3 seconds and 1/3 seconds are within rounding differences the same. However 1/6" (one sixth) second as a decimal is 0.17 seconds so is actually 0.43 seconds shorter than 0.6 seconds. If we only used full stops, then shutter speed displays could work fine with just the denominator of the fraction, or whole seconds. It is only when we complicate things by using third or half stops that we have difficulties. The half/third stops between half a second and one second would either require the use of a numerator for the fraction, or as Canon do it by switching to using a fully decimal display, although of course they are using the seconds symbol in the place of the decimal point. This sort of use of different symbols standing in place of the decimal, so that additional information can be quickly conveyed is actually quite common in engineering.

Alan